Evaluation of squint

N
OF A CASE
OF
SQUINT
PRESENTER-DR. SIDDHARTH
GAUTAM

 Squint is misalignment of the visual axes.
 It is a failure of the co-ordination of binocular
alignment. It leads inevitably loss of binocular
single vision. Fusion of the two images is
replaced either by diplopia or suppression of
one image.
 Strabismus may be caused by orbit, muscle,
motor nerve, or brainstem pathology.

Classification
STRABISMUS
Apparent /
Pseudo-
strabismus
Latent
Strabismus /
Heterophoria
Manifest
Strabismus /
Heterotropia
Concomitant
Strabismus
Incomitant
Strabismus

Apparent / Pseudo-strabismus
 The visual axes are parallel, but the eyes seem to have a
squint.
 This term is applied to a false appearance of squint in the
absence of any deviation and it may occur under different
condition.
 Any abnormality of lids, canthi or orbit may lead to pseudo
strabismus

Latent Strabismus /
Heterophoria
 It is a condition in which the tendency of the eyes to
deviate is kept latent by fusion. Therefore, when the
influence of fusion is removed the visual axis of one eye
deviates away.
 Types
 1. Esophoria- It is a tendency to converge.
 2. Exophoria- It is a tendency to diverge.
 3. Hyperphoria- It is a tendency to deviate upwards,
while hypophoria is a tendency to deviate downwards.
 4. Cyclophoria- It is a tendency to rotate around the
anteroposterior axis. When the 12 O’clock meridian of
cornea rotates nasally, it is called incyclophoria and
when it rotates temporally it is called excyclophoria.

Manifest Strabismus / Heterotropia
Concomitant squint
 It is a type of manifest squint in which the amount of
deviation in the squinting eye remains constant
(unaltered) in all the directions of gaze; and there is no
associated limitation of ocular movements.
 Types
 1. Esotropia- inward turning of the eyes

 2. Exotropia- outwards turning of the eyes

 3. Hypertropia- upwards turning of eyes
 4. Hypotropia- downwards turning of eyes

Incomitant squint
 It is a type of heterotropia in which the amount
of deviation varies in different directions of gaze.
 1. Paralytic squint
 2. ‘A’ and ‘V’ pattern heterotropias
 3. Restrictive squint

EVALUATION
History:
A careful history is important in the diagnosis
 Age of onset of deviation
 Is the deviation constant or intermittent?
 Is the deviation present for distance, near or
both?
 Is it unilateral or alternating?
 Is it present only when the patient is inattentive
or fatigued?

 Is it associated with trauma or physical stress?
 Old photographs
 Birth history
 Is there a family history of strabismus?.
 Are there any other medical problems?
Headaches, diplopia, vertigo

Ocular examination
 Visual acuity adapted for age
 For school children and adults-
1. Snellen’s test type
2. Landolt’s test type
 For 3-5 years-
1. Illiterate E-count test
2. Tumbling E-test
3. Isolated hand – figure test
4. Sheridan- Gardiner HOTV test
5. Pictorial vision charts
6. Broken wheel test
7. Bork candy bead test

 For 2-3 years
1. Dot visual acuity test
2. Coin test
3. Miniature toy test
 For 1-2 years
1. Marble game test
2. Sheridan’s ball test
3. Worth’s ivory ball test
 For infants
1. Optokinetic nystagmus test
2. Preferential looking test
3. Visually evoked response
4. Catford drum test
5. Indirect assessment – Blink reflex, Menace reflex

Determination of 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.

REFRACTION AND
FUNDOSCOPY
 It should be emphasized that dilated
fundoscopy is mandatory in the context of
strabismus, to exclude any underlying ocular
pathology such as macular scarring, optic disc
hypoplasia or retinoblastoma.
 Strabismus is often secondary to refractive
error.
 Hypermetropia, astigmatism, anisometropia
and myopia may all be associated with
strabismus.

CYCLOPLEGIA
 The commonest refractive error causing
strabismus is hypermetropia. Accurate
measurements of hypermetropia necessitate
effective paralysis of the ciliary muscle
(cycloplegia), in order to neutralize the effect of
accommodation, which masks the true degree
of this refractive error.

1.CYCLOPENTOLATE
 It affords cycloplegia in most children. The
concentration employed is 0.5% under the age of 6
months and 1 % thereafter. One drop, repeated after
5 minutes, usually results in maximal cycloplegia
within 30 minutes, with recovery of accommodation
within 2-3 hours and of mydriasis within 24 hours.
 The adequacy of cycloplegia can be determined by
comparing retinoscopy readings with the patient
fixating for distance and then for near.
 If cycloplegia is adequate, there will be little or no
difference. If cycloplegia is incomplete there will be a
difference between the two readings and it may be
necessary to wait another 15 minutes or to instil
another drop.

2. ATROPINE
 It may be necessary in some children with either high
hypermetropia or heavily pigmented irides, in which
cyclopentolate may be inadequate.
 Atropine may be used as drops or ointment. Drops are easier
for an untrained person to instil, but there is less risk of
overdose with ointment. The concentration is 0.5% under the
age of 12 months and 1% thereafter.
 Maximal cycloplegia occurs at 3 hours: recovery of
accommodation starts after about 3 days and is usually
complete by 10 days.
 Atropine is instilled (by the parents) b.d. for 3 days before
retinoscopy, but not on the day of examination. The parents
should be warned to discontinue medication if there are signs
of systemic toxicity, such as flushing, fever or restlessness
and seek immediate medical attention.

CHANGE OF REFRACTION
 Because refraction changes with age, it is
important to check atleast every year and
more frequently in smaller children and if
acuity is reduced.
 At birth most babies are hypermetropic.
 After the age of 2 years there may be an
increase in hypermetropia and decrease in
astigmatism.
 Hypermetropia may continue to increase until
the age of about 6 years and then between the
ages of 6 and 8 year levels off subsequently
decreasing until the early teenage years.

WHEN TO PRESCRIBE
 1. HYPERMETROPIA
 In general up to 4D of hypermetropia should
not be corrected in a child without a squint
unless they are having problems with near
vision.
 With degrees of hypermetropia greater than
this a two-thirds correction is usually given.
 However,in the presence of esotropia the full
cycloplegic correction should be prescribed,
even under the age of 2 years.

WHEN TO PRESCRIBE
 2. ASTIGMATISM
 A cylinder of 1.50D or more should be
prescribed, especially in cases of
anisometropia after the age of 18 months.

WHEN TO PRESCRIBE
 3. MYOPIA
 The necessity for correction depends on the
age of the child. Under the age of 2 years,-
5.00D or more of myopia should be corrected:
between the ages of 2 and 4 the amount is -
3.00D.
 Older children should have correction of even
milder degrees of myopia to allow clear
distance vision.

WHEN TO PRESCRIBE
 4. ANISOMETROPIA
 After the age of 3 the full difference in
refraction between the eyes should be
prescribed if it is more than 1D.
 If there is no squint then any associated
hypermetropic correction may be equally
reduced for each eye.

Examination of anterior and
posterior segment
 Examination of associated lid problems, ptosis
or media opacities in anterior segment are of
direct importance.
 Examination of pupillary reflexes may reveal the
underlying optic nerve or retinal pathologies
which are responsible for poor vision.
 Examination of fundus has assumed more
importance, recently, in light of objectively
observing torsion of the eyes.

Measurement of deviation
1. Hirschberg test
 It gives rough objective estimate of the angle
of a manifest squint
 Useful in young or uncooperative patients or
when fixation in deviating eye is poor.
 Procedure - Here 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.

 Each mm of deviation is approximately equal
to 7 degree. (1 degree = 2 prism dioptre)
 The angle of squint is 15 degrees and 45
degrees when the corneal light reflex falls on
the border of pupil and limbus, respectively

2. Krimsky and Prism reflection
tests-
 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.

 Prism reflection tests- involves the
placement of prisms in front of deviating eye
until the corneal light reflections are
symmetrical.

3. Cover – Uncover test
 Test consists of two parts-
 Cover test- to detect heterotropia.
 Procedure - To perform it, the patient is asked to
fixate on a point light. Then, the normal looking
/ fixating 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 fixation
(i.e., at 33 cm) distance fixation(i.e., at 6
metres).

 Uncover test- to detect heterophoria.
 Procedure - To perform it, one eye is covered
with an occluder and the other is made to fix
an object.

 In the presence of heterophoria, the eye under
cover will deviate.
 After a few seconds the cover is quickly removed
and the movement of the eye (which was under
cover) is observed.
 Direction of movement of the eyeball tells the type
of heterophoria (e.g., the eye will move outward in
the presence of esophoria).

4. Alternate cover test
 It is a dissociation test which reveals the total
deviation when fusion is suspended.
 Procedure - Suppose Rt eye is covered for
several seconds. The occluder is quickly shifted
to opposite eye for 2 seconds, then back and
forth several times. After the cover is removed,
the examiner notes the speed and smoothness
of recovery as the return to their pre-dissociated
state.

 A patient with a well compensated
heterophoria will have straight eyes before and
after the test has been performed whereas a
patient with poor control may decompensate to
a manifest deviation.
 It reveals whether the squint is unilateral or
alternate and also differentiates concomitant
squint from paralytic squint.

5. Prism cover test
 It measures angle of deviation on near or distance
fixation and in any gaze position.
 It combines alternate cover test with prisms.
 Procedure - 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.

 It gives the amount of deviation in prism
dioptres.
 Both heterophoria as well as heterotropia can
be measured by this test.

6. Maddox wing
 Maddox wing is an instrument by which the
amount of phoria for near (at a distance of 33 cm)
can be measured.
 Based on the basic principle of dissociation of
fusion by dissimilar objects.
 It measures heterophoria.
 The instrument is designed in such a way
that, through its two slits, right eye sees
a vertical white arrow and a horizontal
red arrow and the left eye sees a
vertical and a horizontal line
of numbers.

 Procedure - The patient is
asked to tell the number on
the horizontal line which
the vertical white arrow is
pointing (this will give
amount of horizontal
phoria) and the number on
the vertical line at which
the red arrow is pointing
(this will measure the
vertical phoria).
 The cyclophoria is
measured by asking the
patient to align the red
arrow with the horizontal

7. Maddox rod
 A Maddox rod consists of many
cylindrical glass rods of red
colour set together in a metallic
disc which converts the
appearance of a white spot of
light into a red streak.
 Procedure - Patient is asked to
fix on a point light in the centre
of Maddox tangent scale at a
distance of 6 metres. A Maddox
rod is placed in front of one eye
with axis of the rod parallel to

 The Maddox rod converts the
point light image into a line.
Thus, the patient will see a point
light with one eye and a red line
with the other. Due to dissimilar
images of the two eyes, fusion is
broken and heterophoria
becomes manifest.
 The number on Maddox tangent
scale where the red line falls will
be the amount of heterophoria in
degrees.
 In the absence of Maddox
tangent scale, the dissociation
between the point light and red
line is measured by the
superimposition of the two
images by means of prisms
placed in front of one eye with

Tests for grade of binocular
vision and sensory functions.
 Grades of BSV-
1. Simultaneous perception
2. Fusion
3. Steriopsis

1. Worth four dot test-
 This is a dissociation test which can be used
with both distance and near fixation &
differentiates between BSV, ARC and
suppression.
 Procedure- For this test patient wears goggles
with red lens in front of the left and green lens in
front of the right eye and views a box with four
lights – one red, two green and one white.

 Interpretation:
 All the four lights in the
absence of manifest squint–
normal BSV
 In abnormal retinal
correspondence (ARC)
patient sees four lights even
in the presence of a
manifest squint.
 Only three green lights--left
suppression.
 Only two red lights-- right
suppression.
 Three green lights and two
red lights, alternately--
alternating suppression.
 five lights (2 red and 3
green)-- diplopia

2. 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.

3. 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 RC will draw a cross
 An esotropic patient with abnormal retinal
correspondence (ARC) will draw vertical image to the
left of horizontal
 An exotropic patient with ARC will draw vertical image
to the right of horizontal

4. Bagolini Striated Glasses
 It detects BSV, ARC or suppression.
 Each lens of Bagolini glass lens has fine striations
which convert a point source of light into a line.
 Procedure -two lenses are placed at 45 and 135
degree in front of each eye and patient fixates a small
light source. Each eye perceives an oblique line of
light, perpendicular to that perceived by fellow eye.
Dissimilar images are thus presented to each eye
under binocular viewing conditions.

 Results-
 Two streaks intersect
at their centers in the
form of a oblique
cross– BSV
 Two lines but not
forming cross—
Diplopia
 Only one streak—no
simultaneous
perception and
suppression
 Small gap in one of
the streak– Central
Diplopia
Suppression Central
suppression
scotoma
Normal or ARC

5. Sensory function tests with
Synoptophore.
 Synoptophore compensates for
the angle of squint and allows
stimuli to be presented to both
eyes simultaneously.
 Synoptophore (major
amblyoscope) consists of two
tubes, having a right-angled
bend, mounted on a base.
 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. The two
tubes can be moved separately

 Synoptophore is used for
many diagnostic and
therapeutic indications in
orthoptics.
 Synoptophore tests for
sensory functions include:
Estimation of grades of
binocular vision
 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.

6. 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.

7. Tests for Stereopsis
 Tests on stereopsis can be based on two principles-
 Using targets which lie in two planes, but are so
constructed that they stimulate disparate retinal
elements and give a three dimensional effect, for
example:
 Circular perspective diagram such as the concentric
rings
 Titmus fly test, TNO test, Random dot stereograms,
Polaroid test
 Langs stereo test
 Stereoscopic targets presented haploscopically in
major amblyoscope

 Stereopsis is measured in seconds of arc.
 Qualitative tests for Stereopsis:
 Lang’s 2 pencil test
 Synaptophore
 Quantitative tests for Stereopsis:
 Random dot test
 TNO Test
 Lang’s stereo test
 Methods using Polarization: Targets are
provided as vectographs and images seen by one
eye is polarized at 90 degree using polarized
glasses.
• Titmus stereo fly test
• Polaroid test
• Random dot stereograms
• TNO test

 1. Synoptophore / Stereoscope tests /
Stereograms: Stereogram with three concentric
circles and a check dot for each eye is to be seen
with both eyes together. Stereograms with three
eccentric circles are to be seen with each eye
separately.
 If the patient reports seeing concentric circles, it
means stereopsis is present. If they are seen
eccentrically one may ask whether the inner
circles are closer to the right or left of the outer
circle.
 It determines whether the disparate elements are
suppressed in the right or the left eye.

 2. Vectographs: Consists of Polaroid material
on which the two targets are imprinted so that
each target is polarized at 90 degrees with
respect to the other.
 Patient is provided with Polaroid spectacles so
that each target is seen separately with the two
eyes.
 Titmus stereo test –The three-dimensional
polaroid vectograph which constitutes the
Titmus test is basically made up of two plates in
the form of a booklet.
 To perform the test the plates are reviewed with
polaroid glasses.
 The Titmus stereo test consists of three parts:

 Fly test- The right side of
the test booklet contains a
large housefly to test gross
stereopsis (threshold 3000
sec of arc). It is especially
useful in young children. The
subject is asked to pick up
one of the wings of the fly, If
the subject sees
stereoscopically, he will
reach above the plate. In the
absence of gross stereopsis
the fly will appear as an
ordinary flat photogrpah.
Fig. Titmus test using fly for gross
stereopsis –A- no stereopsis B-
Stereopsis present

 Animal test- It is performed if the
gross stereopsis is present. This
test consists of three rows of five
animals each; one animal from
each row is imaged disparately
(thresholds 10, 200 and 400 see of
arc. respectively) And, in each row,
one of the animals correspondingly
imaged in two eyes is printed
heavily black (serves as a
misleading clue). The subject is
asked which one of the animals
stands out. A subject without
stereopsis will name the animal
printed heavily (misleading clue);
while in the presence of stereopsis
he will name the disparately
imaged animal.

 Circle test - It consists of nine
squares, each containing four
circles arranged in the form of
a lozenge . Only one of the
circles in each square is
disparately imaged at random
with threshold ranging from
800 to 40 sec of arc. If the
subject has passed other two
tests, he is asked to 'push-
down' the circle that stands
out, beginning with the first
set, When he makes mistakes
or finds no circle to push
down, the limit of his
stereopsis is presumably
reached,
 Circle No. 5, equivalent to 1(X)
sec of arc is considered to he
lowest limit of fine central
stercoacuity and is designated

 3. Random dot stereogram tests- The random dot
stereogram tests are devoid of monocular clues and
the patients cannot guess what the stereo figure is
and where it is located on the test plate. So, this test
provides truer measurement of stereopsis than the
Titmus test .

Other tests- Frisby test
-Stereoscopic contours induced
optokinetic nystagmus test and
Television random dot stereotest

 4. Simple motor task test
based on stereopsis-
 Two pencil test- It is very
simple primitive bin an effective
test for detecting presence or
absence of gross stereopsis
(threshold value 3000 - 5000
sec of arc).
 To perform this test, examiner
holds a pencil vertically in front
of the patient, who is asked to
touch its upper tip with the tip of
the pencil held ill his hand by
one swill movement from
above. Patient having
stereopsis passes the test with
both eyes open. Patients fail
the test with one eye closed or
when both eyes are open but

Diplopia
 The simultaneous appreciation of two images
of the same object in different positions and
result from images of the same object falling
on non-corresponding retinal points.
 Types
- Binocular
- Uniocular

 Binocular diplopia-
 It occurs due to formation of image on dissimilar
points of the two retinae.
 Causes-
 Paralysis or paresis of the extraocular muscles
 Displacement of one eye ball
 Mechanical restriction of ocular movements as
caused by thick pterygium, symblepharon and
thyroid ophthalmopathy.
 Deviation of ray of light in one eye as caused
by decentred spectacles.
 Anisometropia

 Types-
 Uncrossed diplopia- In uncrossed
(harmonious) diplopia the false image is on the
same side as deviation. It occurs in convergent
squint.
 Crossed diplopia- In crossed
(unharmonious) diplopia the false image is
seen on the opposite side. It occurs in
divergent squint.

 Uniocular diplopia
 In uniocular diplopia an object appears double from
the affected eye even when the normal eye is
closed.
 Causes-
 Subluxated clear lens (pupillary area is partially
phakic and partially aphakic).
 Subluxated intraocular lens (pupillary area is
partially aphakic and partially pseudophakic).
 Double pupil due to congenital anomaly, or large
peripheral iridectomy or iridodialysis.
 Incipient cataract-Usually polyopia i.e., multiple
images may be seen due to multiple water clefts
within the lens.

Evaluation of diplopia
 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

2. Hess screen test.
 Hess screen plot the dissociated
ocular position as a function of
extraocular muscle action and
enables differentiation of paralytic
squint caused by neurological
pathology from restrictive
myopathy
 Hess screen test tells about the
paralysed muscles and the
pathological sequelae of the
paralysis, viz., overaction,
contracture and secondary

 Electronic Hess screen contains a tangent
pattern (2 D projection of a spherical surface)
printed onto a dark grey background.
 Red lights that can be individually illuminated
by a control panel indicate the cardinal
positions of gaze within a central field (15
degree from primary position and a peripheral
field 30 degree), each square represents 5
degree of ocular rotation.
 The two charts are compared. The smaller
chart belongs to the eye with paretic muscle
and the larger to the eye with overacting
muscle.

 Procedure-
 Patient is seated 50 cm from screen and wears red-
green goggle ( red lens in front of right eye) and
holds a green pointer.
 The examiner illuminated each point in turn which is
used as the point of fixation. This can now be seen
only with RE, which therefore becomes the fixating
eye.
 The patient is asked to superimpose their green light
on red light, so plotting the relative position of the left
eye. All points are plotted in turn.
 In orthophoria the two lights should be more or less
superimposed in all nine positions of gaze.
 The goggles are then reversed (red filter in front of
left eye) and procedure is repeated.
 The relative positions are marked by the examiner on

 Interpretation-
 Two charts are compared
 Smaller chart indicates eye with paretic muscle
(RE)
 Larger chart indicates eye with overacting yoke
muscle (LE)
 Smaller chart will show its greatest restriction in
main direction of action of paretic muscle (Rt LR)
 Larger chart will show its greatest expansion in
main direction of action of yoke muscle (Lt MR)
 The degree of disparity between plotted point and
template in any position of gaze gives an estimate
of angle of deviation.

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.

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-
 To weaken the strong muscle by
recession (shifting the insertion
posteriorly)
 To strengthen the weak muscle by
resection (shortening the muscle)

Types-
 Weakening procedures-
1. Recession
2. Disinsertion
3. Posterior fixation suture
 Strengthening procedures-
1. Resection
2. Tucking
3. Advancement of muscle near limbus

 Type and amount of muscle surgery-depends
upon the type and angle of squint, age of patient,
duration of the squint and the visual status.
 The maximum limit allowed
 - MR -resection - 8 mm
 - MR -recession - 5.5 mm
-----
 - LR -resection - 10 mm
 - LR -recession - 8 mm
Muscle Resection Recession
MR 1-1.5 degree 2-2.5 degree
LR 1-2 degree 1-2 degree

Evaluation of squint

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