Strabismus - Fundamentals of Clinical Ophthalmology.pdf

STRABISMUS
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the pattern of the abnormal eye movement is
constant at a particular test distance.
The underlying cause may be progressive, for
example chiasmal glioma 1 (see Figure 4.12), or
non-progressive, for example some forms of rod
monochromatism. It is important to detect the
defect in vision, to recognise that the strabismus
is secondary to pathology and to determine
that the child’s vision is abnormal. It is not
uncommon for the visual deterioration in
preverbal children with craniopharyngioma or
optic nerve glioma to go undetected until later. In
these cases, often more attention is given to the
eye movement disorder than the defect in vision
and occasionally eyes are operated on without
recognising the underlying visual defect until
later. It is equally important to distinguish the
presence of a pseudosquint, most commonly due
to the configuration of the eyelids, particularly
epicanthal folds, creating an optical illusion
(Figure 6.1). It is important to bear in mind that
a true deviation of one eye may be apparent at the
same time as visual axis alignment. In such cases
normal binocular vision is present. This may be
due to heterotopia of the macula, occasionally
seen in children who have had retinopathy of
prematurity, to exclude retinal pathology.
Epicanthal folds have different significance with
relation to race and presence of developmental
disorders. A diagnosis of pseudosquint can be
made only after the exclusion of true strabismus,
which may coexist with epicanthal folds. Other
clinical features should be looked for which may
give clues to an underlying cause of epicanthal
folds and strabismus, for example Down
syndrome (Figure 6.2).
It is important to determine whether the
parents have noticed inattention to the visual
field of either side, rubbing of the eyes
(oculodigital reflex), or whether the child makes
eye contact or is fascinated by mobiles over the
cot. A child’s disinterest in a visual object can
reflect intellectual delay.
In the older child, it must be determined
whether the child prefers to be in dull or bright
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(a)
Figure 6.1 Epicanthial folds in children (a, b) giving
rise to the appearance of pseudostrabismus
Figure 6.2 In a younger baby, milder forms of
syndromes, e.g. Down syndrome, may be missed. In
this case there was an associated central cataract
typical of Down syndrome in addition to epicanthal
folds. Cataracts were removed in the first week of life
and contact lenses fitted. Children such as these and
premature infants need to be assessed carefully and
monitored for development of subsequent strabismus
light, and whether the child becomes frightened
in the dark and seeks to hold onto parents.
Marked intolerance of bright light may indicate
rod monochromatism, in which case the child
may behave as if totally blind in bright light.
Such a case may also present with esotropia and
nystagmus and needs consideration as a case of
congenital esotropia. It is important to ask how
close the child holds toys to examine them, and
what is the child’s behaviour with the television.
(b)