Investigations of a case of paralytic squint

A. Evaluation for squint
Every case of squint should be evaluated utilising
the tests described on page 327-329. Additional tests
Fig. 13.26. Diplopia chart of a patient with
right lateral rectus palsy. Fig. 13.27. Hees screen.
required for a case of paralytic squint are :
1. Diplopia charting. It is indicated in patients
complaining of confusion or double vision. In it
patient is asked to wear red and green diplopia
charting glasses. Red glass being in front of the
right eye and green in front of the left. Then in
a semi-dark room, he is shown a fine linear light
from a distance of 4 ft. and asked to comment on
the images in primary position and in other
positions of gaze. Patient tells about the position
and the separation of the two images in different
fields. Fig. 13.26 shows diplopia charting in a
patient with right lateral rectus palsy.
2. Hess screen test. Hess screen/Lees screen (Fig.
13.27) test tells about the paralysed muscles and
the pathological sequelae of the paralysis, viz.,
overaction, contracture and secondary inhibitional
palsy.
The two charts are compared. The smaller chart
belongs to the eye with paretic muscle and the
larger to the eye with overacting muscle (Fig.
13.28).
3. Field of binocular fixation. It should be tested
in patients with paralytic squint where applicable,
i.e., if patient has some field of single vision. This
test is performed on the perimeter using a central
chin rest.
4. Forced duction test (FDT). It is performed to
differentiate between the incomitant squint due
to paralysis of extraocular muscle and that due to
mechanical restriction of the ocular movements.
FDT is positive (resistance encountered during
passive rotation) in cases of incomitant squint
due to mechanical restriction and negative in
cases of extraocular muscle palsy.
B. Investigations to find out the cause of paralysis
These include orbital ultrasonography, orbital and
skull computerised tomography scanning and
neurological investigations.
Paralytic vs. non-paralytic squint
Differences between paralytic and non-paralytic
squint are depicted in Table 13.2.
Management
1. Treatment of the cause. An exhaustive
investigative work-up should be done to find out
the cause and, if possible, treat it.
2. Conservative measures. These include: wait and
watch for self-improvement to occur for a period
of 6 months, vitamin B-complex as neurotonic;
and systemic steroids for non-specific
inflammations.
3. Treatment of annoying diplopia. It includes use
of occluder on the affected eye, with intermittent
use of both eyes with changed headposture to
avoid suppression amblyopia.
4. Surgical treatment. It should be carried out in
case the recovery does not occur in 6 months.
Aim of treatment is to provide a comfortable field
of binocular fixation, i.e., in central field and lower
quadrants. The principles of surgical treatment
involve strengthening of the paralysed muscle
by resection; and weakening of the overacting
muscle by recession.