Strabismus - Fundamentals of Clinical Ophthalmology.pdf

CHILDHOOD ONSET OF STRABISMUS
(a)
(b)
Figure 4.13 Alternating divergent strabismus. Constant alternating divergent strabismus in a 3 year old
child. Note alternation of fixation. Most children have a transient exotropia in the first weeks of life.
It is important to exclude any neurological deficits. This child had no binocular vision in the absence of a
neurological defect
Though the vast majority of Intermittent
exotropias are probably the result of a static
underlying cause, it is important to keep in mind
any clue alerting the clinician to a possible loss
of visual field, frustrating sufficient overlapping
to meet the needs of normal binocular vision.
Congenital exotropia that persists is a different
matter. A large angle up to 50 prism dioptres may
be present with a constant exotropia. Because of
the frequency of associated neurological disease,
referral to a paediatric neurologist is advised.
Differential diagnosis includes developmental
defects in the deviating eye and congenital cranial
nerve palsies. Local causes of defective vision
need to be excluded. A careful developmental
history will frequently reveal abnormal milestones
if there is underlying neurological disease. In the
context of neurological disease, for example
neurofibromatosis, the exotropia may signal the
presence of a progressive disease (Figure 4.12),
frequently affecting the sensory arc of the visual
path. Early surgery by the age of 2 years will
achieve a more stable alignment for distance, but
is often at the cost of a monofixation syndrome.
Surgery by the age of 4 or 5 years appears to be
associated with a higher risk of intermittent
divergence persisting. Surgery for patients under
the age of 4 years gives complete cure in about
50% of cases. Lateral incomitance may exist in
about 5% of exotropes, 10 and needs to be
identified as a failure to recognise it may result in
surgical overcorrections. It is also important to
note that a child with an alternating divergent
fixation present at distance and near may have no
underlying neurological defect (Figure 4.13).
Management
The options in management include minus
lenses in glasses if the patient is myopic.
Deliberate overcorrection with concave lenses
aims to induce accommodation to assist control
of the deviation, and may have a limited place
in management. Surgical correction involves
bilateral lateral rectus recessions up to 11 mm
from the limbus. Medial rectus resection in
patients with a convergence insufficiency type of
exophoria also has a limited value. Complications
of surgery include underactions in over 25% of
cases. Surgical alignment occurs in as many as
80% with good cosmetic prospects, but only 50%
have good binocular vision after surgery.
35