I. History
A meticulous history is very important. It should
include: age of onset, duration, mode of onset (sudden
or gradual), any illness preceding squint (fever,
trauma, infections, etc.), intermittent or constant,
unilateral or alternating, history of diplopia, family
history of squint, history of head tilt or turn and so
on.
II. Examination
1. Inspection. Large degree squint (convergent
or divergent) is obvious on inspection.
2. Ocular movements. Both uniocular as well as
binocular movements should be tested in all the
cardinal positions of gaze.
3. Pupillary reactions. These may be abnormal in
patients with secondary deviations due to diseases
of retina and optic nerve.
4. Media and fundus examination. It may reveal
associated disease of ocular media, retina or optic
nerve.
5. Testing of vision and refractive error. It is most
important, because a refractive error may be
responsible for the symptoms of the patient or for the
deviation itself. Preferably, refraction should be
performed under full cycloplegia, especially in
children.
6. Cover tests
i. Direct cover test (Fig. 13.16). It confirms the
presence of manifest squint. To perform it, the
patient is asked to fixate on a point light. Then, the
normal looking eye is covered while observing the
movement of the uncovered eye. In the presence of
squint the uncovered eye will move in opposite
direction to take fixation, while in apparent squint
there will be no movement. This test should be
performed for near texation (i.e., at 33 cm) distance
tixation(i.e., at 6 metres).
ii. Alternate cover test. It reveals whether the squint
is unilateral or alternate and also differentiates
concomitant squint from paralytic squint (where
secondary deviation is greater than primary).
7. Estimation of angle of deviation
i. Hirschberg corneal reflex test. It is a rough but
handy method to estimate the angle of manifest
squint. In it the patient is asked to fixate at point
light held at a distance of 33 cm and the deviation
of the corneal light reflex from the centre of pupil is
noted in the squinting eye. Roughly, the angle of
squint is 15o and 45o when the corneal light reflex
falls on the border of pupil and limbus, respectively
(Fig. 13.17).
ii. The prism and cover test (prism bar cover test
i.e., PBCT). Prisms of increasing strength with apex
towards the deviation are placed in front of one eye
and the patient is asked to fixate an object with the
other. The cover-uncover test is performed till there
is no recovery movement of the eye under cover.
This will tell the amount of deviation in prism
dioptres. Both heterophoria as well as heterotropia
can be measured by this test.
iii. Krimsky corneal reflex test. In this test the
patient is asked to fixate on a point light and prisms
of increasing power (with apex towards the direction
of manifest squint) are placed in front of the normal
fixating eye till the corneal light reflex is centred in
the squinting eye. The power of prism required to
centre the light reflex in the squinting eye equals the
amount of squint in prism dioptres.
iv. Measurement of deviation with synoptophore.
All types of heterophorias and heterotropias (both
objective and subjective angle of squint) can be
measured accurately with it. In addition, many other
tests can also be performed with this instrument (for
details see pages 329).
8. Tests for grade of binocular vision and sensory
functions. Normal binocular single vision consists
of three grades. Sensory anomalies include
disturbances of binocular vision, eccentric fixation,
suppression, amblyopia, abnormal retinal
correspondence and diplopia. A few common tests
for sensory functions are as follows:
i. Worth’s four-dot test.: For this test patient wears
goggles with red lens in front of the right and green
lens in front of the left eye and views a box with
four lights – one red, two green and one white (Fig.
13.18).
Interpretation.:
If the patient sees all the four lights in the
absence of manifest squint, he has normal
binocular single vision (Fig. 13.18A).
In abnormal retinal correspondence (ARC) patient
sees four lights even in the presence of a manifest
squint.
If the patient sees only three green lights, he has
right suppression (Fig. 13.18D).
When the patient sees only two red lights, it
indicates left suppression (Fig. 13.18C).
When he sees three green lights and two red
lights, alternately, it indicates presence of
alternating suppression.
If the patient sees five lights (2 red and 3 green),
he has diplopia (Fig. 13.18E).
ii. Test for fixation. It can be tested with the help
of a visuoscope or fixation star of the
ophthalmoscope. Patient is asked to cover one eye
and fix the star with the other eye. Fixation may be
centric (normal on the fovea) or eccentric (which
may be unsteady, parafoveal, macular, paramacular,
or peripheral (Fig. 13.19).
iii. After-image test. In this test the right fovea is
stimulated with a vertical and left with a horizontal
bright light and the patient is asked to draw the
position of after-images.
Interpretation:
A patient with normal retinal correspondence will
draw a cross (Fig. 13.20A).
An esotropic patient with abnormal retinal
correspondence (ARC) will draw vertical image to
the left of horizontal (Fig. 13.20B).
An exotropic patient with ARC will draw vertical
image to the right of horizontal (Fig. 13.20C).
iv. Sensory function tests with synoptophore.
Synoptophore (major amblyoscope) consists of two
tubes, having a right-angled bend, mounted on a
base (Fig. 13.21). Each tube contains a light source
for illumination of slides and a slide carrier at the
outer end, a reflecting mirror at the right-angled
bend and an eyepiece of +6.5 D at the inner end
(Fig. 13.22). The two tubes can be moved separately
or together by means of knobs around a semicircular
scale. Synoptophore is used for many diagnostic
and therapeutic indications in orthoptics.
Synoptophore tests for sensory functions
include:
Estimation of grades of binocular vision
(page 318).
Detection of normal/abnormal retinal correspondence
(ARC). It is done by determining the
subjective and objective angles of the squint. In
normal retinal correspondence, these two angles
are equal. In ARC, objective angle is greater than
the subjective angle and the difference between
these is called the angle of anomaly. When the
angle of anomaly is equal to the objective angle,
the ARC is harmonious. In unharmonious ARC
angle of anomaly is smaller than the objective
angle.
(v) Neutral density filter test. In this test, visual
acuity is measured without and with neutral
density filter placed in front of the eye. In cases
with functional amblyopia visual acuity slightly
improves while in organic amblyopia it is markedly
reduced when seen through the filter.
TREATMENT OF CONCOMITANT STRABISMUS
Goals of treatment. These are to achieve good
cosmetic correction, to improve visual acuity and to
maintain binocular single vision. However, many a
time it is not possible to achieve all the goals in every
case.
Treatment modalities. These include the following:
1. Spectacles with full correction of refractive error
should be prescribed in every case. It will improve
the visual acuity and at times may correct the
squint partially or completely (as in
accommodative squint).
2. Occlusion therapy. It is indicated in the presence
of amblyopia. After correcting the refractive error,
the normal eye is occluded and the patient is
advised to use the squinting eye. Regular followups
are done in squint clinic. Occlusion helps to
improve the vision in children below the age of
10 years.
3. Preoperative orthoptic exercises. These are given
after the correction of amblyopia to overcome
suppression.
4. Squint surgery. It is required in most of the cases
to correct the deviation. However, it should always
be instituted after the correction of refractive
error, treatment of amblyopia and orthoptic
exercises.
Basic principles of squint surgery. These are
to weaken the strong muscle by recession
(shifting the insertion posteriorly) or to
strengthen the weak muscle by resection
(shortening the muscle).
Type and amount of muscle surgery. It depends
upon the type and angle of squint, age of
patient, duration of the squint and the visual
status. Therefore, degree of correction versus
amount of extraocular muscle manipulation
required cannot be mathematically determined.
However, roughly 1 mm resection of medial
rectus (MR) will correct about 1°-1.5° and 1
mm recession will correct about 2°-2.5°. While
1 mm resection and recession of lateral rectus
(LR) muscle will correct 1°-2°. The maximum
limit allowed for MR resection is 8 mm and
recession is 5.5 mm. The corresponding figures
for LR muscle are 10 mm and 8 mm,
respectively.
5. Postoperative orthoptic exercises. These are
required to improve fusional range and maintain
binocular single vision.
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