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Table of Contents
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 1 The Development of Vision in Childhood
2 Children At High Risk Of Eye Pathology
3 The Apparently Blind Infant
4 Amblyopia
o 4.1 Classification and Treatment
5 Strabismus (Squint)
o 5.1 Convergent Squint (Esotropia)
 5.1.1 Acquired Esotropia
o 5.2 Divergent Squint (Exotropia)
o 5.3 Vertical and Latent Squints
o 5.4 Testing and Treatment for Strabismus
6 Refractive Errors
o 6.1 Signs, Symptoms and Diagnosis of Refractive Errors in Children
o 6.2 Treatment of Refractive Errors
References
1 The Development of Vision in Childhood
Vision is a developed sense. The period of visual immaturity extends from birth until about
age eight. The most crucial time for visual development is the first few months of life. The
development of equal, normal vision in both eyes requires clear focussed images on the
same point in each retina during the period of visual immaturity. Any factor which interferes
with visual development will cause poor vision in the affected eye(s) (amblyopia) unless it is
corrected for during the period of visual development. Examples of such adverse factors are:
large refractive errors, misaligned eyes or a congenital cataract. When a sight threatening
disorder is present in early life, prompt intervention offers the best chance of ultimately
obtaining useful vision.
Golden Rule!
All children should fix on and follow an object by three months of age.
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2 Children At High Risk Of Eye Pathology
Certain children are at high risk of ocular pathology.
Almost any condition which results in cerebral dysfunction can produce a squint. Children with
cerebral palsy and Down Syndrome fall into this category.
Premature babies are at high risk of visual dysfunction. Not only do very small babies face the
risk of retinopathy of prematurity (old name - retrolental fibroplasia) but these children
subsequently have a higher incidence of both squint and refractive errors and deserve close
supervision during childhood.
Illustration: A premature infant is given an eye examination to check for retinopathy of
prematurity. (Photo courtesy of the Children's Hospital, Buffalo, NY)
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3 The Apparently Blind Infant
Caution!
Apparently blind infants require urgent referral to an ophthalmologist.
The apparently blind infant with nystagmus
Nystagmus is uncommon in children. The apparently blind child with pendular, searching
(sometimes jerky) nystagmus appearing around 3 months of age usually has sensory
deprivation nystagmus. Sensory deprivation nystagmus is a bilateral disorder of the anterior
visual pathway potentially caused by albinism, cataract, or retinal dystrophy.
A newborn child with nystagmus often has a congenital motor defect and a family history
should be sought.
Caution!
Many of the patterns of infantile nystagmus overlap, so immediate referral to an
opthalmologist is necessary.
The apparently blind infant without nystagmus
Infants with poor vision who do not have nystagmus may simply have delayed visual
maturation. Such infants are usually otherwise neurologically normal. The vision usually
comes up to normal by age one. The diagnosis is usually made in retrospect.
Cortical vision impairment (CVI) refers to visual failure due to brain damage. The vision
often fluctuates on a day to day basis. These children almost always have other neurological
signs. CVI may follow intraventricular haemorrhage in premature infants or other neurological
insults such as birth asphyxia, meningitis, trauma or near death drowning. Some recovery
almost always occurs in time but may take some years. Cortical vision impairment is now the
most common cause of poor vision in childhood in Australia.
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4 Amblyopia
The main cause of poor eyesight until middle age is amblyopia.
Definition!
Amblyopia is a reduction in visual acuity due to abnormal visual experience early in life.
Amblyopia is almost invariably due to some interference with visual development during the
period of visual immaturity. Most cases are treatable if detected early enough.
Amblyopia can be inferred when there is a definite fixation preference of one eye to the
exclusion of the other. Any infant with a squint should be suspected of amblyopia.
There is an interaction between amblyopia, squint and refractive errors. For example, an eye
which squints constantly from an early age will almost certainly become amblyopic, and an
eye which becomes amblyopic for some reason e.g. a unilateral cataract will often develop a
squint. Large refractive errors, especially hypermetropia (long sightedness) may produce
strabismus or amblyopia or both together.
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4.1 Classification and Treatment
Functional Amblyopia
This is the most common type of amblyopia and is usually diagnosed by finding a difference
in visual acuity between the eyes of two or more lines on the Snellen chart (or its equivalent)
in the absence of organic disease.
In younger children, if one eye is preferred for fixation, amblyopia should be suspected in the
non-preferred eye. It is almost always unilateral and is believed to result from a competition
between the two eyes to develop connections with binocularly driven neurones in the occipital
cortex i.e. it is cortically based. Most cases are treatable if detected early.
There are four subtypes of functional amblyopia, more than one of which may coexist in the
same patient.
Subtypes of
Amblyopia
Features
Strabismic
Amblyopia
This develops as a defence against diplopia (double vision) when the eyes
are aligned in two different directions. Any eye which squints (especially a
convergent squint) constantly from an early age will develop strabismic
amblyopia.
Anisometropic
Amblyopia
This is caused by a significant difference in the refractive error of the two
eyes (anisometropia), particularly if the child is hypermetropic (long
sighted). It is also relatively common. It is often asymptomatic as there is
no presenting squint and is usually detected during school years. It is
easily detected by looking at the Bruckner reflex (see later).
Ametropic
Amblyopia
This is caused by a large refractive error in both eyes, particularly
hypermetropia. Ametropic amblyopia is frequently associated with a
convergent squint.
Deprivation
Amblyopia
This occurs when a clear retinal image cannot be formed e.g. because of a
congenital cataract or a corneal opacity.
Organic Amblyopia
Organic amblyopia which develops due to organic disease e.g. a structural abnormality of the
eye such as optic nerve hypoplasia or acquired disease such as retinal scarring from
retinopathy of prematurity (formerly known as retrolental fibroplasia).
Treatment Of Amblyopia
The principles of treatment of amblyopia are simple: patch the good eye to force usage of the
affected eye, correct any refractive error (usually by the prescription of glasses) and remove
the cause if possible (e.g. by squint surgery). Strabismic amblyopia should always be
corrected prior to squint surgery to ensure the maximum possibility of a stable post-operative
alignment.
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5 Strabismus (Squint)
Misalignment of the eyes on the object of gaze (strabismus) is common during childhood (up
to 5% of children in some series).
Definition!
Fusion: the cortical integration of the images received by the two eyes.
Eso-: a convergent deviation.
Exo-: a divergent deviation.
Hyper-: a vertical deviation (left or right used with this term denotes the higher eye).
-tropia: a constant deviation of the eyes.
-phoria: a latent deviation of the eyes, brought out when fusion is interrupted eg by the
cover test.
Alternating: a squint occurring for an equal amount of time in each eye.
Manifest Squint: a constant squint.
Comitant squint: the angle is constant in all directions.
Noncomitant /incomitant squint: the angle varies in different positions of gaze eg
sixth nerve palsy.
Transient squints are occasionally seen in the neonatal period but a constant squint is
abnormal at any age. Any squint seen after the age of six weeks requires formal assessment.
There is often a family history.
Types of Strabismus
The detailed classification of squint is quite complex, but it can be simply classified as
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convergent
divergent
vertical
Golden Rule!
1. A constant squint at any age requires ophthalmic referral and treatment.
2. In any squint exclude intraocular pathology by a dilated fundus examination.
Pupil dilatation using cyclopentolate or tropicamide is completely safe in
children.
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5.1 Convergent Squint (Esotropia)
Illustration: Esotropia in an infant (Photo courtesy of John Crompton, Department of
Ophthalmology, Royal Adelaide Hospital)
Infantile (Congenital) Esotropia
Definition!
Infantile (Congenital) Esotropia: A convergent squint which manifests itself in the first
six months of life (usual onset between 4 and 6 months).
The aetiology is unknown but is probably a disorder of the binocular cells in the visual cortex
which detect eye misalignment. The angle of squint is usually quite large (and hence the
squint is usually obvious to the parents). Refractive errors are not an important cause of
squint in this age group, so glasses are uncommonly prescribed. Eye muscle surgery is
usually necessary.
Caution!
The inability of an eye with organic pathology to fixate may lead to infantile esotropia. It
is mandatory when assessing children with infantile onset squints to exclude such
conditions as congenital cataract and retinoblastoma by a dilated fundus examination.
The squint usually alternates between the two eyes and so amblyopia is uncommon. Cross
fixation is often seen i.e. the squinting eye is used to fixate in the contralateral field e.g.
objects in the left field of gaze will be fixated by a squinting right eye and vice versa. As a
result, neither eye has to abduct as vision out to the side is taken care of by the fellow eye
fixating across the nose; an erroneous diagnosis of bilateral sixth nerve palsy may then be
made.
Practice Tip!
Abduction can usually be demonstrated by spinning the child around in one's arms and
observing a normal doll's eye manoeuvre.
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5.1.1 Acquired Esotropia
Definition!
Acquired esotropia: A convergent squint appearing after the first six months of life.
This is the second most common convergent squint encountered in clinical practice. It usually
appears between the ages of eighteen months and four years. Hypermetropia is often an
important aetiological factor.
If accommodation is a factor in a convergent squint, the prescription of glasses to fully correct
for the hypermetropia will usually correct the deviation partially or totally. After correcting any
refractive error (often determined by a trial of glasses wearing) and patching to eliminate any
amblyopia present, the remaining deviation (if any) is corrected by squint surgery.
Caution!
A convergent squint developing in any child should raise the suspicion of a sixth nerve
palsy due to intracranial disease.
Golden Rule!
All children presenting with a convergent squint should have the optic disc examined
through a dilated pupil to exclude papilloedema. Retinoblastoma should also be
excluded even in older children.
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5.2 Divergent Squint (Exotropia)
The aetiology of divergent squints is less well understood than for convergent squint. Most
probably begin with some disorder of innervation; either a weakness of convergence or an
excess of divergence. In the older child (and adult) deprived of fusion (e.g. by a traumatic
cataract) tonic divergence prevails and such an eye will ultimately diverge. Anatomical factors
are also important: shallow orbits such as those that occur in many craniofacial syndromes
predispose to divergent squint.
Illustration: Exotropia in an infant
Intermittent Exotropia
Most divergent squints have onset in infancy or early childhood. They are usually intermittent
at the time of onset. Fatigue and intercurrent illness can precipitate a manifest squint. Sunlight
also can precipitate a breakdown of fusion resulting in a frank divergent squint with the
diverging eye often closed, probably to avoid diplopia. The parents may then present
complaining that the child is 'screwing up the eye (squinting) in sunlight'.
Practice Tip!
In children with intermittent extropia, bright sunlight may precipitate eye closure. When
the lid is elevated by the examiner, the divergent squint is notable.
The natural history of intermittent exotropia is poorly documented. With time, many children
with this condition squint more often and for longer periods, finally developing a constant
squint. Binocular vision cannot be developing in this circumstance so surgery is often offered
to these children when the squint is manifest more than fifty percent of the time.
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5.3 Vertical and Latent Squints
Vertical Squints
Small vertical squints due to oblique muscle dysfunction are commonly associated with
horizontal squints. Isolated vertical squints are uncommon in children. There is a large
differential diagnosis.
The commonest isolated vertical squint in childhood is due to a fourth nerve palsy, usually
related to trauma. The child often presents with a head tilt or a face turn, both of which are
used to put the eyes into a position where the effect of the palsy on fusion is least.
Caution!
Some children with 'torticollis' are merely attempting to compensate for a vertical squint.
Unless there is an obvious lesion of the sternomastoid, infants with torticollis should be
assessed by an ophthalmologist to avoid missing a congenital fourth nerve palsy.
Third nerve palsy may also lead to a vertical squint. The causes in childhood include
congenital, trauma and ophthalmoplegic migraine.
Golden Rule!
Because of the large differential diagnosis, children with a vertical squint should be
referred to an ophthalmologist without delay.
Latent Squint
Latent squints are normally kept under control by fusion. Most people have a latent divergent
squint (exophoria) at near. They do not have the potentially serious connotations of manifest
squints because amblyopia cannot develop while the eyes are fusing.
They can lead to problems, however, if the fusional mechanism has little reserve to keep
squint under control. The patient may then develop symptoms of eye strain and intermittent
diplopia, often for close work. Glasses, orthoptic exercises and occasionally even surgery
may be necessary to relieve the symptoms.
The mere presence of a latent squint does not indicate a problem unless there are relevant
symptoms and signs. A slow realignment of the eyes after removing the cover following the
alternate cover test, indicating poor fusional ability, is usually seen in those latent squints
which are producing symptoms. Intraocular disease rarely, if ever, produces a latent squint.
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5.4 Testing and Treatment for Strabismus
Examination Techniques
(More information on examination techniques can be found in LPR-004 Paediatric Eyes 4 Examination Techniques.)
Squint is detected by discovering a misalignment of eyes. Useful tests to determine the
presence of a squint include:
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Hirscherg corneal reflex test
Bruckner reflex test
Cover tests
Eye movements should be tested by having the child follow a toy in the direction of each
individual eye muscle movement.
Treatment Of Squint
Treatment should begin as soon as the squint is diagnosed. Aside from transient squints in
the neonatal period, very few children will spontaneously straighten a constant squint.
Thorough examination is necessary to exclude organic pathology.
Treatment is necessary to enable binocular fusion to develop (which will predispose to a
stable alignment) and to improve the child's appearance. Treatment may involve prescription
of glasses, patching and surgery or a combination of these. Referral to an ophthalmologist is
necessary.
Caution!
A squint may occasionally be the presenting sign of serious intraocular or intracranial
disease. In the case of retinoblastoma, the eye disease is life threatening. All children
with squint should be considered to have a retinoblastoma until proven otherwise by a
dilated fundus examination. Papilloedema should likewise be excluded.
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6 Refractive Errors
Refractive errors are important causes of amblyopia and strabismus in the younger child and
infant. In the older child, refractive errors may cause problems in school.
Caution!
In the younger child and infant, refractive errors should be excluded if squint or
amblyopia are diagnosed.
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6.1 Signs, Symptoms and Diagnosis of Refractive Errors in Children
These are many and varied and are said to include blinking, frowning, rubbing the eyes, head
tilting, closing one eye, clumsiness, photophobia, red eye and epiphora (tearing). In practice
these symptoms are only rarely explained by refractive errors.
In the younger child and infant, refractive errors are most likely to present as a squint. In the
older child, refractive errors may cause school problems with an inability to read the
blackboard or visual fatigue on prolonged close work. Headaches in children are rarely due to
refractive errors. In this case, there is usually a clear association between visual effort and the
onset of headache.
Precise measurement of refractive errors in children is possible using a retinoscope.
In the verbal child, refractive errors should be suspected if the child complains of blurring of
vision particularly for distant objects such as the blackboard, of if there is a complaint of visual
fatigue especially after visually demanding tasks such as reading. The task of deciding
whether a refractive error is present is made much easier in the older child because visual
acuity can be formally assessed for distance on the Snellen chart and for near using a near
reading card.
Practice Tip!
A significant refractive error can be suspected if you must rack up more than -l or +3 on
the ophthalmoscope to get a clear fundus view through a dilated pupil when your own
refractive error is taken into account.
In the over 5 year old, if uncorrected distance vision is worse than 6/9 and near vision is good,
myopia should be suspected. If blurred vision clears when looking through a pinhole, a
significant refractive error is almost certainly present.
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6.2 Treatment of Refractive Errors
Refractive errors causing symptoms or suspected of causing a squint are prescribed
appropriate glasses or contact lenses. Anisometropia requires treatment if the difference
between the two eyes is sufficiently large to cause amblyopia. (In the hypermetropic child one
diopter of difference between the eyes can cause amblyopia).
Golden Rule!
Significant anisometropia in a child requires referral to an ophthalmologist.
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References
1. Gole, G.A. 2001, PAEDIATRIC OPHTHALMOLOGY NOTES 2001, Dept of
Ophthalmology, Royal Children's Hospital, Brisbane.
2. Simon, J.W., Kaw, P. Aug 2001, 'Commonly Missed Diagnosis in the Childhood Eye
Examination' American Family Physician, vol. 64, no. 4, pp. 623-8
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