Special considerations for prescription of glasses in children

Abstract

The most common cause of visual impairment in children is refractive error. All general ophthalmologists and most specialists come across children in their practice and treating a refractive error is the basic moral responsibility of any ophthalmic caregiver. Limited cooperation, low reliability, and risk of amblyopia make prescribing glasses for children more challenging than for adults. The basic rules of prescribing glasses take into account the visual needs according to age, strong accommodative elements, risk of amblyopia, age-related emmetropization, and associated conditions like strabismus, prior to prescribing glasses for children. This article focuses on the standard protocols of assessment and prescription of glasses for simple refractive errors as well as some special refractive situations in children.

Full text

Journal of Clinical Ophthalmology and Research - Sep-Dec 2013 - Volume 1 - Issue 3 169
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DOI:
10.4103/2320-3897.116861
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Department of Ophthalmology, PD Hinduja Hospital and Medical
Research Center, Mahim, Mumbai, India
Correspondence to: Dr. Ashwin Sainani, Department of Ophthalmology,
PD Hinduja Hospital and Medical Research Center, Veer Savarkar
Marg, Mahim (W), Mumbai - 400 016, India. E-mail: ashwinsainani@
hotmail.com
Manuscript received: 15.02.2013; Revision accepted: 06.05.2013
Refractive error is the most common cause of reduced vision in
children, affecting 2 to 11% of the population below 16 years of
age.[1,2] It is also responsible for 60 to 80% of visual impairment
in children.[3,4] It is the responsibility of every ophthalmologist to
reduce the number of this form of preventable blindness.
Prescribing glasses for children is always a challenge due
to limited cooperation, low reliability in vision assessment,
and risk of amblyopia. One must take into account the visual
needs according to age, strong accommodative elements, risk
of amblyopia, age-related emmetropization, and associated
conditions like strabismus, prior to prescribing glasses for
children. Until the age of six to seven years, prescription of
glasses is primarily done on objective findings rather than on
subjective refraction; this is mainly due to limited reliability and
strong accommodation. Apart from refraction a complete eye
examination should be done before prescribing glasses for the first
time. This article focuses on the standard protocols of assessment
and prescription of glasses for simple refractive errors as well as
for some special refractive situations in children.
Assessment of refractive error
Cycloplegic refraction is a rule in children due to the presence
of strong accommodation. This is done to reveal the total
refractive status of the eye with the accommodation at rest. A
dry retinoscopy can be done prior to cycloplegia to assess the
accommodative effort and to get a rough estimate of the refractive
error. To begin with, visual assessment should be done, one eye
at a time, using the age-appropriate methods:
Less than 2.5 years: Fixation and following movements, preferential
looking charts (Cardiff cards), objection to cover, fixation
preference, and cake sprinkles.
2.5 years to 4 years: Symbol / Alphabet matching cards (e.g., Allens,
HOTV, Lea symbols)
Above 4 years: Snellen’s / LogMAR chart
A complete eye examination should include a cover test,
extraocular movements, convergence, anterior segment, and
fundus examination. A complete squint examination is done if
strabismus is detected. The cycloplegic agents most commonly
used are as follows:
Atropine (1%) eye ointment is the strongest cycloplegic agent,
which is instilled twice a day for three days prior to the refraction
(retinoscopy). The parents should be warned that the child will
experience blurred vision and photophobia for a period of 10 to
14 days. Also, some children may experience flushing of the face,
confusion, tachycardia or an allergic reaction. The possibility of this
should also be explained to the parents when atropine is prescribed
for the first time. Atropine eye drops have a higher chance of being
absorbed systemically via the nasolacrimal passage, and thus,
atropine eye ointment and punctal pressure is preferred, especially
in infants. The more commonly used regimen for cycloplegia
includes cyclopentolate (1%) eye drops instilled twice followed
by tropicamide (0.8%) with phenylephrine (5%), commercially
available combination eye drops, once, at 5 minute intervals.
Retinoscopy should be performed about 45 minutes after the
first drop is instilled. This regimen is found to induce comparable
cycloplegia to atropine (1%) with a maximum undercorrection of
+ 0.5 D Sph. In infants (< 1 year) the cyclopentolate (1%) should
be diluted (with water for injection) to 0.5%, to avoid side effects
like flushing of the face, confusion, and tachycardia.
The gold standard of objective refraction is retinoscopy
although the newer autorefractometers do give comparable
results. Autorefractometers induce some amount of proximal
convergence, and thus, in turn produce some accommodation,
Special considerations for prescription of glasses in children
Ashwin Sainani
The most common cause of visual impairment in children is refractive error. All general ophthalmologists and most
specialists come across children in their practice and treating a refractive error is the basic moral responsibility of any
ophthalmic caregiver. Limited cooperation, low reliability, and risk of amblyopia make prescribing glasses for children
more challenging than for adults. The basic rules of prescribing glasses take into account the visual needs according to
age, strong accommodative elements, risk of amblyopia, age-related emmetropization, and associated conditions like
strabismus, prior to prescribing glasses for children. This article focuses on the standard protocols of assessment and
prescription of glasses for simple refractive errors as well as some special refractive situations in children.
Key words: Amblyopia, children, glasses, refraction, refractive error
Commissioned Article
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170 Journal of Clinical Ophthalmology and Research - Sep-Dec 2013 - Volume 1 - Issue 3
Sainani: Prescription of glasses in children
in spite of the cycloplegia, leading to a mild undercorrection
of the hypermetropia. Also, in young, uncooperative children,
it is difficult to convince the child to place the head on to the
autorefractometer, although hand-held autorefractometers help
overcome this problem. It goes without saying that the age-old
skill of retinoscopy is a vital aid in calculating the accurate
refractive error in children. Streak retinoscopes as well as plane
mirror retinoscopy give similar results.
Factors to consider prior to prescription
of glasses
The refractive status of a child is constantly changing with
age. Neonates are normally hypermetropic, with minimal
astigmatism. This hypermetropia is usually symmetrical, which
is usually less than 4 D. The astigmatism is also less than 2 D.
Both the hypermetropia and astigmatism reduce with age. This
emmetropization has to be taken into account with regard to
age and refractive error. A child below the age of two years has
minimal interest in distant objects, and thus, a small myopic
correction is not required to be prescribed until this age. Taking
into account the visual needs of a child, hypermetropia is corrected
earlier than myopia Also, risk of amblyopia is dependent on the
magnitude of the refractive error, type of refractive error (lesser
risk in myopes, as near vision is clear), as well as age of the child.[5]
Anisometropia is the most common cause of amblyopia.[5] The
presence of strabismus also plays a vital role in the decision
making of glass prescription for children. Finally, the strong
accommodation should be taken into account by performing
cycloplegic refraction in all children prior to prescribing glasses.
Thus, to summarize, age-related emmetropization, visual needs of
the child, visual assessment of the child, amblyopia, strabismus,
magnitude and type of refractive error, and strong accommodation
are some of the factors that one has to consider before prescribing
glasses. Following are some of the rules of prescription, based on
the type of refractive error.
Rules of prescription
Hypermetropia
Children have a strong accommodation, which can overcome
minimal amounts of hypermetropia with ease. A plus power of
more than 5 D becomes difficult to overcome; also the amount of
accommodation needed for near tasks would then be in the range
of + 8 D, which can easily cause asthenopia. Children with a weak
accommodation can have asthenopia at lower powers. Amblyopia
and esotropia are the most common outcomes of uncorrected
hypermetropia. Amblyopia can occur if the child cannot overcome
hypermetropia at all times, especially for near vision. Also, lower
amounts of hypermetropia can lead to a refractive accommodative
esotropia, further increasing the risk for amblyopia; thus, the
presence of strabismus must always be checked in these children.
The amount of hypermetropia that needs to be corrected
depends on the age although a power of around 5 D needs to be
corrected due to the risks of amblyopia. Please refer to the American
Association for Pediatric Ophthalmology and Strabismus (AAPOS)
guidelines given below [Table 1]. As long as there is no esotropia, a
mild undercorrection (reduce by 0.75D) can be prescribed, to allow
for some accommodation to occur. Undercorrection should always
be equally done in both eyes, as accommodation is a binocular
phenomenon. It is thus extremely important to perform a cover
test in all children with hypermetropia, to rule out the presence
of esotropia. If the accommodation is weak, then a full cycloplegic
correction is considered.
Hypermetropia with esotropia
In cases of esotropia even smaller amounts (> 1.5 D) of
hypermetropia should be corrected by prescribing the full
cycloplegic correction. Refractive accommodative esotropia
commonly occurs in the age range of two to four years.
Esotropia is often intermittent to begin with and can then
progress to a constant strabismus over time. A cover test is
mandatory in all children with suspected hypermetropia prior
to instillation of cycloplegic eye drops. Performing cycloplegia
with atropine is recommended, at least for the first time, to
ensure full prescription of the hypermetropia in these children.[6]
It is the moderate hypermetropes (2.5 to 5 D) that present with
accommodative esotropia, while the higher hypermetropes
do not squint, due to lack of accommodative effort for such a
high power.
Myopia
Myopia (less than 3-5 D) does not pose a high risk of amblyopia, as
near vision is almost always unaffected except in the high myopes.
The prescription of glasses in low myopes is best done at a pre-
school age of three to four years, as this is the age the children
start having significant hours of distant viewing. Prescription of
glasses should be considered earlier if the power is beyond the
range of 3 to 5 D. The aim is to prescribe the lowest minus power
needed for best visual acuity and over-correction should definitely
be avoided. As small children will not give reliable responses to
the duochrome test, the value on cycloplegia would be close to
the least minus power the eye may need. The other guide for
prescription of low minus powers is the distant visual acuity of
older children and their school requirements according to age.
Please refer to the AAPOS guidelines below [Table 1]. Intermittent
exotropes should be prescribed even with the smallest myopic
correction with the aim of inducing convergence, to overcome
exotropia.
Astigmatism
Accommodation can change only the spherical refractive status
of the eye by a change in the curvature of the crystalline lens.
Astigmatism cannot be overcome by accommodation, and thus,
any cylindrical power above 1.5 to 2 D can be amblyogenic.
Cylindrical powers beyond this range should be prescribed, again
based on the age of the child. Please refer to the AAPOS guidelines
below [Table 1]. As opposed to adults the total cylindrical power
is prescribed in children with the aim of correcting both the
meridians entirely, thus preventing any chance of amblyopia.
Children accept high cylindrical powers far more easily than
adults and no attempt to undercorrect should be made, at least
in the younger children. Smaller cylindrical powers (< 1.5 D)
should be prescribed in older children if visual acuity is mildly
reduced and also in children who primarily have spherical powers
with additional small cylindrical powers. Spectacle fitting and
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Sainani: Prescription of glasses in children
centration is extremely important in the higher cylindrical
powers. Parents should be explained the importance of centration,
as children often bend their frames and prompt repair and
tightening will ensure optimum benefit of the glasses at all times.
Anisometropia
Hypermetropic anisometropia is more amblyogenic then myopic
anisometropia. A difference of > 1.5 D of hypermetropia is
considered amblyogenic and should be prescribed early. Myopia
on the other hand can be overcomed by accommodation and a
myopic anisometropia of up to 3 D can be considered as a very
low risk of amblyopia. Thus, any difference beyond 3 D should
be prescribed early. Eventually a unilateral myope of up to 3 D
will need glasses by pre-school age. Similar to hypermetropia,
astigmatism of > 1.5 D is also amblyogenic and should be
prescribed early.
Extra tips
1. Vision assessment is more accurately possible by 2.5 years
of age and can also be taken as a guide to prescribe glasses.
Children of this age would only cooperate for matching charts
with single optotypes, which tend to underdiagnose amblyopia
due to the absence of the crowding phenomenon. This should
be taken into account before starting amblyopia therapy.
2. In younger children the above rules serve as important
guidelines to prescribe glasses. The amount of refractive error
that needs to be corrected is based on the risks of amblyopia
with that error, for that age.
3. More than 80% of the children can cope with a high
powered prescription for the first time, and thus, prescribing
undercorrected lenses for better compliance may be needed
in only less than 20% of the children. Thus, prescribing
the full correction in the first instance is recommended to
save time and resources, but undercorrection should be
considered if the child is not wearing the glasses in spite of
sincere attempts by the parents for more than four months.
4. Hyperopes can be prescribed cycloplegic drops like atropine
or homatropine for a couple of weeks to help relax the
accommodation and get used to the high plus power.
5. Myopes on the other hand respond and get used to glasses
more easily, especially if they have started doing distant visual
activities.
6. Astigmatic children often need convincing to start using their
glasses, due to a very small difference in the visual clarity on
correcting small cylindrical errors.
7. After prescribing glasses for the first time, the patient must
be reviewed in six to eight weeks to assess the compliance
and the vision with glasses. This time is usually adequate for
the parents to ensure that the child is using the glasses most
of the day. Treatment of amblyopia in the form of patching or
penalization can be started only after this.
Special Situations
Intermi ent Exotropia
Intermittent exotropia is a condition in which there is a loss of
fusion for brief periods of time during which the eyes go into a
divergent squint. This varies in frequency and duration based
on a number of factors. Prescribing concave lenses induces
convergence and helps reduce the frequency of the exotropia. The
general rules of prescription in exotropes are as follows:
1. Any refractive error resulting in reduced vision should be
corrected to improve fusion
2. Minor amounts of myopia should also be corrected
3. Hypermetropia with normal vision does not warrant a
prescription, as it reduces the need to converge.
4. High hypermetropia with reduced vision should be prescribed,
but undercorrected.
The aim of treating intermittent exotropia: Prescription
of concave lenses is a conservative yet effective modality for
improving the control of the intermittent exotropia during the
time the glasses are being used by the child. Some studies have
shown that prescribing a low minus power (- 1.5 D) in patients
who do not have myopia also has beneficial effects, although some
children can have asthenopia, and also it is difficult to convince
the parents regarding the use of glasses when the child does not
need them for vision.
Progressive addition lenses for progressive
myopia
A number of studies have been published in the last decade on the
role of progressive addition lenses (PALs) for progressive myopia.
The basis of these studies, the Correction of Myopia Evaluation
Trial (COMET), states that some myopic children have a weak
accommodation or accommodation lag, which leads to a retinal
defocus for a near object (< 50 cm) producing an image behind
the retina.[8] This retinal defocus is a stimulus for the growth
of the eye-ball. Thus, prescribing addition lenses in myopic
children with accommodation lag ensures a clear image of the
near object, getting rid of the retinal defocus. This can lead to
reduction in the progression of the myopia. Progressive glasses
Table 1: American Association for Pediatric Ophthalmology
and Strabismus guidelines for prescription of glasses for
children[7]
Condition Diopters beyond which glasses should be
considered
Age 0-1 years Age 1-2
years
Age 2-3 years
Isometropia
Myopia ≥ - 4.00 ≥ - 4.00 ≥ - 3.00
Hyperopia
(no eso)
≥ + 6.00 ≥ + 5.00 ≥ + 4.50
Hyperopia
(eso)
≥ + 2.00 ≥ + 2.00 ≥ + 1.50
Astigmatism ≥ 3.00 ≥ 2.50 ≥ 2.00
Anisometropia
Myopia ≥ - 2.50 ≥ - 2.50 ≥ - 2.00
Hyperopia ≥ + 2.50 ≥ + 2.00 ≥ + 1.50
Astigmatism ≥ 2.50 ≥ 2.00 ≥ 2.00
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Sainani: Prescription of glasses in children
have been preferred over bifocals, as they produce a clear image
at all distances. These comparative studies have claimed that
these children do progress less than their counterparts who wear
single vision glasses, although the results are not so significantly
different to warrant a change of practice. They start by prescribing
anywhere from a plus 1.5D to 3.0D addition, based on the amount
of accommodation lag. This modality is used by a few pediatric
ophthalmologists only for rapidly progressing myopia.
High AC/A ratio
Children who have an esotropia that measures more for near
fixation as compared to distance fixation (by 10 to 15 PD) should
be checked for a high AC/A ratio (normal 5:1). There are two
methods for checking the AC/A ratio.
Gradient method can be used in two ways:
• (Deviation for near) - (deviation for near with + 3 D sph)
divide by 3
• (Deviation for distance with – 3 D sph) - (deviation for distance)
divide by 3
Heterophoria method is the preferred method and is as follows:
• IPD (in cm) + (Deviation for near) – (deviation for distance)
divide by diopteric power needed to read at near (33 cm)
In children with a high AC/A ratio, prescribing the full
cycloplegic distance correction can correct the distance deviation
completely, but the near deviation may persist. These children
should be prescribed bifocals to correct the near deviation as
well. One can start with an addition of plus 2.50 to 3.00 D sph,
which later can be reduced based on the response. It is important
to see the effect of the distance glasses on the deviation by first
prescribing only single vision glasses and then considering
bifocals, only if near deviation (> 10 pd) persists. In case the
distance deviation only reduces by a small amount with single
vision glasses, but does not come within 10 pd of orthophoria,
then surgery should be offered and not bifocals. Bifocals should
ideally be the executive style with the reading segment bisecting
the pupil. This ensures that the child starts using the near segment
with minimal depression of eyes and one does not rely on the child
using the near segment on near tasks. Specific instructions should
be given to the opticians to make the reading segments at the
level of the pupil, which is usually higher than when prescribed
in adults. Executive glasses are expensive and a flat top ‘D’ bifocal
segment is an alternative to it.
Prescription after cataract surgery
Bilateral aphakia
Bilateral cataracts in neonates are often treated with bilateral
cataract extraction, with posterior capsulotomy and anterior
vitrectomy. These babies can be prescribed aphakic glasses
or contact lenses. Although contact lenses have significant
advantages over glasses in this situation, risks of infection,
training parents, and the cost factor, limit its use and aphakic
glasses are the only other alternative. Contact lens fitting is
beyond the topic of this article. Retinoscopy should be performed
after dilating the pupil, although no cycloplegia is needed as
the eye is aphakic. After taking away the working distance an
addition of + 2.00 to + 3.00 D sph is added to the correction. This
ensures that the child is corrected for near activities in the absence
of accommodation. Infants mainly have an interest in objects
within a few feet from the face. This addition can be reduced as
the child grows older and bifocals should be considered by one-
and-a-half to two years of age. This reduction of the addition is
approximately based on the age and near activities of the child.
Executive bifocals at the level of the pupil are preferred for the
same reasons mentioned earlier.
Unilateral Aphakia
If only a unilateral cataract exists, then placing an intraocular
lens or using a contact lens becomes extremely vital, as unilateral
aphakic glasses cannot be prescribed due to extreme aniseikonia.
Pseudophakia
Children who have undergone cataract surgery with intraocular
implants should be prescribed the entire spherical and cylindrical
power calculated on a dilated retinoscopy. These children are
usually older than a year, and thus, executive bifocals of + 2.50
to 3.00 D sph should be prescribed at the level of the pupil. Any
glass prescribed after cataract surgery should ideally have an
ultraviolet (UV) protective coating, as the natural protection of
the crystalline lens is absent, although most of the intraocular
lens (IOLs) now have UV protection properties.
Polycarbonate glasses
Ideally all glasses in children should be made with polycarbonate
material. It is not only shatter-resistant but also has an inherent
property of UV protection. The only disadvantage of this material
is that it is expensive. It should definitely be prescribed for one-
eyed children or children with a precious eye like in the case of
monocular gross amblyopia or corneal injury. It is often prescribed
only during sporting activities, to avoid injury to a precious eye.
Tinted glasses / Photochromatic lenses /
Utraviolet protection
Tinted and photochromatic lenses should not be routinely
prescribed for children because they can affect visual contrast
while indoors. These lenses should be reserved for children with
albinism and aniridia. An amber tint is prescribed for aniridia
and albinism. UV-rays have been implicated as a risk factor in a
number of eye conditions. The presence of a tint does not provide
UV protection. In fact tinted glasses without UV protection are
more harmful than untinted glasses, as the tint causes dilatation
of the pupil, which allows more light to enter the eyes, thus
causing more UV damage. The level of UV protection is recognized
by the ‘nm 400 mark’ or the ‘99 – 100% UV protected’ instruction
on the glasses. However, mainly prescription glasses can be UV
protective by adding a coating on the lenses or by having the
lenses made of polycarbonate material.
Conclusion
Prescription of glasses in children is not the same as prescribing
them in adults. Accommodation, visual requirements,
emmetropization, amblyopic age, and ocular alignment should
be taken into account before prescribing the glasses. Cycloplegic
retinoscopy is a must in all patients and the prescription can be
then based on the amblyogenic potential of that power, calculated
for that age, by following the basic rules, as discussed earlier in the
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Journal of Clinical Ophthalmology and Research - Sep-Dec 2013 - Volume 1 - Issue 3 173
Sainani: Prescription of glasses in children
text. Special situations like strabismus can only be considered if
detected, and thus, a cover test should be performed in all children
prior to prescribing glasses. Detection and accurate prescription of
glasses in children is possible only if the general ophthalmologist
is aware of these basic steps of assessment and prescription.
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Cite this article as: Sainani A. Special considerations for prescription of
glasses in children. J Clin Ophthalmol Res 2013;1:169-73.
Financial support: Nil, Confl ict of Interest: I have no fi nancial or personal
considerations that may have compromised my professional judgement in
reporting this article.
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