Strabismus - Fundamentals of Clinical Ophthalmology.pdf

ASSESSMENT OF STRABISMUS
pick up single hundreds and thousands indicates
not only good vision but good hand–eye
coordination.
Teller acuity cards and forced
preferential looking
In the preverbal child, the forced preferential
looking depends on the child’s inherent interest
in patterns as opposed to other targets. Here the
child is observed through a small hole and
various grating sizes are presented and the child’s
response noted. 2,3,4 Teller acuity cards consist of
cards with varying sizes of vertical gratings (see
Figure 2.3). They are useful for assessing the
vision of the preverbal child as well as the ability
to maintain and hold fixation. 5,6 They may also
be particularly helpful in comparing the vision
between the two eyes although they overestimate
visual acuity in amblyopia.
Matching tests
Matching tests such as the E test, Sheridan–
Gardiner and Mackay tests may be used in
children as young as 2–3 years. Other picture
matching card tests may also be useful. In the
very small child cooperation is better if the test is
performed at a distance of one third of a metre.
Poor vision testing
Useful tests particularly in preverbal children
suspected of poor vision include:
Figure 6.7
Cycloplegic refraction of a young child
Occlusion
The use of an occluder card or paddle is often
preferable to ensure that an eye is properly
occluded, although using a thumb may often be
as efficient.
Refractive error
It is important to perform full cycloplegic
retinoscopy on the child in order to determine
the degree of refractive error present in each eye,
which may contribute to strabismus and
subsequent amblyopia. Instillation of cycloplegic
drops 2 days prior to examination ensures
adequate effect; however, it is important to
warn parents of possible systemic side effects
(Figure 6.7).
●
●
Optokinetic nystagmus induced with optokinetic
tape. The tape is passed in front of the child’s
eyes and the nystagmus made up of refixation
pursuit episodes is observed.
Vestibulo-ocular reflex test. The examiner rotates
with the child held at arms length and facing the
examiner which induces horizontal nystagmus.
After cessation of rotation it is noted how
quickly the vestibulo-ocular reflex is overridden
by the visual fixation reflex as the child takes
up visual fixation on the examiner’s face. If
nystagmus is prolonged, it suggests that the
baby is blind or has severe cerebellar disease.
Colour vision
Ishihara plates are useful, although they only
test red–green deficiency. The test may be
simplified by asking the child to trace the
coloured path with a finger. Errors that do not
conform to red–green deficiency may indicate
optic nerve disease.
Pupil
Examination of the pupil may give
information about the optic nerve and the third
cranial nerve.
61