Strabismus - Fundamentals of Clinical Ophthalmology.pdf

STRABISMUS
Iatrogenic deprivation amblyopia
The treatment of an ocular condition such as
an eyelid lesion or corneal ulcer with an
occluding eye patch may also result in
deprivation amblyopia, especially in the first
weeks of life. Occlusion may be safe if not used
for more than 80% of the waking day. In a
unilateral dense cataract at birth or bilateral
dense cataract at birth requiring surgery,
bilateral occlusion in the early weeks of life may
prolong the critical period. This allows more
time to achieve equal imaging in both eyes and
reduce the risk of amblyopia.
“Concomitant” strabismus
Congenital esotropia syndromes
Esotropia in childhood is the commonest
form of strabismus seen amongst Caucasians in
clinical practice. It represents more than half the
ocular deviations in childhood (Figure 4.1).
With a presentation of esotropia under the age of
3 months, a motor imbalance will persist and be
seen as an associated latent nystagmus with
defective nasotemporal optokinetic nystagmus
(see Section I).
Concomitant esotropia in infancy includes
congenital (infantile) esotropia, which needs to be
identified and separated clinically from Ciancia
syndrome (esotropia with abduction nystagmus,
nystagmus compensation syndrome) and
refractive accommodative esotropia. Esotropias
associated with neurological abnormalities also
need to be identified. Finally, in cases with poor
vision at birth, particularly microphthalmia with
poor vision in one eye (sensory strabismus), the
eye with good vision may behave like Ciancia
syndrome with abducting nystagmus and
compensatory head posture.
Congenital (infantile) esotropia has been
referred to as either infantile esotropia or essential
esotropia. The term congenital esotropia is used
in this text. The esotropia is not always present
at birth although the underlying causative
mechanism may be. This is a condition that
Figure 4.1
affects as many as 2% of children in the
population, although the incidence may be
declining. The cause of infantile esotropia is
largely unknown. There are risk factors for
infantile esotropia, including family history and
in utero drug exposure – particularly exposure to
smoking. Extreme prematurity and children
with identifiable neurologic injury, for example
perinatal hypoxia–ischaemia, are also at higher
risk for esotropia. Other neurological syndromes
such as hydrocephalus and Arnold–Chiari
syndrome also may cause strabismus identical to
congenital esotropia in the first year of life.
However, the clinical neurological abnormality
may not be recognised early, emphasising the need
for caution for early surgery in the first year of life.
Clinical features
Congenital esotropia
The typical presentation is a child who seems
to have straight eyes for the first 2 or 3 months of
life and then rather suddenly develops a large
angle esotropia. The typical angle of deviation is
from 45 to 60 prism dioptres and the pattern is
usually comitant. In some situations an A or V
pattern may become apparent, although in the
first year of life A and V patterns are usually not
easily recognised. There is seldom any significant
refractive error (for example, hyperopia) greater
than 2·0 dioptres. Many children with infantile
esotropia cross-fixate, converging either eye to
observe the contralateral field. As a consequence
they may appear to have bilateral sixth nerve
palsies. A trial of uniocular patching will readily
demonstrate full ocular movement. Cross-fixation
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