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Childhood
strabismus
Assessing the
child with
possible
strabismus
Treatment of
children
Assessing adults
with squint
Treatment of adult
strabismus
The authors
DR SHANEL SHARMA
consultant ophthalmologist, Eye and
Laser Surgeons, Wollongong and
Sydney, and South Eastern Eye Care,
Miranda; senior lecturer, University
of Wollongong; conjoint lecturer,
University of NSW and University of
Sydney, NSW.
DR GILL ADAMS
director, strabismus and
neuro-ophthalmology, Consultant
Ophthalmologist Paediatric Service,
Moorfields Hospital, London, UK.
Strabismus
Background
STRABISMUS is the term used to
describe eyes that are not simultaneously fixing on a target of interest. It
is commonly referred to as crosseyed, squint or a lazy eye and it
affects 2.5-4% of the population.
Strabismus may present in childhood
or adulthood. If undetected and
untreated in childhood, it can result
in amblyopia, which is the reduced
visual acuity in one or both eyes
caused by disruption of normal
visual development.
In both children and adults, the
development of strabismus may indicate serious underlying pathology.
When faced with the patient presenting with squint, the family physician
needs to decide whether they require
routine referral, urgent referral or
possibly do not need referral at all.
This article updates the GP on
assessment, management and appropriate referral of children and adults
with strabismus.
Visual development and
amblyopia
At birth the visual system is immature and it develops by forming
neural connections and pathways
over the first 7-8 years of life. This
period of visual development is
called the critical period and, once
it is completed, the pathways essentially cannot be altered. Before the
critical period starts there is a sixweek latent period during which the
baby’s visual system is not damaged
by stimulus deprivation. Colour
vision and depth perception also
develop during the critical period,
but because of the latent period,
early detection and treatment offers
the chance of restoring vision.
If the visual cortex does not receive
clearly focused, aligned images from
each eye, the child will not develop
high-quality vision with depth perception. This is the reason that early
treatment of squint and significant
refractive errors is required to ensure
good visual development.
Factors needed for ocular alignment
For alignment of the eyes to occur and
be maintained, there needs to be
simultaneous visual perception of an
object by both eyes, with the images
transmitted to the visual cortex, where
they are fused together. Finally due to
the slight disparity of the images
reaching the brain, depth perception
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(stereopsis) can be appreciated.
Fusion of the images is important
and involves both sensory aspects of
image integration and motor control
to keep the eyes physically aligned. If
a patient does not have fusion, or
stereopsis, and they undergo corrective squint surgery, the chance of
their maintaining a good ocular position long term is reduced.
For this reason there has been a
shift in the management of strabismus with the goal of regaining ocular
alignment in children more promptly
after they develop a squint, while they
still have the potential to achieve
stereopsis. The shorter time a child
has a squint, the more likely they are
to maintain long-term alignment after
surgical correction.
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HOW TO TREAT Strabismus
from previous page
Amblyopia
Disruption of normal visual neurodevelopment during the critical
period results in reduced vision in
one or both eyes, called amblyopia.
There are several causes of amblyopia.
Refractive errors. Amblyopia most
commonly occurs because the
child has an undiagnosed refractive error, which impairs the focusing of images on the retina and
hence reduces the quality of the
visual stimulus to the neural pathways. The greater the refractive
error, the more amblyogenic it is
to the child.
Refractive amblyopia usually
develops in one eye, when there is
a significant difference in the
refractive error between the two
eyes; this is termed anisometropic
amblyopia. If vision is reduced in
both eyes due to uncorrected high
focusing errors, it is termed
ametropic amblyopia.
Strabismus. Strabismus is the
second most common cause of
amblyopia. When a child has a
squint, the visual information from
the squinting eye is cortically suppressed to avoid confusion and
diplopia. If the squint alternates
between the two eyes, both eyes
are providing sensory stimulation
to the brain and amblyopia does
not develop, but the brain will still
suppress a second image when both
eyes are open.
In the older child and adults who
develop misaligned eyes, the typical
complaint is the development of
diplopia.
Visual obstruction. Amblyopia can
also occur with visual deprivation
caused by conditions that obstruct
the visual axis, which prevents a
clear visual image reaching the
retina. These include ptosis,
corneal pathology, congenital
cataract and retinoblastoma.
Amblyopia from stimulus deprivation often results in a secondary
squint.
In the case of congenital
cataract, unilateral cases are very
amblyogenic and urgent treatment
is crucial, emphasising the importance of being sure that the infant
has a good red reflex at the time of
the newborn screening. Surgery
and visual rehabilitation during the
latent period of visual development
before the onset of the critical
period gives the child the potential for developing good sight.
Importance of early treatment
Early treatment in childhood of
refractive errors, strabismus and
visual obstruction, and the resultant amblyopia, allows for the
development of good vision. If
these conditions remain undetected
and untreated, they can lead to permanent uncorrectable visual loss.
Good vision during a child’s
early years is vital as about 80% of
learning is acquired through sight.
If good vision is not developed in
childhood, it cannot be acquired as
an adult. Poor vision, even if unilateral, can have significant and
long-term consequences for future
employment and quality of life.
In addition, there is an increased
risk of further visual handicap if
there is damage or disease to the
good eye. It has been shown that
the risk of losing the healthy eye is
two per thousand in children with
monocular amblyopia, of which
more than 50% is due to trauma.1
This is about 20 times the blindness rate of children without
amblyopia of 0.11 per thousand.
This risk increases if one considers
the whole length of the child’s life.
In the UK about 185 people with
monocular amblyopia (with acuity
less than 6/12) have vision loss in
their non-amblyopic eye annually;
75% of these patients are left visually impaired or blind. More than
half of those in paid employment
are unable to continue due to the
visual loss, with significant impact
on their quality of life. They also
have an increased risk of death or
morbidity including hip fractures
after fall and tend to suffer from
social isolation as a consequence
of their visual loss.2
have been documented to be about
four times higher in children born
prematurely than in full-term infants.4
Many children have intermittent
neonatal ocular misalignments, usually convergent, which disappear by
15 weeks of age. Infantile esotropia is
a large-angle convergent squint developing within the first six months of
life in a normal child. Children with
underlying neurological problems
may also present with an early-onset
squint. The presence of a large-angle
divergent squint in the young child is
uncommon, and the possibility of
neurological or ophthalmic disease
should be considered.
Some children are suspected of
having a squint when in fact their
eyes are straight. In most children
these pseudo-squints are due to epicanthic folds of skin at the inner
canthi, which give the appearance
of convergent deviation. However,
5% of children thought to have a
pseudo-squint at the first attendance will progress and be found
to have a squint by age four. It is
therefore recommended that children be followed until good linear
acuity can be obtained in each eye
with no evidence of squint.
Childhood strabismus
Risk factors
THE key risk factors predisposing a
child to strabismus are listed in the
box, right. Obstruction of the ocular
media can cause a secondary squint.
Particular vigilance is also
required for children with developmental delay or cerebral palsy. A
child with cerebral palsy has a
50% chance of developing a
squint, and a child with a syndrome has about a one in three
chance of developing strabismus.
Premature birth is a significant
risk factor for developing ophthalmic problems. A child born pre-
Risk factors for developing a squint in a child
• Family history
• Premature birth and low birthweight
• Drugs taken during pregnancy eg, sodium valproate
• Refractive error
• Intraocular pathology, eg, cataract, retinoblastoma
• Neurological disease, eg, cerebral palsy
• Craniofacial disease
maturely is five times more likely to
develop strabismus by age 10 compared with children born at term.3
Similarly, significant refractive errors
Assessing the child with possible strabismus
CHILDREN can be difficult to
assess, particularly very young
infants, and more than one assessment may be required. The family
physician should try to ascertain the
child’s vision, ocular alignment,
ocular movements and presence of a
red reflex when assessing a child with
possible strabismus.
Figure 1: The top image demonstrates an exotropia, with the light reflex
centrally located in the left eye and visible over the nasal iris on the right. In
the central image the patient is orthotropic, as the light reflex is noticeable in
the same position in both eyes. In the lower image the patient is esotropic.
Figure 2: How to perform a cover–uncover test. As the right eye (fixing eye) is
covered, the left eye takes up fixation on the target and an inwards movement
is noted as the exotropic eye takes up fixation. The flash reflex in the pupil of
the left eye is initially nasal and after the cover is applied, it moves centrally.
Testing vision
When testing vision in a child an ageappropriate test should be used. At
birth, visual acuity is normally 12/60. It improves significantly up to
age two years when acuity of 6/66/9 would be expected.
It is often helpful to start testing
the vision with both eyes open,
which will give you the vision in the
better eye, and this is often easier
for the child as an initial test. Then
check the eye you suspect has the
worst vision before moving on to
what you believe is the better eye. If
the child resists the covering of one
eye, this suggests you are occluding
the better-seeing eye and the other
eye is amblyopic. When checking
vision uniocularly, make sure the
other eye is well covered, for example, with an occlusive patch.
In a baby, assess if they can fix and
follow a toy or light. See if they smile
back when you smile at them.
Another helpful test for assessing
vision in infants and very young children without the use of specialist testing is to use a mirror, as children like
looking at their own reflection in mirrors. The child is held about 20cm
from a mirror until they look at their
own reflection, and then is moved
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slowly backwards until they lose fixation. This can be used as a measure of
acuity; the further the distance from
the mirror before fixation is lost, the
better the infant’s vision.
In non-verbal children, ‘preferential looking tests’ are used, knowing
that a child prefers to look at a picture rather than a blank background.
Cardiff cards are an example of this
type of test. It uses pictures that will
interest a child (house, car, duck, etc)
located either at the top or at the
bottom of an otherwise plain card.
There are 11 visual acuity levels, with
three cards at each level.
In the verbal child, ‘crowded tests’
are preferable because, particularly
in amblyopia, children can perform
better with single letter tests than
with a line of text (the so-called
crowding effect). By presenting a
single image to the child it is easier to
ensure they are looking and describing the letter or picture being presented. However, to simulate the
effect of having more than one letter
on a page, the letter is surrounded
by a black blocking bar. This gives a
more accurate assessment of vision.
The older child can be checked
with letter tests or using an adult
logMAR or Snellen chart.
Alignment
The alignment of the eyes can be
assessed using light reflexes or with
cover tests. Use a torch to shine a
light on both eyes; if they are aligned,
the corneal reflexes sit in the same
position in both eyes. If the child is
esotropic (has a convergent squint),
the light reflex will be more temporal
in one pupil compared with the other
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side. An exotropic child (has a divergent squint) will have one light reflex
more nasal compared with the other
(figure 1).
The cover–uncover test will identify a manifest squint. The alternate
cover test will identify latent squint.
Cover–uncover test
This is the test used to assess for
the presence of a manifest squint.
The terminology used to describe a
squint indicates the position of
deviation: ‘eso-’ for inward deviation, and ‘exo-’ for outward. The
term ‘-tropia’ indicates that the
squint is manifest (not latent). Thus
an inwards-turning squint is termed
an esotropia, and an out-turned eye
an exotropia.
To perform a cover–uncover test in
an infant, use a light or a bright toy.
In the older child, use a detailed fixation target to perform the test. Start
by covering the suspected squinting eye and observe the other eye
for any movement. If there is no
squint and the patient is using central fixation, the eye will remain
still when the cover–uncover test is
performed on each eye in turn.
No movement means the eyes
are straight, unless the eye being
tested has extremely poor vision
and cannot take up fixation. An
outward movement of the uncovered eye to take up fixation indicates a manifest esotropia, and an
inward movement indicates an
exotropia or divergent squint
(figure 2). A downward movement
indicates a hypertropia and an
upward movement indicates a
hypotropia of the uncovered eye.
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Alternate cover test
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Figure 4: A: A normal red reflex. B: An abnormal left red reflex.
Figure 3: An alternating cover test.
This test dissociates the eyes by
occluding vision in one eye at a time.
It is used to identify a ‘phoria’, or
latent squint, which is seen when the
fusion of the two images is disrupted.
This is achieved by rapidly moving
the occluder from one eye to the
other. The eye under the occluder
drifts out of alignment but is seen to
recover when dissociation stops
(figure 3).
A
Ocular movements
Check eye movements by getting the
child to follow either a torchlight or a
moving toy, keeping the head still.
Doll’s head rotations can be used to
rapidly rotate the head to one side,
initiating deviation laterally to the
opposite side. In particular, check
that abduction is full.
The presence of nystagmus or
wobbly eyes is abnormal and
requires early referral for ophthalmological evaluation.
Red reflex test
This is best done by turning the room
lights down and using an ophthalmoscope at a distance of about 45cm
from the child. The ophthalmoscope
dial is set at zero if the examiner has
no refractive error or is wearing
glasses, or the dial can be set to correct for the examiner’s refractive error
if the examiner is testing without
wearing glasses.
The pupil red reflex will be
redder in Caucasian infants and
slightly paler in dark infants (figure
4). If there is uncertainty about the
red reflex, dilate the pupils with
tropicamide or cyclopentolate (a
B
cycloplegic that both impedes
accommodation and dilates the
pupil) 0.5% and re-examine.
The red reflex should be clear. If
there is any disruption to this clarity
or if any smudging is still present
after cleaning the ophthalmoloscope viewing lens, this suggests the
child has a significant obstruction in
their visual axis such as a cloudy
cornea, congenital cataract or retinal problem. In particular, beware
the white pupil, which might suggest the diagnosis of retinoblastoma.
The child with an absent or white
red reflex should be referred to an
ophthalmologist to be seen within
a couple of days. Even a short
period of unilateral asymmetric
retinal stimulation will result in
dense amblyopia, as can be seen in
children with unilateral dense congenital central cataract of over
2mm, who will have permanent
deprivation amblyopia if they are
not treated within the first two
months of life. If there are any
doubts as to the findings, these
children should be referred for
urgent assessment.
Further tests
When an older child is seen by a
paediatric ophthalmologist, as well
as vision testing and assessment
for squint, the child can be tested
for the presence of stereopsis. The
child’s pupils will then be dilated
to assess for the presence of refractive error, to check the media and
to allow fundoscopy to be performed to exclude any underlying
retinal pathology such as
retinoblastoma, macular scarring
or optic nerve hypoplasia.
As children are unable to concentrate for a prolonged period of time
and fix on a distant target and
cannot reliably indicate which lens
gives clearer vision, retinoscopy is
performed as it is an objective
means of measuring the refractive
error. Topical cyclopentolate is
instilled to enable retinoscopy to be
performed. In most cases cyclopentolate takes about 30-45 minutes
to have its effect.
In some children, retinoscopy is
performed after instillation of
atropine (an anticholinergic that is
a strong cycloplegic) nightly for 23 nights before assessment. Parents
often find it easiest to instill the
drops after the child is asleep. As
atropine has a long half-life, it can
take up to a week for the dilation
to wear off completely. During this
period the child should wear sunglasses and a hat outdoors, as their
pupil is unable to constrict when
they go into bright light.
to choose the child they preferred
and with whom they would share
their favourite toy. A similar study
has been done asking children which
child they would invite to a birthday
party — one with, or one without, a
squint. The children were found to
have a negative social reaction
towards their peers with a noticeable
squint, demonstrating that children
with noticeable strabismus may be
subjected to social alienation and
social biases that can lead to negative
psychosocial development, particularly when experienced at a young
age.5
Children are now operated on earlier, as this gives the best potential
for the development of three-dimensional vision and long-term ocular
alignment.
Two methods can be used to align
the eyes — either surgery or botulinum toxin A injection(s), or a combination of both.
• Discomfort.
• Wound infection.
• Suture complications.
Vision-threatening problems such
as endophthalmitis and scleral perforation are rare but can lead to profound visual loss. Patients need to
understand that surgery aims to
improve alignment but does not treat
amblyopia, and thus the child usually needs to continue wearing their
glasses and patching as treatment for
amblyopia. The risk of amblyopia has
been shown to spike postoperatively.
If this is not emphasised as sometimes
happens, parents may believe that as
the alignment has improved, their
child has been ‘fixed’ and hence they
think follow-up is optional.
As a general rule, no more than
two of the recti muscles are operated
on simultaneously in the same eye,
as this is associated with a risk of
anterior-segment ischaemia, a visionthreatening complication. However
the oblique muscles may safely be
operated on in addition to the recti.
Treatment of strabismus in children
THE aims of managing any child
with squint are to achieve the best
vision in each eye, to optimally align
the eyes, to correct any abnormal
head posture which is adopted to
alleviate double vision and, if possible, to obtain binocular function.
Treatment usually includes that for
any amblyopia and for correction of
malalignment. It may involve glasses,
occlusion therapy, and sometimes
surgery. Treatment may have to be
continued until the age of visual
maturity (6-7 years).
Amblyopia treatment
The aim of amblyopia treatment in a
child is to obtain equal and good
vision in both eyes. This may be
achieved with glasses, occlusion therapy or a combination of both.
Glasses
When glasses are prescribed in children, they are given to ensure accurate focusing of visual images on the
retina and to allow clear focused
images to be transmitted along the
neural pathways to the visual cortex.
The lenses must be large enough to
ensure that the child looks through
and not above them. Glasses should
be worn all the time except for
during sport or activities where they
may get damaged. Prescription goggles can be obtained for swimming.
Occlusion
Glasses alone are often insufficient
to improve the acuity maximally and
occlusion may also be required.
Occlusion may be in the form of
patching or atropine drops.
Patching involves applying an
adhesive patch over the good eye
then placing the glasses on top to
force the weaker (amblyopic/more
amblyopic) eye to do more visual
work. The patching regimen depends
on the child’s vision and is prescribed
and monitored closely, usually starting with three hours each day, with
at least one hour of near work,
which can include reading, doing jigsaws or (often more acceptable to
the child) handheld computer games.
Compliance with patching is often
difficult to achieve, particularly when
the sight in the amblyopic eye is very
poor and the child is frightened or
distressed by covering up their betterseeing eye. In these cases, using
atropine penalisation is often helpful. This involves the use of atropine
1% drops instilled into the better eye
on two evenings a week. The
atropine drops are long-lasting and
produce dilation with visual blurring
in the good eye, encouraging the
weaker eye do more visual work.
The side effects include light sensi-
tivity, allergic reactions and possible
tachycardia and facial flushing if too
much atropine is instilled, resulting in
significant systemic absorption.
The vision should be monitored
regularly to ensure that acuity is
improving. Once the maximum
vision is achieved, the patching or
atropine is tapered off slowly to prevent visual regression. The child must
continue to be monitored, as vision
can deteriorate for up to one year
after treatment has ended. Most children will complete their amblyopia
management by age six.
Treatment of the older child with
occlusion or atropine can result in
loss of the suppression of the
amblyopia, with resultant double
vision. This is not appropriate in
most cases unless specialist tests
confirm that there is a low risk of
inducing diplopia.
Achieving alignment
After maximising the vision using
glasses and/or occlusion, the next
step is to align the eyes. In most cases
this will improve the aesthetic
appearance, but in some children
accurate alignment may also achieve
binocularity, or reduce a compensatory head posture that has been
adopted to reduce double vision.
The presence of a squint can have
a significant impact on a child’s
psychosocial development. A recent
study explored the perception of children aged 5-6 years towards pictures
of peers who were ocularly aligned
compared with those who were digitally modified to have a noticeable
exotropia.5 The children were asked
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Surgery
In children surgery is the most
common treatment of choice. Squint
surgery is performed under general
anaesthesia and the muscle being
operated on is detached from the
globe and reattached at a new position, through a conjunctival incision,
either tightening or weakening the
action of the muscle.
Surgical risks include:
• Under- or over-correction of the
deviation.
• The patient requiring further squint
correction during their life.
• A red eye.
• Slipped muscle.
Botulinum toxin
Botulinum toxin (BTX) type A is produced by Clostridium botulinum. If
injected into an extraocular muscle it
produces temporary muscle weakness. It works by irreversibly blocking
the acetylcholine receptors on the
muscle end of the neuromuscular
junction. Acetylcholine released from
the nerve is unable to bind with the
acetylcholine receptors, as they are
bound to the toxin. The muscle generates new acetylcholine receptors
and the muscle action is restored.
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HOW TO TREAT Strabismus
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This usually takes about three months
to occur in the recti muscles.
In young children, BTX is injected
under general anaesthetic. It has been
used to treat infantile esotropia, in the
hope that early realignment would
allow the brain to maintain long-term
alignment. Variable success has been
reported.
When to refer children with strabismus
• Accurate ophthalmic examination in infants and children is not easy, even for ophthalmologists. If the GP has any doubt about visual normality in a child, the
child should be referred to an ophthalmologist, or if possible, to a paediatric ophthalmologist.
• If the young child has a neonatal malalignment or pseudo-squint, they can be observed. However, some children with pseudo-squints may develop squint,
so they should be observed until good uniocular acuity can be obtained, with evidence of straight eyes and stereopsis.
• Refer any child in whom there is still a squint at 15 weeks of age, and if the squint is noticeable, then refer earlier.
• Refer a young child with a divergent squint.
• A child with a sudden-onset squint, particularly if there is restricted eye movement, or a child with a dull or absent red reflex should be referred urgently.
Referral of children with
strabismus
Timely referral for strabismus may
significantly alter visual outcomes.
The box, right, summarises when to
refer.
• Children with strabismus but with full ocular movements and a normal red reflex should be referred for a full paediatric ophthalmological examination, including
cycloplegic refraction and fundoscopy.
• Refer promptly any child with restricted eye movements.
• Refer urgently any child complaining of double vision.
Assessing an adult presenting with squint
History
ADULTS with strabismus usually
present complaining of diplopia or
of the effect of the ocular misalignment on their appearance. The history helps guide the clinician to the
underlying cause of the strabismus,
in conjunction with the clinical
findings.
Childhood squints often recur in
adulthood. These patients may
have previously undergone surgery,
or have decompensated a squint
that they were previously able to
control. Most of these patients who
have a recurrence of previous strabismus do not have double vision.
However, new-onset squint in an
adult produces double vision,
which may be constant or intermittent or only in some positions of
gaze. New-onset adult strabismus
may be caused by systemic conditions or problems isolated to the
ocular muscles and orbit. Neurological conditions include:
• Neurogenic palsies caused by
microvascular disease such as
diabetes and hypertension.
• Demyelinating disease, including
multiple sclerosis.
• Space-occupying lesions, with
raised intracranial pressure and
cranial nerve palsies (figure 5).
Mechanical problems that interfere with normal extraocular muscular contraction and relaxation or
that hinder global movement can
give rise to diplopia. These can
occur with thyroid eye disease and
orbital lesions.
Diseases that may weaken ocular
muscle include myasthenia gravis
or chronic progressive external
ophthalmoplegia.
With systemic conditions it is
important to remember that the eye
disease may occur without obvious
systemic involvement and even
with normal blood tests; this is
especially true of myasthenia gravis
and thyroid eye disease.
If the patient is over 55, consider
the possibility of giant cell arteritis
(temporal arteritis), as this can be a
blinding or occasionally fatal condition, and can present with a cranial nerve palsy. Ask if there is any
associated pain, headache or other
systemic symptoms such as weight
loss or jaw claudication, possibly
indicating giant cell arteritis.
The clinical history should
enquire about any prior childhood
treatment for lazy eye or squint.
The patient should be questioned
about general health, in particular
vascular risk factors such as blood
pressure and diabetes. Microvascular cranial nerve palsies caused by
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| Australian Doctor | 4 November 2011
Figure 5: MRI of a woman presenting with a new-onset, progressing fourth
nerve palsy. The top panel is the sagittal section of MRI T2 weighted image.
The lower panel is an axial section, both demonstrating an exophytic tumour
of the dorsal midbrain.
When to refer adults with strabismus
Immediate referral
Patients with a fixed, dilated pupil indicating a third nerve palsy
Patients with suspected giant cell arteritis
Patients with disc swelling in association with a sixth nerve palsy
Refer as soon as possible (within days)
Patients with other cranial nerve palsies, including an isolated sixth nerve palsy
or multiple cranial nerve palsies, should be considered for neurological and
ophthalmological assessment within days particularly if intracranial pathology is
suspected.
Patients who have diplopia, which does not appear to be due to a cranial nerve
problem, should be referred for assessment of possible systemic disease such
as myasthenia gravis and thyroid eye disease.
Non-urgent routine referral
Adults who present with a worsening of known childhood squint without
double vision can be referred routinely for specialist assessment.
Adults who are not aligned but are unsuitable for surgery should be referred
routinely for possible toxin injection if they are concerned by their appearance.
New-onset adult
strabismus may be
caused by systemic
conditions or
problems isolated to
the ocular muscles
and orbit.
diabetes or hypertension would be
expected to resolve within three
months.
Examination
Check the vision. If it is reduced in
one eye and does not improve with
a pinhole test to exclude a refractive error, this may indicate that
the patient has amblyopia due to
a longstanding squint or that the
patient has an optic neuropathy.
Perform a cover test to identify
the type of squint.
Examine the ocular movements,
in particular looking for restricted
movements suggestive of a cranial
nerve palsy. Asking the patient if the
double vision is worse in particular
positions of gaze is often helpful.
Check the pupils, specifically looking for a fixed dilated pupil, which
might suggest a compressive lesion
of the third nerve caused by a posterior communicating artery aneurysm.
Examine the discs, as discs
swelling with a sixth nerve palsy
can be a presenting sign of raised
intracranial pressure.
The presence of ptosis could suggest a third nerve palsy or, if fatigable, myasthenia gravis.
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Proptosis, either unilateral or
bilateral, can be seen with thyroid
eye disease, which can occur with
or without a background of systemic thyroid disease. Other causes
of unilateral proptosis include
orbital lesions.
Investigations
If giant cell arteritis is suspected,
the patient should have immediate
blood tests looking for a raised ESR
or CRP, and FBC looking for a
thrombocytosis. These tests may be
normal in a patient with giant cell
arteritis, as this is a clinical diagnosis; if in doubt the patient should
be referred for urgent assessment.
Neuroimaging of the brain and
orbit may be required. This will be
needed urgently in patients with
disc swelling and also in younger
patients with no history of systemic
disease.
Investigations for systemic disease include thyroid function tests
and thyroid antibodies, and for
myasthenia gravis, tests for acetylcholine receptor antibody and
muscle-specific kinase antibody.
Tensilon testing (the use of edrophonium chloride, an anticholinesterase, to temporarily
reverse the ptosis or diplopia of
myasthenia gravis) is rarely used in
testing for myasthenia but an icepack test is often useful, with ptosis
or double vision improving after
application of ice.
When to refer
Referral within an appropriate time
frame can have important clinical
implications. The box above summarises the indications for referral.
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HOW TO TREAT Strabismus
Treatment of adult strabismus
ONCE the underlying pathology
has been determined and appropriate therapy instituted, further treatment for any persistent diplopia
may be considered, using occlusion,
botulinum toxin intramuscular
injections, or surgical correction.
References
Figure 6: Ocular alignment of this patient before surgery and after adjustment.
Occlusion
If it is thought that the double
vision will resolve, for example, in
diabetic sixth nerve palsy, the
patient will be treated symptomatically. This is achieved either with a
Fresnel stick-on prism on one spectacle lens, or occlusive tape if a
prism does not achieve single
vision. Longer-term options include
prisms incorporated into spectacles
if a temporary prism was found to
be helpful but gave blurred vision.
Psychosocial impact
Botulinum toxin
BTX is a temporary treatment that
lasts on average three months and
can be used to treat small to large
angle squints. The toxin is injected
into the ocular muscle under local
anaesthetic with electromyographic
guidance. It takes 2-3 days before
any effect is noticed and about two
weeks to reach full effect.
The complications are usually
temporary and can include underor over-correction of the strabismus, diplopia, ptosis, haematoma
or infection. An extremely rare
complication is ocular perforation
with damage to the sight.
In patients who have lost control of a previously well-compensated deviation, toxin treatment
may only be required on one occasion, to enable the patient to regain
satisfactory alignment without the
need for formal squint surgery.
BTX has a major use in assessing
patients whose orthoptic tests have
suggested that they have a risk of
developing double vision if their
eyes are straightened by operation.
This risk is present because the
visual cortex has adapted to having
deviated eyes and realigning them
overcomes cortical suppression and
produces double vision.
For other patients, toxin injec-
three months. If required, further
surgery can be considered at this
time.
Patients who have had repeated
previous surgery have an increased
risk of chronic redness postoperatively. There is increased associated
scarring of the conjunctiva with
each operation and for this reason
in some patients BTX treatment is
a better option. Both BTX and surgery have an important role to
play in the treatment of patients
with strabismus.
tions may be given repeatedly as a
way of maintaining ocular alignment. This is often the best treatment option in a patient who is
unfit or unable to undergo an operation, for example a patient with a
sixth nerve palsy secondary to a
brain tumour where the squint
would recur after surgery.
It is also a good option when the
patient has poor vision or a blind
eye on one side, as these patients
do not have any visual drive to
maintain long-term ocular alignment after surgery, and their squint
tends to recur. BTX is also useful in
patients who have a squint despite
having undergone several previous
strabismus operations.
Surgery
With the accuracy and precision
that has been achieved in cataract
and refractive surgery, patients
often believe that the aim of strabismus surgery is to gain precise
alignment. However, this is
unachievable, as the position of the
eyes is not purely related to the
length of the muscles or the posi-
tion of their insertions.
The aim of surgery or BTX
treatment is to reduce the angle of
deviation. In patients who have
stereopsis or fusion, by reducing
the angle of deviation between the
eyes and getting them into their
fusional range, alignment may be
achieved by the neural feedback
loop to the brain, which normally
controls the position and alignment of the eyes. In patients without fusion potential, reducing the
angle of deviation makes the strabismus less obvious.
Squint surgery is a good treatment option for many patients,
particularly those with no or limited previous surgery (figure 6). In
adults, an adjustable suture technique is often used, in which most
of the surgery is performed with
the patient under general anaesthetic, and the final muscle position is fine-tuned and tied off after
the patient has been woken up.
The patient is usually advised to
take two weeks off work after the
operation, with most of the scarring no longer visible by about
Treatment of strabismus in adults
who do not experience diplopia
or who do not have binocular
potential has sometimes been
regarded as ‘cosmetic’. However,
many adults with strabismus have
stated that it has had a negative
impact on their lives, including a
negative effect on their interpersonal relationships and limiting
employment opportunities.
A number of publications have
confirmed that the presence of an
eye turn has a negative impact on
the way that person is perceived
with respect to their physical
appearance, personality and perceived capability. It has a negative impact on the overall judgement of a potential employer,
reducing the strabismic applicant’s
ability to obtain employment and
therefore having an impact on
their economic status.6-10
It also has an impact on their
personal lives, with potential partners perceiving a person with strabismus as significantly less attractive, erotic, likeable, interesting,
successful, intelligent and sporty.11
A physician therefore should
not underestimate the psychosocial impact of such social biases,
which can lead to social isolation
and alienation. The benefit of
treatment should also not be
underestimated, as improvement
of the patient’s ocular alignment
appears to herald major improvements in the quality of psychosocial functioning for most adults.
Authors’ case study
A GIRL initially presented aged
two-and-a-half with a childhood
esotropia. She underwent her first
squint operation aged four, on her
right eye. Her eyes remained
straight for some years before
becoming divergent and requiring
further squint surgery at age 15.
She had a very large angle of deviation and despite two squint operations had a residual small angle
exotropia. She therefore underwent
a third operation later that same
year. Her vision was 6/9 in the right
eye 6/5 in the left.
By age 17 her eyes had begun to
diverge again. As she had already
undergone three operations and
had had surgery on all four horizontal muscles (with a redo operation on two of the muscles) she was
offered BTX injections into her
right lateral rectus muscle under
electromyographical guidance. She
has now had a BTX injection into
this muscle 32 times over the past
17 years (figure 7).
34
| Australian Doctor | 4 November 2011
Figure 7: The upper image demonstrates the exotropia in this patient. She
underwent botulinum toxin injection into the right lateral rectus muscle. The
bottom image demonstrates her eye position two weeks after injection.
Comment
Squint operations on average last
10 years, as was the case for the
original surgery here. Squints in
children tend to be esotropic, while
those in adulthood tend to become
www.australiandoctor.com.au
exotropic. The main problem is
that the patient is unable to hold
the alignment of their eyes.
This woman wrote a letter to
express her feelings about the BTX
treatment.
“Having the toxin treatment has
allowed me to look at the world in
the eye with confidence. Prior to
my treatment, my squint was still
bad enough that when I looked at
someone, they sometimes thought I
was looking at someone behind
them — which was pretty cringey!
So much of professional life is
down to whether your face fits,
and I don’t think I’d have landed
the jobs that I’ve had over the years
if my eyes had looked odd. I’m
happily married with a family and I
have an interesting job at a major
international law firm. I’m not sure
I would have such blessings in my
life without the treatment, particularly because I wouldn’t have been
as confident to pursue opportunities that have come my way.”
1. Tommila V, Tarkkanen A.
Incidence of loss of vision in the
healthy eye in amblyopia. British
Journal of Ophthalmology 1981;
65:575-77.
2. Rahi J et al. Risk, causes, and
outcomes of visual impairment
after loss of vision in the nonamblyopic eye: a populationbased study. Lancet 2002;
360:597-602.
3. Holmstrom G, et al. Prevalence
and development of strabismus
in 10-year-old premature
children: a population-based
study. Journal of Pediatric
Ophthalmology and Strabismus
2006; 43:346-52.
4. Larsson EK, et al. A populationbased study of the refractive
outcome in 10-year-old preterm
and full-term children. Archives
of Ophthalmology 2003;
121:1430-36.
5. Lukman H, et al. Strabismusrelated prejudice in 5-6-year-old
children. British Journal of
Ophthalmology 2010; 94:134851.
6. Burke JP, et al. Psychosocial
implications of strabismus
surgery in adults. Journal of
Pediatric Ophthalmology and
Strabismus 1997; 34:159-64.
7. Coats DK, et al. Impact of large
angle horizontal strabismus on
ability to obtain employment.
Ophthalmology 2000; 107:40205.
8. Olitsky SE, et al. The negative
psychosocial impact of
strabismus in adults. Journal of
AAPOS: the official publication
of the American Association for
Pediatric Ophthalmology and
Strabismus/American
Association for Pediatric
Ophthalmology and Strabismus
1999; 3:209-11.
9. Mojon-Azzi SM, Mojon DS.
Strabismus and employment: the
opinion of headhunters. Acta
Ophthalmologica 2009; 87:78488.
10. Mojon-Azzi SM, Mojon DS.
Opinion of headhunters about
the ability of strabismic
subjects to obtain employment.
Ophthalmologica 2007;
221:430-33.
11. Mojon-Azzi SM, et al.
Opinions of dating agents
about strabismic subjects’
ability to find a partner. British
Journal of Ophthalmology
2008; 92:765-69.
Online resources
• American Association for
Pediatric Ophthalmology and
Strabismus: www.aapos.org
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HOW TO TREAT Strabismus
GP’s contribution
ate patching and became distressed
when the patch was applied to Katie.
Katie’s mother reluctantly agrees to
further specialist review.
with the second image from an
amblyopic eye very close to the main
image.
Questions for the author
DR JON FOGARTY
Point Clare, NSW
Case study
AT the time of Katie’s sixth-month
vaccination, Dr L wonders if she has
an intermittent squint. Katie’s mother
feels that Katie’s eyes are normal. She
admits that some friends have suggested that Katie has a “lazy eye”.
Dr L is unsure if she can confirm a
squint. She is able to elicit a definite
red reflex from the right eye but Katie
is distressed during the examination
and a left red reflex is not confirmed.
Her mother declines referral to an
ophthalmologist. She says that her
oldest son “had a squint but he grew
out of it”.
At 18 months Katie re-presents,
this time with her grandmother, who
says that Katie’s left eye “turns” when
she is tired. The GP is concerned that
Katie has a left convergent squint.
Katie is referred to a local ophthalmologist, who recommends surgery
to correct the squint. Katie’s mother
declines this therapy but agrees to a
trial of eye patching. Two months
later, Katie is again seen and her
mother says that she would not toler-
Can you give some tips on how to
determine whether a squint is caused
by wide epicanthic folds, or genuine
strabismus?
Use a torch to shine a light on
both eyes; if they are aligned and
it is a pseudo squint, the corneal
reflexes sit in the same position in
both eyes. However continue to
monitor the child, as 5% of children who are initially diagnosed
as having a pseudo squint have a
squint detected within a couple of
years.
When is the ideal time to repair
squint in children?
This depends on the child’s vision,
squint type and age at assessment.
However, as a general rule, the
longer the squint has been present,
the less likely binocularity can be
achieved.
Will binocular vision be restored if
squint treatment is delayed for
several years?
The chance of developing binocularity is higher in children who have
had binocularity before developing a
squint. The sooner the eyes are
aligned, the better the chance of
regaining binocularity.
Could you comment generally on
Katie’s management?
This is a difficult situation for the
general practitioner when the patient
or carer refuses assessment. Patients
can be referred to a public ophthalmology clinic for assessment if cost is
an issue. At the initial consultation,
as the left red reflex could not be
elicited, it would be worth assessing
this child for the red reflex at a subsequent GP visit if ophthalmic assessment is refused, at a time where the
child is less distressed, such as at an
early morning appointment.
Further, patching has been commenced for this child, indicating that
the child has amblyopia, and the
child’s distress with treatment, suggests that the amblyopia is significant. This child needs urgent referral
in an attempt to improve the vision.
If this opportunity is missed, the child
will always have weaker vision in the
eye. Using atropine treatment in the
How to Treat Quiz
good eye may be helpful in a child
who has found patching treatment
difficult and is a good therapy for
amblyopia.
General questions for the
author
Considering that children are often
seen by their GP for vaccination at
six weeks, four months, six months,
12 months, 18 months and four
years, which routine eye checks
should we do and at what age?
Vision should be assessed with an
age appropriate test as this is a good
screening test for visual development.
A red reflex should be assessed at six
weeks, and light reflexes assessed at
six months, and beyond.
What is the implication of ‘ghosting’
of images?
Some patients complain of ghosting when they have cataract, or occasionally it may describe double vision
Some patients complain of vertical
diplopia. What tests should the GP
do to assess this symptom?
In adults, the most common causes
of vertical diplopia are a fourth nerve
palsy, thyroid eye disease and an
orbital floor fracture. Assess the
patient’s vision, and look for signs
of thyroid eye disease including conjunctival chemosis, proptosis, lid
retraction, lid lag and limitations of
ocular rotations. An orbital floor
fracture is usually associated with a
history of trauma. A fourth nerve
palsy is best diagnosed using the
Bielschowsky three-step test.
Some patients complain of diplopia
after facial or head injuries. What
tests should the GP do to assess this
symptom?
Binocular diplopia is a symptom
of loss ofocular alignment. For
example, a patient with an orbital
floor fracture, with inferior rectus
entrapment can present with
diplopia after a facial injury. These
patients should be assessed within a
few days. Children with a floor
fracture and inferior rectus entrapment may present with a white eye
and parasympathetic stimulation
on upgaze. These children need to
be seen immediately and have corrective surgery urgently.
INSTRUCTIONS
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by post or fax.
The mark required to obtain points is 80%. Please note that some questions have more than one correct answer.
Strabismus — 4 November 2011
1. Which TWO statements are correct?
a) A dense unilateral cataract may be left
untreated during the first 16 weeks of life
without resulting in amblyopia
b) Visual pathways can be altered by therapeutic
interventions until early adulthood
c) Clearly focused, aligned images from each eye
must reach the visual cortex for a child to
develop high-quality vision with depth
perception
d) The slight disparity of the images reaching the
brain from each normal eye allows for depth
perception
2. A white red reflex is detected during the sixweek newborn screen. What TWO
conditions could it be due to?
a) Retinoblastoma
b) Congenital cataract
c) A pterygium of the eye
d) Amblyopia
3. A three-year-old boy presents with right
vision 6/6, and left 6/24 due to amblyopia. It
is important to refer the child to a paediatric
ophthalmologist for assessment. Which
TWO statements are correct?
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a) This child has more than 10 times the risk of
developing blindness in his right eye compared
with other children
b) The patient will not be able to get a driver’s
licence if his right eye vision drops to less than
6/12
c) Amblyopia treatment is beneficial until visual
maturation, which usually occurs around
puberty
d) Amblyopia is a rare condition that is easy for
the patient to identify
4. Which TWO statements relating to botox
treatment for adult strabismus are correct?
a) It is a good treatment option when the patient
is not suitable for surgery and to reduce the
turn to make it less noticeable
b) It is a permanent treatment in most cases
c) It cannot be used in someone if squint surgery
is being considered in the future
d) It may only require one injection for ocular
alignment to be re-established in some
patients
5. When assessing a sudden-onset squint in a
65-year-old man, which THREE conditions
must be considered?
a) Giant cell arteritis
b) A space-occupying lesion in the brain
c) Microvascular disease, including diabetes or
hypertension
d) Amblyopia
6. Which TWO statements are correct?
a) When a cover–uncover test is performed, if
there is no squint, each eye will remain still
b) When a cover–uncover test is performed, if
there is both a squint and very poor vision in
one eye, that eye may remain still
c) When a cover–uncover test is performed, an
outward movement of the uncovered eye to
take up fixation indicates an exotropia
d) A cover–uncover test is the best way to identify
a latent squint
7. In what TWO situations is neuroimaging of
the brain and orbits needed?
a) When the patient has optic disc swelling
b) When the patient with squint has a fixed and
dilated pupil suggesting a third nerve palsy
c) To exclude giant cell arteritis
d) If the patient had a childhood esotropia that
was surgically corrected and they present with
an adult-onset exotropia
8. Treatment for a childhood squint aims to
achieve which TWO outcomes?
a) Reduction of the psychosocial impact of the
appearance of a turned eye on the child’s
development
b) Achievement of binocularity in all children
operated on within the first year of life
c) Improvement of the child’s vision
d) Treatment of the compensatory head posture
9. In which TWO scenarios is urgent referral
required?
a) A child is noted to have a unilateral or bilateral
reduced red reflex
b) A child complains of double vision, as this
indicates the eye turn is of acute onset
c) A child has a head tilt
d) A six-week-old baby noted to have a
convergent squint and no other detectable
ocular abnormality
10. Amblyopia treatment may involve which
TWO of the following approaches?
a) Glasses
b) Squint surgery
c) Patching or atropine dilation
d) Botox therapy
CPD QUIZ UPDATE
The RACGP requires that a brief GP evaluation form be completed with every quiz to obtain category 2 CPD or PDP points for the 2011-13 triennium. You can
complete this online along with the quiz at www.australiandoctor.com.au. Because this is a requirement, we are no longer able to accept the quiz by post or
fax. However, we have included the quiz questions here for those who like to prepare the answers before completing the quiz online.
HOW TO TREAT Editor: Dr Giovanna Zingarelli
Co-ordinator: Julian McAllan
Quiz: Dr Giovanna Zingarelli
NEXT WEEK The next How to Treat is a two-part series looking at stem cell therapies and the promise they may hold for treating presently incurable conditions. In Part 1, we explain stem cells and examine their
clinical uses. In Part 2, we highlight clinical trials that are already underway. The authors are Dr Kirsten Herbert, consultant haematologist, Peter MacCallum Cancer Centre, East Melbourne, and Cabrini Medical
Centre, Malvern; Professor Andrew Elefanty, joint head, embryonic stem cell differentiation laboratory, Monash Immunology and Stem Cell Laboratories, Clayton; Rebecca Skinner senior manager,
communications, Australian Stem Cell Centre, Clayton; Dr Megan Munsie (PhD), director, education, ethics, law and community awareness unit, Stem Cells Australia, Melbourne, formerly senior manager,
research and government, Australian Stem Cell Centre, Clayton, Victoria.
36
| Australian Doctor | 4 November 2011
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