![Cases sorted by mean Ac/A ratio. The mean is denoted by the dot ([ratio 1/3 m þ ratio 6 m ]/2). For all patients except numbers 5 and 20 (black filled bars), the top of the bar represents the Ac/A ratio at 6 m and the bottom of the bar represents the Ac/A ratio at 1/3 m. Patients 5 and 20 had a near Ac/A ratio that exceeded the distance Ac/A ratio, therefore the top of the bar denotes the near ratio and the bottom of the bar the distance ratio.](https://www.researchgate.net/profile/Tess-Garretty/publication/262344775/figure/fig2/AS:606964111400965@1521722929829/Cases-sorted-by-mean-Ac-A-ratio-The-mean-is-denoted-by-the-dot-ratio-1-3-m-th-ratio-6-m_Q320.jpg)
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Convergence excess accommodative esotropia: a descriptive
review of patients presenting over a period of 10 years
TESS GARRETTY DBO
Department of Orthoptics, St James University Hospital, Leeds
Abstract
Aim: Convergence excess accommodative esotropia
describes an esotropia on accommodation at near
fixation that is controlled to an esophoria/orthophor-
ia at distance fixation with binocular single vision.
Sixty-four cases have presented to the Leeds Teach-
ing Hospitals NHS Trust over the last 10 years. This
descriptive paper outlines the clinical characteristics
of this cohort of patients.
Methods: Information was reviewed regarding all
children diagnosed as having convergence excess
accommodative esotropia entered onto a departmen-
tal database between 1999 and 2009.
Results: Only 3 children complained of diplopia at
presentation. The mean refractive error of the group
was right þ2.90DS and left þ2.80DS. The median
angle of deviation was 25
D
BO at 1/3 m and 4
D
BO at
6 m. The mean Ac/A ratio using the gradient method
was 6:1 at 1/3 m and 10:1 at 6 m. The angle of
deviation was found to be altered by a period of
monocular occlusion and prism adaptation. Twenty
per cent of children required occlusion for amblyo-
pia. Nine per cent of those with convergence excess
were found to decompensate to constant esotropia
with time.
Conclusions: Testing distance, a period of monocular
occlusion and prism adaptation have been shown to
alter the angle of deviation and the Ac/A ratio in
convergence excess accommodative esotropia. Simi-
larities between convergence excess and fully accom-
modative esotropia are outlined.
Key words: Accommodative convergence to accom-
modation (Ac/A) ratio, Convergence excess esotropia
Introduction
The term ‘convergence excess esotropia’ defines an
esotropia that is greater at near fixation than distance and
was first described by Donders in 1864.
1,2
Much con-
fusion has been generated by the term through the years.
For some, it simply defines a constant esotropia greater
at near than distance with no evidence of binocular
single vision.
3
Others use it to define an esotropia at near
fixation with orthotropia at distance that can be further
categorised into accommodative, non-accommodative
and hypo-accommodative convergence excess.
4,5
This
study examines those with convergence excess accom-
modative esotropia – esotropia on accommodation at
near fixation that is controlled to an esophoria/ortho-
phoria at distance fixation with binocular single vision
(BSV) and a high Ac/A ratio.
1
Convergence excess
esotropia is differentiated from near esotropia by
examining the effect of þ3.00DS lenses on the near
angle of deviation. In near esotropia the near angle will
remain unchanged through the additional lenses, whereas
in convergence excess esotropia the near angle will be
significantly reduced – invariably resulting in binocular
single vision at near.
Following previous investigation by the author into
the influence of testing distance on the Ac/A ratio in
fully accommodative esotropia
6
where the testing
distance was found to affect the results, it was decided
to routinely assess the Ac/A ratio at 1/3 m and 6 m in
children with convergence excess esotropia to investi-
gate whether similar changes occurred in this cohort. As
the Ac/A ratio is frequently altered by a period of
monocular occlusion in intermittent exotropia,
7,8
it was
also decided to investigate the influence of occlusion on
the Ac/A ratio for this cohort of patients.
Previous departmental audit revealed poor surgical
success in cases of convergence excess esotropia, with
approximately one-third of patients remaining esotropic
post-operatively, one-third being successfully aligned
and the remaining third becoming consecutively exo-
tropic. It was thought that the variable surgical outcome
may be a result of not revealing the true angle of
deviation pre-operatively; therefore prism adaptation
was undertaken in those wishing to consider squint
surgery in an attempt to reveal the true angle of deviation
and improve surgical results. Also, during scrutiny of the
records of patients who had decompensated from
convergence excess esotropia to constant esotropia the
author observed a marked change in the distance angle
of deviation with time without extra-ocular muscle
weakness. It was postulated that this represented an
uncovering or decompensation of the true distance angle
of deviation due to changing fusional ability rather than
an actual change in muscle balance. This would also be
investigated with prism adaptation.
Sixty-four patients with accommodative convergence
excess esotropia have presented to Leeds Teaching
Hospitals NHS Trust over the last 10 years. This
descriptive paper will outline the presentation, charac-
teristics, treatment and outcomes of those children
presenting with convergence excess in Leeds.
Br Ir Orthopt J 2011; 8: 23–28
Correspondence and offprint requests to: Tess Garretty, Department
of Orthoptics, Chancellor Wing, St James University Hospital,
Beckett Street, Leeds LS9 7TF. e-mail: tess.garretty@leedsth.nhs.uk
Methods
Details of all children attending Leeds Teaching
Hospitals with a diagnosis of convergence excess
esotropia were prospectively entered onto a departmental
database at the point at which the diagnosis was made.
Differential diagnosis between near esotropia and
convergence excess was made before entering the patient
onto the database. This may have been at the first visit
following refractive correction or at any point during the
child’s subsequent attendance, for example at a change
in diagnosis. The database is updated at each clinic
appointment. All orthoptic investigations entered onto
the database were achieved by a standardised testing
protocol and were performed in the vast majority of
cases by the author, with a small amount of data being
provided by two other very experienced examiners. All
data used for measuring the Ac/A ratio were performed
by the author using a strict testing protocol.
Sixty-four children (35 female, 29 male) attending
with convergence excess esotropia were identified from
the database and the following information was
gathered: age at presentation, signs/symptoms at pre-
sentation, duration of signs/symptoms, refractive error
and initial diagnosis after correction of refractive error,
angles of deviation, strength of BSV, change in
diagnosis, etc. The angle of deviation was measured
using the prism and cover test at 1/3 m and 6 m and the
presence of microtropia and necessity for occlusion was
examined. The Ac/A ratio was measured using the
gradient method at 1/3 m and 6 m. Treatment prescribed
and binocular outcomes were collated. All children
included in this study had undergone cycloplegic
refraction, full refractive correction was issued in all
cases and any spectacles issued were worn full time.
Results
Age at presentation
The mean age at presentation was 3 years 11 months
(median 4 years, range 1 year 1 month to 9 years 1
month). The mean duration of signs/symptoms prior to
presentation was 8.5 months (median 6 months, range 3
weeks to 48 months).
Signs and symptoms at presentation
Fourteen patients did not have a record of presenting
signs in the hospital notes (3 of whom had been referred
from other hospitals). Of the remaining 50 patients,
38 had a history of intermittent esotropia and 12 patients
had a history of constant esotropia. Only 3 children
volunteered symptoms of diplopia at presentation.
Initial diagnosis
Of the 64 children who, after refractive correction,
subsequently met the criteria for convergence excess
accommodative esotropia at presentation (before refrac-
tive correction) the provisional working diagnosis was:
Convergence excess esotropia: 22 (34%)
Constant esotropia: 18 (28%)
Non-specific intermittent esotropia/decompensating
esophoria: 16 (25%)
Esophoria: 1 (2%)
No squint detected: 1 (2%)
Esotropic at near but distance cover test was not
possible: 1 (2%)
Information not available: 5 (8%)
Refractive error
Sixty-one (95%) children were issued spectacles for full-
time wear. The full prescription was issued in all cases.
Hypermetropia 5þ1.00DS was corrected due to the
esotropia. Correction of myopia and astigmatism was
issued related to visual acuity. The mean spherical
equivalent following cycloplegic refraction was: right
þ2.90DS (median þ2.50 range 0.25 to þ7.50), left
þ2.80DS (median þ2.50, range 0.25 to þ7.00).
Diagnosis after refractive correction
Two months after refractive correction/adaptation the
diagnoses were:
Convergence excess esotropia: 36 (56%)
Fully accommodative esotropia: 13 (20%)
Constant esotropia: 9 (14%)
Non-specific intermittent esotropia: 1 (2%)
Too young for distance assessment: 1 (2%)
No abnormality detected: 1 (2%)
Information unavailable: 3 (5%)
All these patients subsequently met the criteria of
convergence excess esotropia following a further period
of time. Details are given in the section ‘Progression of
esotropia’.
Angle of deviation
Full refractive correction was worn and an alternate
prism and cover test was performed whilst the child
named pictures or letters of the smallest size discernible
to each eye (Fig. 1). The median angle of deviation at
1/3 m was 25
D
BO (SD 12
D
, range 12
D
to 65
D
). The
median deviation at 6 m was 6
D
BO (SD 5.5
D
, range 0
D
to 20
D
).
Ac/A ratio
The Ac/A ratio was measured using the gradient method
in 57 patients at 1/3 m and at the same visit in 48
children at 6 m. The full refractive correction was worn.
In an attempt to control accommodation the child was
asked to name pictures or letters of the minimum size
viewable by each eye whilst the measurements were
undertaken with and without the 3.00DS lenses. If the
3DS lenses were not cleared with each eye, the patient
was excluded from the results. After sufficient time,
encouragement and explanation, all those tested were
able to clear the þ3.00DS lenses at 1/3 m. One child was
not able to clear the 3.00DS lenses at 6 m. Details of
those measured at 1/3 m and 6 m are found in Fig. 2. At
1/3 m the mean Ac/A ratio was 6:1 (SD 3:1, range
1.7:1 to 13.3:1). At 6 m the mean Ac/A ratio was 10:1
(SD 3.7:1, range 2:1 to 17.7:1). The mean difference in
24 T. Garretty
Br Ir Orthopt J 2011; 8
the Ac/A ratio subtracting the 1/3 m from 6 m results
was 4.9:1 (SD 3.6). The Ac/A ratio was significantly
greater at 6 m than at 1/3 m (paired t–test, p<0.001,
95% CI 3.89 to 5.97).
Ac/A ratio following occlusion
Ten children underwent re-measurement of the deviation
following a 30 m in period of monocular occlusion as
part of a previously reported study.
6
Following occlusion
there was a change in the angle of deviation at 1/3 m of
between 5
D
and þ25
D
. At 6 m the change ranged from
12
D
to þ21
D
. Following occlusion, a change in the
Ac/A ratio of 2:1 or more was found in 7 patients at
1/3 m with 2 of these demonstrating a change of more
than 4:1. Similarly, 6 of the 10 cases changed by 2:1 or
more at 6 m with 2 of them changing by more than 4:1.
Whilst these changes do not reach statistical significance
(change in near Ac/A ratio: paired t-test, p¼0.557, 95%
CI 11.8 to 6.8; change in distance Ac/A ratio: paired
t-test, p¼0.200, 95% CI 11.8 to 2.8), there is a clear
clinical significance in many of the cases.
Prism adaptation
Prism adaptation (PAT) was undertaken in 21 patients
considering squint surgery. Criteria for consideration for
surgery were the inability to control the deviation
following treatment with bifocals or orthoptic exercises,
or parental choice to discontinue bifocal wear. The near
angle of deviation was fully corrected with Fresnel
prisms that were split equally between the two eyes and
the patient was reviewed 1 or 2 weeks later. The mean
age at time of PAT was 7.2 years (range 4.42–9.25
years). Each patient tolerated the prisms well. The mean
change in angle of deviation at 1/3 m following PAT
Fig. 1. Cases sorted by near angle of deviation. Top of bar represents near angle of deviation, bottom of bar represents distance angle of
deviation (prior to prism adaptation).
Fig. 2. Cases sorted by mean Ac/A ratio. The mean is denoted by the dot ([ratio 1/3 m þratio 6 m ]/2). For all patients except numbers 5 and 20
(black filled bars), the top of the bar represents the Ac/A ratio at 6 m and the bottom of the bar represents the Ac/A ratio at 1/3 m. Patients 5 and 20
had a near Ac/A ratio that exceeded the distance Ac/A ratio, therefore the top of the bar denotes the near ratio and the bottom of the bar the distance
ratio.
Convergence excess accommodative esotropia: 10-year review 25
Br Ir Orthopt J 2011; 8
was 18.5
D
(SD 12.1
D
, range 10
D
to þ35
D
) This was
statistically significant (paired t-test, p<0.001, 95% CI
15
D
to 26
D
). At 6 m the mean change in deviation was
17.5
D
(SD 10.9
D
, range 2
D
to þ36
D
). Again this was
statistically significant ( p<0.001, 95% CI 16
D
to 27
D
).
Bifocals
Thirty-seven patients were issued bifocal spectacles as a
primary treatment; 4 additional children were issued
bifocals post-operatively. The minimum additional plus
lens that produces esophoria with reasonable fusion and
stereopsis is prescribed initially. The mean age at issuing
bifocals as a primary treatment was 63 months (SD 17
months, range 23 to 109 months). The mean length of
time wearing bifocals was 32 months (SD 29, range 3 to
113 months). Some of these children are still wearing
bifocals so the length of wear data are not complete. Six
of the 37 children appeared to be successfully weaned
from the bifocals; however, 3 of these children decom-
pensated between 6 and 8 months later and required
further intervention. Two children were discharged
wearing bifocals. Nineteen of the 37 children treated
initially with bifocals went on to have (or be listed for)
surgery once it was shown that it was not possible to
reduce the bifocal addition further without inducing a
manifest deviation at near.
Microtropia
Nine (14%) children had a microtropia confirmed by
fixation examination. Of these, only 4 had anisometropia
of 1.25DS or more. Seven further children had suspected
microtropia (evidenced by 4
D
prism test) but not
confirmed by fixation examination.
Occlusion
Thirteen (20%) of the 64 were prescribed occlusion
therapy for amblyopia. Six of these had a confirmed
associated microtropia, 4 had a suspected microtropia
and the remaining children had normal central fixation.
Progression of esotropia
The 13 children initially diagnosed with fully accom-
modative esotropia following refractive correction con-
trolled the deviation at near whilst wearing the
spectacles for a mean period of 20 months before a
manifest deviation at 1/3 m was first seen (median 16,
SD 11, range 2 to 35 months). The mean spherical
equivalent refractive error for this group was þ3.60DS
(range þ1.00DS to þ7.00DS). The median age at
decompensation from fully accommodative esotropia to
convergence excess accommodative esotropia was 58
months (mean 59, SD 11, range 39–75 months).
Six (9.8%) children spontaneously decompensated
from convergence excess esotropia to a constant
esotropia. Of these 6, following initial refractive
correction, 3 had convergence excess accommodative
esotropia immediately, 1 had remaining constant eso-
tropia for 2 months before settling to convergence excess
accommodative esotropia and 2 children had controlled
to a fully accommodative esotropia for 14 and 15 months
before losing control of the deviation at near. The angle
of deviation at 6 m was seen to change considerably
over this time. Details are given in Table 1. Four of these
6 children complained of diplopia at 6 m when manifest.
Surgery
Twenty-eight children have undergone squint surgery
during the 10 years of data collection. Twenty underwent
bilateral medial rectus (MR) recessions, 1 of whom also
had bilateral inferior oblique myectomies. Five had
single MR recession, 2 underwent unilateral MR
recession with lateral rectus resection and 1 had a Faden
posterior fixation suture to one MR. Since mid-2007, all
children (n¼17) undergoing squint surgery have under-
gone pre-operative prism adaptation.
Discussion
The characteristics of convergence excess accommoda-
tive esotropia are described in Ansons and Davis’ book
Diagnosis and Management of Ocular Motility Dis-
orders.
1
The age at presentation and degree of refractive
error found in the present study relate well to those
quoted. Ansons and Davis state that the Ac/A ratio ‘often
exceeds 8:1’. In this study 14 (25%) of the 57 children
tested at 1/3 m had an Ac/A ratio of at least 8:1 as did
36 (75%) of the 48 tested at 6 m.
Ansons and Davis state that presentation of conver-
gence excess accommodative esotropia is usually
between 2 and 5 years of age. This study found the
age of presentation to be between 2 and 9 years. The
anecdotal clinical impression is that accommodative
esotropia will tend to manifest itself when the child
begins to really exert accommodation when becoming
interested in fine detail. One would expect accommoda-
tive effort to be truly exercised when the child starts
school at the age of 5 years; therefore an upper age for
presentation of this degree would be expected. However,
the intermittent nature of this type of strabismus and the
lack of diplopia means that the age at presentation will
be dependent not only on the observations of family and
teachers – the deviation may have been present for some
Table 1. Change to 6 m angle of deviation following spontaneous decompensation to constant esotropia
Patient no. Age at decompensation
(years)
Time after presentation
(months)
Diplopia 6 m pre-decompensation
angle (prism dioptres)
6 m post-decompensation
angle (prism dioptres)
1 6.75 13 No 6 30
2 7.25 33 Yes 4 25
3 8.3 62 Yes 10 30
4 8.9 26 Yes 4 16
5 5.3 27 No 6 20
6 7.3 76 Yes 6 16
26 T. Garretty
Br Ir Orthopt J 2011; 8
time before being noticed – but also their motivation to
seek a medical opinion. Of course it is also feasible that
the deviation in these older children actually manifested
itself at an older age.
This paper has outlined the progression of conver-
gence excess esotropia. Some of the patients included in
this study initially behaved as fully accommodative
esotropes for some time before their vision broke down
at near to convergence excess esotropia. Interestingly,
the mean age that this decompensation generally
occurred was around the age when children start school
in the UK. A small number of these children with
convergence excess esotropia then further decompen-
sated to become constant esotropes. This occurred at a
slightly older age, with the youngest being just over 5
years of age and the oldest being nearly 9. The
decompensation of accommodative esotropia has been
documented by others. Vivian
5
reported an increase in
the near deviation in patients presenting initially with
fully accommodative esotropia in 6–11% of cases and
Dickie and Scott
9
reported that 13% of 114 patients with
fully accommodative esotropia deteriorated to lose
binocularity despite good compliance with spectacle
wear. They found that the decompensation occurred at a
mean age of 7.6 years (range 3.8 to 13.3 years) and was
not related to Ac/A ratio. The age at decompensation
was therefore slightly older in their study than in this
present study. Dickie and Scott’s study described the
decompensation as ‘total’, i.e. the child decompensated
at 1/3 m and 6 m not to a convergence excess esotropia.
However, Dickie and Scott, in this American study, also
state that ‘almost all of the patients had at least
peripheral fusion’ prior to decompensation. This would
imply that not all of their included patients would be
categorised as true fully accommodative esotropes in the
UK.
Havertape et al.
10
compared different methods of
measuring the Ac/A ratio in accommodative esotropia
and found that using 3.00DS lenses at 6 m fixation
revealed a higher Ac/A ratio than using þ3.00DS lenses
at 1/3 m. Gage
11
examined the Ac/A ratio using the
gradient method at 1/3 m and 6 m in a small group of
esophoric and exophoric subjects and found that there
was no statistical difference in outcome using the two
methods in esophoria (although 2 subjects showed a
change of 9:1 and 10:1 which would certainly be
considered clinically significant); she also found that
those with exophoria had a slightly reduced Ac/A ratio
on distance fixation. A study by this author of the Ac/A
ratio in fully accommodative esotropia
6
found that the
testing distance did not influence the Ac/A ratio in a
control group of subjects with small, well-compensated
heterophoria (mean 2.2:1 at 1/3 m and 2.9:1 at 6 m ), but
in those with fully accommodative esotropia the Ac/A
ratio was significantly larger when measured at 6 m
(mean 9:1) than when measured at 1/3 m (mean 4:1).
This present study similarly demonstrates the signifi-
cance of testing distance when measuring the Ac/A ratio
in convergence excess esotropia: the measure of the
Ac/A ratio at 6 m exceeded the near ratio in 39 (81%) of
48 cases. Therefore it would appear that the testing
distance used for measuring the Ac/A ratio has little
influence on the results in small heterophoria but that in
accommodative esotropia, both fully accommodative
and convergence excess, the distance gradient method
reveals a significantly larger result than the near
method. It is feasible that the effort to accommodate
through concave lenses at 6 m fixation results in a
different (and perhaps more accurate) accommodative
response from that when asking a patient to relax their
accommodation through convex lenses at 1/3 m.
The effect of target size on the angle of deviation at
1/3 m and 6 m was also outlined in this author’s fully
accommodative esotropia study.
6
The paper compared
the angle of deviation at 1/3 m and 6 m measured with
the patient viewing a 6/60 and 6/6 target and, perhaps not
surprisingly, demonstrated that the angle of deviation
increased when viewing a 6/6 target compared with a
6/60 target in fully accommodative esotropia.
All the papers mentioned have measured the stimulus
Ac/A ratio. It cannot be assumed that viewing a detailed
target through plus and minus lenses will elicit an
accommodative response exactly equal to the strength of
the lens used. Dynamic retinoscopy would reveal the
accuracy of accommodation in these children but few
UK orthoptists currently have the skills to undertake this
procedure. (Three children included in this study under-
went dynamic retinoscopy with the hospital optometrist
and showed accurate accommodative responses to a
detailed target at 1/3 m. However, due to the small
numbers tested, details are not included in the results.)
Instructing the patient to read small letters whilst
measurements are undertaken attempts to ensure that
accurate accommodative change occurs in the clinical
environment.
The usefulness of the stimulus Ac/A ratio as a
diagnostic tool and its use in surgical planning should
perhaps be re-considered. Many papers have outlined the
differences in stimulus and response ratios
12–14
and this
paper has outlined changes to the angle of deviation
resulting from differing target size, fixation distance,
prism adaptation and occlusion. These effects will affect
the Ac/A ratio results. The number of factors influencing
the measure of the Ac/A ratio means that the results will
vary considerably depending on the testing regime
adopted. Unless strict protocols in testing regimes are
undertaken, the results are likely to be so variable as to
render them of little diagnostic value. The size of the
deviation following prism adaptation (or to a lesser
extent following a period of monocular occlusion) is
likely to be of more value when planning management of
convergence excess esotropia than the actual Ac/A ratio.
It is no longer routine practice to measure the Ac/A ratio
in convergence excess within the department in Leeds.
This paper has demonstrated the close relationship
between convergence excess and fully accommodative
esotropia. The mean refractive error in this author’s fully
accommodative esotropia study
6
was þ4.30DS (range
þ2.00DS to þ8.00DS); the mean refractive error within
this present study of convergence excess esotropia was
þ2.90DS (range 0.25 to þ7.50). The Ac/A ratio is
often high in both categories of strabismus. The fully
accommodative esotropia study
6
split the subjects into
two groups: those who learnt to control the deviation
without the spectacles with time and those who did not.
The study found that the group with fully accommoda-
Convergence excess accommodative esotropia: 10-year review 27
Br Ir Orthopt J 2011; 8
tive esotropia who did not learn to control the deviation
without spectacles had mean Ac/A ratios of 2.6:1 at
1/3 m and 9:1 at 6 m. This study of convergence excess
accommodative esotropia found a higher mean Ac/A of
6:1 at 1/3 m but a similar Ac/A of 10:1 at 6 m. A
proportion of children with fully accommodative eso-
tropia are seen to decompensate to convergence excess
over time, further linking these two conditions. It is
proposed that convergence excess esotropia and fully
accommodative esotropia are not truly distinct entities
but represent different points on a spectrum of the same
condition.
Horwood
15
has described the various drivers to
accurate vergence (blur, accommodation, proximity,
disparity) and has reported that disparity is the main
driver for accurate vergence in most non-squinting
individuals. Perhaps these main drivers are different in
the sub-categories of intermittent strabismus? Maybe
those hypermetropes who develop esotropia have
vergence that is more driven by accommodation than
those who remain fully binocular? Perhaps those who
develop convergence excess esotropia have even more
accommodative drive than those who develop fully
accommodative esotropia? As yet we do not have
knowledge of the drive to vergence in differing
categories of strabismus.
Treatment of convergence excess esotropia with
bifocals has produced limited success for the children
in this cohort. Bifocals are routinely prescribed within
the department as a first-line treatment. The minimum
additional plus lens that produces esophoria with
reasonable fusion and stereopsis is prescribed initially.
The aim is to endeavour to reduce the addition by
0.50DS every 6 months (departmental guideline). If
the deviation was not controlled with the reduced
additional lens, the parents were given the option of
increasing the addition again or considering surgery. It is
the author’s experience that reducing the bifocal addition
down to þ1.00DS is usually uncomplicated, but weaning
the child from this small additional lens is often
unsuccessful even with the addition of orthoptic
exercises. Stewart and Scott
16
reported similar difficul-
ties. Forty-three per cent of those with convergence
excess wearing bifocals became ‘bifocal failures’ – the
deviation increased beyond the patient’s fusional
capabilities during their bifocal treatment. Parents in
Leeds are now counselled that bifocals are prescribed to
maintain comfortable BSV until such time as accurate
prism and cover test measurements are possible and
prism adaptation can be undertaken. At this point
surgery is planned.
Prism adaptation or a period of monocular occlusion
may reveal a hidden large angle of deviation at 6 m in
convergence excess accommodative esotropia that has
been shown to decompensate to constant esotropia over
time in a small group of patients. It is postulated that
tenacious fusion masks the true distance angle of
deviation in many patients with convergence excess in
a similar way as described by Kushner
7
and Rosenfield
et al.
8
in intermittent exotropia. The author’s previous
paper investigating convergence excess esotropia
17
suggested two subcategories of convergence excess
accommodative esotropia:
.True convergence excess: Esotropia at 1/3 m with a
small well-controlled esophoria at 6 m. No signi-
ficant increase in the distance angle of deviation
following a period of monocular occlusion or prism
adaptation.
.Simulated convergence excess: The esophoria at
6 m increases significantly following occlusion or
prism adaptation.
The paper postulated that sub-categorisation of this
condition may influence its management. Those with
true convergence excess may be at risk of consecutive
distance exotropia following surgery and are possibly
best managed with long-term bifocal use. Those with
simulated convergence excess pose a low risk of
consecutive exotropia and more aggressive surgery can
be proposed. These patients may be at a greater risk of
decompensating to constant esotropia over time.
Clinicians should be aware of the effect of fixation
target size and the testing distance on the results of prism
and cover test and consequently on the Ac/A ratio, and
should consider a period of monocular occlusion or
prism adaptation to reveal the true angle of deviation
before planning surgical interventions.
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