Content uploaded by Sameera Irfan
Author content
All content in this area was uploaded by Sameera Irfan on Aug 16, 2023
Content may be subject to copyright.
JAYPEE BROTHERS MEDICAL PUBLISHERS
UNDERSTANDING
STRABISMUS
Prelims.indd 1 26-09-2013 18:24:49
JAYPEE BROTHERS MEDICAL PUBLISHERS
Prelims.indd 2 26-09-2013 18:24:49
JAYPEE BROTHERS MEDICAL PUBLISHERS
UNDERSTANDING
STRABISMUS
Sameera Irfan FRCS (Edin)
Consultant Oculoplastic Surgeon and Strabismologist
Mughal Eye Trust Hospital
Lahore, Pakistan
Foreword
Amjad Akram
JAYPEE BROTHERS MEDICAL PUBLISHERS (P) LTD
New Delhi • London • Philadelphia • Panama
®
Prelims.indd 3 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
Headquarters
Jaypee Brothers Medical Publishers (P) Ltd
4838/24, Ansari Road, Daryaganj
New Delhi 110 002, India
Phone: +91-11-43574357
Fax: +91-11-43574314
Email: jaypee@jaypeebrothers.com
Overseas Oces
J.P. Medical Ltd
83 Victoria Street, London
SW1H 0HW (UK)
Phone: +44-2031708910
Fax: +02-03-0086180
Email: info@jpmedpub.com
Jaypee Brothers Medical Publishers (P) Ltd
17/1-B Babar Road, Block-B, Shaymali
Mohammadpur, Dhaka-1207
Bangladesh
Mobile: +08801912003485
Email: jaypeedhaka@gmail.com
Jaypee-Highlights Medical Publishers Inc.
City of Knowledge, Bld. 237, Clayton
Panama City, Panama
Phone: + 507-301-0496
Fax: + 507-301-0499
Email: cservice@jphmedical.com
Jaypee Brothers Medical Publishers (P) Ltd
Shorakhute, Kathmandu
Nepal
Phone: +00977-9841528578
Email: jaypee.nepal@gmail.com
Website: www.jaypeebrothers.com
Website: www.jaypeedigital.com
© 2014, Jaypee Brothers Medical Publishers
The views and opinions expressed in this book are solely those of the original contributor(s)/author(s) and do not necessarily represent
those of editor(s) of the book.
All rights reserved. No part of this publication may be reproduced, stored or transmitted in any form or by any means, electronic,
mechanical, photocopying, recording or otherwise, without the prior permission in writing of the publishers.
All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their
respective owners. The publisher is not associated with any product or vendor mentioned in this book.
Medical knowledge and practice change constantly. This book is designed to provide accurate, authoritative information about the
subject matter in question. However, readers are advised to check the most current information available on procedures included and
check information from the manufacturer of each product to be administered, to verify the recommended dose, formula, method and
duration of administration, adverse eects and contraindications. It is the responsibility of the practitioner to take all appropriate safety
precautions. Neither the publisher nor the author(s)/editor(s) assume any liability for any injury and/or damage to persons or property
arising from or related to use of material in this book.
This book is sold on the understanding that the publisher is not engaged in providing professional medical services. If such advice or services
are required, the services of a competent medical professional should be sought.
Every eort has been made where necessary to contact holders of copyright to obtain permission to reproduce copyright material. If any
have been inadvertently overlooked, the publisher will be pleased to make the necessary arrangements at the rst opportunity.
Inquiries for bulk sales may be solicited at: jaypee@jaypeebrothers.com
Understanding Strabismus
First Edition: 2014
ISBN: 978-93-5090-990-4
Printed at
Jaypee Brothers Medical Publishers (P) Ltd
Jaypee Medical Inc.
The Bourse
111 South Independence Mall East
Suite 835, Philadelphia, PA 19106, USA
Phone: + 267-519-9789
Email: joe.rusko@jaypeebrothers.com
Prelims.indd 4 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
To
My Papa Ji,
Prof. Daljit Singh
Prelims.indd 5 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
Prelims.indd 6 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
FOREWORD
Plenty of comprehensive books are available on strabismus in the market which are read by
ophthalmology residents and junior ophthalmologists. But when a patient with strabismus
walks into the ophthalmic outpatients department, the resident has a blackout as to where to
start and how to proceed.
The good thing about Dr Sameera’s book is that it describes the management of such patients
in a way that is concise, to the point and easy to understand; rather than being comprehensive,
it provides a stepwise approach to the target audience, i.e. the ophthalmologist in training.
Amjad Akram FCPS FRCS (Edin) FRCS (Glasgow)
Consultant Ophthalmologist
Armed Forces Institute of Ophthalmology
Pakistan
Prelims.indd 7 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
Prelims.indd 8 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
PREFACE
The subject of strabismus is like a vast ocean; standing by its shores, one cannot assess its full
expanse but only by taking a deep plunge into it does one realize its true depth and dimension.
I have been a practicing strabismologist for more than 20 years and have been giving lectures
to postgraduate trainees and general ophthalmologists, during which I realized a lack of basic
understanding of the pathogenesis of strabismus. This formed the foundation of this book.
I wanted to develop an insight into this complex problem and to develop a stepwise approach
in the treating ophthalmologist.
Eyes are the organs that receive and reect the intelligence of thought and the warmth
of sensibility. According to JC Lavater, Physiognomist (London, 1826), “The images of our
secret agitations are particularly painted in the eyes. The eye at once receives and reects the
intelligence of thought, and the warmth of sensibility. It is the sense of the mind, the tongue of
the understanding.” Hence, it is our duty and responsibility as strabismologists to ensure equal
vision in both eyes, which are, therefore, locked into equal and simultaneous movement in all
directions.
Strabismus (squint) is a sign; it is Nature’s way of telling us that something is wrong with
the eye itself, either structurally or functionally, or with the visual pathways and higher centers
controlling the ocular motility. It has a multifactorial etiology. In order to plan the correct
management, it is important to nd the causative factors and an attempt should be made to
rectify them rst before embarking on strabismus surgery. A clear conceptual knowledge of
refractive errors is mandatory to understand it completely. About 80-85% cases of strabismus are
due to mismanaged refractive errors. A sound understanding of refractive errors is the backbone
of strabismus management.
It is also very important to realize that except the truly Essential Infantile Esotropia, all other
kinds of strabismus have defective vision in either one or both eyes as a contributory factor.
Normally, equal visual acuity in both eyes causes a state of sensory fusion that locks the two eyes
to move together. If this locking mechanism does not occur due to poor vision in one eye, that
eye either turns inwards (esotropia) in an infant or a toddler or it turns outwards (exotropia) if
visual loss occurs after the age when accommodation is less active.
Although a strabismus surgeon is mainly concerned with “How” to correct the misalignment, it
is important to understand “Why” a particular procedure works. This is discussed in detail in Chapter
10, “Basic Surgical Principles”. There is always a choice of surgical options for correcting a particular
ocular misalignment and the procedure that gives an easy solution without compromising any
other ocular movement should be opted for.
There are certain Laws governing the ocular movement, which should be kept in mind while
assessing a strabismus patient. Listing’s Law describes how a xed ocular movement takes place
around an equatorial plane going through the center of rotation of the eye; hence, the strabismic
surgeon should not disturb this plane by too much recession/resection of the recti. According to
the Hering’s Law, there is an equal and simultaneous innervation of the yoke muscles in both eyes
Prelims.indd 9 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
x
for any direction of gaze (while assessing ocular motility, both yoke muscles should act to the
same extent without any under-action/over-action of either member of the group). Sherrington’s
Law describes reciprocal innervation of the agonist and the antagonist, so when one muscle
contracts, its direct antagonist relaxes. Hence, the strabismologist must understand these basic
concepts to interpret complex ocular motility patterns, particularly in paralytic strabismus where
secondary muscle changes commonly occur in longstanding cases.
Finally, always remember, “Vision before Surgery”; only equal vision in both eyes allows
sensory fusion to Lock the ocular alignment in all directions of gaze. However, if the vision is
poor in one eye, absence of sensory fusion will not allow the eyes to Lock even after an excellent
squint surgery, and the eye with poor vision will drift outwards under the inuence of active
divergence in adults.
Sameera Irfan
Prelims.indd 10 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
CONTENTS
Chapter 1:
Assessment of Strabismus 1
History 1
Examination 2
Chapter 2:
Refractive Errors 12
Hypermetropia 12
Normal Development of the Refractive State of the Eye 12
Optics of Hypermetropia 13
Myopia 17
Etiology 17
Optics 18
Symptoms 18
Management 19
Astigmatism 23
Causes 23
Optics 23
Symptoms 24
Management 24
Chapter 3:
Amblyopia 26
What is Amblyopia? 26
Etiology 26
Clinical Types of Amblyopia 27
Management of Amblyopia 29
Occlusion Therapy 31
Part-time Occlusion Therapy 31
Full-time Occlusion Therapy 32
Cycloplegic Drugs 33
Chapter 4:
Essential Infantile Esotropia 35
Essential Infantile Esotropia 35
Clinical Features 36
Risk Factors for Developing Infantile Esotropia (ET) 36
Prelims.indd 11 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
xii
Dissociated Vertical Deviation 36
Clinical Features 37
Management of DVD 38
Dierential Diagnosis of Essential Infantile Esotropia 38
Examination 39
Chapter 5:
Esotropia 42
Fully Accommodative Esotropia 42
Clinical Features 42
Management 43
Partially Accommodative Esotropia 44
Clinical Features 44
Management 45
Near Esotropia 45
Measurement of Accommodative Convergence/Accommodation ratio 45
Management 46
Distance Esotropia 46
Secondary Esotropia 47
Management 47
Consecutive Esotropia 47
Management 47
Chapter 6:
Exotropia 49
Intermittent Primary Exotropia 49
Examination 50
Management 50
Constant Primary Exotropia 51
Early Onset Exotropia 51
Decompensated Intermittent Exotropia 51
Examination 51
Management 51
Secondary Exotropia 52
Management 52
Consecutive Exotropia 52
Management 53
Chapter 7:
A and V Patterns 55
Chapter 8:
Paralytic Strabismus 58
Characteristics 58
Aims of Examination 59
Etiology 59
Prelims.indd 12 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
Contents xiii
Third Nerve Palsy 60
Neuro-ophthalmic Examination 61
Aims of Examination 61
Dierential Diagnosis 62
Investigations 63
Management 63
Superior Division Palsy 64
Muscle Sequelae 64
Characteristics 64
Management 65
Double Elevator Palsy/Superior Division Palsy 65
Clinical Presentation 66
Inferior Division Palsy 67
Characteristics 67
Management 68
Fourth Nerve Palsy 71
Diagnosis 71
Dierential Diagnosis: Sudden Onset Fourth Nerve Palsy in an Adult 72
Investigations 73
Sixth Nerve Palsy 74
Surgical Anatomy of the Sixth Nerve 75
Localization of Site of Sixth Nerve Palsy 75
Management 77
Chapter 9:
Restrictive Strabismus 78
Duane’s Retraction Syndrome 78
Surgical Plan 81
Brown’s Syndrome 83
Dierential Diagnosis 84
Fibrosis Syndrome 86
Strabismus Fixus 86
Thyroid Eye Disease 86
Signs and Symptoms of Thyroid Eye Disease 88
Proptosis and pseudoptosis 88
Lid Retraction, Lid Lag and Glabellar Furrows 89
Corneal and Conjunctival Findings 89
Orbital Muscle Involvement 89
Increased Intraocular Pressure 90
Cutaneous Findings 90
TED Classication 90
Prelims.indd 13 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
xiv
NOSPECS 90
Outpatient Management 92
Sight-threatening Disease 92
Medical Treatment for Moderate-to-Severe Disease 93
Overview of Surgical Intervention 93
Orbital Decompression 94
Strabismus Surgery 95
Chapter 10:
Basic Surgical Principles 97
Surgical Anatomy 97
Physiology of Extraocular Muscles 101
Factors Aecting the Surgical Outcome 102
Management Plan in Strabismus 105
Surgical Options in Esotropia 105
Exotropia 107
Intermittent Exotropia 107
Alternate XT with Deviation Equal for Near and Distance Fixation 107
Postoperative Follow-up 109
SURGICAL COMPLICATIONS 109
Intraoperative Complications 110
Early Postoperative Complications 111
Late Postoperative Complications 112
Chapter 11:
Case Presentations 114
Case 1: Congenital Bilateral Sixth Nerve Palsy 114
Case 2: Acute Traumatic Unilateral Sixth Nerve Palsy 115
Case 3: Constant, Unilateral Esotropia in an Infant 115
Case 4: Alternating Esotropia 116
Case 5: Constant, Partially Accommodative Esotropia 117
Case 6: Consecutive Exotropia 119
Case 7: Lost Lateral Rectus Muscle 120
Case 8: Congenital Fibrosis of Extraocular Muscles 121
Case 9: Traumatic Inferior Division Palsy of the Third Nerve 121
Case 10: Double Elevator Palsy 122
Case 11: Intermittent Exotropia 123
Case 12: Dissociated Vertical Deviation (DVD) 124
Case 13: Constant Exotropia 125
Case 14: An Alternating Exotropia with A V-Pattern 126
Index 129
Prelims.indd 14 26-09-2013 18:24:50
JAYPEE BROTHERS MEDICAL PUBLISHERS
A patient with an ocular motility disorder may present with the following clinical complaints:
1. Subjective symptoms of headache, diplopia, asthenopia.
2. A manifest strabismus.
3. An abnormal head posture.
4. Defective ocular movement.
5. Decreased vision in one or both eyes.
6. Nystagmus.
An accurate and detailed history, and a step-by-step clinical examination not only helps in
diagnosing the cause of strabismus but also helps in outlining a management plan.
HISTORY
Many visual problems in children are associated with developmental anomalies, hereditary
disorders or diseases of the childhood.
1. Detailed medical history: Regarding child’s developmental milestones, his progress at
school. Any medical illness, e.g. epilepsy, jaundice, diabetes, meningitis may result in
poor mental capabilities; history of head injury may result in paralytic strabismus. Child
receiving any current medications.
2. Obstetric history: Regarding child’s gestational age and birth weight, any trauma sustained
during labor, mother’s health during pregnancy.
3. Family history: Regarding refractive errors, particularly myopia, astigmatism and
strabismus.
4. History of strabismus: Its age of onset, direction (eye turning inwards or outwards),
whether intermittent or constant, any increase in the angle of deviation, therapy already
received in the form of glasses, occlusion, surgery; diplopia indicates either an increase in
the angle of strabismus or a strabismus of recent onset.
Assessment of Strabismus
CHAPTER
1
Chap-01.indd 1 23-09-2013 12:16:15
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
2
EXAMINATION
Idea of examination is to nd answers to the following questions:
Is the Squint really present? Exclude pseudo-strabismus, + angle kappa.
Why in this particular patient? Must nd the cause of strabismus.
How much? Need to have a proper objective measurement.
What will be the Management plan?
1. General Appearance: As a patient walks into the clinic, note his gait, posture, appearance.
Conditions commonly associated with strabismus in a child are: Hydrocephalus,
microcephaly, Down’s syndrome, albinism, cerebral palsy commonly associated with
congenital esotropia/exotropia of a large and variable angle.
In adults: Facial palsy, dysthyroid ophthalmopathy, tremors, ataxia, deafness, trauma.
2. Abnormal Head Posture (AHP:
Face Turn: Indicates a horizontal deviation (Figs 1.1A to C).
Head Tilt: Torsional deviation in oblique muscle palsies.
Chin Up/down: It indicates a vertical deviation or ptosis (Fig. 1.2). A chin up posture is
adopted to increase the eld of vision.
In a child, AHP indicates good binocular visual potential. In an adult, AHP is adopted to
avoid diplopia.
Dierences between an ocular and a non-ocular cause of AHP:
i. e ability to straighten the head in ocular torticollis.
iii. e presence of squint/nystagmus on straightening the head.
Ocular causes: Paralytic squint, A/V pattern, to obtain better vision in ptosis, nystagmus,
eld defect, restricted ocular movement (Duane’s retraction syndrome).
3. Position of Eyelids: Epicanthus, telecanthus blepharophimosis syndrome (Fig. 1.2),
ptosis (Fig. 1.3A) may result in pseudo-strabismus.
Lid retraction: It is seen in facial palsy (Fig. 1.3B) thyroid eye disease may point towards a
restrictive myopathy, orbital blow out fractures with muscle entrapment.
Ptosis causes amblyopia and may be the result of 3rd nerve palsy, myasthenia, chronic
progressive external ophthalmoplegia. Narrowing/widening of palpebral aperture on eye
Figs 1.1A to C: (A) Face turn to the right, orthophoric; (B) In primary position, right exotropia seen;
(C) Right esotropia with face turn to the right and fixing with the left eye only to avoid diplopia
A B C
Chap-01.indd 2 23-09-2013 12:16:15
JAYPEE BROTHERS MEDICAL PUBLISHERS
Assessment of Strabismus 3
Fig. 1.2: Chin up with bilateral ptosis and telecanthus (Blepharophimosis syndrome)
movement indicates lid retraction in restrictive disorders, aberrant 3rd nerve regeneration
(Figs 1.4A and B).
4. Assessment of Visual Acuity: Aims of examination are:
–To nd the functional status of either eye.
–To record patient’s vision according to his age.
–Before proceeding on to ophthalmic examination, it is important to get an idea of visual
potential of either eye.
Figs 1.3A and B: (A) Bilateral ptosis with chin-up posture and broad nasal bridge
(pseudo-strabismus); (B) Right lid retraction in right sided facial palsy
A B
Figs 1.4A and B: (A) Right ptosis and left lid retraction in primary position; (B) Narrowing
of left and widening of the right palpebral aperture on left gaze
A B
Chap-01.indd 3 23-09-2013 12:16:15
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
4
Visual assessment in toddlers:
i. Assessment of xation and following of light: A xation light is used at child’s eye
level, at a distance of 33 cm and the position of corneal reections from both eyes
are observed; the steadiness and persistence of xation is also noted. Observe if the
infant follows the light source with both eyes. Avoid auditory stimuli so that there is
no reex eye movement in the direction of sound.
ii. Visually directed reaching for small objects: A poorly sighted infant will move his
hand in an exploratory manner rather than directly reaching it.
iii. Presence and type of manifest strabismus: is is detected by noting the position
of corneal reections from both eyes (Hirschberg’s test) and then by performing a
cover-uncover and alternate cover test to detect the presence of a phoria as well as a
tropia.
iv. Check for amblyopia: If the child protests covering one eye, the other eye may be
amblyopic (ask the mother to cover child’s eye as this is less threatening to the child
than an examiner’s hand).
v. Preferential looking: is is a quantitative assessment of a child’s visual potential
using either Keeler cards or Forced Choice Preferential Looking. It is helpful in
monitoring progress in amblyopia therapy in infants and mentally subnormal
children.
vi. A 10 PD test: Holding a 10D prism in
front of one eye and note a correcting
eye movement to diagnose microtropia
or orthophoria.
Assessment of visual acuity in illiterate
children (3–5 years age group)
is is done by matching the symbols or
pictures with a replica held in hand to be
used at 33 cm or 6 m. ese tests include:
i. Stycar letters: ey are in the form of
square, circle and triangle shapes, and
the rst to be recognized and copied by
young children (Fig. 1.5).
ii. E test: Capital letter E can be presented
with the limbs directed up, down, right
or left as single letters on a card or as a
standard chart.
iii. Allen picture test: Pictures of a car,
house, and apple are presented on ip-
over cards, which are viewed at 3 m or
6 m distance (Fig. 1.6).
Fig. 1.5: Stycar letters
Fig. 1.6: Allen picture test
Chap-01.indd 4 23-09-2013 12:16:15
JAYPEE BROTHERS MEDICAL PUBLISHERS
Assessment of Strabismus 5
In literate children, record the Snellen’s visual acuity for distance as well as near for either
eye. is is important to monitor amblyopia therapy as near visual acuity starts improving
rst than the distance.
5. Diagnosis of Amblyopia: is usually requires a 2-line dierence of visual acuity between
the two eyes but a smaller dierence should not be ignored.
Crowding phenomenon: is is a common characteristic of amblyopia, visual acuity is
better for single optotypes rather than the whole line. is is particularly important in
patient follow-up once occlusion therapy is instituted as visual acuity improvement for
single letters starts earlier than the whole line.
Grading of amblyopia: Severity of amblyopia must be graded for planning the
management as duration of therapy and visual prognosis depends upon it.
Grade 0: No xation preference; xation held with either eye on cover test—amblyopia
not presents.
Grade 1: Fixation held with either eye after removing the occluder and maintained through
a blink but not after an ocular movement—mild amblyopia present.
Grade 2: Fixation held briey after removing the occluder and then switches to the other
eye after a blink—mild to moderate amblyopia.
Grade 3: Fixation held only for a few seconds after removing the occluder—moderate
amblyopia.
Grade 4: Fixation immediately shifts to the other eye after removing the occluder—dense
amblyopia.
6. Cover test, cover/Uncover and alternate cover tests:
Principle: ese tests are based on the principle of “Breaking Binocularity” and then
noting how each eye behaves when covered or uncovered. ey depend upon the patient’s
ability to xate with either eye. It needs patient’s attention and cooperation.
ey are performed for both near and distance xation with the patient wearing the
glasses. An occluder or the examiner’s hand can cover the eye.
Indications:
i. To detect whether the patient is orthophoric or has a latent (phoria) or a manifest
(tropia) strabismus.
ii. Prisms (Prism cover test) use them as a part of measuring total deviation.
iii. When patients are followed-up for their refractive correction, these tests are used
to assess muscle balance; if a patient is wearing his hypermetropic correction and
an exophoria is noted by an alternate cover test, the hypermetropic correction has
to be reduced. However, if the child is developing an esophoria with his refractive
correction, then the amount of plus correction has to be increased.
Similarly, if a patient wearing a myopic correction is noted to have an esophoria, his myopic
correction has to be reduced. However, if he has an exophoria, the myopic correction
should be increased.
Why? Plus correction relaxes accommodation/convergence while minus correction
induces it.
Chap-01.indd 5 23-09-2013 12:16:15
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
6
Cover Test (Fig. 1.7):
It conrms the presence of a manifest strabismus (tropia).
Although the patient xates on a near target, the normal looking eye is covered and the
behavior of the uncovered eye is noted as it takes up xation. If that eye moves inwards,
then and exotropia was present and if it moves outwards, then it was esotropic.
e test is then performed for distant xation and behavior of either eye is noted as one
eye is covered alternately.
If no movement of one eye occurs as the other eye is covered, then there is either no
strabismus or the uncovered eye has dense amblyopia.
Cover/Uncover Test: is detects a heterophoria (latent deviation). It is performed once
cover test does not demonstrate a manifest deviation (Fig. 1.8).
Method: While the patient xates at a distant target, one eye is covered and the behavior
of the eye under cover is noted as the cover is removed. If it moves to take up xation, a
heterophoria is present. e direction in which it moves is noted; if it moves outward, an
exophoria is present and if it moves inward, an esophoria is present.
Alternate Cover Test: is test detects the presence of an alternate or a unilateral deviation
(Fig. 1.9).
Method: In this test, occluder is placed in front of one eye for a few seconds to dissociate
the two eyes while the patient xates on the light in front of both eyes. While he is xating,
the cover is shifted quickly from one eye to the other to prevent fusion. e examiner
should note the movement of the eye as cover is being moved from it to the opposite eye.
If either eye moves when cover is removed to take up xation, an alternate strabismus is
present.
However, if one eye stays straight and only the other eye moves to take up xation, a
unilateral strabismus is present.
Fig. 1.7: Cover test: Noting the behavior of un-covered eye as the fixing eye is covered
Chap-01.indd 6 23-09-2013 12:16:15
JAYPEE BROTHERS MEDICAL PUBLISHERS
Assessment of Strabismus 7
Fig. 1.8: Cover-uncover test: Behavior of eye under the cover is noted as the cover is
being removed, whether it moves to take up fixation which indicates heterophoria
Fig. 1.9: Alternate cover test: Cover is rapidly moved from one eye to the other and behavior
of either eye is noted as it takes up fixation indicating an alternate strabismus
7. Eccentric Fixation (Fig. 1.10):
–When a normal eye xates, the image of the object falls on the retinal foveola. Some
amblyopic patients consistently xate with a non-foveal area of retina under monocular
use of amblyopic eye. Eccentric xation can be para-foveolar, para-foveal or peripheral.
Chap-01.indd 7 23-09-2013 12:16:16
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
8
–is can be diagnosed by holding a xation light in the midline in front of the patient
and ask him/her to xate on it while the normal eye is covered; the reection of light
will not be centered.
–e exact site of eccentric xation can be conrmed by looking through a visuoscope and
asking the patient to xate on the central spot. A visuoscope is a direct ophthalmoscope
with a xation target incorporated into the ophthalmoscope beam.
–e incidence of eccentric xation is far higher in longstanding esotropia than exotropia.
–e visual acuity depends upon the site of eccentric xation; the farther it is from the
foveola, the lesser is the visual acuity in that eye.
–In the presence of eccentric xation, full visual recovery by occlusion therapy should
not be expected unless the xation changes to the foveola.
8. Refraction: First subjective and then cycloplegic refraction is performed. Usually the
more myopic, hypermetropic or astigmatic eye has amblyopia.
9. Examination of Pupillary Response to Light: Direct and consensual. Even in dense
amblyopia, pupils react normally to light. An organic cause should be suspected if a
relative aerent pupillary defect or bilaterally sluggish pupils are detected.
A paradoxical response to light: Pupils constrict in the dark and dilate when light is
switched on. is is seen in congenital stationary night blindness, cone dystrophy and
Leber’s congenital amaurosis.
10. Color Vision: Presence of defective color vision indicates an organic cause for amblyopia.
11. Full Ophthalmic Examination: Slit-lamp examination and fundoscopy to nd any
organic cause of amblyopia, which may need treating prior to specic amblyopia therapy.
12. Imaging Studies: If an organic cause for decrease in visual acuity is suspected in the
presence of a normal ophthalmic examination, then further investigation of the visual
pathway is indicated, i.e. CT scan, MRI or uorescein fundus angiography (FFA).
13. Measurement of Ocular Deviation:
Hirschberg’s test: is is a rough estimate of the degree of deviation by comparing
corneal reections in both eyes as the patient xates on a light source 33 cm away. If the
Fig. 1.10: Eccentric fixation
Chap-01.indd 8 23-09-2013 12:16:16
JAYPEE BROTHERS MEDICAL PUBLISHERS
Assessment of Strabismus 9
light reection is situated at the temporal
border of an undilated pupil, the rough
angle of strabismus is 15°; if it is at the
limbus, then the angle of deviation is
about 45° and in the middle of these two
points, it is about 30° (Fig. 1.11).
Advantages: It is an easy test and gives a
quick estimate of the degree of strabismus.
It can be performed easily in uncooperative
patients.
Disadvantages: It gives a rough measure-
ment. Errors are introduced in a dilated
pupil or in the presence of an angle Kappa;
it is the angle between the visual axis and
the anatomical axis of the eye. Fovea is
normally situated temporal to the visual
axis so light falling on the cornea will cause a reection nasal to the center of cornea,
hence causing a positive angle kappa. A large, positive angle kappa will give an erroneous
impression of an exotropia. Similarly, a negative angle kappa will give a false impression
of an esotropia.
Krimsky test: In this text, prisms are placed in front of the deviated eye, with the apex of
the prism in the direction of deviation, till the corneal light reexes are symmetrical in
both eyes. Its value is mainly in esotropia in children where it is dicult to maintain their
xation in order to perform a prism cover
test (PCT).
Prism cover test: is provides an accurate
measurement of the total deviation (Phoria
+ Tropia). First a hand held prism of the
rough estimate detected by the Hirschberg’s
test is placed in front of the deviating eye
with its apex in the direction of deviation.
e measurement is done rst for near
(33 cm) and then for far distance (>6 m).
It should also be done for side-gaze, if
possible (Fig. 1.12).
For example, in exotropia, prism is placed
in front of the deviating eye with its apex
outwards. With the other eye xing,
alternate cover test is performed till no ocular movement occurs. is is called the
Neutralization Point, (65 PD in above example).
In exotropia, patients have a strong divergence, hence the strength of prisms is kept
on increasing till a small movement of the eye in the opposite direction occurs, i.e.
Fig. 1.11: Hirschberg’s test
Fig. 1.12: Prism set: Loose prisms (top) as
well as a vertical and a horizontal prism-bars
(bottom)
Chap-01.indd 9 23-09-2013 12:16:16
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
10
in exotropia, the point at which the eye starts to move outwards. is is called the
Reversal Point (Fig. 1.13). is point gives the measurement of divergence amplitude in
a patient and varies from person to person. Its exact measurement is very important for
proper management of exotropia surgically.
14. Tests for Stereopsis: e two commonly used tests are Titmus and TNO.
Titmus: is consists of two plates in the form of a booklet, which are viewed with poloroid
glasses that should be worn over the patient’s refractive glasses. e plates contain a three-
dimensional picture of a y or animals and are graded.
TNO: is consists of seven plates that contain various shapes like squares, crosses created
by random dots in complementary colors viewed with red and green glasses.
15. Measurement of Amplitude of Convergence:
Signicance: Convergence may alter in dierent conditions presenting either as an
insuciency resulting in symptoms of asthenopia with headache, eye strain and sore
eyes. is particularly occurs following prolonged close work in children resulting in an
exophoria and diplopia.
Fig. 1.13: Left exotropia. A 45 PD loose prism is placed in front of left eye with its apex pointing outwards;
still inward movement of the left eye is noted on alternate cover test. The strength of prism is gradually
increased to 65 PD at which no eye movement is detected on alternate cover test (Neutralization point).
Then the strength of prisms is further increased till at 75 PD a reversed movement of left eye in outward
direction is noted (Reversal Point)
Chap-01.indd 10 23-09-2013 12:16:16
JAYPEE BROTHERS MEDICAL PUBLISHERS
Assessment of Strabismus 11
Measurement:
Near point of convergence: is is the closest point at which an object can be seen clearly.
It is usually less than 8 mm. It is measured by a ruler placed at the outer canthus while
a xation target, a pencil, is brought towards the eyes. e point is noted where one eye
begins to diverge.
Far point of convergence: is is at innity.
Amplitude of convergence: is is measured by a prism bar. e test is performed for near
at 33 cm with the patient xating on a target. e prism bar, base-out is placed in front of
one eye and the strength of prisms gradually increased. e eyes converge till a point is
reached when the patient develops diplopia. is is called the Break Point.
e prism power is gradually reduced till the diplopia disappears. is is called the
Recovery Point. e dierence between the break point and recovery point gives the
amplitude of convergence.
Chap-01.indd 11 23-09-2013 12:16:16
JAYPEE BROTHERS MEDICAL PUBLISHERS
HYPERMETROPIA
Normal Development of the Refractive State of the Eye (Fig. 2.1)
At birth, almost all eyes are hypermetropic (2–3D).
As the eyeball’s axial length increases with body growth, by the age of one year, 50% of
infants become emmetrope while hypermetropia persists in about 40–45% children and
continues to increase as accommodation starts increasing by the age of 2 years. en, as the
accommodation amplitude begins to decrease after the age of 10 years, hypermetropia also
starts decreasing (Fig. 2.2).
Refractive Errors
CHAPTER
2
Fig. 2.1: Graph plotted between % age of population exhibiting refractive errors, along Y-axis in terms
of age, plotted along the X-axis. Green color indicates the prevalence of hypermetropia and red color
depicts myopia in the general population
Chap-02.indd 12 23-09-2013 17:01:52
JAYPEE BROTHERS MEDICAL PUBLISHERS
Refractive Errors 13
Physiological Hypermetropia (HMR): As a rule, the decrease in axial length rarely exceeds
2 mm; each mm of eyeball shortening causes 3D of hypermetropia, hence more than 6 D is
uncommon.
Pathological Hypermetropia: It is seen in any lesion attening the posterior pole, e.g. tumor,
edema (CSR), inammation, detached retina.
Optics of Hypermetropia (Fig. 2.3)
In emmetropia, the lens (in a relaxed state) onto the retina (fovea) focuses parallel light rays
from a distant object.
In hypermetropia, because of short axial length, parallel light rays from the distant
object are focused behind the retina resulting in a blurred image. However, this is avoided by
increasing the curvature/thickness of the lens of the eye by calling upon the accommodation;
this increases the refractive power of the lens and distant rays are brought to focus upon the
retina. Since the hypermetropic eye has a short axial length, the retina is closer to the nodal
point, hence the image formed on the retina by increasing the accommodation is of relatively
smaller size than in an emmetrope.
e rays coming from a near object are divergent. A hypermetropic eye is already utilizing
accommodation to focus distant parallel rays, hence the divergent rays from the near object
are focused behind the retina resulting in a blurred near image. As the accommodative
eort increases to focus the near object, the eye converges as well due to accommodation/
convergence synkinesis resulting in esotropia.
Fig. 2.2: Normal growth pattern of an eye: 50% infants become emmetrope by 1 year age.
40–45% show an increase in hypermetropia. 5–10% become myope with increasing age
Chap-02.indd 13 23-09-2013 17:01:52
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
14
Types of Hypermetropia
1. Latent: is portion of hypermetropia is corrected by the physiological tone of ciliary
muscle. Hence, full extent of hypermetropia is only revealed when the ciliary muscle is
relaxed fully by atropine. Generally, this is up to 1 D.
2. Manifest: e remaining portion of hypermetropia, which under normal physiological
conditions remains uncorrected, is called Manifest HyM. An individual can correct the
entire error by accommodating and this is called Facultative HMR.
If the error is large, then even by fully accommodating, the objects are not seen clearly,
especially for near, hence this remaining amount of HyM that still remains uncorrected by
accommodation is called Absolute (and needs correcting glasses).
Total HMR = Latent + Manifest (Facultative + Absolute)
= (muscle tone) + (Active accommodation + Glasses).
Symptoms
A hypermetrope accommodates constantly for distance to see clearly. is constant eort
caused headache and fatigability.
For near work, the person needs extra accommodation; this results in more headache,
eye strain and blurring of vision. is situation continues for some time, until the child gives
up the eort to see binocularly, and the more hypermetropic eye turns inwards causing
accommodative esotropia.
Sometimes, intense close work for long hours and continuous accommodation causes
spasm of ciliary muscle and articial myopia.
Fig. 2.3: Optics of hypermetropia
Chap-02.indd 14 23-09-2013 17:01:53
JAYPEE BROTHERS MEDICAL PUBLISHERS
Refractive Errors 15
In high HMR, accommodation is not enough for either a clear distant and near vision
resulting in dense amblyopia. e high hypermetrope may hold the book close to get an
enlarged retinal image that compensates for its blurring and indistinctness.
Management
How much to prescribe—following guidelines are suggested:
1. e patient is examined for the presence or absence of esophoria/esotropia or exophoria/
exotropia with the patient’s glasses o rst and then on (his old prescription). Prescription
of new glasses will depend upon the state of muscle balance between the two eyes.
2. For children under 6 years of age, visual acuity in either eye is checked rst and then
cycloplegic refraction is done.
3. If there is no esophoria/tropia then cycloplegia with cyclopentolate 1% eyedrops will
suce; however, if there is associated esophoria or esotropia, then full cycloplegia is
necessary with atropine eyedrops or ointment to abolish the ciliary muscle tone and
determine the total hypermetropia and astigmatism.
4. If there is no esotropia/esophoria and hypermetropia is less than 6.5D, then 2/3 of
cycloplegic correction is given; the plus cylinder is fully prescribed while 1/3 is deducted
from the spherical correction. e child is instructed for constant use of spectacles.
5. In children more than 6 years old and without esotropia/esophoria, subjective refraction is
done, once the eect of cycloplegia has worn o (in a week’s time), that will give maximum
correction for near and distance vision.
6. If hypermetropia is more than 6.5D, it results in blurred vision at all distances as
accommodation is not sucient to have a clear image either for near or distance. is
results in ametropic amblyopia bilaterally. In such cases, full plus correction is given for
children under 6 years age group while for children more than 6 years age group, maximum
plus correction that the child tolerates after subjective refraction.
7. In the presence of esophoria or esotropia, if full cycloplegic correction is not given, the
child will continue to accommodate for near with resultant convergence and persistence of
esotropia for near in the more hypermetropic eye. Persisting esotropia results in extrafoveal
xation (temporal) with resultant decrease in vision in the more hypermetropic eye and
amblyopia while the child is constantly wearing glasses (Fig. 2.4).
8. If the child is already wearing hypermetropia correction, which is associated with
exophoria/exotropia, it means this much correction is too strong and is relaxing the
accommodation and convergence to such an extent causing the strabismus. In this
situation, the minimum plus is given which retains 6/6 vision. If astigmatism is also
present, then plus cylinder is prescribed in full while minimum plus sphere is given.
9. In unilateral, high hypermetropia, phakic IOL implantation into the sulcus or iris claw lens
is an option in children > 14 years age.
10. Follow-up of patients wearing hypermetropic correction:
It is very important to bear in mind that accommodation amplitude at rst increases from
the age 2 years till 10–12 years (Fig. 2.5). Hence, the amount of hypermetropia increases.
Chap-02.indd 15 23-09-2013 17:01:53
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
16
Children need to be followed-up every 6 months if strabismus is also present or annually,
in the absence of strabismus.
–At each visit, the state of muscle balance is rst assessed with the child wearing the
glasses with cover/uncover and alternate cover test.
–If esophoria/esotropia is detected while wearing the correction, cycloplagic refraction
is repeated in order to increase the amount of plus correction.
–If the child is orthophoric with the present glasses and the visual acuity is 6/6 Snellen’s,
then there is no need to change the correction for another 6 months.
–If an exophoria/exotropia is detected on alternate cover test with the present correction,
then the amount of plus has to be decreased to that extent which retains 6/6 vision
(Figs 2.6A to C).
Fig. 2.4: Principle of correction of hypermetropia: If only 2/3 of hypermetropia is corrected by refractive
glasses, slight esotropia persists and so does the extrafoveal fixation. Only with full hypermetropic
correction, the eyes are straight and achieve foveal fixation
Fig. 2.5: Graph depicting changes in accommodation with increasing age
Chap-02.indd 16 23-09-2013 17:01:53
JAYPEE BROTHERS MEDICAL PUBLISHERS
Refractive Errors 17
MYOPIA
e term myopia means “I close eyes”, a myope sees distant objects with half-closed eyes.
Etiology
1. Axial: In most cases, it is the continued increase in axial length of the eye as the child grows
that results in myopia. Simple myopia is seen as a normal physiological variant and the
myopia does not exceed 6D. Pathological or progressive myopia is determined genetically
and myopia keeps on increasing with pathological changes in all coats of the eyeball due
to continuous stretching and thinning.
2. Curvature: A 1 mm increase in corneal curvature results in 6D myopia. However, this is
less common and seen in keratoconus, anterior or posterior lenticonus or in spasm of
accommodation.
3. Index: Increase in refractive index of lens, seen in diabetics or in nuclear sclerosis.
At birth, 94% eyes are slightly hypermetropic (+2.5D) due to smaller size of the eyes as
compared to the rest of the body. By the age of 4 years, the eye and the brain attain 85% of their
full size while the rest of the body has grown to only 20%. Myopia results from a continuation
of this growth pattern, which is genetically determined and due to the presence of adjuvant
factors like physical disability, close work for prolonged periods of time that produces strain
and consequent stretching of coats of the eyeball with resultant increase in myopia. is factor
is a particularly important cause of progressive increase in myopia seen in teenagers (Fig. 2.7).
Progress of Myopia: At birth, myopia is rare and is usually of the pathological variety, determined
congenitally.
Figs 2.6A to C: Principles of follow-up of patients wearing hypermetropic correction; (A) Patient
orthophoric wearing OD +4.00 D and OS +5.00 D; (B) After 1–2 years of wearing this correction
in a 7–8 year old patient, the eye may become exotropic; (C) Following subjective refraction, the plus
correction is reduced to OD +3.00 D and OS +3.50 D, the eyes become orthophoric again and 6/6
visual acuity is also retained
A
B
C
Chap-02.indd 17 23-09-2013 17:01:53
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
18
It starts appearing at teens, may remain stable or progresses for a few years as the body is
growing and then stabilizes at 20–22 years.
If myopia appears after adolescence, it is important to exclude causes of index myopia
particularly diabetes.
Optics (Fig. 2.8)
In myopia, parallel rays of light from a distant object are focused in front of the retina resulting
in a blurred distant image.
Rays from a near object are divergent; hence, they focus on the retina causing a clear
image. Hence, a myope can see near objects clearly and the furthest distance at which the
vision is clear is called the Far Point (Punctum Remotum).
In an emmetrope, the far point is at innity while in a myope, the higher the degree of
myopia, shorter is the distance, e.g. in myopia of 1D, far point is at 1 meter, in myopia of 2D, far
point is ½ meter.
Symptoms
1. A limited horizon; a myope can only see clearly till the far point. Hence, his whole world is
limited to that distance.
2. Eye strain, diplopia for near (Fig. 2.9). e eyes have to converge for close work; convergence
causes accommodation as well because of accommodation/convergence synkinesis in
the brain (both reexes operate together). e divergent rays from near objects focus
clearly on the retina without the need for accommodation, but because of the synkinetic
reex, this extra accommodation focus rays in front of the retina resulting in a blurred
Fig. 2.7: Age distribution curve for refractive errors
Chap-02.indd 18 23-09-2013 17:01:53
JAYPEE BROTHERS MEDICAL PUBLISHERS
Refractive Errors 19
Fig. 2.8: Optics of myopia: Parallel light rays from a distant
object are focussed in front of the retina, resulting in a blurred
distant image. The rays from a near object are seen clearly as
they are focussed on the retina. Holding a concave (minus/
diverging) lens in front of the eye focusses distant light rays on
the retina
Fig. 2.9: Physiology of myopia
near image. Hence, the myope gives up the eort
to converge allowing one eye to deviate outwards
resulting in diplopia for near and exophoria initially,
progressing later to exotropia.
3. Amblyopia occurs if > -4D myopia in one eye with
constant exotropia.
Management
Children
1. e weakest minus lens is prescribed that gives 6/6 vision for distance.
2. e minus correction should be worn constantly for near and distance to restore
convergence/accommodation relationship (Fig. 2.10). Relation for near as well, e.g. the
-2D lens restores 6/6 vision for distance and for near, it negates and balances the extra
accommodation as a result of convergence for near resulting in a clear near image as well
and correction of exophoria/exotropia and diplopia.
3. If the patient has exotropia, then full myopic correction is given to stimulate
accommodation/convergence.
4. If the patient is developing esophoria with his present myopic correction, then it is
important to reduce the minus correction.
5. If the patient has to be prescribed glasses for the rst time and he has esophoria/esotropia,
then transpose the minus cylinder to a plus cylinder to relax the accommodation.
Chap-02.indd 19 23-09-2013 17:01:54
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
20
6. In adults, it is important to decrease the minus correction for near as the amplitude of
accommodation decreases with age (Fig. 2.11).
7. If amblyopia is associated with myopia only and no strabismus, children under 6 years
of age are given 2/3 of cycloplegic correction while more than 6 years old are given the
minimum minus sphere and full minus cylinder that gives maximum distance vision.
Fig. 2.10: Correction of myopia in children; the same number of
minus correction is worn for both distant and near vision
Fig. 2.11: Myopic correction in adults: in children, same number is worn constantly but in adults, due
to the onset of presbyopia, accommodation decreases for near. Hence, adults need a lesser minus
correction for near
Chap-02.indd 20 23-09-2013 17:01:54
JAYPEE BROTHERS MEDICAL PUBLISHERS
Refractive Errors 21
8. If myopia is associated with exophoria/exotropia, then full minus correction is prescribed.
is will enable the patient to exert accommodation and convergence, and control the
strabismus.
9. High degrees of myopia at birth can result in esotropia in early childhood. In this case,
the infant’s far point is very close to the eyes making the eyes converge all the time to see
clearly at this distance; the vision for more remote distance is poor so convergence is not
relaxed on looking further away resulting in constant esotropia.
10. Dispensing spectacles: e spectacle frames should be well tted and accurately centered
to avoid spherical and chromatic aberrations. e frames should be of light material so the
child can wear them comfortably, and the lenses of plastic material so they do not break
easily and are light weight.
11. e child is examined again after one month of constant spectacle wear and visual
improvement in either eye is noted. Amblyopia has been found to be improved to 50% by
wearing correct spectacle correction constantly.
12. Surgical options:
Corneal refractive surgery: RK, PRK, LASIK.
Clear lens extraction (CLE), also called refractive lens exchange (RLE), is the removal of a
non-cataractous, natural lens of the eye with or without intraocular lens placement.
Indications: It is usually reserved for patients with high myopia (> 8 diopters [D]) that is not
easily managed by other refractive procedures, such as laser in situ keratomileusis (LASIK) or
photorefractive keratoplasty (PRK). However, CLE may be an even better choice for patients
with high hyperopia (> 4 D) because of the smaller risk of postoperative retinal detachment.
Aims of refractive surgery: Accuracy, stability, safety, and quality of vision.
Regarding accuracy, ideally, a standard deviation of less than 0.25 D is wanted, yielding
20/25 (or better) uncorrected acuity in 95% of patients for all amounts of myopia, hyperopia,
and astigmatism. Currently, no procedure produces this result, but the closest are LASIK
or PRK for low or moderate myopia and LASIK for patients with mild hyperopia. Currently,
A-scan measurements and IOL choice, even using the IOL Master, especially in patients with
high hyperopia and those with myopia, yield an accuracy of signicantly less than ± 0.25 D.
Regarding stability, CLE is probably the most stable refractive procedure available, with ±
0.02 D per year reported over a 9-year observation period. PRK has a signicantly higher risk of
regression or progression, while LASIK carries a risk of corneal ectasia.
Quality of vision is far superior in an unoperated cornea. Any surgical procedure on the
cornea creates abnormal contours, hence optical aberrations. e greater the correction, the
greater the amount of induced aberration and the concurrent decrease in quality of vision,
especially in low-contrast situations (e.g. driving at night). Clearly, CLE is an optically superior
choice in some situations.
Regarding safety, complications like endophthalmitis, retinal detachment following
intraocular surgery are much greater than the worst complications of other refractive
procedures, e.g. ap loss, corneal scarring requiring corneal transplant.
Chap-02.indd 21 23-09-2013 17:01:54
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
22
Toric IOLs are now available for intraocular correction of astigmatism. Now, many
surgeons are using multifocal IOLs and accommodative IOLs for the intraocular correction of
presbyopia. e intracapsular placement of a exible, plate-haptic, foldable, accommodative
IOL, called Crystalens, with its hinged haptics, facilitates back and forth movement along the
optical axis of the eye in response to pressure changes resulting from ciliary muscle contraction
and relaxation.
Contraindications include retinal disease. With high myopia, a higher rate of retinal
detachment exists than with other types of refractive errors.
Phakic IOLs: Angle supported, iris supported, or placed in the posterior chamber.
e important considerations are the ease of application, the accuracy, the period of
recovery, the quality of vision, the long-term stability of the results, and the minor or major
complications. Also important is the possibility of the reversal of the procedure and the
successful management of complications.
ese surgical procedures are commonly used in adult patients but there is a limited
experience in the pediatric age group. Slight or moderate myopes do extremely well with glasses
or contact lenses. However, high myopes do experience serious handicaps, both cosmetic and
visual, for which surgery becomes a matter of importance.
e angle-supported lens becomes xated somewhere in the angle structures. A well-
xed lens rests its haptics on the scleral spur; the haptics press against the corneoscleral
trabeculae, Schlemm canal, the blood vessels in the vicinity and can impinge on the nerve
endings in the angle of the anterior chamber. When the haptics press on the segmental blood
supply of the iris, ischemia, atrophy and progressive ovalization of the pupil occurs. e haptics
can erode through the angle tissues and become lodged in the ciliary body.
A loose angle-supported lens can move around and damage the corneal endothelium.
Tissue reactions and damage to the angle of the anterior chamber can cause breakdown of the
blood-aqueous barrier, uveitis-glaucoma-hyphema (UGH) syndrome.
Iris claw lenses are made of PMMA; the overall length of the implant varies from 7.2–8.5
mm, the size of the optic varies from 5–6 mm. e optic is convexo-concave, with a maximum
height of 0.96 mm. e lens also is vaulted at the haptic to clear the natural vault of the iris.
e haptics become xed to the midperiphery of the iris through claws located on either
side of the lens. No pupil or posterior pigment epithelium-related problems occur because
the lens does not come into contact with either of them. e inclusion of excessive iris tissue
in the claws during surgery can push the lens against the iris and the crystalline lens. is can
interfere with the free circulation of the aqueous through the pupil, possibly resulting in the
formation of posterior synechia and inammation.
Micromovements, such as blinking and squeezing, does not allow the corneal endothelium
to touch the optic of the IOL. However, forcible rubbing for any reason has the potential to
damage the endothelium.
Posterior chamber lenses or the precrystalline lens is made of a soft material, such as
silicone or collamer. e overall length varies from 11–13 mm (posterior chamber lens is sized
by adding 0.5 mm from the white-to-white corneal diameter). e central biconcave optical
zone varies from 4.5–5.5 mm. e average thickness of the haptic is 60 µm, it remains clear of
the crystalline lens by 100–200 µm.
Chap-02.indd 22 23-09-2013 17:01:54
JAYPEE BROTHERS MEDICAL PUBLISHERS
Refractive Errors 23
e vaulting of the lens is produced by the elastic single piece lens getting lifted from
the ciliary body. is puts some constant pressure on it. e vaulting may let it stay clear of
the crystalline lens, but it pushes the iris anteriorly; resulting in mild to moderate uveitis or
shedding of posterior pigment epithelium. It also may prevent free passage of aqueous across
the pupil. A mistakenly larger sized lens will exaggerate these problems. A peripheral iridectomy
is important to prevent angle-closure glaucoma. In diabetic patients, these problems are
worsened. In all phakic IOLs, increased crystalline lens size with increasing age and cataract
formation leading to a decrease in the depth of the anterior chamber and crowding in the
posterior chamber tend to exaggerate the pathologic processes. While the results of phakic
IOLs are highly predictable, long-term data are limited.
ASTIGMATISM
In this condition, no single point of focus is
formed on the retina resulting in a slightly
blurred image.
Causes
Physiological: Because of the pressure of upper
lid on the cornea making the vertical curvature
greater than the horizontal. It is also called
direct astigmatism and is around 0.25–0.50D. it
reverses or corrects itself by the age of 7 years.
Acquired causes: Corneal inammations
like VKC, a healed corneal ulcer (resulting in
a corneal opacity), corneal surgery or trauma
(causing scarring), eyelid tumor/swelling
causing increased pressure on the cornea,
Keratoconus.
Lens decentration, cataract results in an index
astigmatism.
Optics (Fig. 2.12)
Normally, a point object forms a point focus on
the retina.
In astigmatism, there are two focal lines
separated by a focal interval. e length of
focal interval depends upon the degree of
astigmatism. Astigmatism can only be corrected
by reducing these two foci into one. Fig. 2.12: Optics of astigmatism
Chap-02.indd 23 23-09-2013 17:01:54
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
24
In simple myopic astigmatism, one focal line is on the retina and the other one in front of
retina, depending upon the degree of astigmatism.
In simple hypermetropic astigmatism, one meridian is focused behind the retina while the
other one on the retina.
In mixed astigmatism, one meridian is focused in front of retina while the other one behind
it.
In compound astigmatism, both foci are either in front or behind the retina.
Symptoms
Since no sharp image is formed on the retina for any distance, even small degree of astigmatism
causes blurring of vision and eye strain. Circles are viewed as ovals, and point of light appears
tailed o. A single line object is viewed as a series of strokes fused into a blurred image. All these
symptoms are more severe in hypermetropic astigmatism because of constant accommodative
eort by the individual that increases the eye strain.
Management
1. Smaller degree of astigmatism (0.50–1.00 DC) not causing any eye strain can be ignored
but even correcting such a minor amount of astigmatism improves clarity of vision.
2. However, in the presence of asthenopic symptoms, the cylindrical defect should be fully
corrected, the sphere prescribed according to the rules already mentioned (under-
corrected, depending upon the age and state of muscle balance of the two eyes).
3. If a patient is to be prescribed cylinder for the rst time and the error is large, it is better
to under-correct the cylinder, let the patient accustomed to it in a month’s time and then
gradually increase it.
FURTHER READING
1. Arne JL. Phakic intraocular lens implantation versus clear lens extraction in highly myopic eyes of 30- to
50-year-old patients. J Cataract Refract Surg. Oct 2004;30(10):2092-6.
2. Bron AJ, Tripathi RC, Tripathi BJ. Wol’s Anatomy of the Eye and Orbit. 8th ed. London: Chapman and Hall
Medical; 1997:322-325, 350-351.
3. Colin J, Robinet A. Retinal detachment after clear lens extraction in 41 eyes with high axial myopia. Retina.
1997;17(1):78-9.
4. El-Helw MA, Emarah AM. Assessment of phacoaspiration techniques in clear lens extraction for correction
of high myopia. Clin Ophthalmol. Mar 24 2010;4:155-8.
5. Fechner PU, Singh D, Wul K. Iris-claw lens in phakic eyes to correct hyperopia: preliminary study. J Cataract
Refract Surg. Jan 1998;24(1):48-56.
6. Jimenez-Alfaro I, Miguelez S, Bueno JL, et al. Clear lens extraction and implantation of negative-
power posterior chamber intraocular lenses to correct extreme myopia. J Cataract Refract Surg. Oct
1998;24(10):1310-6.
7. Koivula A, Zetterstrom C. Phakic intraocular lens for the correction of hyperopia. J Cataract Refract Surg. Feb
2009;35(2):248-55.
Chap-02.indd 24 23-09-2013 17:01:54
JAYPEE BROTHERS MEDICAL PUBLISHERS
Refractive Errors 25
8. Lyle WA, Jin GJ. Clear lens extraction for the correction of high refractive error. J Cataract Refract Surg. May
1994;20(3):273-6.
9. Lyle WA, Jin GJ. Clear lens extraction to correct hyperopia. J Cataract Refract Surg. Sep 1997;23(7):1051-6.
10. Munoz G, Alio JL, Montes-Mico R, Albarran-Diego C, Belda JI. Artisan iris-claw phakic intraocular lens
followed by laser in situ keratomileusis for high hyperopia. J Cataract Refract Surg. Feb 2005;31(2):308-17.
11. Rosen E, Gore C. Staar Collamer posterior chamber phakic intraocular lens to correct myopia and hyperopia.
J Cataract Refract Surg. May 1998;24(5):596-606.
12. Sanders DR, Martin RG, Brown DC, Shepherd J, Deitz MR, DeLuca M. Posterior chamber phakic intraocular
lens for hyperopia. J Refract Surg. May-Jun 1999;15(3):309-15.
13. Verma A, Singh D. Active vision therapy for pseudophakic amblyopia. J Cataract Refract Surg. Sep
1997;23(7):1089-94.
14. Zaldivar R, Rocha G. The current status of phakic intraocular lenses. Int Ophthalmol Clin. 1996;36(4):107-11.
Chap-02.indd 25 23-09-2013 17:01:54
JAYPEE BROTHERS MEDICAL PUBLISHERS
WHAT IS AMBLYOPIA?
Amblyopia refers to a decrease in vision, either unilaterally or bilaterally (Fig. 3.1), for which no
organic cause can be found by physical examination of the eye. e term “functional amblyopia”
is used to describe a decrease in vision that can be reversed by appropriate therapy. On the
other hand, “organic amblyopia” is a decrease in vision due to an organic condition resulting
in irreversible visual loss. Most of the visual loss from amblyopia can be reversed depending
on the following factors:
1. e maturity of visual connections.
2. e length of visual deprivation.
3. e age at which therapy was started.
4. e type of therapy.
5. Patient’s compliance to treatment.
If the visual connections are fully developed
when visual deprivation occurred, visual loss will
not be profound. e longer the period of visual
deprivation, the denser will be amblyopia, and
the later the age of the patient when therapy was
instituted, the longer will it take to respond to
treatment.
Etiology
It is a developmental defect of spatial visual process-
ing that occurs in the central visual pathways of
brain. Animal studies have conrmed a reduction in
the number of binocularly driven cells in the lateral
geniculate body and the visual cortex. Two important
Amblyopia
CHAPTER
3
Fig. 3.1: Amblyopia: A lazy eye
Chap-03.indd 26 23-09-2013 12:15:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Amblyopia 27
pathogenic mechanisms are proposed; each may contribute dierent amounts to each specic
type of amblyopia:
1. Abnormal binocular interaction or competition: is occurs when incompatible images
are formed on the fovea of either eye that cannot be fused. is can be seen in the following
circumstances:
i. A normal image is formed in one eye and a blurred image in the other eye (stimulus
deprivation).
ii. Images of dierent objects are projected from the foveae (strabismic amblyopia).
iii. Image of a dierent size or a distorted image is superimposed on the image projected
from a normal fovea (anisometropic amblyopia).
Abnormal binocular interaction occurs only in unilateral amblyopia; in bilateral amblyopia,
both eyes are aected to the same extent. Neurons from the two eyes compete for control
over cortical connections during the developmental period; those from the better eye gain
control at the expense of neurons from the aected eye. Hence, the distorted or blurred
image from the aected eye is suppressed resulting in active inhibition of that eye and
amblyopia.
2. Deprivation of formed vision: is occurs when there is little or no stimulation of fovea of
one eye with no sensory input from ganglion cells and resultant atrophy of cells of lateral
geniculate body (LGB) corresponding to that eye. is has been conrmed by histologic
studies of lateral geniculate nucleus in kittens. e characteristics of visual deprivation
syndrome:
––Loss of vision in the deprived eye.
––Loss of binocular vision and stereopsis.
––Decrease in cell size in relevant layers of LGB of that side.
––Reduction in number of cortical neurons receiving input from that eye and loss of
binocularly driven cells.
Some of the changes in cell structure are reversible only if the deprived eye is forced to be
used during the critical period.
Critical periods: Both these pathogenic mechanisms cause amblyopia if they operate during
the critical period of visual development; once that period is over, amblyopia does not develop.
ree critical periods of human visual acuity development have been determined:
– e development of visual acuity to 20/20 or 6/6 occurs from birth to age 5.5 years; most
important period is between 2–18 months during which binocular vision and stereopsis
develops.
– e period of highest risk of deprivation amblyopia is from 2 months to 5.5 years.
– e period during which recovery from amblyopia can be obtained is from the time of
deprivation up to even adult years.
ese periods may help planning the treatment strategies.
Clinical Types of Amblyopia
ere are three basic causative mechanisms, hence three clinical types of amblyopia. In
majority of cases, some form of anisometropia exists; unless that is corrected, amblyopia
cannot be reversed successfully.
Chap-03.indd 27 23-09-2013 12:15:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
28
Stimulus deprivation amblyopia: Its characteristics are:
– It occurs in any condition obstructing the visual axis and preventing foveal stimulation or
formation of a clear image on the fovea.
– It can be unilateral or bilateral depending upon the amount of light permitted to enter the
eye and stimulate the fovea. Constant monocular occlusion for more than one week per
year of life places a child at signicant risk for developing this type of amblyopia till the age
of 5.5 years.
– It is seen in congenital ptosis, corneal opacity (even a nebula in the visual axis causes a
poor quality foveal image), hyphema, congenital cataract, vitreous opacities and foveal
cyst or scarring. Congenital nystagmus results in bilateral stimulus deprivation due to
constant movement of image across the retina and preventing a steady foveal stimulation.
Anisometropic amblyopia: Its characteristics are:
– Patients with anisometropia have a decreased visual acuity in the more ametropic eye.
– e dierence in refraction between the two eyes is such that only one eye sees clearly for
all distances resulting in monoxation syndrome.
– Anisometropia has to be present for 2 years or more for amblyopia to occur prior to the age
of 5.5 years.
– It occurs in anisohypermetropia, anisomyopia and astigmatism.
Anisohypermetropia of 1–2D can cause amblyopia. Such patients exert sucient
accommodation in the less hypermetropic eye resulting in a clear image in that eye and leaving
the other eye blurred. Accommodation is poor in the more hypermetropic eye; they have a
better distant than the near vision.
Anisomyopia of more than 4D causes amblyopia; up-till 4D, the more myopic eye is used
for a clear near vision and the less myopic eye for distant vision. However, in higher degrees
of myopia, the far point of more myopic eye is too close to the eye to get a clear near vision
resulting in amblyopia in that eye.
Astigmatic dierence of more than 1.25D between the two eyes is sucient to cause
amblyopia. In this, a relatively clear image is formed along the emmetropic axis and a blurred
image along the ametropic axis resulting in meridional amblyopia. Higher degrees of ametropia
particularly bilateral hypermetropia of more than 6D results in a blurred image for all distances
as it cannot be compensated by accommodation. In high myopia, there is a blurred image
for distance as well as near vision as the far point is too close to the eye; degenerative retinal
changes also contribute.
Strabismic amblyopia
– is is seen in constant, unilateral strabismus in which the patient strongly favors xation
with one eye resulting in inhibition of visual input to the retinocortical pathways and
suppression amblyopia.
– Depth perception, stereopsis and xation preference develops at the age of 1–1.5 years.
– ere is active inhibition of the deviating eye to prevent diplopia.
– ese patients have some degree of anisometropia as well contributing to the amblyopia.
– Incidence of amblyopia is greater in esotropia than exotropia; exotropia is intermittent
initially when visual development is occurring and decompensates later to become
Chap-03.indd 28 23-09-2013 12:15:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Amblyopia 29
constant, alternating exotropia in which either eye is used for xation; both eyes retain
good vision. Only in constant, unilateral exotropia of early onset, amblyopia occurs.
– In patients with amblyopia and strabismus (strabismic and anisometropic component),
amblyopia should be treated rst as the end point of both types of amblyopia is freely
alternating xation and equal vision. If surgery is performed prior to amblyopia therapy,
this end point cannot be gauged accurately; also patients will not attend for follow-up
once good cosmetic result has been obtained after surgery.
Management of Amblyopia
Why treat it? Amblyopia needs to be detected and treated as early as possible because of the
following reasons:
– Prevalence of amblyopia is about 2% in the general population. It is the number one cause
of monocular visual loss in adults.
– Person with one amblyopic eye is at a higher risk of becoming blind because of potential
loss to the sound eye from other causes, e.g. trauma, cataract, glaucoma, etc.
– Visual loss in amblyopia is treatable, provided if it is diagnosed at an early age and therapy
instituted appropriately.
– We need to increase the awareness among parents, ophthalmologists and opticians that
amblyopia is a silent threat to vision but is treatable at any age according to recent studies.
– Risk factors for developing amblyopia are a positive family history, delayed development,
prematurity; visual development in these children should be closely monitored.
– In patients with amblyopia and strabismus (strabismic and anisometropic component),
amblyopia should be treated rst as the end point of both types of amblyopia is freely
alternating xation and equal vision. If surgery is performed prior to amblyopia therapy,
this end point cannot be gauged accurately; also patients will not attend for follow-up
once good cosmetic result has been obtained after surgery.
A step-to-step approach to successful amblyopia management:
e basic principle to improve vision in an amblyopic eye is to promote its use by blocking
the inhibitory inuence of the better-seeing eye.
is can be achieved by:
A. Refractive correction by glasses (constant wear).
B. Occlusion of the good eye.
C. Cycloplegic drugs.
Any organic cause for amblyopia is ruled out rst by a complete history and examination, then
denitive therapy is started in a step-to-step manner:
Cycloplegic Refraction: Cycloplegia is achieved either by cyclopentolate 1% eye drops instilled
into both eyes for 3 days or by atropine 1% eye drops/ointment (in infants, ½% atropine drops
or ointment is recommended). It is important to check whether the pupils are fully dilated or
not before proceeding to the refraction.
Chap-03.indd 29 23-09-2013 12:15:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
30
How much to prescribe—following guidelines are suggested:
1. For children under 6 years of age, full cycloplegic correction of hypermetropia and
astigmatism is given if there is associated esophoria or esotropia.
2. If there is no esotropia/esophoria and hypermetropia is less than 6.5D, then 2/3 of
cycloplegic correction is given; the plus cylinder is fully prescribed while 1/3 is deducted
from the spherical correction.
3. In children more than 6 years old and without esotropia/esophoria, subjective refraction is
done once the eect of cycloplegia has worn o (in a week’s time), that will give maximum
correction for near and distance vision. However, in the presence of strabismus, full
hypermetropic correction is given.
4. If hypermetropia is more than 6.5D, it results in blurred vision at all distances, as
accommodation is not sucient to have a clear image either for near or distance. is
results in ametropic amblyopia bilaterally. In such cases, full plus correction is given for
children under 6 years age group while for children more than 6 years age group, maximum
plus correction that the child tolerates after subjective refraction.
5. If amblyopia is associated with myopia only and no strabismus, children under 6 years age
are given 2/3 of cycloplegic correction while more than 6 years old are given the minimum
minus sphere and full minus cylinder that gives maximum distance vision.
6. If myopia is associated with exophoria/exotropia, then full minus correction is prescribed.
is will enable the patient to exert accommodation and convergence and control the
strabismus.
7. High degrees of myopia at birth can result in esotropia in early childhood. In this case,
the infant’s far point is very close to the eyes making the eyes converge all the time to see
clearly at this distance; the vision for more remote distance is poor so convergence is not
relaxed on looking further away resulting in constant esotropia.
8. If hypermetropia is associated with exophoria/exotropia, then prescription of plus
correction will further relax accommodation and convergence and will worsen the
strabismus. In this situation, either give minimum plus or if astigmatism is present, then
transpose the cylinder and prescribe minus cylinder with a minimum plus sphere to
have maximum vision. As the vision improves and if the exophoria/exotropia is not fully
corrected, then reduce the amount of plus sphere.
9. If myopia in a teenager or adult is associated with esophoria, then reduce the minus
correction. But if there is esotropia, then transpose the correction to plus cylinder and a
minimum minus sphere.
10. Dispensing spectacles: e spectacle frames should be well tted and accurately centered
to avoid spherical and chromatic aberrations. e frames should be of light material so the
child can wear them comfortably and the lenses of plastic material so they do not break
easily and are light weight.
11. e child is examined again after one month of constant spectacle wear and visual
improvement in either eye is noted. Amblyopia has been found to be improved to 50% by
wearing correct spectacle correction constantly.
Chap-03.indd 30 23-09-2013 12:15:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Amblyopia 31
OCCLUSION THERAPY
Once the child is used to wearing glasses, the denitive treatment of amblyopia is started, which
is to force the use of amblyopic eye by occlusion of the better seeing eye. Occlusion therapy
has been the mainstay of amblyopia management since the 18th century. It can be full-time or
part-time. It can be done by applying tape on the spectacles or grounding the spectacles but the
main problem will be that the child will look from above the spectacles as the occluded eye is
the good eye and tempts the patient to cheat. e best option is a stick-on eye patch (Figs 3.2A
and B), available commercially which fully covers the good eye and if the child removes it any
time during the day, it will not stick again. Hence, the parents will know if the child has been
complying to therapy.
Part-time Occlusion Therapy
– According to the Amblyopia Treatment studies conducted by the AAO in 2008, 193 children
aged 7 to 12 years were assigned randomly to either weekend atropine or only 2 hours
patching of the sound eye per day. Visual acuity improved to 20/25 in only 15 participants
in the atropine group (17%) and 20 (24%) in the patching group.
– In another study, 507 patients with unilateral amblyopia received optimal optical
correction and were then randomly assigned to either 2–6 hours of patching per day plus
atropine eye drops in children aged 7–12 years.
– In the 7–12 years age group, improvement in vision by at least two lines occurred in only
53% while in the 13–17 years age group not previously treated with patching or atropine,
visual improvement occurred in 47%. Most patients had a residual visual acuity decit
after treatment. In this study, 13–17 years age group did not respond to treatment if they
had previously been treated with patching.
– Advantage of part-time occlusion therapy is that it is less disturbing to an individual’s daily
routine and is more practical resulting in better compliance. However, visual improvement
only occurs in 50% of cases as demonstrated by the ATS studies and majority of patients
had a residual visual decit.
A B
Figs 3.2A and B: Commercially available eye patches for occlusion therapy; Commercially available
eye-patch is a stick-on patch that is worn over the closed, good eye and glasses can comfortably be
worn over it
Chap-03.indd 31 23-09-2013 12:15:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
32
Full-time Occlusion Therapy
is is the treatment of choice in any age group with any severity and type of amblyopia.
About 100% improvement in visual acuity occurs in a relatively shorter time as compared to
part-time patching because of the following important reasons:
i. e inhibitory eect of sound eye hindering the improvement of vision in the amblyopic
eye is removed (Fig. 3.3).
ii. Abnormal binocular interaction is prevented by full-time occlusion of sound eye.
iii. Both these factors start operating as soon as the occlusion is removed in part-time therapy,
hence resultant improvement in visual acuity is slow and partial.
Fig. 3.3: Occlusion therapy removes the inhibitory influence of the
good eye over the amblyopic eye
Chap-03.indd 32 23-09-2013 12:15:12
JAYPEE BROTHERS MEDICAL PUBLISHERS
Amblyopia 33
Guidelines for Full-time Occlusion Therapy
1. Once full-time occlusion therapy is started, children need to be examined at regular
intervals of 1 day per year of age to avoid occlusion amblyopia in the sound eye.
2. Patching, whether full-time or part-time, need to be combined with near visual activities
for at least 2–3 hours per day.
3. Parent’s education regarding treatment goals, treatment plan is a must in order to ensure
compliance to therapy and proper patient follow-up. Parents and children need to be
encouraged at each visit to ensure their cooperation.
4. Patching should be gradually weaned: Once optimal visual acuity, i.e. 20/20 or 6/6 Snellen’s
acuity has been achieved by patching, then it should be gradually weaned. ere is no
standard protocol for weaning and gradually reducing the number of hours of patching
per day has been suggested. We recommend reducing patching by one day every week
while monitoring the patient’s visual acuity. If the vision drops during weaning period,
then switch back to full-time schedule once again.
5. All patients need to be regularly followed-up for at least 18 months after stopping patching
as recurrence of amblyopia can occur particularly during the rst year after stopping
patching.
CYCLOPLEGIC DRUGS
Many clinical studies demonstrate that treatment with atropine eye drops and part-time
patching achieve similar results (17–25% improvement in visual acuity) in children aged 7–12
years as well as the younger age group (aged 3–7 years).
e Amblyopia Treatment Studies have demonstrated that weekend use of atropine
improved visual acuity similar to that of daily use when treating moderate amblyopia in
children aged 3–7 years.
We recommend that the use of weekly atropine be reserved for maintenance therapy only
in children with mild amblyopia if the child refuses to wear an eye patch any longer or an
allergic reaction develops to the patch.
Other options include optical blurring with applying nail varnish or tape on the glasses.
FURTHER READING
1. American Academy of Opthalmology. Amblyopia. In: Basic and Clinical Science Course. Pediatric
Ophthalmology and Strabismus. 1997:259-65
2. Cotter SA, Edwards AR, Wallace DK, et al. Treatment of anisometropic amblyopia in children with refractive
correction. Ophthalmology. Jun 2006;113(6):895-903.
3. Daw NW. Critical periods and amblyopia. Arch. Ophthalmol. Apr 1998;116(4):502-5.
4. Flynn JT, Woodru G, Thompson JR, et al. The therapy of amblyopia: an analysis comparing the results of
amblyopia therapy utilizing two pooled data sets. Trans Am Ophthalmol Soc. 1999;97:373-90; discussion.
390-5.
5. Flynn JT. 17th annual Frank Costenbader Lecture. Amblyopia revisited. J Pediatr Ophthalmol Strabismus.
Jul-Aug 1991;28(4):183-201.
Chap-03.indd 33 23-09-2013 12:15:12
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
34
6. Flynn JT. Amblyopia: Its treatment today and its portent for the future. Binocul Vis Strabismus Q. Summer.
2000;15(2):109.
7. Holmes JM, Beck RW, Kraker RT, et al. Impact of patching and atropine treatment on the child and family in
the Amblyopia Treatment Study. Arch Ophthalmol. 2003;121:1625-32.
8. Holmes JM, Beck RW, Kraker RT, et al. Risk of amblyopia recurrence after cessation of treatment. J AAPOS.
2004;8:420-8.
9. Holmes JM, Kraker RT, Beck RW, et al. A randomized trial of prescribed patching regimens for treatment of
severe amblyopia in children. Ophthalmology. Nov 2003;110(11):2075-87.
10. Kirschen DG. Understanding Sensory Evaluation. In: Rosenbaum AL, Santiago AP, eds. Clinical Strabismus
Management: Principles and Practice. 1999: 22-35.
11. Kushner BJ. Amblyopia. In: Nelson LB, ed. Harley’s Pediatric Opthalmology. 1998:125-39.
12. Lempert P. Retinal area and optic disc rim area in amblyopic, fellow and normal hyperopic eyes: a hypothesis
for decreased acuity in amblyopia. Ophthalmology. Dec 2008;115(12):2259-61.
13. Levartovsky S, Oliver M, Gottesman N, Shimshoni M. Factors aecting long-term results of successfully
treated amblyopia: initial visual acuity and type of amblyopia. Br J Ophthalmol. Mar 1995;79(3):225-8.
14. Mansouri B, et al. Amplyopia Study May Lead to New Types of Treatments. ARVO 2008 Annual Meeting.
Medscape News.
15. Mein J, Trimble R. Diagnosis and Management of Ocular Motility Disorders. 1991:199-211.
16. Pediatric Eye Disease Investigator Group. A comparison of atropine and patching treatments for moderate
amblyopia by patient age, cause of amblyopia, depth of amblyopia, and other factors. Ophthalmology.
2003;110:1632-1637.
17. Repka MX, Beck RW, Holmes JM, et al. A randomized trial of patching regimens for treatment of moderate
amblyopia in children. Arch Ophthalmol. 2003;121:603-11.
18. Sche iman MM, Hertle RW, Kraker RT, et al. Patching vs atropine to treat amblyopia in children aged 7 to 12
years: a randomized trial. Arch Ophthalmol. Dec 2008;126(12):1634-42.
19. Scheiman MM, Hertle RW, Beck RW, et al. Randomized trial of treatment of amblyopia in children aged 7 to
17 years. Arch Ophthalmol. Apr 2005;123(4):437-47.
20. vonNoorden GK. Binocular Vision and Ocular Motility. Theory and Management. 1996:216-54.
21. Wallace DK, Chandler DL, Beck RW, et al. Treatment of bilateral refractive amblyopia in children three to less
than 10 years of age. Am J Ophthalmol. Oct 2007;144(4):487-96.
22. Wallace DK, Edwards AR, Cotter SA, Beck RW, Arnold RW, Astle WF, et al. A randomized trial to evaluate
2 hours of daily patching for strabismic and anisometropic amblyopia in children. Ophthalmology. Jun
2006;113(6):904-22
Chap-03.indd 34 23-09-2013 12:15:12
JAYPEE BROTHERS MEDICAL PUBLISHERS
ESSENTIAL INFANTILE ESOTROPIA FIGS 4.1A TO C
The term Esotropia is derived from 2 Greek words: ésò, meaning inward, and trépò,
meaning turn, or crossed eyes, while one eye looks straight ahead, the other eye is turned
in towards the nose. This can begin as early as in infancy, childhood, or even in adulthood.
Greenberg et al reported an annual age- and gender-adjusted childhood esotropia
incidence of 111 per 100,000 patients younger than 19 years. This rate corresponds to a
cumulative prevalence of approximately 2% of all children younger than 6 years, with a
significant decrease in older ages.
Esotropia with an onset before the age of one year is considered to be a congenital esotropia.
In most cases, true essential infantile esotropia is noted at 2 months of age. It is thought to
aect about 1% of full-term, healthy newborns and a much higher percentage of newborns
with perinatal complications due to prematurity or hypoxic/ischemic encephalopathy. Its
classical features are given below and it has to be distinguished from other causes of esotropia
that have a dierent management.
Essential Infantile Esotropia
CHAPTER
4
Figs 4.1A to C: (A) Large angle left ET with face turn. (B and C) On straightening the head, alternate ET
A B C
Chap-04.indd 35 23-09-2013 17:03:10
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
36
Clinical Features (Figs 4.1D to F)
Age of onset : It is between 2 months - one year; the child presenting with a large angle deviation
of 30–70 PD and cross xation (right eye being used for looking to the left and left eye being
used for looking towards the right).
Risk Factors for Developing Infantile Esotropia (ET)
An ophthalmologist should evaluate all children with a history of prematurity,
hydrocephalus, seizures, developmental delay, intraventricular hemorrhage and a family
history of strabismus.
Pathophysiology: Its exact cause remains unknown but following pathogenic mechanisms
have been proposed:
i. Excessive tonic convergence.
ii. An inborn and irreversible defect of fusion (Worth). As such, it is a primary dysfunction in
the normal development of binocular sensitivity.
iii. A few authors have implicated practically everything from and between the extraocular
muscles to the visual cortex in the causation of infantile esotropia.
Associated with:
Dissociated vertical deviation (DVD): Less chances of binocular vision, inferior oblique over-
action.
CNS or developmental disorders, manifest latent nystagmus.
DISSOCIATED VERTICAL DEVIATION FIG. 4.2A TO D
In this condition, there is upturning of the non-xing eye in cases of horizontal strabismus when
fusion or xation of both eyes is temporarily suspended.
Etiology: Instability of central control of ocular alignment when there is a weak or absent
sensory fusion. Its essential feature is a disregard for the Hering’s Law, i.e. the eyes tend to
move independently of one another.
Figs 4.1D to F: Alternate esotropia with bilateral inferior oblique overaction.
DEF
Chap-04.indd 36 23-09-2013 17:03:10
JAYPEE BROTHERS MEDICAL PUBLISHERS
Essential Infantile Esotropia 37
Clinical Features
1. In the presence of a horizontal strabismus, the covered eye drifts upwards independent of
the xing eye. is is mostly seen in essential infantile esotropia but it may be seen in any
strabismus; DVD is to strabismus as fever is to infection. Its presence indicates that the eye
is strabismic with poor sensory fusion. Hence it drifts upwards under the cover.
2. is up-drift is the same in adduction, primary position and in abduction, dierentiating
it from the inferior oblique over-action, which is also fairly common in essential
infantile esotropia; it is readily dierentiated from DVD as it is present only in adduction.
However, the two may co-exist in the same patient. If one eye goes up higher in
adduction than abduction, then inferior oblique over-action is also present along with
DVD.
3. Since central suppression is well developed, patients do not complain of diplopia as the
eye drifts upwards.
4. e diagnosis is made by observing that each eye goes up under cover, regardless of
whether the test is made in straight ahead gaze, right or left.
5. It should also be dierentiated from true hypertropia, when one eye is always up under
cover and the other is always down under the cover. In addition, DVD is associated with
latent occlusion nystagmus, in which when one is covered, the other eye develops a latent
jerky nystagmus.
Figs 4.2C and D: Fixing with the left eye, a large angle Right ET. B: Fixing
with the right eye, a left DVD/inferior oblique over-action
CD
Figs 4.2A and B: DVD: Fixing with the right eye, the left eye drifts upwards
in both abduction and adduction
AB
Chap-04.indd 37 23-09-2013 17:03:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
38
Management of DVD
Since the cause of a DVD is horizontal misalignment and secondarily absent sensory fusion,
the rst consideration in surgical correction of DVD is to fully correct the horizontal strabismus.
Once the sensory fusion and binocularity develops, DVD lessens on its own with the passage of
time; it rarely persists into adult life if managed properly in childhood.
ere are many options to correct DVD surgically but easier procedure is a small
recession (4–5 mm) of superior rectus combined with a posterior xation suture,
Faden, applied to the sclera posterior to the equator of the eye (12 mm from insertion of superior
rectus muscle). e advantage of this technique is that the action of superior rectus is reduced in
its eld of action and vertical alignment is minimally disturbed in the primary position.
Dierential Diagnosis of Essential Infantile Esotropia
1. Secondary Esotropia (visual loss): Corneal opacity, congenital cataract, development
anomaly of retina or optic nerve, intraocular tumor.
2. Early Onset Accommodative Esotropia: Hypermetropia > 2–3 D.
3. Bilateral 6th Nerve Palsy (Figs 4.3A to D): Congenital, traumatic, Mobius syndrome: VI, VII,
IX, XII cranial nerve palsies.
4. Strabismus Fixus (Figs 4.4A to C): an ankylosing band of brous tissue between medial
orbital wall and medial rectus muscle prevents abduction.
Figs 4.3A to D: Sixth nerve palsy: (A) Face turn to the right; (B) A right ET in straight ahead
position; (C) Limited abduction of the right eye; (D) Full abduction of the left eye
Figs 4.4A to C: Strabismus fixus: (A) Looking straight ahead, bilateral esotropia; (B) Absent abduction
of either eye on turning the head; or (C) on covering the left eye and asking the patient to look to the
right (abduct)
A
A B C
B C D
Chap-04.indd 38 23-09-2013 17:03:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Essential Infantile Esotropia 39
Fig. 4.6: Pseudostrabismus: flat nasal bridge, epicanthic folds
5. Nystagmus Blockade Syndrome: In abduction, the infant has marked nystagmus, which is
blocked in adduction hence the child xates in adduction.
6. Bilateral Duane’s Syndrome: Narrowing and retraction of lid ssures in adduction is
present.
In order to exclude all these conditions, it is very important to demonstrate full abduction in
either eye.
1. Occlude xing eye and attract child’s attention laterally.
2. Doll’s eye head maneuver (Fig. 4.5).
3. Note position of eyes during sleep and general anesthesia. Eyes are in slight abduction
during deep general anesthesia.
Examination
1. General appearance: It is important to exclude pseudostrabismus (Fig. 4.6)—large
epicanthic folds, broad nasal bridge and a small, at nose. But corneal reex is central in
both eyes.
2. Vision: Must get an idea of visual acuity in either eye as mentioned in Chapter 1.
3. Head posture and position of eyelids in all positions of gaze.
4. Pupil examination: To have an idea of retina and optic nerve function, to know the visual
potential in that eye as well as to exclude secondary esotropia.
Fig. 4.5: Demonstrating abduction by doll’s eye maneuver
Chap-04.indd 39 23-09-2013 17:03:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
40
5. Slit lamp and fundus examination: To exclude secondary esotropia.
6. Hirschberg’s test, Cover/uncover and alternate cover test.
7. Ocular movements in all positions of gaze to nd any muscle over- or under-action.
8. Measurement of deviation by Prisms.
9. Cycloplegic refraction: Preferably by atropine to neutralize tonic hypermetropia as well.
Management (Figs 4.7A and B): Treatment is surgical correction of strabismus by the age of
18 months. At this age, binocular perception and fusion develops.
Till that age, child should be prescribed glasses with full astigmatic correction for constant
wear in order to avoid amblyopia. Amblyopia is present even though there is cross-xation
and this is due to some degree of hypermetropia as well as astigmatism. Astigmatism of any
degree must be fully corrected. Amblyopia must be treated preoperatively as the end point
of amblyopia therapy is a freely alternating esotropia with the child xating with either eye.
If surgery is performed for a constant ET without changing it rst to an alternating ET by
occlusion therapy, it is very dicult to assess postoperatively if amblyopia has been corrected.
In one study, chances of amblyopia in congenital ET are 6% but if surgery is performed
without looking for it and treating it preoperatively, chances of amblyopia increase to 50–60%.
If the parents refuse amblyopia therapy, then it is important to under-correct ET by 10 PD and
warn the parents that eye has a tendency to go out.
Goal of Surgery: To reduce ET to within 10 PD to allow binocularity to develop.
In binocular ET, bimedial recession + conjunctival recession + LR resection
In uniocular cases, recess/resect of the involved eye.
Always perform FDT at the time of surgery.
Regular follow-up postoperatively and manage glasses accordingly.
Botulinum toxin (BOTOX®) injection into the medial rectus has been explored as an alternative
to surgery. Long-term post-injection follow-up up to 7 years showed not only a signicant
reduction in esotropic angle but also successful binocular alignment (±10 PD) in 89% of the
patients.
Figs 4.7A and B: Alternate esotropia, not corrected with glasses. However, glasses
for the associated hypermetropic astigmatism must be worn to prevent amblyopia
AB
Chap-04.indd 40 23-09-2013 17:03:12
JAYPEE BROTHERS MEDICAL PUBLISHERS
Essential Infantile Esotropia 41
FURTHER READING
1. Birch E, Stager D, Wright K, Beck R. The natural history of infantile esotropia during the rst six months of life.
Pediatric Eye Disease Investigator Group. J AAPOS. Dec 1998;2(6):325-8; discussion 329.
2. Birch EE, Fawcett S, Stager DR. Why does early surgical alignment improve stereoacuity outcomes in
infantile esotropia? J AAPOS. Feb 2000;4(1):10-4.
3. Birch EE, Stager DR. Monocular acuity and stereopsis in infantile esotropia. Invest Ophthalmol Vis Sci. Nov
1985;26(11):1624-30.
4. Drover JR, Stager DR Sr, Morale SE, Leer JN, Birch EE. Improvement in motor development following
surgery for infantile esotropia. J AAPOS. Apr 2008;12(2):136-40.
5. Friendly DS. Management of infantile esotropia. Int Ophthalmol Clin. 1985;25(4):37-52.
6. Greenberg AE, Mohney BG, Diehl NN, Burke JP. Incidence and types of childhood esotropia: a population-
based study. Ophthalmology. Jan 2007;114(1):170-4.
7. Mohindra I, Zwaan J, Held R, et al. Development of acuity and stereopsis in infants with esotropia.
Ophthalmology. May 1985;92(5):691-7.
8. Polling JR, Eijkemans MJ, Esser J, Gilles U, Kolling GH, Schulz E, et al. A randomised comparison of bilateral
recession versus unilateral recession-resection as surgery for infantile esotropia. Br J Ophthalmol. Jul
2009;93(7):954-7.
9. Rowe FJ, Noonan CP. Botulinum toxin for the treatment of strabismus. Cochrane Database Syst Rev. Apr 15
2009;CD006499.
10. Simonsz HJ, Kolling GH, Unnebrink K. Final report of the early vs. late infantile strabismus surgery study
(ELISSS), a controlled, prospective, multicenter study. Strabismus. Dec 2005;13(4):169-99.
11. Tychsen L. Infantile esotropia: Current neurophysiologic concepts. In: Rosenbaum AL, Santiago AP (eds).
Clinical Strabismus Management: Principles and Surgical Techniques. 1999:117-138.
12. Uretmen O, Civan BB, Kose S, Yuce B, Egrilmez S. Accommodative esotropia following surgical treatment of
infantile esotropia: frequency and risk factors. Acta Ophthalmol. May 2008;86(3):279-83.
13. Weakley DR, Urso RG, Dias CL. Asymmetric inferior oblique overaction and its association with amblyopia in
esotropia. Ophthalmology. Apr 1992;99(4):590-3.
14. Wong AM. Timing of surgery for infantile esotropia: sensory and motor outcomes. Can J Ophthalmol. Dec
2008;43(6):643-51.
Chap-04.indd 41 23-09-2013 17:03:12
JAYPEE BROTHERS MEDICAL PUBLISHERS
Clinical Types:
1. Congenital: Early onset accommodative esotropia (ET)
2. Fully accommodative ET
3. Partially accommodative ET
4. Near ET, convergence excess
5. Distance ET
6. Secondary ET
7. Consecutive ET.
FULLY ACCOMMODATIVE ESOTROPIA
Most cases of esotropia presenting clinically fall into this category. ese children have
undiagnosed and uncorrected hypermetropia and have a history of intermittent ET initially. As
the infant grows, he starts accommodating to get a clear distant vision. As the accommodative
eort increases to focus the near objects around the age of 1.5–2 years, the eyes converge and
due to accommodation/convergence synkinesis, this results in Esotropia. If the degree of
hypermetropia is the same in both eyes, it results in an alternate esotropia with equal vision
in either eye. However, a constant, unilateral esotropia occurs in the more hypermetropic eye,
which sees a blurred distant and near image resulting in dense amblyopia.
Clinical Features
Onset: age > 2–5 years alternating or unilateral in the more hypermetropic eye.
Associated with amblyopia in unilateral, constant esotropia in one eye; check xation
preference by asking the child to xate on a target and perform cover/un-cover test. If
the child always xates with one eye, the other eye is amblyopic. If there is an alternate
xation, it means equal vision in either eye.
Esotropia
CHAPTER
5
Chap-05.indd 42 23-09-2013 17:04:26
JAYPEE BROTHERS MEDICAL PUBLISHERS
Esotropia 43
Exclude abduction decit and sensory element in unilateral cases by checking extraocular
movements in all directions and complete ophthalmological examination.
Measure the deviation for both near and distance xation with prisms.
Inferior oblique over-action is usually seen bilateraly which distinguishes accommodative
ET from 6th Nerve Palsy in which no inferior oblique over-action should be present
(Figs 5.1A to C).
Management
1. Full correction of hypermetropia up to the age 6 years following atropine refraction
(in order to measure and correct the total hypermetropia) (Figs 5.2A to D).
2. Age: More than 8 years. Max amount of plus lens tolerated for near and distance.
3. Amblyopia therapy in cases of constant, unilateral ET. Full cycloplegic correction is given
for constant wear for a month and visual acuity in either eye is measured. About 20–40%
amblyopia corrects by full correction (foveal xation; Chapter 2). en full-time occlusion
therapy is commenced under strict supervision as outlined in Chapter 2. Once vision has
equalized in both eyes, occlusion is gradually weaned and stopped.
4. Six monthly follow-up: Measure VA with glasses, angle of deviation, xation preference.
As the child grows, hypermetropia increases initially till the age of 10 years and then
starts reducing as accommodation amplitude decreases. Hence, spectacles need to be
monitored accordingly.
Figs 5.1A to C: Alternate ET; (A) Looking straight ahead, left ET when fixing with the right eye; (B)
Right inferior oblique over-action on looking to the right; (C) Left inferior oblique over-action on looking
to the left
A B C
Figs 5.2A to D: Fully accommodative esotropia, fully corrected with glasses; (A) Left constant ET
(B) Not fully corrected with 2/3rd hypermetropic correction; (C) Left ET; (D) Fully corrected with full-
hypermetropic correction
A B C D
Chap-05.indd 43 23-09-2013 17:04:26
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
44
5. Gradually reduce the hypermetropic correction in older children depending upon the state
of muscle balance: if on the 6 monthly visit, the eyes are orthophoric with the correction
and the vision is 6/6 Snellen’s, then the same prescription should be worn for the next 6
months. If a small esophoria or esotropia is noted, the amount of plus correction has to
be increased that will retain 6/6 vision. Hence, repeat the cycloplegic refraction and after
1 week when the eect of cycloplegia has worn o, subjective refraction is done and the
maximum amount of plus correction tolerated by the child is prescribed.
If on the follow-up, a slight exophoria or exotropia is noted with the plus correction, the
amount of plus is reduced. e patient is re-examined after one month and the state of
muscle balance examined. If exophoria is still detected, the amount of plus is further
reduced to the extent that retains 6/6 vision.
NOTE: If hypermetropia is properly managed, the ET disappears and there is no need for
any strabismus surgery.
PARTIALLY ACCOMMODATIVE ESOTROPIA (FIGS 5.3A AND B)
ese are the cases that present with ET at a later age; they had never been prescribed glasses
or their hypermetropia has never been fully corrected at a younger age. Hence, some degree of
residual esotropia results in secondary changes in the medial rectus muscle due to a constant
and prolonged accommodative eort, causing muscle hypertrophy or contracture.
Clinical Features
It presents as a constant, unilateral esotropia in a child > 4–6 years of age. ere is a history of
intermittent ET at 1–3 years age.
ere is a mild to moderate degree of uncorrected hypermetropia and astigmatism.
Moderate to dense amblyopia is present in the squinting eye due to constant extra-foveal
xation.
e criteria to label a patient with partially accommodative ET:
Total cycloplegic refraction with atropine has been performed.
Full hypermetropic correction is given to the patient in order to neutralize even the tonic
hypermetropia.
Figs 5.3A and B: Partially accommodative esotropia, not fully corrected with glasses
A B
Chap-05.indd 44 23-09-2013 17:04:26
JAYPEE BROTHERS MEDICAL PUBLISHERS
Esotropia 45
Glasses have been worn constantly by the patient.
In spite of the above measures, some residual ET is detected. ET is reduced by glasses for
distance but not fully corrected.
Must exclude convergence excess.
Management
1. Full cycloplegic correction of hypermetropia and astigmatism.
2. e child should wear glasses constantly for 1 month and then visual status and angle of
strabismus is assessed again.
3. Any degree of amblyopia is managed by full-time occlusion. As vision improves in the
squinting eye, the angle of deviation also lessens.
4. Once full visual improvement has been attained, the residual ET is measured with the
prisms while patient is wearing correcting glasses. e procedure of choice is either recess
or resect of the squinting eye or bimedial recession combined with resection of lateral
rectus of the squinting eye for a large angle ET.
5. e hypermetropic correction needs to be reduced gradually as the child grows.
NEAR ESOTROPIA (FIGS 5.4A AND B)
Esotropia is seen for near only noted when the patient looks at very ne detail and looks up from
a book or a toy. e eyes remain straight for distance or an esophoria < 10 PD may be detected for
far distance. Amblyopia is rare as eyes are mostly straight for distance. e majority of patients
are hypermetropic. e cause is a high accommodative convergence exerted in response to
each diopter of accommodation. An individual’s AC/A ratio is genetically determined, the
normal being 4:1 that means 4 PD of convergence results from each PD of accommodation. If
this ratio alters, it can cause esthenopia or a manifest strabismus.
Measurement of Accommodative Convergence/Accommodation Ratio
Heterophoria Method: Measurements are carried out as described below:
1. Measure the inter-pupillary distance (IPD) in cm; this inuences the amount of
convergence needed.
Figs 5.4A and B: Near esotropia: (A) Preoperative, (B) Postoperative after bimedial recession
A B
Chap-05.indd 45 23-09-2013 17:04:26
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
46
2. Ask the patient to wear his refractive correction.
3. Measure the deviation for near, i.e. at 33 cm (n). At this distance, the accommodation (D)
exerted is a reciprocal of the distance, hence is equal to 3 PD.
4. Measure the deviation for 6 meter distance (d).
5. Calculation: e measurements are denoted by a positive sign in case of an esotropia and
a negative sign in an exotropia.
AC/A ratio = IPD + n – d
D
Example: IPD = 60 mm = 6 cm, Esotropia for near (n) = 30 PD, Esotropia for distance
(d) = 5 PD, and accommodation exerted normally at 33 cm = 3 PD
AC/A ratio = 30 = 10 = 10 : 1
3 1
Management
1. Correction of refractive error: Hypermetropia should be fully corrected is prescribed.
Rarely, if patient is myopic, then a minimum myopic correction prescribed, which gives
clear vision.
2. If there is associated amblyopia, this should be treated by occlusion therapy.
3. AC/A ratio is measured. If the ratio is 6:1, then bifocal glasses with a reading addition are
prescribed.
4. If the AC/A ratio > 8:1, then surgery is indicated in the form of recession of both the medial
recti or a Faden suture on the recessed MR.
DISTANCE ESOTROPIA (FIGS 5.5A AND B)
ere is orthophoria for near or a small esophoria. No refractive error is found and equal VA in
both eyes. Mild, intermittent esotropia for distance is sometimes seen.
It is important to exclude: mild VI nerve palsy, dysthyroid eye disease, convergence and
accommodative spasm.
It is managed by bilateral LR resection.
Figs 5.5A and B: Distance esotropia: (A) Preoperative; (B) Postoperative after bilateral lateral
rectus resection
A B
Chap-05.indd 46 23-09-2013 17:04:26
JAYPEE BROTHERS MEDICAL PUBLISHERS
Esotropia 47
SECONDARY ESOTROPIA
is occurs if there is severe visual loss in early childhood while accommodation and
convergence are highly active. However, if visual loss occurs during adulthood, then the blind
eye diverges because at this age divergence is strong.
It presents with a large angle ET, same for near and distance. Due to constant
accommodation and convergence, with no attempt at abduction to xate with that eye,
secondary hypertrophy and contracture of medial rectus muscle results in limited abduction
of that eye.
Management
1. Find the cause and treat it, if possible.
2. Try amblyopia therapy at any age if there is no organic cause for the visual loss because
only equal VA in both eyes will result in sensory fusion and locking of the aligned eyes.
3. It needs a large recess/resect procedure on the same eye.
4. Aim for under-correction of ET by 10 PD as chances of consecutive exotropia are high.
5. Advise convergence exercises postoperative to delay secondary divergence.
CONSECUTIVE ESOTROPIA
A consecutive esotropia following surgery for an initial exotropia causes signicant diplopia
to the patient. Most patients with a primary exotropia have good vision and an over-zealous
surgery resulting in an over-correction and a constant consecutive esotropia is quite
troublesome to the patient.
Management
If it is less than 15 PD, it can be managed conservatively by plus spectacle correction or
base-out Fresnel prisms tted over the glasses.
If this fails to correct the diplopia or if the esotropia is more than 15 PD, then surgical
correction is indicated. If there is limited abduction in the operated eye, it means an overly
tightened lateral rectus (due to a previous over-resection), which needs to be recessed.
If there is no limitation of abduction, then the medial recti need to be recessed.
In a previous recess/resect procedure on one eye, the recessed lateral rectus needs a
combination of resection and advancement while the medial rectus needs to be recessed
a small amount. It is important not to weaken the medial rectus too much in adults as the
accommodation/convergence amplitude is already decreasing at this age.
FURTHER READING
1. American Academy of Ophthalmology Pediatric Ophthalmology/Strabismus Panel. Esotropia and
exotropia. San Francisco (CA): American Academy of Ophthalmology. 2007.
Chap-05.indd 47 23-09-2013 17:04:27
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
48
2. Clark AC, Nelson LB, Simon JW. Acute acquired comitant esotropia. Br J Ophthalmol. Aug 1989;73(8):636-8.
3. Clark RA, Ariyasu R, Demer JL. Medial rectus pulley posterior xation: a novel technique to augment
recession. J AAPOS. Oct 2004;8(5):451-6.
4. Costello PA, Simon JW, Jia Y, Lininger LL. Acquired esotropia: subjective and objective outcomes. J AAPOS.
Jun 2001;5(3):193-7.
5. Goldman HD, Nelson LB. Acute acquired comitant esotropia. Ann Ophthalmol. Dec 1985;17(12):777-8.
6. Kittleman WT, Mazow ML. Reoperations in esotropia surgery. Ann Ophthalmol. May 1986;18(5):174-7.
7. Lyons CJ, Tin PA, Oystreck D. Acute acquired comitant esotropia: a prospective study. Eye. Oct 1999;
13(5):617-20.
8. Mohney BG. Acquired nonaccommodative esotropia in childhood. J AAPOS. Apr 2001;5(2):85-9.
9. Mohney BG. Common forms of childhood esotropia. Ophthalmology. Apr 2001;108(4):805-9.
10. Repka MX, Wentworth D. Predictors of prism response during prism adaptation. Prism Adaptation Study
Research Group. J Pediatr Ophthalmol Strabismus. Jul-Aug 1991;28(4):202-5.
11. Thomas AH. Divergence insuciency. J AAPOS. Dec 2000;4(6):359-61.
Chap-05.indd 48 23-09-2013 17:04:27
JAYPEE BROTHERS MEDICAL PUBLISHERS
is is the outward deviation of the visual axis of one or both eyes. e deviation usually begins
as an exophoria in which the alignment of eyes is straight when both eyes are open but either
eye drifts outward when covered. During this phase, the patient has bifoveal xation.
It has 3 main sub-types:
1. Primary: Intermittent, constant.
2. Secondary: Due to severe visual loss.
3. Consecutive: Following the over-correction for an initial esotropia.
INTERMITTENT PRIMARY EXOTROPIA FIGS 6.1A AND B
is is the most common type of exotropia. It starts intermittently in children around 2–3 years
of age, mainly for distance, noted when the child is inattentive, day-dreaming or following an
illness and closes one eye in bright light. When it develops in a child whose visual system is
still immature, bitemporal suppression develops, and the child does not perceive 2 separate
images (diplopia). As suppression increases, intermittent exotropia nally progresses to a
constant exotropia. If acquired exotropia develops in adults, the patient experiences periods
of diplopia during the tropic (manifest) phase.
Exotropia
CHAPTER
6
Figs 6.1A and B: Alternate exotropia: (A) Fixing with the right, left exotropia;
(B) Fixing with the left, right exotropia
A B
Chap-06.indd 49 23-09-2013 12:08:40
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
50
Its etiologic factors are either a divergence excess or convergence insuciency. Since the
child closes the diverging eye to avoid diplopia, this causes hemi-retinal suppression of the
temporal half of the deviating eye.
e course of intermittent exotropia is variable. Some patients maintain the frequency and
size of the deviation for many years and control it for near; others, with uncorrected myopia
deteriorate quickly (decompensated exotropia, Figs 6.2A and B), resulting in a constant
exotropia, the size of which keeps on increasing with the passage of time as divergence
becomes more active.
Symptoms: Children rarely complain of any symptoms. It is more common in females, 63–70%
than in males.
Examination
1. Vision is equal and almost 6/6 Snellen’s in both eyes.
2. ere may be mild uncorrected myopia.
3. e child may have an exophoria for near on cover test while for far distance, an exotropia
and may be a small hypertropia is noted.
4. Extraocular movements are full in all directions of gaze. A-V patterns of exotropia may be
present in up or down-gaze. It may be associated with a DVD
5. Convergence: e near point of convergence is reduced.
6. Deviation is measured after monocular occlusion to disrupt fusional convergence.
Distance and near measurements are taken after patching either eye for at least 30–45
minutes.
7. Deviation is measured after using either +3.00 D lenses (near deviation) or –2.00 D lenses
(distance deviation) to disrupt the accommodative convergence. e deviation with
+3.00 D lenses should always be measured after the monocular occlusion test to avoid an
erroneous measurement of a high AC/A ratio.
Management
1. Correct even small degrees of myopia/astigmatism.
2. Alternate part-time patching to avoid hemi-retinal suppression in the deviating eye.
Figs 6.2A and B: Decompensated intermittent exotropia
A B
Chap-06.indd 50 23-09-2013 12:08:40
JAYPEE BROTHERS MEDICAL PUBLISHERS
Exotropia 51
3. Regular follow-up: Note the frequency and the size of deviation. If the deviation is
becoming constant and of larger angle, then book for surgery, preferably when the child is
5–6 years old. Why at this age? Patient cooperation is needed for accurate measurement
of the deviation and instituting convergence exercises postoperatively.
CONSTANT PRIMARY EXOTROPIA
Early Onset Exotropia
It may present at 1 year of age with either constant unilateral or alternating exotropia. ere
will be dense amblyopia in a constant unilateral deviation with absent binocular single vision.
ere may be associated DVD (dissociated vertical deviation) in which the deviating eye drifts
upwards and then slowly comes down; it indicates poor vision in that eye.
It can be associated with craniofacial abnormalities.
Decompensated Intermittent Exotropia (Figs 6.5A and B)
is is the more common variety of exotropia. It is seen in teenagers and adults due to
breakdown of a previously intermittent exotropia, as the accommodation amplitude reduces
and the divergence becomes more active.
Symptoms: e patient is only concerned with the cosmetic aspect of the strabismus and there
are no symptoms of diplopia or asthenopia because of hemi-retinal (temporal) suppression.
Examination
1. ere will be 6/6 Snellen’s visual acuity in both eyes in most cases.
2. Patients usually have uncorrected myopia/astigmatism.
3. ere will be a freely alternating exotropia, usually of a large angle.
4. In adults, there will be absence of convergence and under-action of medial recti. ere
may be an associated V-pattern, with exotropia increasing on upgaze.
5. e eyes will be otherwise normal on complete ophthalmological examination.
Management
1. Correct the myopia and astigmatism fully prior to surgery (Figs 6.4A and B).
2. In children with early onset constant exotropia, treat the associated amblyopia prior to
surgery.
3. Surgery: Aim for overcorrection by 10 PD, particularly in an amblyopic eye because of an
absent locking mechanism for ocular alignment.
Either do a recess-resect procedure in the constantly deviating eye or a bilateral lateral
rectus recession along with a medial rectus resection in large angle deviations.
4. Postoperatively, must institute convergence exercises to prevent recurrence of exotropia.
5. Patient should continue to wear the myopic/astigmatic correction.
6. Regular follow-up is mandatory.
Chap-06.indd 51 23-09-2013 12:08:40
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
52
SECONDARY EXOTROPIA FIGS 6.5A AND B
It is seen either in infants with severe visual loss since birth or in adults following loss of vision
in an eye; the blind eye diverges out under the inuence of active divergence while that eye is
not being used for xation and hence convergence.
Management
1. Establish the cause for visual loss and treat it if possible.
2. If the eye is disorganized, degenerated, strabismus surgery can precipitate anterior
segment ischemia, chronic inammation and pain; hence avoid surgery.
3. Surgery: Maximum lateral rectus recession, preferably with hang-loose technique, and
medial rectus resection of the blind eye. is can be combined with LR recession of the
good eye for large angle strabismus.
4. Aim of surgery should be over-correction by at least 10 PD to avoid recurrence.
5. Postoperatively, convergence exercises are mandatory.
CONSECUTIVE EXOTROPIA
is is seen either following over-zealous strabismus surgery for esotropia or mismanaged
hypermetropia. If the hypermetropic correction is not gradually reduced as the child grows,
with the decrease in accommodation amplitude, the eye starts to diverge out as convergence
is also relaxed and divergence is active.
Figs 6.3A and B: Exotropia for near increasing with distance fixation
Figs 6.4A and B: (A) Decompensated exotropia; (B) Fully corrected with minus glasses
A B
A B
Chap-06.indd 52 23-09-2013 12:08:41
JAYPEE BROTHERS MEDICAL PUBLISHERS
Exotropia 53
Management
1. Hypermetropic correction should be reduced to the extent that retains 6/6 vision.
2. In small degrees of hypermetropia or astigmatism, transpose a plus cylinder to minus in
order to stimulate convergence and accommodation.
3. Prescribe convergence exercises.
4. Patients developing exotropia years after surgery for an esotropia need reoperation.
5. Principles of a reoperation:
–Consider the previous surgical procedure: whether a recess/resect done and on which
muscles.
–It is better to operate on the unoperated muscles.
In cases of consecutive exotropia following surgery for an esotropia, there are two
important considerations:
i. Reoperation on a previously weakened medial rectus requires more resection as it has
been in a weakened state for many years.
ii. Lateral rectus recession should not be extensive as it was an already weak muscle, which
had led to an esotropia initially.
iii. Choice of surgery: It is very important to observe the position of eyes under deep general
anesthesia and perform the forced duction test before deciding on the surgical procedure:
–If deviation is larger for near than distance with limited abduction, a medial rectus
resection combined with advancement is indicated. e amount of resection depends
upon the condition of the muscle: if it is abby, more resection is needed but if it looks
and feels scarred/atrophic, then a small resection combined with advancement is the
appropriate procedure.
–If the deviation is larger for distance, it is better to recess a previously unoperated lateral
rectus.
–If the previously operated lateral rectus feels tight on forced duction test, it needs to be
recessed; but over-recession should be avoided as it may limit abduction.
–An appropriate amount of conjunctival resection may be done to prevent heaping up of
stretched conjunctiva as the eye is straightened.
–e desired position of eyes at the end of surgical procedure is orthophoria or a small
esotropia. If they are left in a slight exotropic state under general anesthesia, there is a
likelihood that the exotropia has not been fully corrected.
Figs 6.5A and B: Secondary exotropia: (A) Preoperative, marked left XT; (B) Postoperative
AB
Chap-06.indd 53 23-09-2013 12:08:41
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
54
FURTHER READING
1. Baloh RW. Neuro-ophthalmology. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa:
Saunders Elsevier. 2007:chap 450.
2. Biglan AW, Davis JS, Cheng KP, et al. Infantile exotropia. J Pediatr Ophthalmol Strabismus. Mar-Apr
1996;33(2):79-84.
3. Goldstein HP, Scott AB. Ocular motility. In: Tasman W, Jaeger EA, eds. Duane’s Ophthalmology. 15th ed.
Philadelphia, Pa: Lippincott Williams and Wilkins. 2009: chap 23.
4. Hunter DG, Ellis FJ. Prevalence of systemic and ocular disease in infantile exotropia: comparison with
infantile esotropia. Ophthalmology. Oct 1999;106(10):1951-6.
5. Hunter DG, Kelly JB, Buenn AN, et al. Long-term outcome of uncomplicated infantile exotropia. J AAPOS.
Dec 2001;5(6):352-6.
6. Kushner BJ. The distance angle to target in surgery for intermittent exotropia. Arch Ophthalmol. Feb
1998;116(2):189-94. [MedLine].
7. Matsuo T, Yamane T, Ohtsuki H. Heredity versus abnormalities in pregnancy and delivery as risk factors for
dierent types of comitant strabismus. J Pediatr Ophthalmol Strabismus. Mar-Apr 2001;38(2):78-82.
8. Mohney BG, Huaker RK. Common forms of childhood exotropia. Ophthalmology. Nov 2003;110(11):
2093-6.
10. Olitsky SE, Hug D, Plummer LS, Stass-Isern M. Disorders of eye movement and alignment. In: Kliegman RM,
Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders
Elsevier. 2011:chap 615. References
11. Parks MM. Binocular vision. In: Tasman W, Jaeger EA, eds. Duane’s Ophthalmology. 15th ed. Philadelphia, Pa:
Lippincott Williams and Wilkins. 2009: chap 5.
12. Parks MM. Concomitant exodeviations. In: Ocular Motility and Strabismus. Hagerstown, Md: Harper and
Row. 1975:113.
13. Rosenbaum AL, Stathacopoulus RA. Subjective and objective criteria for recommending surgery on
intermittent exotropia. Am Orthopt J. 1992;42:46.
14. Rosenbaum AL. Exodeviations. In: Current Concepts in Pediatric Ophthalmology and Strabismus. Ann
Arbor: University of Michigan. 1993:41.
15. Santiago AP, Ing MR, Kushner BJ, Rosenbaum AL. Intermittent exotropia. In: Clinical Strabismus Management:
Principles and Surgical Techniques. WB Saunders Co. 1999.
16. Von Noorden GK. Binocular Vision and Binocular Motility: Theory and Management of Strabismus. 5th ed.
St Louis: Mosby Year Book. 1996:341.
17. Wright KW, Buckley EG, Del Monte MA. Pediatric Ophthalmology and Strabismus. 1995.
Chap-06.indd 54 23-09-2013 12:08:41
JAYPEE BROTHERS MEDICAL PUBLISHERS
A and V patterns in horizontal strabismus refer to the condition when the angle of deviation
measures dierently between up and down gaze. e deviation should be measured 25 degrees
above or below the horizontal position for both near and distance xation.
A-Esotropia: An esotropia greater in upward gaze by 15 PD is clinically signicant (Figs 7.3A
and B).
A-Exotropia: e deviation is more in downgaze than upgaze by 15 PD (Figs 7.2A and B).
V-Exotropia: e deviation is more in upgaze by 10 PD (Figs 7.1A and B).
V-Esotropia: An esotropia greater in downward gaze by 10 PD is clinically signicant.
Figs 7.1A and B: V-exotropia
Figs 7.2A and B: A-exotropia
A and V Patterns
CHAPTER
7
A
A
B
B
Chap-07.indd 55 23-09-2013 12:07:46
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
56
Figs 7.3A and B: A-esotropia
Etiology: ere are three schools of thought:
1. ese patterns are secondary to the horizontal misalignment since in most cases, an
oblique muscle dysfunction may not be apparent.
2. e A and V patterns are due to the secondary adducting action of the vertically acting
muscles.
3. e abducting eects of oblique muscles may be responsible.
Management: It is important to diagnose accurately that which muscles are causing the
pattern, so that they can be dealt with appropriately.
If there is a signicant oblique muscle over-action, that muscle needs to be weakened.
However, if there is no demonstrable oblique muscle over-action, then the horizontal
muscle insertions are displaced in the direction in which one wants to weaken its action.
In A-esotropia, bilateral medial rectus recession is combined with upwards displacement
of both MR tendons; in V-esotropia, they are displaced downwards (towards the apex
of the V or A). For a dierence of 15 PD, displacing the insertions by half tendon width
suces.
If the dierence is more than 20 PD, it is usually due to an oblique over-action. In this case,
weakening of that oblique muscle, superior or inferior, is indicated.
If a recess-resect procedure on one eye is being considered, then in case of a V-esotropia,
the medial rectus tendon is moved downwards and the lateral rectus tendon is moved
upwards.
Similarly, if V-exotropia is associated with signicant oblique dysfunction, then surgery on
the obliques is indicated.
But if there is no oblique muscle over-action, then horizontal muscle insertions are
displaced away from the apex of the V, i.e. both the recessed lateral recti are displaced
upwards to correct a V-exotropia and downwards to correct an A-exotropia.
It must be remembered that weakening the obliques improves exotropia and worsens
esotropia as obliques are secondary abductors.
e measurement of A and V patterns must be done in every case of horizontal strabismus
in 25 degrees up and down gaze. ey should be corrected but not at the risk of not
suciently correcting the deviation in primary position.
A B
Chap-07.indd 56 23-09-2013 12:07:46
JAYPEE BROTHERS MEDICAL PUBLISHERS
A and V Patterns 57
FURTHER READING
1. Biedner B, Rothko L. Treatment for ‘A’ or ‘V’ pattern esotropia by slanting muscle insertion. Br J Ophthalmol.
Sep 1995;79(9):807-8.
2. Brown HW. Symposium; strabismus; vertical deviations. Trans Am Acad Ophthalmol Otolaryngol. Mar-Apr
1953;57(2):157-62.
3. Campion GS. Symposium: the A and V patterns in strabismus. Clinical picture and diagnosis. Trans Am Acad
Ophthalmol Otolaryngol. May-Jun 1964;68:356-62.
4. Chen J, Mai G, Deng D. Clinical features and surgical treatment of A-pattern exotropia. Yan Ke Xue Bao. Sep
2004;20(3):163-7.
5. Clark RA, Miller JM, Rosenbaum AL, Demer JL. Heterotopic muscle pulleys or oblique muscle dysfunction?
J AAPOS. Feb 1998;2(1):17-25.
6. Diamond GR, Parks MM. The eect of superior oblique weakening procedures on primary position
horizontal alignment. J Pediatr Ophthalmol Strabismus. Jan-Feb 1981;18(1):35-8.
7. Jampolsky A. Bilateral anomalies of the oblique muscles. Trans Am Acad Ophthalmol Otolaryngol. Nov-Dec
1957;61(6):689-98; discussion 698-700.
8. Kushner BJ. The role of ocular torsion on the etiology of A and V patterns. J Pediatr Ophthalmol Strabismus.
1985;22(5):171-9.
9. Miller JE. Vertical recti transplantation in the A and V syndromes. Arch Ophthalmol. 1960;64:39-43.
10. Parks MM. Commentary on superior oblique tenotomy for A-pattern strabismus in patients with fusion.
Binocular Vision. 1988;3:39.
11. Urist MJ. Horizontal squint with secondary vertical deviations. Arch Ophthalmol. 1951;46:245-267.
Chap-07.indd 57 23-09-2013 12:07:46
JAYPEE BROTHERS MEDICAL PUBLISHERS
Any patient with a paralytic strabismus, a child or an adult, will present either with an abnormal
head posture or with a manifest strabismus.
CHARACTERISTICS
1. Increase in the angle of deviation as the eyes turn in the direction of limitation of
movement.
2. e primary deviation (measured when xating with the good eye) is less than the
secondary deviation, (measured with the aected eye xating). It means that the angle of
deviation increases as the patient xates with the aected eye.
3. Diplopia: In congenital paralytic strabismus, diplopia is absent but is present in all
acquired cases.
4. Abnormal head posture: In congenital and acquired paralytic strabismus, the patient
may adopt a compensatory head posture to minimize diplopia, to obtain foveal xation
and fusion of images with both eyes. It may be in the form of chin up or down in vertical
diplopia (superior/inferior rectus muscle involvement), face turn to avoid horizontal
diplopia (medial/lateral rectus muscle involvement) or head tilt to avoid tortional diplopia,
(oblique muscles’ involvement).
5. Muscle sequelae: Following muscle paresis, sequelae develop in the agonist and
antagonist muscles according to the Hering’s and Sherrington’s laws.
i. First, there is over-action of the contralateral synergist, according to Hering’s law of
equal innervation. For example, in right sixth nerve palsy, there is over-action of the
left medial rectus.
ii. Contracture of the ipsilateral antagonist (Sherrington’s law), i.e the right medial
rectus.
iii. Secondary inhibition of the contralateral antagonist (Hering’s law), i.e. left lateral
rectus. All these sequelae take time to develop and can be monitored by the Hess test.
Paralytic Strabismus
CHAPTER
8
Chap-08.indd 58 23-09-2013 12:57:09
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 59
Figs 8.1A to C: Acute VI nerve palsy: (A) Face turn to the left. (B) Left esotropia in primary position,
absent abduction left eye. (C) Esotropia increases on fixing with the left eye (secondary deviation due
to contralateral medial rectus over-action)
Aims of Examination
1. To nd out which muscle or muscle groups are aected, whether one or more cranial
nerves are involved. Hence, it is important to carefully assess the state of eyes in primary
position and then look for under-action or over-action of any muscle in all positions of
gaze. ey should be noted down in patient’s notes.
In this respect, plotting of serial Hess chart is important to detect improvement, worsening
or development of muscle sequelae.
2. To dierentiate neurogenic palsy from mechanical or restrictive causes: In mechanical
restriction (Blow out fracture or Dysthyroid eye disease), eye movement is restricted in the
opposite direction, e.g. in medial rectus muscle entrapment, abduction will be limited in
that eye and the palpebral aperture will get narrowed on attempted abduction because the
trapped muscle will act as a leash.
3. Complete neurological examination to dierentiate an upper-motor neuron lesion
(cerebral cortical, brainstem involvement) from a lower motor neuron or nerve
involvement. is dierentiation is important regarding patient management.
Etiology
1. Trauma: Head injury is the most frequent cause of single or multiple cranial nerve palsies.
History of birth trauma should be elucidated in all cases of congenital ocular motor nerve
palsies.
2. Vascular disease: Occlusion of vasa nervorum commonly occurs in longstanding diabetes
with poor control. However, the possibility of a dual pathology should not be ignored.
In uncontrolled hypertension, multiple cranial nerves may be involved in brainstem
hemorrhage.
Aneurysms: of vessels constituting the Circle of Willis can aect any ocular motor nerve;
posterior communicating artery aneurysm can compress third cranial nerve, a carotid
artery or a basilar artery aneurysm can involve multiple nerves.
A B C
Chap-08.indd 59 23-09-2013 12:57:09
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
60
Carotico-cavernous stula: Either spontaneous or traumatic can aect all three ocular
motor nerves along with optic nerve and the trigeminal nerve.
Giant cell arteritis: usually causes ischemic optic neuropathy but may cause ocular motor
nerve palsy too.
3. Intracranial space occupying lesions: Primary tumors like pituitary (craniopharyn-
giomas, gliomas) in children aect single or multiple cranial nerves. Brainstem and
cerebellopontine angle tumors, e.g. acoustic neuroma results in sixth nerve palsy.
Cavernous sinus and orbital apex tumors cause multiple nerve involvement and proptosis.
4. Demyelinating disorder (Multiple sclerosis): It commonly causes optic neuritis but
may involve any ocular motor nerve. Diagnosis is suspected if there is a sudden onset of
diplopia in a young adult along with other neurological signs and symptoms.
5. Viral infections: Herpes Zoster ophthalmicus commonly aects the fth cranial nerve but
it can aect the ocular motor nerves too.
Fig. 8.2: Third cranial nerve nucleus
THIRD NERVE PALSY
Clinical Presentation: A 35-year-old man presented with a 4-week history of severe right retro-
orbital pain. en a week ago, he developed horizontal diplopia, followed by drooping of the
right eyelid.
Chap-08.indd 60 23-09-2013 12:57:10
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 61
Neuro-ophthalmic Examination (Figs 8.3A and B)
Right Left
Visual acuity (Snellen’s) 6/6 6/6
Color vision (Ishihara’s plates) 12/12 12/12
Pupils 3 mm, brisk 7 mm, xed
Lids Levator function 13 mm Total ptosis, absent levator
function
Ocular motility full movements exotropia, hypotropia, absent
adduction,
Elevation and depression
Orbits normal normal
Fundus examination normal normal
Confrontation visual elds normal normal
Clinical Diagnosis: Sudden onset of ptosis, with exotropia, hypotropia and pupillary
involvement is diagnosed as total third nerve palsy.
Aims of Examination
1. To decide whether a total or a partial third nerve palsy (Figs 8.4A to D): A partial third
nerve palsy includes either the involvement of all extra-ocular muscles without the pupil
or a superior or inferior division palsy: in a superior division involvement, superior rectus
and levator muscles are aected only; an inferior division palsy aects inferior rectus,
inferior oblique, medial rectus and the sphincter pupillae muscles, or it may rarely be the
involvement of a single muscle only.
2. To see if it is a nuclear involvement: A nuclear involvement causes bilateral abnormalities;
a single central caudate nucleus in the midbrain supplies both the levator muscles; the
superior rectus is supplied by the contralateral nucleus and the remaining extraocular
muscles are supplied by the ipsilateral nucleus. Hence, a nuclear lesion causes an
ipsilateral, partial third nerve palsy with contralateral ptosis as well due to the under-
action of the opposite superior rectus and the levator muscles. (is is seen in brain tumor,
abscess, demyelination.)
Figs 8.3A and B: Neuro-ophthalmic examination. (A) For right eye; (B) For left eye
A B
Chap-08.indd 61 23-09-2013 12:57:10
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
62
A B
DC
Figs 8.4A to D: Congenital partial third nerve palsy with pseudo-ptosis, hypotropia,
lid retraction on attempted down-gaze and adduction
3. To see if other ocular motor nerves are involved: is is important to localize the site of
lesion causing the third nerve paralysis. Multiple cranial nerves may be involved in basal
meningitis, fracture base of skull or cavernous sinus lesions.
Unilateral third nerve palsy with contralateral hemiplegia localizes the lesion to
midbrain as the nerve is exiting the brainstem close to the cerebral peduncles. e cause is
usually a hemorrhage/stroke.
e fourth nerve supplies the superior oblique muscle that causes depression when the
eye is adducted. is can be checked in the presence of third nerve palsy (with the eye abducted
and hypotropic), by asking the patient to look down and noting intorsion of the eyeball (by
observing a conjunctival vessel at 12 o’ clock as a landmark and noting its inward movement).
e sixth nerve is checked if the eye can be fully abducted and there is a marked exotropia.
e fth nerve is checked by testing the corneal sensitivity.
Dierential Diagnosis
1. If there was no pupillary involvement, in case of acute partial third nerve palsy in a young
adult, it is mandatory to rule out Myasthenia and a demyelinating disorder (Multiple
sclerosis).
2. An acute, total, and painful third nerve palsy, is usually due to an acute aneurysmal
compression and is a potentially life-threatening condition; it has to be dierentiated
from an ischemic process (in diabetes, hypertension).
3. Acute aneurysmal compression: Usually by an aneurysm of the circle of Willis:
i. It can present at any age.
ii. It causes severe retro-orbital pain, which is only relieved once the aneurysm
decompresses either spontaneously or surgically.
Chap-08.indd 62 23-09-2013 12:57:10
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 63
iii. Since the parasympathetic bers supplying the constrictor pupillae muscle travel
supercially in the third nerve, an expanding aneurysm compresses these bers,
damages them and results in a xed, dilated pupil.
iv. Signs of aberrant regeneration (Fig. 8.4) may be present in chronic, compressive
lesions or trauma causing disruption of the myelin sheath and axon cylinders. When
new axons sprout, they re-grow into axon cylinders supplying other extra-ocular
muscles. It is characterized by lid retraction or pupillary constriction in attempted
down-gaze or adduction. It is not seen in ischemia, as the axon cylinder is intact.
4. Ischemic third ner ve palsy is usually seen in late adulthood with a history of uncontrolled
diabetes and hypertension. e third nerve palsy is partial; pupil is spared as the pupillary
bers are situated supercially closest to the blood supply provided by the surrounding
vasa nervorum supplying the nerve. e palsy may be associated with mild pain due to
ischemia of trigeminal sensory nerve bers that join the oculomotor nerve within the
cavernous sinus; it is relieved spontaneously.
Investigations
1. CBC, ESR: To rule out giant cell arteritis.
2. Blood sugar: Fasting and two hour post-prandial for undiagnosed diabetics. In a known
diabetic, HbA1c to detect level of diabetic control over the last 6 months.
3. BP reading and monitoring.
4. If acute compression is suspected, then an urgent MRI brain to detect intracranial space
occupying lesion or a cerebral angiography to detect an aneurysm.
5. If all studies are normal, then a lumbar puncture to rule out meningitis.
Management
1. e case was managed by an arteriogram that conrmed the presence of an aneurysm
of the posterior communicating artery. e patient was referred to a neurosurgeon for
clipping of the aneurysm.
2. In a diabetic/hypertensive patient, both diabetes and hypertension needs to be
meticulously controlled. Patient needs to be warned of the possibility of a Stroke. He
should be started on blood thinners, e.g. low dose aspirin.
3. If multiple ocular motor nerves are involved along with the trigeminal nerve, it localizes
the lesion to the cavernous sinus, either a tumor or an aneurysm. Cavernous sinus
syndrome is dened by its resultant signs and symptoms: ophthalmoplegia, chemosis,
proptosis, Horner syndrome, or trigeminal sensory loss. Tumors include meningiomas
or neurobromas, locally spreading tumors like nasopharyngeal carcinoma or pituitary
tumors. Metastatic lesions are most often from the breast, prostate, or lung. Radiotherapy
may oer transient relief, particularly in nasopharyngeal cancer. Lateral extension of
pituitary tumors may be treated with surgical resection and dopamine agonists in the case
of prolactinoma. Total resection of these lesions is challenging and attempted only when
the symptoms are disabling.
Chap-08.indd 63 23-09-2013 12:57:10
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
64
Cavernous sinus aneurysms are more frequent in the elderly, present with an indolent
ophthalmoplegia. ey do not involve a major risk of subarachnoid hemorrhage but they
can rupture, resulting in a direct carotico-cavernous stula, which may lead to cerebral
hemorrhage. ey do not require treatment but only serial observation for worsening of
symptoms and signs; endovascular occlusion may be attempted in selected patients.
SUPERIOR DIVISION PALSY FIGS 8.5A TO D
is presents as unilateral ptosis and hypotropia of a variable degree. Depending upon
the degree of ptosis and obstruction of visual axis, there may be occlusion amblyopia and
secondary outward deviation of the amblyopic eye. e hypotropia with eccentric xation may
be a contributory factor to the amblyopia. Superior division palsy has to be dierentiated from
double elevator palsy since the degree of ptosis and hypotropia is greater in the former than
the latter.
Etiology: e superior division of the third nerve supplies both the SR and the levator muscles.
ere is a variable degree of weakness of the levator muscle as it receives input from both the
3rd nerve nuclei.
Muscle Sequelae
1. Due to constant hypotropia, there may be contracture of the ipsilateral inferior rectus
muscle.
2. ere will be over-action of the opposite inferior oblique (the agonist muscle of paralyzed
SR). ere may be lid retraction of the unaected eye when the patient xes with the
aected eye.
Characteristics
1. Ptosis/pseudo-ptosis; variable levator function.
2. Hypotropia of a variable degree.
Figs 8.5A to D: Marked ptosis with poor levator function and hypotropia of 40 PD (poor SR function)
and dense amblyopia. First, full-time patching of L eye done to restore vision in the R eye. Then, Knapp’s
procedure has done to correct 25 PD hypotropia. After 2 months, brow suspension and inferior rectus
recession done to correct the remaining hypotropia
A B C D
Chap-08.indd 64 23-09-2013 12:57:10
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 65
3. Normal vision if there is a compensatory chin up posture, otherwise constant hypotropia
and complete ptosis results in amblyopia.
4. ere may be secondary exotropia due to uncorrected amblyopia (anisometropia may be
a contributory factor).
5. Variable Bell’s phenomenon.
6. Forced duction test (FDT) may be positive.
Management
1. It is important to measure the degree of ptosis with each eye xing; in case of pseudo-
ptosis, as the aected eye xates, the ptosis disappears. In such patients, simply correcting
hypotropia suces.
2. It is extremely important to correct the amblyopia rst, whatever the age of the patient, by
full-time patching of the good eye. As the vision improves, associated exotropia corrects
itself and once foveal xation is achieved, the eye will stay at its place postoperatively. But
if corrective surgery is performed without treating amblyopia rst, the eye will either turn
outwards (XT) or downwards, again. As the eye becomes orthophoric, levator function
also improves and ptosis surgery may not be needed.
3. To correct hypotropia, measure hypotropia as well as the degree of elevation in abduction,
primary position and adduction. en check for contracture of inferior rectus muscle by
forced duction test under general anesthesia. ere are two surgical options:
i. If there is some restriction of IR muscle on FDT and some SR function is present, then
recess IR preferably an augmented recession if hypotropia is of 25 PD.
ii. If SR is totally paralyzed and FDT for IR is negative, do Knapp’s procedure (Fig. 8.6).
In this, detach both the horizontal recti and reinsert them on either side of insertion of
SR muscle, keeping the muscles at the same distance from the limbus as the original
insertion. is corrects a hypotropia of 25–30 PD; for lesser degrees of hypotropia,
do upward tendon transposition by half tendon width (hypotropia = 10 PD), or 2/3
tendon width (corrects HT = 15–20 PD).
4. Once hypotropia and vision are corrected, assess the degree of ptosis again preferably
6–8 weeks postoperatively and decide for either levator resection or brow suspension
depending upon the levator function.
Double Elevator Palsy/Superior Division Palsy
e term “Double elevator palsy” comprises of weakness of both the superior rectus and the
inferior oblique resulting in limitation of monocular elevation in both abduction (SR) and
adduction (inferior oblique) with resultant hypotropia of the eyeball and secondary ptosis or
pseudo-ptosis.
Etiology: e cause is a congenital defect at the supra-nuclear level. e third nerve nucleus
lies beneath the superior colliculus. Each levator muscle is supplied by both the nuclei; the
superior rectus muscle is supplied by the contralateral nucleus and the remaining extraocular
Chap-08.indd 65 23-09-2013 12:57:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
66
muscles receive input from the ipsilateral nucleus. For the same reason, aberrant regeneration
in the form of Marcus Gunn Jaw winking phenomenon may be seen. Since SR and the levator
muscles share a common sheath, there is either ptosis (due to a partial weakness of the levator
muscle) or pseudo-ptosis (due to hypotropia giving a false impression of ptosis).
Clinical Presentation (Figs 8.7 and 8.8)
1. Mild to moderate congenital ptosis or pseudo-ptosis when xing eye is the normal eye.
2. e ptosis reduces or disappears when the patient xates with the involved eye. As the
eyeball moves up to take the xation, in the presence of a partial paresis of superior rectus,
the ptosis also disappears because SR and levator muscles share a common sheath.
3. A compensatory chin elevation to maintain binocular single vision in moderate weakness
of SR + inferior oblique.
4. Hypotropia of a variable degree depending upon the degree of SR weakness and
involvement of inferior oblique.
5. Amblyopia: If the hypotropia persists and is marked, the child only xates with the good
eye; the involved eye loses foveal xation with resultant amblyopia.
6. As the amblyopia worsens, that eye becomes exotropic as well. It is important to understand
that exotropia in this situation is secondary to amblyopia and not the primary problem.
7. Bell’s phenomenon present in most cases.
8. Continued hypotropia results in secondary contracture of the inferior rectus muscle that
further limits eyeball elevation.
Fig. 8.6: Knapp’s procedure
Chap-08.indd 66 23-09-2013 12:57:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 67
Management: Surgery is indicated to treat compensatory head posture and hypotropia. Proper
clinical assessment regarding visual acuity, estimation of the degree of hypotropia, ptosis with
each eye xing, whether SR weakness is total or partial and degree of exotropia is mandatory.
1. Amblyopia is treated rst by correcting glasses and full-time occlusion of the good eye
according to the age of the patient.
2. Once vision is equalized in both eyes, the exotropia disappears and does not need surgical
correction.
3. Hypotropia is managed depending upon FDT under a general anesthetic. If no contracture
of inferior rectus is found and there is poor SR function, then the choice of surgery is a
Knapp’s procedure. However, if there is limitation to passive globe elevation on FDT, then
inferior rectus recession is indicated.
4. Usually in these cases, levator function is good. If any residual ptosis persists after the
correction of amblyopia and hypotropia, it can be treated by levator resection.
INFERIOR DIVISION PALSY FIGS 8.9 AND 8.10
e inferior division of third nerve supplies the inferior rectus, inferior oblique, medial rectus,
sphincter pupillae and the ciliary muscles. It is rarely seen.
Characteristics
1. e eye is exotropic, intorted and hypertropic.
2. ere will be a face turn to the normal side and a head tilt to avoid diplopia.
Figs 8.7A to C: Right ptosis when looking with left eye. Lift inferior oblique over-action and right
hypotropia. Ptosis disappears when looking with right eye (right pseudo-ptosis due to nuclear SR palsy)
Figs 8.8A to C: Left ptosis, inferior oblique under-action with limited elevation left eye
A B C
A B C
Chap-08.indd 67 23-09-2013 12:57:11
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
68
Figs 8.9A and B: Inferior division palsy: Left hypertropia and exotropia
Figs 8.10A to C: (A) Limited adduction in right eye; (B and C) MRI showing multiple
tuberculomas cerebral and cerebellar cortex
Fig. 8.11: Postoperative left medial rectus and inferior rectus resection
corrected left hypertropia and XT
3. Muscle sequelae in the form of over-action of contralateral superior rectus, superior
oblique and lateral rectus.
Management (Fig. 8.11)
1. Investigate and nd the cause, and treat it if possible.
2. Await spontaneous recovery for at least a year in inammatory conditions or microvascular
occlusion in diabetes/hypertension.
3. If the condition persists and the head posture and diplopia is troublesome, do corrective
surgery to straighten the eye.
A B
AB C
Chap-08.indd 68 23-09-2013 12:57:12
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 69
Case: A 64-year-old man presented with sudden onset diplopia and drooping of the right lid
for 7 months. ere was a history of fatigability, with relapses and remissions of his symptoms.
e patient did not have diabetes or hypertension.
Examination (Figs 8.12A to C): Right sided moderate ptosis, exotropia with slight hypotropia,
limited adduction and depression of the right eye. Vision was 6/9 in both eyes. e pupils were
equal and briskly reacting to light. e levator function was good. Fatigability test was positive
(after continued upgaze for 1 minute, the right lid fell down like a curtain—the Curtain sign).
e saccades were brisk and orbicularis muscle tone was good.
Dierential Diagnosis: In a sudden onset of pupil-sparing partial third nerve palsy in an
elderly person without any systemic illness, must investigate for the following conditions:
1. Myasthenia gravis or Ocular myasthenia: Exclude by history and demonstrating
fatigability test, ice-pack test, tensilon/pro-stigmine test, acetylcholine receptor antibody
assay and MRI chest for thymoma.
2. Chronic progressive external ophthalmoplegia (CPEO) (Figs 8.13A and B): A chronic,
progressive disorder presenting with ptosis, which is bilaterally symmetrical with poor
levator function, bilateral ophthalmoparesis, poor orbicularis muscle tone, slow saccades
of the eyeball.
3. Demyelinating disorder: It can present with any cranial nerve paresis/palsy along with
other neurological symptoms, waxing and waning in character, separated in time and
space. Investigate by an MRI to demonstrate demyelinating plaques in the brain or peri-
ventricular demyelination. A lumbar puncture and testing the spinal uid for gamma
globulins is diagnostic.
Figs 8.12A to C: (A) Right ptosis, exotropia and hypotropia; (B) Upgaze: good LF;
(C) Positive fatigability test
A B C
Figs 8.13A and B: Chronic progressive external ophthalmoplegia (CPEO)/bilateral,
symmetrical ptosis and ophthalmoparesis
A B
Chap-08.indd 69 23-09-2013 12:57:12
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
70
4. yroid eye disease (Figs 8.14 and 8.15): Must exclude Grave’s disease, which may co-
exist with ocular myasthenia as both are autoimmune disorders. e inferior and the
medial rectus muscles are commonly the rst ones to be involved resulting in an esotropia
and a hypotropia.
Note: In a patient of yroid Eye Disease, if exotropia is noted, that patient must be investigated
for ocular myasthenia.
In this patient, the variability of symptoms during the day, demonstration of fatigability,
good levator function and asymmetrical involvement of two eyes pointed towards Ocular
Myasthenia.
A prostigmine test and positive acetylcholine receptor antibodies conrmed the diagnosis.
An MRI chest for thymoma was negative.
Management
1. Patient was educated regarding his illness. He did not have any systemic symptoms yet
but he was warned that any time he feels diculty in swallowing, breathing or generalized
fatigability, he should see an internist.
2. He was started on Pyridostigmine orally.
3. Prednisolone 20 mg on alternate days—Ophthalmoparesis responds better to steroids
while ptosis responds well to pyridostigmine.
4. Azathioprine can be added if no response is seen to the above drug therapy.
5. Plasmaphoresis may be considered too.
Figs 8.14A and B: Thyroid eye disease: Proptosis, lid retraction, ophthalmoparesis
Figs 8.15A and B: Thyroid eye disease: MRI showing muscle hypertrophy
without tendon involvement
A B
A B
Chap-08.indd 70 23-09-2013 12:57:12
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 71
FOURTH NERVE PALSY FIG. 8.16
Clinical Presentation: A 30-year-old man
presented with a sudden onset of vertical diplopia
in primary position getting worse on lateral gaze
and towards the evening. It was accompanied
by generalized tiredness and fatigability. ere
was no history of head injury, diabetes or
hypertension.
Diagnosis (Figs 8.17 and 8.18)
A young man presenting with left hypertropia in primary position, which increased on right gaze
and left head tilt.
Extra-ocular motility showed under-action of left superior oblique (the primary muscle involved)
and over-action of inferior oblique (antagonist). Remaining neuro-ophthalmic examination
was normal. e hypertropia increased on right gaze due to over-action of L inferior oblique;
it increased on left head tilt due to over-action of L superior rectus (compensatory). is is the
Bielschowsky’s ree Step Test. is conrmed the presence of a fourth nerve palsy. Plotting a
Hess chart is helpful in nding which muscles are over-acting or underacting (Fig. 8.19).
Fig. 8.16: Left hypertropia in primary position
Figs 8.17A and B: (A) Under-action of left superior oblique; (B) Hypertropia increasing on right
gaze/over-action of left inferior oblique
Figs 8.18A and B: (A) No hypertropia on right head tilt; (B) Hypertropia increases on left head-tilt
A B
A B
Chap-08.indd 71 23-09-2013 12:57:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
72
Dierential Diagnosis: Sudden Onset Fourth Nerve Palsy in an Adult
Trauma: Fourth nerve exits the brainstem dorsally by ne rootlets, which are damaged by
head injury or where it passes through the superior orbital ssure. Prognosis for traumatic
fourth nerve palsy is good, most cases recover spontaneously.
Intracranial space occupying lesion, e.g. a posterior fossa tumor or an aneurysm of
superior cerebellar artery.
Demyelinating disorder: Multiple sclerosis, accompanied by other neurological
symptoms and signs separated in time and space.
Ocular myasthenia: It can mimic any ocular motor nerve palsy and can aect at any age.
It should be considered in all cases of acute fourth nerve palsy.
Diabetes and hypertension: Isolated fourth nerve palsy is seen in the elderly due to
microvascular occlusion and recovers spontaneously.
Breakdown of a congenital palsy: It is indicated by the absence of cyclotropia and
increased vertical fusion amplitude of more than 4–6 PD.
Fig. 8.19: Hess chart: Fourth nerve palsy—initially, superior oblique under-action results in hypertropia
due to inferior-oblique over-action (direct antagonist). Then it results in over-action of contralateral Inferior
rectus (yoke muscle) with inhibition palsy of superior rectus of the same eye resulting in hypotropia of
the good eye
Chap-08.indd 72 23-09-2013 12:57:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 73
Investigations
Since the patient did not have history of head injury, headache, DM, HTN and other
neurological symptoms, but had a history of intermittency and easy fatigability, Prostigmine
test was performed. It conrmed the diagnosis of Ocular myasthenia.
Other investigations for Myasthenia gravis:
CBC, ESR, BSR, HbA1c: all were normal.
Serum T3, T4, TSH (Graves’ disease can co-exist as both are autoimmune disorders):
normal.
Anti-acetylcholine receptor antibody assay (AChR): 5.1 mmol/L (Normal < 0.2) highly
positive.
MRI chest (Figs 8.20 and 8.21) conrmed the presence of thymoma.
Management of the case:
1. Medical therapy : Stepwise:
i. Pyridostigmine: 60 mg × 4/day, orally.
ii. Prednisolone: 20 mg × alternate day, orally.
iii. Azathioprine: 50 mg × 3/day, orally.
2. Surgery: ymectomy
3. Plasmaphoresis
4. Regular follow-up: To note improvement in symptoms and signs, to note and manage any
complications of medical therapy and to note development of generalized symptoms of
myasthenia gravis or Graves’ disease.
5. Prognosis:
–Neuromuscular junction disorder; peak in 2nd–3rd decade, but can present at any age.
–Usually bilateral ocular involvement in 90%; it is a presenting feature in 60%.
–Course: in 50–70%, ocular symptoms progress to generalized myasthenia within 2 years,
hence monitoring of symptoms and signs is very important.
Fig. 8.20: MRI chest Fig. 8.21: MRI chest
Chap-08.indd 73 23-09-2013 12:57:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
74
–Follow-up: should be every 4–6 months: Keep looking for systemic involvement,
(dysphagia, dysarthria, breathing diculty).
–Patient education: To report if systemic symptoms develop.
6. Surgery for fourth nerve palsy due to causes other than myasthenia gravis: Most fourth
nerve palsies improve spontaneously in 6–9 months. Patient learns to avoid diplopia by
a face turn and slight head tilt. However, if symptoms persist beyond this period, then
surgery should be considered. Hess chart is helpful to decide which muscle should be
operated.
Choice of surgery: Weakening of inferior oblique muscle is usually the rst choice as it is
easy to perform; it can be combined with recession of contralateral inferior rectus for large
deviations. A strengthening procedure of superior oblique can be performed but is dicult.
Inferior oblique can easily be weakened by a myectomy or recession, both giving almost
similar results.
SIXTH NERVE PALSY FIG. 8.22
Case presentation: A 4-year-old boy was
brought with a sudden onset of esotropia
gradually getting worse for 6 months. ere was
no history of fall or head injury. e child was
otherwise healthy with occasional complaints of
headache.
Examination: Vision was 6/6 in both eyes.
Pupils were normal and reacting briskly. ere
was a face turn towards the left with marked
limitation of abduction of the right eye. ere was bilateral medial rectus over-action; no
inferior oblique over-action was detected. Fundus examination showed a swollen and
congested right optic disc.
Dierential Diagnosis: Sixth nerve palsy causes an abduction decit in the eye. It is important
to determine whether this decit is due to:
1. A muscular cause: Myopathy/myositis or muscle restriction as seen in blow out fracture,
Graves’ disease involving the medial rectus muscle.
2. A neuromuscular junction involvement: As in ocular myasthenia.
3. Nerve involvement: Duane’s retraction syndrome, sixth nerve palsy due to trauma, tumor,
aneurysm, raised intracranial pressure.
4. Congenital esotropia: In longstanding, uncorrected ET, medial rectus hypertrophy and
lateral rectus stretching and weakness occurs limiting abduction of that eye. However, in
this situation, inferior oblique over-action is usually present.
Fig. 8.22: Right abduction deficit and face
turn to left
Chap-08.indd 74 23-09-2013 12:57:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 75
Surgical Anatomy of the Sixth Nerve (Fig. 8.23)
e sixth nerve nucleus comprises of a group of motor neurons lying in the oor of fourth
ventricle close to the fascicles of the seventh nerve. e central group of these cells innervates
the lateral rectus muscle while the surrounding cells make up the para-abducens nucleus, the
center for horizontal conjugate gaze.
e sixth nerve fascicles pass through pontine tegmentum to exit at the pontomedullary
junction. After exiting the brainstem, it runs over the petrous pyramid to enter the cavernous
sinus adjacent to carotid artery. en it enters the orbit through the superior orbital ssure in
close proximity to the third, fourth nerves and the sympathetic nerves.
Localization of Site of Sixth Nerve Palsy
A nuclear involvement will aect the adjacent para-abducens nucleus as well as the facial
nerve causing conjugate gaze paresis towards the site of lesion and facial palsy: Foville’s
syndrome.
Mobius syndrome: Congenital, bilateral sixth and seventh nerve palsy, with intact vertical
gaze.
Raised intracranial pressure stretches the nerve at the base of skull and may aect one or
both the sixth nerves. is will be accompanied by other signs and symptoms as well like
headache, dizziness, vomiting, papilledema.
A cavernous sinus lesion will aect the third, fourth nerves and cause Horner’s syndrome
due to involvement of the sympathetic nerves.
Small vessel infarcts of the nerve are commonly seen in uncontrolled diabetes,
hypertension.
Bilateral sixth nerve palsy is never from a vascular disease and should be investigated.
In children, most common causes are trauma, post-viral and neoplasia, the commonest
being a brainstem glioma.
Fig. 8.23: Anatomy of sixth nerve nucleus
Chap-08.indd 75 23-09-2013 12:57:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
76
Figs 8.24A and B: Hess chart: (A) Acute sixth nerve palsy showing under-action of LR;
(B) Over-action contralateral MR
BA
Investigations: ese depend upon the clinical diagnosis:
1. CBC, ESR for a suspicion of myositis.
2. yroid function tests if suspected throid eye disease.
3. Tensilon/Prostigmine test, acetylcholine receptor antibody test for ocular myasthenia.
4. In children, if no history of trauma or viral infection, then MRI is a must, particularly, if the
child complains of headaches accompanied by optic disc fullness, congestion or swelling.
(as shown in the case: a large cerebellar glioma).
5. MRI brain (Fig. 8.25) is also a must for bilateral sixth nerve palsy at any age group.
6. Over the age of 50 years, investigate for diabetes and hypertension.
7. Hess chart (Fig. 8.24): It is very informative showing the degree of lateral rectus under-
action and over-action of medial recti (there is contracture of the ipsilateral medial
rectus with over-action of contralateral medial rectus and secondary inhibitional palsy of
contralateral lateral rectus). It may also show superior oblique involvement in co-existing
fourth nerve palsy. Hence, Hess chart is very important for surgical planning.
Figs 8.25A and B: MRI showing a large cerebellar glioma
A B
Chap-08.indd 76 23-09-2013 12:57:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Paralytic Strabismus 77
Management
In this case, the MRI showed a large cerebellar glioma, which was removed by the
neurosurgeon.
While the child is awaiting surgery, part-time patching of the good eye for 50% of the
waking hours for six days/week is important to prevent contracture of medial rectus as well
as amblyopia in the eye with sixth nerve palsy. As xation in the involved eye improves,
patching is reduced.
Meticulous control of BP and blood sugar in diabetics and hypertensives and warn them
regarding a major stroke.
Wait for spontaneous recovery over 9–12 months.
Surgery: e choice of surgery depends on the degree of recovery of lateral rectus function.
If there is no recovery of lateral rectus function, then abduction of that eye cannot be
achieved by any means. Aim of surgery is to straighten the eye. is can be achieved by a large
medial rectus augmented recession up to 8–10 mm combined with a maximum lateral rectus
resection. e other choice is transpositioning of vertical recti to the lateral rectus insertion.
If there is recovery of lateral rectus function, then recession of ipsilateral medial rectus,
with resection of contralateral lateral rectus combined with contralateral medial rectus
recession preferably with adjustable sutures as the results of surgery are unpredictable in a
previously paralyzed muscle.
Chap-08.indd 77 23-09-2013 12:57:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Duane’s retraction syndrome
Brown’s syndrome
Strabismus xus
Dysthyroid ophthalmopathy
e rst three syndromes are congenital in origin. Acquired causes of muscle restriction are
dysthyroid ophthalmopathy, blow-out fractures, myositis, retinal detachment surgery.
DUANE’S RETRACTION SYNDROME
is is a very common condition described by Alexander Duane in 1905. It is a third nerve
misdirection syndrome with three clinical types, depending upon the degree of misdirection
and innervation of lateral rectus muscle by the third nerve bers. e Type 1 being the most
frequent, its clinical features include:
1. A slight face-turn to the aected side with a small esotropia apparent on straightening the
head.
2. Absent or severely decient abduction of the aected eye.
3. Slight weakness of adduction.
4. Narrowing of palpebral aperture, up-shoot and retraction of the eyeball on adduction.
5. Widening of palpebral aperture on attempted abduction.
e Type 2 syndrome is less common. In it, the limitation of adduction is more pronounced
than abduction. e face turn is towards the normal eye and a slight exotropia is apparent on
straightening the head.
In Type 3 syndrome, there is no face turn and the eyes are straight in primary position.
Abduction and adduction are both severely aected and there is retraction of eyeball on
attempted adduction.
Restrictive Strabismus
CHAPTER
9
Chap-09.indd 78 23-09-2013 12:06:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Restrictive Strabismus 79
Associated systemic abnormalities: Goldenhar’s syndrome (limbal dermoids, pre-auricular
skin tags, vertebral malformation), facial hemi-atrophy, Klippel-Feil syndrome (fusion of
cervical vertebrae, deafness), cervical spina bida, umbilical hernia, polydactyly, sensorineural
hearing decits, cervico-oculo-cutaneus syndrome or Franceschetti syndrome.
Inheritance: It is more common in females, unilateral in 60% cases and more commonly
involves the left eye. Inheritance is autosomal dominant with sex linkage but sporadic cases
are also seen.
Etiology: It is a neurological problem. During embryogenesis, there is hypoplasia or aplasia
of sixth nerve nucleus and consequent atrophy of the nerve trunk. e inferior division of
third cranial nerve gives o branches that innervate the lateral rectus muscle. is view is
supported by a strong association with other congenital neurological, cutaneous and skeletal
abnormalities.
According to Huber, the lateral rectus seems to be having three parts: one part is
normally innervated by the hypoplastic sixth nerve bers, a second part is innervated by the
third nerve bers and the third is a brotic, denervated part. Hence, co-contraction of both
medial and lateral recti on adduction limits the amount of excursion. e brotic portion of
lateral rectus acts as a leash or a tight rope and the co-contraction of its remaining portion
innervated with the third nerve bers results in narrowing of the palpebral aperture and up-
shoot or down-shoot of the eyeball. On attempted abduction, co-contraction of medial rectus
results in pulling of the eyeball medially and widening of the palpebral aperture.
In Type 1 syndrome, the lateral rectus has 1/3rd portion innervated by the sixth nerve, 1/3
portion innervated by the third nerve and 1/3rd is a brotic portion. is explains the varying
degree of abduction decit (Figs 9.1A and B).
In Type 2 syndrome, there is hypoplasia of the sixth nerve nucleus with more third nerve bers
innervating the lateral rectus than in Type 1. is results in a more complete dual character of
lateral rectus; on adduction, it contracts along with the medial rectus, preventing adduction of
the eye. On abduction, it contracts more than in Type 1, resulting in lesser abduction decit
(Figs 9.2 and 9.3).
In Type 3 syndrome, there is total aplasia of the sixth nerve nucleus and only the third nerve
bers supply the lateral rectus, making both medial and lateral recti contract simultaneously
and the eye cannot move in any horizontal direction (Figs 9.4A to C).
Figs 9.1A and B: Type 1 Duane’s syndrome: Left abduction more limited
than adduction, with lid retraction on adduction
A B
Chap-09.indd 79 23-09-2013 12:06:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
80
Figs 9.2A and B: Type 2 Duane’s syndrome: (A) Face turn, no diplopia;
(B) Primary position—Left exotropia and diplopia
Figs 9.3A and B: Type 2 Duane’s syndrome: Left adduction
deficit is more than abduction with slight up-shoot
Figs 9.4A to C: Type 3 Duane’s retraction syndrome with marked up-shoot and dissociated vertical
deviation due to associated amblyopia
Dierential Diagnosis: A neurogenic sixth nerve palsy in which there is minimal narrowing of
the palpebral aperture and no up-shoot or down-shoot phenomenon.
Management: It is surgical. Surgery can only straighten the eyes but will not improve
abduction. is should be made clear to the patient and the parents.
Indications for surgery:
1. A manifest strabismus.
2. Cosmetic reasons to correct a compensatory head posture.
A B
A B
A B C
Chap-09.indd 80 23-09-2013 12:06:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Restrictive Strabismus 81
SURGICAL PLAN
In Type 1 Syndrome (Fig. 9.5): Medial rectus
recession will correct the esotropia. In Duane’s
syndrome, the medial rectus is found to be
hypertrophic and highly vascular with large
vessels over its surface. If there is accompanying
palpebral aperture changes or up-shoot/down-
shoot, this should be combined with a lateral
rectus recession too to undo the leash aect.
In Type 2 Syndrome (Fig. 9.8): Lateral Rectus
recession will correct an exotropia. A Faden
suture placed on the opposite medial rectus will correct the in-committance in lateral gaze by
limiting adduction in the good eye.
In Type 3 Syndrome (Figs 9.6, 9.7 and 9.9): If there is a marked leash aect, it can be corrected
by lateral rectus recession along with a Y-split of the recessed muscle.
Figs 9.6A and B: Postoperatively, after a left LR recession with
a Y-split, exotropia and up-shoot corrected
Fig. 9.7: Lateral rectus recession and Y-split of the muscle
Fig. 9.5: Type 1 syndrome: Postoperative
picture following a medial rectus recession
A B
Chap-09.indd 81 23-09-2013 12:06:13
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
82
Figs 9.8A to C: Type 2 Duane’s syndrome: Left exotropia in primary position with marked up-shoot
on adduction
Figs 9.9A and B: Postoperatively, after LR recession with Y-split, the
exotropia and up-shoot are corrected
Note: Transpositioning procedures involving transfer of vertical recti to the insertion of
lateral rectus can be attempted but they will not improve the abduction of that eye. ey are
complicated and can result in anterior segment ischemia.
FURTHER READING
1. Alexandrakis G, Saunders RA. Duane retraction syndrome. Ophthalmol Clin North Am. September
2001;14(3): 407-17. PMID 11705140.
2. Brown HW. Congenital structural muscle anomalies. In Allen JH. Starbismus Ophthalmic Symposium. St
Louis: Mosby. 1950;pp.205-36.
3. Huber A. Electrophysiology of the retraction syndromes. Br J Ophthalmol. March 1974;58(3):293-300. PMC
1214741. PMID 4834602.
4. Mehel E, Quére MA, Lavenant F, Pechereau A. “[Epidemiological and clinical aspects of Stilling-Turk-Duane
syndrome]” (in French). J Fr Ophtalmol. 1996;19(8-9):533-42. PMID 8944136.
5. Mein J, Trimble R. Diagnosis and management of ocular motility disorders (2nd ed). Blackwells. 1991.
6. Morad Y, Kowal L, Scott AB x. Lateral rectus muscle disinsertion and reattachment to the lateral orbital wall.
Br J Ophthalmol. October 2004;89(8):983-5. doi:10.1136/bjo.2004.051219. PMC 1772789. PMID 16024848.
7. Rosenbaum AL. Costenbader Lecture. The ecacy of rectus muscle transposition surgery in esotropic
Duane syndrome and VI nerve palsy. J AAPOS. October 2004;8(5):409-19. doi:10.1016/S1091853104001600.
PMID 15492732.
A B C
A B
Chap-09.indd 82 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Restrictive Strabismus 83
BROWN’S SYNDROME
Figs 9.10A to C: Elevation in abduction is normal and in primary gaze but limited elevation in adduction
Brown described this condition in 1950 characterized by limitation of elevation of the eye in
adduction while elevation in abduction was normal. ere is normal depression in adduction.
It is also called “the superior oblique tendon sheath syndrome”, the superior oblique tendon
being the culprit.
Etiology: ere is an inammation
in the region of trochlea through
which the superior oblique
tendon passes. Superior oblique is
a direct antagonist of the inferior
oblique muscle. Unless the
antagonist relaxes fully, the eye
will not elevate in adduction by
the inferior oblique muscle, which
is normal in this case. From this
relaxed state, the muscle shortens
to move the eyeball down and
inwards.
Congenital causes: ere is a
taut superior oblique tendon
(resulting in its shortening and
a failure to relax) either due to
an anomalous broad insertion,
fascial restrictions or intra-sheath
septae.
Acquired causes: Inammation
in the region of trochlea seen in
rheumatoid arthritis. Trauma,
causing hematoma and edema in
the region of trochlea, limits the Fig. 9.11
A B C
Chap-09.indd 83 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
84
passage of the tendon. Trochlear entrance restriction, cyst of the reected tendon, tuck of
the superior oblique tendon usually done at or near its insertion on the globe resulting in an
iatrogenic Brown’s syndrome.
Clinical Features: All or a few of the features may be present.
1. It is mostly unilateral but can be bilateral with normal vision.
2. Restricted elevation in adduction, with normal depression.
3. Elevation is normal with the eye abducted but it slowly drifts downwards below midline as
it moves into adduction.
4. Absence of over-action of superior oblique, a direct antagonist of inferior oblique and
dierentiates this condition from an inferior oblique paresis.
5. A compensatory head posture comprising of head tilt and face turn to the normal side
with chin elevation.
6. Widened palpebral ssure on adduction.
7. Positive forced duction test in adduction only.
Dierential Diagnosis
1. Inferior oblique paresis: A negative forced duction test and over-action of superior oblique
present.
2. Inferior rectus restriction in thyroid eye disease, blow-out fracture and brosis syndrome.
Forced duction test is positive in both abduction and adduction.
Management: is depends on nding the cause and treating it accordingly. It is important
to release the mechanical limitation to elevation in adduction caused by abnormalities in or
around, the trochlea/tendon of the superior oblique.
is is a dicult condition to treat, surgery should only be limited to cases with a marked
chin up posture. Aim of surgery is to weaken the taut superior oblique. is can be done by:
1. A tenotomy at the nasal border of superior rectus.
2. A tenectomy to remove a small part (2 mm) of the tendon.
3. A lengthening procedure. is is only attempted if there is free movement in the trochlea.
e superior oblique tendon spacer of Wright has been successful in some cases. In this
procedure, the tendon is lengthened by a silicone spacer (#240 retinal band) approximately
5mm is sewn between the two cut ends of the superior oblique tendon, thereby lengthening
it while preserving its “sheath” of fascial surround.
4. Other options: Weakening of ipsilateral inferior rectus by a recession to correct hypotropia.
5. Injecting steroids in the retro-trochlear region in cases of inammation/edema. is can
hasten recovery. is is indicated if pain and local tenderness is present in the trochlear
region.
FURTHER READING
1. Brown HW. Strabismus ophthalmic symposium 1. St. Louis: Mosby Year Book. 1950.p.205.
2. Brown HW. True and simulated superior oblique tendon sheath syndromes. Doc Ophthalmol. 1973;34(1):
123-36.
Chap-09.indd 84 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Restrictive Strabismus 85
3. Katz NN, Whitmore PV, Beauchamp GR. Brown’s syndrome in twins. J Pediatr Ophthalmol Strabismus.
1981;18(1):32-4.
4. Lobefalo LT, Mancini AT, Petitti MT, Verrotti AE, Della Loggia GE, Di Muzio AE, et al. A family with autosomal
dominant distal arthrogryposis multiplex congenital and Brown syndrome. Ophthalmic Genet.
1999;20(4):233-41. Comment in: Ophthalmic Genet. 2001;22(2):125-30.
5. Parks MM, Brown M. Superior oblique tendon sheath syndrome of Brown. Am J Ophthalmol. 1975;79(1):
82-6.
Chap-09.indd 85 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
86
FIBROSIS SYNDROME
Figs 9.12A to C: Bilateral symmetrical ptosis, esotropia, absent depression or globe elevation
is is a conglomerate of clinical presentations, which may be unilateral, bilateral,
symmetrical or asymmetrical in which there is replacement of normal extraocular muscles by
brous tissue. It may aect the levator muscle too. e brosed muscle neither contracts nor
relax fully, hence there is poor muscle force in the agonists and a restriction of the antagonists.
It may be seen sporadically or autosomal dominant in which case a positive family history is
present.
e brotic process aects the conjunctiva and tendon fascia as well with strong adhesions
between it and the muscles. e inferior rectus muscle is the most frequently involved, causing
a limitation in depression due to poor active muscle contraction. At the same time, failure
to relax results in restricted elevation in abduction. e eyes assume a position of marked
downward deviation with ptosis. e forced duction test is positive.
Systemic associations: Nystagmus, Marcus Gunn Jaw winking phenomenon, optic nerve
hypoplasia, colobomata, intraventricular septal defects in heart, facial palsy, musculoskeletal
defects.
Management: Since inferior rectus muscle is primarily aected, large recession preferably
with adjustable sutures. Ptosis is managed by levator resection. Since there is poor Bell’s
phenomenon, only clearing the visual axis should suce.
STRABISMUS FIXUS
It is a congenital condition with brotic dysplasia of the medial rectus so the eyes are xed in
adduction. ere is absence of active and passive horizontal eye movement and a marked face
turn to the side of the xing eye.
Management: To perform extensive recession of both medial recti with hang loose technique.
THYROID EYE DISEASE
yroid eye disease (TED) is an autoimmune process that aects the orbital and periorbital
tissues. e disease process is actually an orbitopathy in which the orbital and periocular soft
tissues are primarily aected with secondary eects on the eye.
A B C
Chap-09.indd 86 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Restrictive Strabismus 87
e majority of patients with TED also have
an underlying hyperthyroid Graves’ disease,
which is an autoimmune disorder characterized
by the presence of circulating antibodies directed
against the thyrotropin receptors as well as the
deregulated stimulation of thyroid hormone
synthesis. e increase in the circulating thyroid
hormones tri-iodothyronine (T3) and thyroxin
(T4) leads to the clinical symptoms and signs
of hyperthyroidism, including weight loss, heat
intolerance, tremor, insomnia, tachycardia,
hyper-reexia and warm, moist skin.
Pathogenesis: e inammatory reactions are initiated by autoreactive T lymphocytes that
migrate into the fat, extraocular muscles and other soft tissues of the orbit, and become
activated by reacting to autoantigens present in these tissues. e activated T lymphocytes
then trigger an inammatory reaction that involves the release of cytokines, which in turn
stimulates the proliferation of broblasts, secretion of glycosaminoglycans, expansion of fat
cells and inammation of the extraocular muscles.
Orbital broblasts dierentiate into fat cells and synthesize increased levels of extracellular
matrix glycosaminoglycans such as hyaluronin. is results in volume expansion in the orbit.
ey also secrete proinammatory cytokines, which result in progression of autoimmune
diseases. Orbital broblasts are not only the targets of proinammatory signals, but are also
ampliers and contributors of the same. erefore, they may be a potential target for therapy
development.
Important points regarding TED that need to be kept in mind:
Approximately 50% of patients with Graves’ disease develop clinically apparent TED.
However, when patients without overt ocular involvement are investigated with orbital
imaging, enlargement of the extraocular muscles is detected in an additional two-thirds
of patients. e thyroid gland and ocular adnexa share one or more antigens that are the
target of autoreactive T and B lymphocytes and antibodies. e prevalence of the disease
is estimated at between 0.5 and 2%.
Based on blood levels of T3, T4 and TSH, approximately 10% of patients are clinically
euthyroid or hypothyroid. In this group, thyroid-specic autoantibodies, also called the
antimicrosomal antibody test, can be detected in approximately 75% of individuals.
e onset of ocular disease may coincide with, precede or follow the systemic disease
manifestations, usually within 6 months before or after the onset of hyperthyroidism.
Systemic Graves’ disease and TED may present and progress independently from one
another. What causes the dierential expression of these two entities are currently not well
understood.
e TED aects women more frequently than men in a ratio 5⋅5:1. ere are two peaks in
the incidence of age of onset, one in the fth decade and another in the seventh decade,
Fig. 9.13: Thyroid eye disease
Chap-09.indd 87 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
88
with women being slightly younger on average than men. In older patients, disease tends
to be more severe.
e TED is bilateral in 85–95% of patients. However, orbital changes may present
asymmetrically, especially in those with eu- or hypothyroid disease.
A positive family history is present in approximately 50% of patients with Graves’ disease.
e TED develops between two and ten times more in Graves’ disease patients who smoke
as compared to nonsmokers. Smoking decreases the ecacy of orbital radiotherapy and
systemic steroid administration, and increases the incidence of optic neuropathy.
A detailed histor y and clinical examination dierentiates between the active inammatory
phase and the inactive brotic phase. Approximately two thirds of TED patients improve
spontaneously without medical intervention; surgical interventions should be delayed
until a state of disease inactivity, and of stability of clinical signs and symptoms, has been
achieved.
SIGNS AND SYMPTOMS OF THYROID EYE DISEASE
Eyelid retraction (80%), exophthalmos (62%), extraocular muscle dysfunction, with or without
diplopia (43%), and pain (30%). Other common complaints include excessive tearing, foreign
body sensation, redness of the eyes and eyelids, blurred vision and photophobia; visual loss
from a compressive optic neuropathy may occur. e morbidity of TED resulting from ocular
irritation and discomfort, tearing, double vision and cosmetic disgurement is high.
e natural history of TED is not completely understood. ere is an initial, active phase
of progressive exacerbation, followed by a subsequent partial regression and eventually an
inactive phase in which the residual manifestations of the disease are unlikely to show any
further substantial change. e time from initial symptoms to inactivity is usually 2–5 years in
most patients.
Proptosis and Pseudoptosis
e thyroid eye disease (TED) is the most common cause of unilateral and bilateral proptosis
in adults. Unilateral proptosis reects asymmetric muscle involvement. e orbit can be
described as a pear-shaped cavity with an anterior opening; the stalk of the pear represents the
optic nerve. In TED, the increase in orbital volume from the extraocular muscles and fat causes
forward protrusion (proptosis or exophthalmos) and, occasionally, optic nerve compression at
the narrow posterior apex of the orbit. e edema results in tissue damage and brosis, with
restriction in extraocular motility and lagophthalmos.
Retropulsion (digital palpation of the globes through closed eyelids) is a useful test; it is
decreased in patients with severe thyroid-associated orbitopathy. Various exophthalmometers
can be used to measure orbital protrusion.
Pseudoptosis may be observed if contralateral lid retraction is present.
Ptosis may occur if levator dehiscence is present.
Lacrimal gland enlargement is not uncommon.
Chap-09.indd 88 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Restrictive Strabismus 89
Lid Retraction, Lid Lag and Glabellar Furrows
Normally, the upper lid is located 1–1.5 mm below the superior limbus, and the lower lid is
located at the inferior limbus.
Upper lid retraction (Dalrymple’s sign), often with temporal are and scleral show, is
the most common ocular sign of thyroid-associated orbitopathy. is sign is an important
dierentiating feature to note in all patients with proptosis. Mechanisms for upper lid retraction
include proptosis, sympathetic drive of the Muller muscle, upgaze restriction, brosis of the
levator muscle, and contralateral ptosis (myasthenia). Lid retraction may occur in both the
upper and lower lids because of a sympathetically innervated tarsal muscle in both lids.
In the absence of eyelid retraction, TED may be diagnosed only if: (1) proptosis, optic
nerve involvement, or restrictive extraocular myopathy is associated with thyroid dysfunction
or abnormal regulation, and (2) no other confounding ophthalmic features are apparent.
Lid lag on down gaze (von Graefe sign) is another important feature of thyroid-associated
orbitopathy. While slowly moving the xation object from upward to downward, the examiner
should observe if the eyelid lags behind the globe on down gaze.
Other lid signs include lid edema and glabellar furrows. A statistically signicant association
is present between deep glabellar folds and thyroid ophthalmopathy. is is presumably
caused by hypertrophy of brow depressor muscles compensating for lid retraction.
Corneal and Conjunctival Findings
Anterior segment signs in thyroid-associated orbitopathy include supercial punctate keratitis,
superior limbic keratoconjunctivitis, and conjunctival injection usually over the rectus muscle
insertions, and conjunctival chemosis.
With severe proptosis, corneal exposure with frank corneal ulceration may occur. Superior
limbic keratoconjunctivitis is a chronic, often recurrent condition of ocular irritation and
considered a prognostic marker for severe thyroid-associated orbitopathy.
e corneal light reexes should be examined closely, because asymmetric proptosis and
lid retraction may mask the true relative positions of the globes.
Orbital Muscle Involvement
Strabismus is commonly seen as hypotropia or esotropia, because the inferior and the medial
rectus muscle are most commonly involved in the disease process. Initially, the muscles are
inamed and later undergo brosis with resultant limitation in contraction and relaxation.
e restrictive myopathy can be conrmed with forced duction test or elevated intraocular
pressure with eye movement (e.g. upgaze in hypotropic patients).
Inferior rectus muscle restriction may mimic double elevator palsy.
In patients with thyroid-associated orbitopathy and exotropia, the possibility of concurrent
myasthenia gravis should be considered.
Pseudo nerve palsies and nerve compression may occur resulting in blurring of vision,
visual loss, dyschromatopsia, or eld loss. Patients with optic nerve compression may not have
Chap-09.indd 89 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
90
marked proptosis or have seemingly mild proptosis, but they usually show markedly decreased
retropulsion (tight orbits). In addition, most cases of compressive thyroid optic neuropathy
occur without visible optic nerve edema. For this reason, documenting visual acuity, color
vision, and the presence or absence of a relative aerent pupillary defect is important during
each visit.
Increased Intraocular Pressure
Glaucoma may result from decreased episcleral venous outow. Because of restrictive
myopathy, intraocular pressure may rise more than 8 mm Hg on upgaze. Choroidal folds may
also be seen with thyroid ophthalmopathy.
Cutaneous Findings
Pretibial dermopathy and thyroid acropachy (which mimics the appearance of clubbing) are
less commonly encountered dramatic, cutaneous signs of dysthyroidism.
TED Classication
Numerous classication systems for thyroid eye disease exist, but they all have shortcomings.
Types I and II: is is the simplest classication. Type I is characterized by minimal
inammation and restrictive myopathy. Type II is characterized by signicant orbital
inammation and restrictive myopathy.
NOSPECS
e Werner NOSPECS classication uses a mnemonic to describe the presence or absence
of signs or symptoms (NO) and grade the various clinical features (SPECS) (S-soft tissue
involvement, P-proptosis, E-extraocular muscles, C-corneal involvement and S-sight loss).
Table 9.1: NOSPECS classification of thyroid eye disease
Class Definition
0 No physical signs or symptom
1 Only signs, no symptoms (signs limited to upper lid retraction, stare, lid lag and proptosis up to 22 mm)
2 Soft tissue involvement (symptoms and signs)
3 Proptosis
4 Extraocular muscle involvement
5 Corneal involvment
6 Sight loss (optic nerve involvement)
NOSPECS: No signs or symptoms; only signs; soft tissue; proptosis; extraocular muscle; cornea; sight loss.
Chap-09.indd 90 23-09-2013 12:06:14
JAYPEE BROTHERS MEDICAL PUBLISHERS
Restrictive Strabismus 91
Unfortunately, the NOSPECS classication has some weaknesses that may limit its
prognostic value. Patients may fall into more than one particular class, and they may not
progress in an orderly fashion from class 1 to class 6. In addition, patients with visual loss from
compressive optic neuropathy may not show marked proptosis or other signs of severe disease.
Disease activity can be assessed using the Clinical Assessment Score (CAS). is set of
clinical criteria was initially described in 1989 and has been widely used in assessing patients
with TED and in planning their treatment. e criteria include seven clinical parameters of
inammation easily determined in the clinic. Furthermore, they include changes in three
functional parameters over a period of 1–2 months.
For each sign or symptom listed, one point is assigned. Points are added to determine the
total clinical activity score:
Ocular pain at rest
Ocular pain on attempted up, side or down gaze
Redness of the eyelids
Swelling of the eyelids
Redness of the conjunctiva
Chemosis of the conjunctiva
Chemosis of the caruncle
Increase in proptosis by > 2 mm
Decrease in eye movement in any direction by > 5 degrees
Decrease in pinhole visual acuity by > one line on the Snellen chart.
For each criterion met by the patient, one point is assigned, with a total CAS of 10. patients
with a low score (< 3) respond poorly to immunosuppressive therapy, indicating that they
have passed the disease stage of active inammation. Other studies have conrmed the
clinical value of the CAS in determining disease activity and the likelihood of a response to
immunosuppressive therapy. One study found that a CAS of 4 or more has a positive predictive
value for a treatment response with corticosteroids of 80%.
Although similar clinical parameters are used in describing disease activity and severity
(such as soft tissue involvement, proptosis, extraocular motility disturbance and visual
acuity), the two are not interchangeable and do not necessarily have a linear relationship, as
emphasized by the following two examples.
A patient who presents with ocular pain, swelling and redness of the eyelids, caruncle
and conjunctiva, but without any disturbance in vision, extraocular motility or signicant
proptosis, would be considered to have active disease with a high clinical activity score (CAS)
of 7. is patient is most likely in the early inammatory phase. e patient’s severity is mild
according to the NOSPECS scheme (class 2).
On the other hand, a patient without any signs of active inammation (no pain, redness
or swelling of the soft tissues), but with severe visual disability from proptosis, restriction
of extraocular motility, eyelid retraction and a compressive optic neuropathy, would be
considered to have inactive disease with a low CAS, most likely in the late, brotic, non-
inammatory phase. is patient’s severity would be rated as sight threatening according to
the NOSPECS scheme (class 6).
Chap-09.indd 91 23-09-2013 12:06:15
JAYPEE BROTHERS MEDICAL PUBLISHERS
Understanding Strabismus
92
e two outlined examples demonstrate the importance of distinguishing between disease
activity and severity, and this distinction has important implications for treatment.
OUTPATIENT MANAGEMENT
Most patients with thyroid eye disease can be observed; the follow-up interval depends on
disease activity.
1. Monitor for visual loss: due to corneal exposure or optic neuropathy.
2. Visual eld and color vision testing.
3. In patients with strabismus and diplopia, Fresnel prisms may be tted on glasses with
small-angle and relatively comitant deviations.
4. If a patient has dry eye symptoms, prescribe articial tears during the day, lubricating
ointment at night, and punctal plugs. Tape occlusion of eyes at night.
5. Patient education: Inform patients that the disease usually runs a self-limited but
prolonged course over 1 or more years. ere is no immediate cure available. ey should
be encouraged to stop smoking.
6. Sleeping with the head of the bed elevated may decrease morning lid edema.
SIGHTTHREATENING DISEASE
i. Dysthyroid optic neuropathy, a compressive optic neuropathy usually due to volume
expansion in the orbital apex may be seen in 6% of patients while only 2% were left with
mild persistent visual loss that did not recover despite treatment.
ii. Corneal ulceration from severe exposure due to lagophthalmos in a patient with a poor
Bell’s phenomenon.
iii. Other possible mechanisms of visual loss include globe subluxation, choroidal folds
and postural visual obscurations, but these are even less frequent than dysthyroid optic
neuropathy. Any form of vision loss must be recognized promptly and treated aggressively
to bring about reversal and to prevent deterioration that may become permanent.
Dysthyroid optic neuropathy can be treated with high-dose systemic steroids rst;
immediate surgical decompression as rst-line therapy does not result in a better outcome
than the use of intravenous steroids followed by decompression in those patients that do
not respond. As some patients respond adequately to high-dose steroid treatment alone and
decompression surgery carries the risk of side eects such as postoperative diplopia, surgery
should not be the rst-line treatment. High-dose intravenous steroids given in pulses are more
ecacious than oral steroids and have a lower side eect prole. Orbital radiotherapy may be
tried.
For patients who are at risk of vision loss secondary to corneal breakdown, aggressive
topical lubrication is recommended, but this alone may not be sucient. As temporizing
measures, a moisture chamber can be applied or the eyelids can be closed over the corneal
surface with a tarsorrhaphy until the cornea has healed. If there is no adequate response,
patients may benet from systemic steroids and orbital decompression.
Chap-09.indd 92 23-09-2013 12:06:15