Strabismus - Fundamentals of Clinical Ophthalmology.pdf

ASSESSMENT OF STRABISMUS
PATIENT VIEWS POINTER HELD IN LOWER FIELD
BY EXAMINER.
LEFT
RIGHT
ANGLE FORMED BY FALSE IMAGE AND TRUE
IMAGE POINTS TO SIDE OF PARESIS.
Figure 6.14 The pointer test
alternation. These tests are useful to establish a
baseline and compare progress. The Hess tangent
screen plots the relative position of each eye
(posture) in nine positions of gaze. The patient
wears complementary red and green goggles to
disassociate the eyes and the test is done at 50 cm.
The screen has small red lights that can be
illuminated. The patient holds a green light and
attempts to place it on the illuminated red light.
The eye with the red goggle views the red light
and is the fixing eye. The eye with the green
goggle is the eye in which the posture is being
studied. The Lees screen and Foster screen are
variants of this test. The Foster screen is a
simple inexpensive test that can be easily made
(Figure 6.15). Note that further objective
information about the paretic muscle can be
obtained by measuring the deviation in prisms in
the direction of action of the affected muscle.
Determining muscle restriction or paresis
Determining whether a muscle is restricted or
paretic may be based on observation of eye
movements. In the paretic eye, there will be
slowing of saccades. In the eye with mechanical
restriction (for example, muscle entrapment) the
velocity of saccade is normal until movement
ceases with the restriction.
Restriction – forced duction test The eye
is anaesthetised with a cotton bud soaked with
4% lignocaine (or cocaine). Fine toothed forceps
Figure 6.15 The Foster test. Note the underaction
of the right superior oblique muscle and the
overaction of the synergistic left inferior rectus
hold the globe. The patient is asked to look in
the direction of the muscle under investigation.
The eye is then moved in that direction. In the
eye with the paretic muscle it will be possible to
extend the movement, whereas restriction will
be experienced as resistance to movement. In
children under 12 years, the case should be done
in theatre under anaesthetic prior to the
commencement of strabismus surgery. In our
experience, the eye should be kept in the
position of primary action although others
believe the muscles should be pushed or lifted
up. 11 The test is only useful if obviously positive.
Paresis – active force generation test
The eye is grasped with forceps after instilling
the area with anaesthetic on a cotton bud tip
and the patient is asked to move the eye in the
primary direction of action. For example, in a
lateral rectus palsy the globe is grasped medially
whilst the patient attempts to adduct the eye and
the amount of force generated is noted.
Assessment in the older child
and the adult
The techniques of assessment in preverbal
children are applicable to the older child and
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