Strabismus - Fundamentals of Clinical Ophthalmology.pdf

STRABISMUS
torsional deviations can be measured using
another Maddox rod.
Saccade velocity and pursuit
The examination is not complete without
examining for saccades and pursuit, and being
alert to the possibility of internuclear ophthalmoplegia,
oculomotor apraxia or progressive
external ophthalmoplegia. The examiner with
experience rapidly learns to recognise normal
and abnormal pursuit.
Assessment of abnormal head posture
Measurements of deviation are made in the
primary position and in all positions of gaze.
This is important for two main reasons:
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determining the basis of abnormal head
positions, and
detection of incomitant squints associated
with cranial nerve palsies as well as A and V
patterns.
The examination provides information about
third, fourth, and sixth cranial nerves together
with supranuclear control of eye movement.
The differential diagnosis of abnormal head
posture includes:
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causes of torticollis, including hemivertebra,
sternomastoid tumour or monoaural deafness
ocular causes, including nystagmus, fourth
nerve palsy, and homonymous hemianopia.
Assessment of paretic strabismus
Useful information can be obtained by the
clinician via a number of simple tests.
Head tilt
If head tilt has been assumed to maintain
binocular vision and avoid diplopia, a cover test
with the head in the tilted position will
demonstrate that the eyes are straight and that
fusion is probably present. It can be tested also
by simple tests of fusion, including the Lang test.
Having taken visual acuity, the head can be tilted
to the opposite side to see if this disrupts fusion.
Diplopia test
If it is on the basis of binocular imbalance,
one image will disappear on occlusion of either
eye. The angle of deviation will be greatest in the
deviation of the paretic muscle when the eye is
fixing with the paretic muscle (Hering’s Law).
This test is of more use in the older child or
adult. Dissociating the eyes with red and green
glasses may assist evaluation.
Diplopia tests may be helpful in several
scenarios, including facilitating the diagnosis of
a horizontal muscle palsy; for example, in a left
sixth nerve paresis, the diplopia and deviation
will be greatest in the direction of the left lateral
rectus. Cyclovertical muscle imbalance may be
determined by direct observation of the patient
or by questioning. The Parks 3-step test may be
used both subjectively as well as objectively
(see Chapter 5). The patient may be asked the
following questions.
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In which eye is the image higher?
Whether vertical separation is wider on head
tilt to the left or right.
Whether vertical separation is greater on right
or left gaze.
This information is sufficient to make the
presumptive diagnosis as to which cyclovertical
muscle is involved.
The pointer test
A useful diagnostic test to confirm diagnosis
of a fourth nerve palsy is the pointer test
(Figure 6.14).
Plotting ocular posture
The Hess chart, Lees screen or Foster screen
tests can be initiated by suppression or
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