Strabismus - Fundamentals of Clinical Ophthalmology.pdf

CONCEPTS IN STRABISMUS
(a)
(b)
Figure 1.1 V pattern strabismus demonstrating
divergence in upgaze (a) and convergence in
downgaze (b). Note the association of hypertelorism
in this case
(a)
deviation occurring with elevation and depression
of the eye. A V pattern of movement, not
infrequently seen with congenital esotropia,
refers to the fact that convergence is greater in
depression of both eyes than in elevation. By
contrast an A pattern is the reverse (Figure 1.2).
Measurement of an A or V pattern is done at
distance fixation. Maintaining distance fixation
with the refractive error neutralised, we achieve
elevation and depression of the eyes by flexing
and extending the neck. If distance fixation is
not maintained, simply looking down may
induce accommodation and a pseudo-V pattern.
Amblyopia
Amblyopia is poor vision due to interference
with normal visual development during a critical
period of development. The earlier amblyopia is
recognised and treated in the critical period, the
greater is the possibility of avoiding poor vision.
The importance clinically of the different types
of amblyopia lies in timing and ease of reversing
the amblyopia. Pattern deprivation amblyopia
may occur in the early weeks of life, for example
with a dense congenital cataract. The critical
period extends for a few months. Strabismic
(b)
Figure 1.2 (a) A pattern strabismus demonstrating
convergence in upgaze and divergence in downgaze.
(b) V pattern strabismus demonstrating divergence in
upgaze and convergence in downgaze
amblyopia may occur some months later after a
brief period of ocular alignment. The malaligned
eye with an imperfect view of the object of
regard is at risk of poor vision because of
dominance of the fixing eye. Anisometropia
amblyopia is due to difference in refractive error
between the two eyes. Its critical period extends
until 7–8 years of age. If the eyes are aligned,
amblyopia may still develop because of
imperfect imaging on the retina of one eye,
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