EVALUATION OF A SQUINT PATIENT (4).pptx

EVALUATION OF A SQUINT PATIENT
• CHAIR PERSON- DR SUNDIP SHENOY
• MODERATOR – DR SPOORTHY
• PRESENTOR – DR RAGHAVENDRASWAMY D

• Strabismus is misalignment of eyes,
irrespective of the etiology.
• Normal ocular alignment involves parallelism
of the visual axes for distance vision, or
intersection of the visual axes at the point of
fixation for near.

GOALS OF STRABISMUS EVALUATION
• To find the etiology of strabismus
• To assess the binocular status
• To measure the amount of deviation
• To diagnose amblyopia
• To define a plan of management.

A strabismus patient may be examined in the
following order:
• Eliciting a detailed history
• Visual acuity assessment
• Cycloplegic refraction
• Fundus examination
• Sensory tests
• Measurement of deviation
• Ocular motility examination
• Special tests for specific diagnosis.

INSTRUMENTS IN STRABISMUS
PRACTICE
Essential equipments Other equipments
1. Prism bars/ Loose prisms set
2. Occluder
3. Fixation targets for near
4. Stereoacuity test cards
5. Bagolini’s striated glasses
6. Double Maddox rod set
7. Red and green goggles
8. Vision chart

Other equipments
• Synoptophore
• Hess Chart
• Ophthalmoscope (direct distance and indirect)
• Camera for documentation

Classification of strabismus
FUSIONAL STATUS
• Phoria: A latent deviation in which fusional
control is always present.
• Intermittent tropia: A deviation in which
fusional control is present part of the time.
• Tropia: A manifest deviation in which fusional
control is not present

VARIATION OF THE DEVIATION WITH
GAZE POSITION OR FIXATING EYE
Comitant (concomitant): The deviation does not
vary in extent by more than a few prism diopters
with change in direction of gaze or change in the
fixating eye.
Incomitant (noncomitant):
• The deviation varies in size with change in the
direction of gaze or the fixating eye.
• Most incomitant strabismus are paralytic or
restrictive in nature.
• Acquired incomitant strabismus may indicate
neurologic or orbital disease.

FIXATION
Alternating: Spontaneous alternation of
fixation from one eye to the other.
Monocular: Definite preference for fixation
with one eye.

AGE OF ONSET
Congenital:
This denotes a deviation documented prior to
six months, presumably related to a defect
present at birth.
Acquired:
This denotes a deviation with later onset,
after a period of apparently normal visual
development and for which a plausible cause
can be explained

TYPE OF DEVIATION
• The Classification of Eye Movement
Abnormalities and Strabismus (CEMAS) was
formulated at the National Eye Institute in
2001 where the classification is based on the
type, the direction and the associations of the
deviation.
• The proposed classification describes three
broad categories of abnormalities, comprising
eight major areas. These categories are:

• Horizontal deviations
• Vertical deviations and special forms of
strabismus
• Nystagmus and other ocular oscillations.
The major areas are:
– Ocular motor aspects of vision
– Sensory aspects of binocular vision
– Horizontal heterotropias
– Horizontal heterophorias

– Cyclovertical heterotropias and special forms
of strabismus
– Cyclovertical heterophorias
– Accommodative disorders
– Nystagmus and other ocular motor
oscillations.

Clinical Approach to
a Patient with Strabismus
HISTORY
• The history is given by the patient or his family.
• The age of onset and duration of squint is very
important for the prognosis regarding attainment
and maintenance of binocular single vision.
• deviation is intermittent or constant, unilateral or
alternating has to be asked.
• A history of significant head posture, confirmed
by old photographs, may indicate good binocular
potential.

• Antenatal and perinatal history is important for
any squint appearing since birth.
• A patient with recent onset of squint may
present with diplopia, past-pointing, abnormal
eye movements and headache.
• History of treatment taken in the past like
spectacles, patching, previous surgery
(strabismus or others like glaucoma , retinal
detachment, etc) should be noted.
• Family history should be taken for presence of
hereditary forms of strabismus

EXAMINATION
General Inspection of the Patient
• Observation of the degree and direction of squint.
• Presence of wide nasal bridge with increased inter-
pupillary distance and epicanthal folds which may be the
cause of pseudoesotropia, needs to be noted.
• Observation of facial asymmetry.
• Presence of an abnormal head posture is noted.
• Upward or downward slanting of palpebral fissures.
• Ptosis.
• Any lid/conjunctival scarring.
• Pupillary reactions are abnormal in patients with sensory
deviation due to diseases of retina and the optic nerve.

Media and fundus examination
• It is important to evaluate the eye for any
organic abnormality that could be causing
visual loss and secondary or sensory
strabismus.

Refraction
• Refraction is the starting point for evaluation for
strabismus.
• A refractive error could be the primary or a
contributing cause of the strabismus.
• Correction of the refractive error is paramount to
the management of strabismus.
• It is performed at the end of strabismus
examination and preferably under full cycloplegia
for children.

Assessment of Visual Acuity
Assessment of Vision
• Depending on age, the parameters for assessment is
different.
• In infancy upto 3 years
a. Fixation of either eye should be checked whether it
is Central, Steady and Maintained.
b. Optokinetic nystagmus
c. Teller acuity cards based on preferential looking
d. Visual evoked potential
e. Cardiff acuity cards

Verbal children (3 to 5 years): matching cards
a. Sheridan Gardiner chart
b. Allen Acuity cards
c. Illiterate E test
d. HOTV chart
e. Cambridge-Cardiff acuity cards
In children above 5 years various Snellen’s
charts can be used

Fixation Patterns
• Some children may show transient fixation
and following responses as early as 3 months.
• By 6 months of age, infant should clearly
fixate and follow an object.
• The words “Central, Steady and Maintained”
are used to describe fixation ability.

• (A) (Central) -
Location of corneal
light reflex as the
patient fixates the
examiner’s light
under monocular
conditions (B)
(Steady) – steadiness
of fixation on the
examiner’s light as it
is held motionless
and as it is slowly
moved about

• Central refers to a corneal light reflex from a
fixation light falling in the center of the pupil.
• Steadiness of fixation is assessed by moving a
penlight in front of the child slowly.
• Maintenance of fixation refers to the ability to
keep the eye fixed on a target when either eye
is covered.

Assessment of Vision in Nystagmus
• Before assessing monocular vision in nystagmus patients,
the smallest distance and near acuity targets visible with
binocular viewing must be ascertained.
• Anomalous head posture and repeat vision should be
checked with forced primary position.
• When assessing monocular vision, an occluder placed in
front of one eye worsens the nystagmus and leads to a
decline in visual acuity.
• This decline can be avoided by high plus lenses by fogging
or neutral density filters.
Examination of squint can be considered in two aspects:
• a. Examination of sensory status
• b. Examination of motor status.

Sensory Examination
• Sensory testing comprises the assessment of
the binocular status of the eyes and the
nature of correspondence between them.
• All sensory testing is performed with the
appropriate refractive correction.

• Before going to sensory examination, the different sensory
adaptations that can take place in response to clinical
situations that disrupt binocular vision must be understood.
• The specific type of sensory adaptation depends on when
the sensory anomaly occurred, the severity and the type of
binocular disruption.
They are divided into two sections based on the onset of
the sensory insult:
1. Visually mature (occurring after the visual system is
mature)
2. Visually immature (occurring during visual development).

Visually Mature
• The following sensory adaptations occur after the
development of bifoveal fusion, when the visual
system is mature.
• These are associated with normal retinal
correspondence.
• Visual neural development mature by around 9 to
10 years of age, and at this point there is not
enough cortical plasticity for adaptations such as
cortical suppression and ARC.

Diplopia
• The patients with diplopia fixate with one fovea,
and suppress the fovea of the deviated eye.
• The diplopic images come from the perifoveal
retina of the deviated eye.
• The foveal image from the fixing eye is perceived
as being located directly in front of the patient,
while the perifoveal retinal image from the
deviated eye projects to its corresponding visual
field.

• Exotropia causes the image to fall temporal to
the fovea, which projects to the nasal field
producing “crossed diplopia”.
• Esotropia causes the image to fall on the nasal
retina, which projects temporally and causes
“uncrossed diplopia”.
• In cases of vertical strabismus, the
hypertropic eye sees the lower image.

Confusion
• Instead of diplopia, strabismic patients with
confusion perceive two different images
superimposed on top of each other.
• Confusion is caused by the simultaneous
perception of two different images from the
two foveae that are pointing to different
objects of regard.
• It is rarely seen clinically.

Rivalry
• Rivalry, sometimes termed retinal rivalry, is a
condition where a patient with normal binocular
vision is presented with different images to
corresponding retinal points of each eye.
• Instead of seeing two different images
superimposed on each other (confusion) the
subject perceives patchy dropout of each image
where the images binocularly overlap.

Visually Immature
• The sensory adaptations occur when the
binocularity is disrupted during the first few
years of life, usually before 8 to 10 years of
age.
• The specific type of sensory adaptation that
occurs depends on the magnitude of the
deviation, whether it is intermittent or
constant, the age of onset of strabismus, and
the strabismus is corrected.

Monofixation and suppression:
• Small angle strabismus (<10 PD), or mild to
moderate unilateral retinal image blur, in
young children and infants causes a central
suppression scotoma of the deviated or
blurred eye and central fixation of the
preferred eye, but peripheral fusion is
maintained.

• Central suppression occurs because the central
retina has small receptive fields and high spatial
resolution potential, so that relatively small
differences in image clarity or retinal image
position are recognized.
• The size of the suppression scotoma is directly
proportional to the amount of image disparity.
• These patients usually have stereoacuity in the
range of 3000 arc seconds to 70 arc seconds and
the central suppression scotoma measures
between 2 and 5 degrees.

Retinal correspondence
• Retinal correspondence refers to the ability of
the sensory system to appreciate the perceived
direction of the fovea and other retinal elements
in each eye relative to the other.
• The two eyes have corresponding retinal
elements that have a common visual direction.
• The two foveae represent the highest degree of
correspondence.

• Abnormal retinal correspondence (ARC) is a
sensory adaptation of the immature sensory
visual system to an abnormal motor position of
the eye.
• Depending on whether the fovea has completely
taken over as the primary point of fixation in the
presence of measurable obvious strabismus, the
abnormal correspondence can be labeled as
harmonious or unharmonious

• If the fovea has completely taken over implying that
the subjective angle of the strabismus is nil in the
presence of an objective measurable angle of
strabismus, making the angle of anomaly equal to the
objective angle of strabismus, then it is termed as
harmonious ARC
• If there is a component of existing subjective angle of
strabismus, which is less than the objective angle of
strabismus, thus creating a measurable angle of
anomaly, which is a measure of the difference
between the two values, it is termed as unharmonious
ARC.

Tests for Sensory Anomalies
Worth’s Four Dot
Test:
The patient wears
a red glass in front
of right eye and a
green glass in front
of left eye. then
views a box with
four lights; one
red, two green and
one white

• If all four lights are seen, normal fusion
is present.
• If all four lights are seen in the presence
of a manifest deviation, ARC is present.
• If two red lights are seen, left
suppression is present.
• If three green lights are seen, right
suppression is present.
• If two red and three green lights are
seen, diplopia is present.
• If the red and green lights alternate,
alternating suppression is present

Bagolini’s Striated Glasses
• Each lens is covered with fine striations which
convert a point source of light into a line,
similar to the Maddox rod.
• The two lenses are placed at 45 degrees and
135 degrees in front of each eye and the
patient fixates a punctate light source placed 6
meter away.

It permits determination of whether the patient is:
• Fusing
• Suppressing one eye
• Suppressing centrally only
• The type of retinal correspondence present.
• It is a good idea to get the patients to draw their
results, especially children.
• A cover test must be performed to determine whether
a crossed response indicates fusion with NRC or an
ARC. If there is a manifest deviation in the presence of
a crossed response, it implies ARC.

After Image Test:
• This test demonstrates the visual direction of the
fovea.
• One fovea is stimulated by a vertical bright flash
of light and the fellow eye is stimulated by a
horizontal flash of light.
• The vertical flash of light is harder to suppress
and should be applied to the deviating eye.
• The patient then draws the relative positions of
the after images

Synoptophore
• This is an instrument for assessing strabismus, quantifying
binocular single vision (BSV) and detects ARC and
suppression
Grades of binocular vision:
First grade(simultaneous macular perception)
• is tested by introducing two dissimilar but not mutually
antagonistic pictures.
• Retinal rivalry ensures the image from one eye or the other
dominates here one picture is smaller than the other so
that the smaller picture is seen by the fovea of one eye and
the larger picture is seen by the parafoveal area of the
other eye.

Second grade–(fusion)
• is the ability of the two eyes to produce a
composite picture from two similar pictures each
of which is incomplete in one small different
detail.
Third grade–(stereopsis)
• is the ability to obtain an impression of depth by
the superimposition of two pictures of the same
object which has been taken from slightly
different angles.

Tests for Stereopsis:
• Stereopsis is measured in seconds of arc (1
degree=60 minutes of an arc; 1 minute =60
seconds of an arc).
• Normal stereoacuity is 40 to 60 seconds and is
an indicator of bifoveal fixation. The lower the
value, the better visual acuity it indicates.

Titmus fly test:
• This consists of a 3 dimensional polaroid vectograph
viewed through polaroid spectacles.
• The test is performed with the book held at a distance
of 16 inches (405 mm) from the observer.
• Perception of the wings of the fly is a measure of
gross stereopsis (3000 arcs).
• The circles measure 800 to 40 seconds and the animals
on the lower left hand side of the booklet measure
400 to 100 seconds of an arc. The fly is used to assess
whether stereopsis is present or not.

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.

TNO test:
• This random dot
test consists of
seven plates which
are viewed
through red green
glasses. The
degree of
disparity that can
be measured,
ranges from 480 to
15 seconds of an
arc.

Lang test:
• It is a simple test,
useful in children,
does not require
special spectacles
and measures
1200 to 600
seconds of an
arc.

Tests for Diplopia:
• These tests use one fixation target that is seen by both
eyes.
• Here we disrupt fusion by obscuring or eliminating
peripheral fusion clues, or providing different images to
each eye, which invokes retinal rivalry. These include:
Diplopia charting test
Maddox rod (Most dissociating)
Worth four dot test
Red filter test
Bagolini’s lenses (least dissociating).

Diplopia test
• Plotting of diplopia fields is indicated in patients
complaining of confusion or double vision
• The patient is asked to wear red-green charting goggles;
red in front of the right eye and green in front of the left
eye. The patient is made to sit with his head straight in a
semi dark room and is shown a fine linear light from a
distance of 4 feet.
• The light is moved from primary position into all of other
eight directions of gaze.
• For each direction, the patient is asked to comment on the
position, brightness, separation between the red and green
images and the relative angle of one image to the other.

This test is a prototype of the diplopia pattern
of testing where by the image perception of
two images of the same object by the two
eyes, brought about by an active process of
dissociation is used to delineate the
extraocular muscle that may be overacting or
underacting.

Representative diplopia charting of
cranial nerve palsies

Disadvantages of diplopia test:
• The test is qualitative.
• The test requires intelligent interpretation and hence may
Evaluation of Strabismus not be reliable in children,
uncooperative patients or mentally challenged patients.
• It is not possible to perform the test in color blind patients.
• The interpretation of red and green may not exist in such
patients.
• The test is not of use in congenital palsy and long standing
of palsies with contractures as the interpretations may not
be correct.

Maddox Rod Test
• The Maddox rod consists of a series of
parallel glass cylinders of higher power
(usually red color) set together in a metallic
disk.
• The Maddox rod produces a linear image of a
point light, when viewed through the rod the
line image is formed perpendicular to the axis
of the cylinders.

Maddox rod to assess
vertical deviation
Maddox rod to assess
horizontal deviation

• The rod is placed in front of the right eye. This
dissociates the two eyes because the red streak
seen by the red eye cannot be fused with the
unaltered white light seen with the left eye.
• The amount of dissociation is measured by the
superimposition of the two images by prisms.
• Both horizontal and vertical deviations can be
measured, but the test does not differentiate
between tropia and phoria.

Maddox Wing Test
• Maddox wing is an instrument by which the
amount of heterophoria for near (1/3rd m)
can be measured subjectively.
• The instrument is constructed in such a way
that the right eye sees only a white vertical
arrow and a red horizontal arrow, whereas the
left eye sees the horizontal and vertical rows
of numbers only

Measurements are made as follows:
The horizontal deviation is measured by
asking the patient towards which number
the white arrow points.
The vertical deviation is measured by asking
the patients regarding the number the red
arrow intersects.
The amount of cyclophoria is measured by
asking the patient to move the red arrow so
that it is parallel with the horizontal row of
numbers.

Hess Screen Test
• This test is based on the haploscopic principle, whereby in the
presence of bifoveal fixation and no sensorineural anomaly, the
image of the object seen by one eye is compared with the image
interpretation of the other eye, to arrive at a conclusion of an
ocular motor underaction/ overaction.
• The test is performed with each eye fixating in turn. The patient
wears the red and green dissociating glasses with the red glass over
right eye first and sits at 50 cm from an illuminated screen on which
each red target can be lit up in turn and its position indicated by the
patient using a linear green light.
• In orthophoria, the two lights are more or less superimposed in all
nine positions of gaze. The relative positions are connected with
straight lines.

Lee’s Screen
• The apparatus consists of two opalescent
glass screens at right angles to each other,
bisected by a two sided plane mirror which
dissociates the two eyes.
• Each screen has a tangent pattern marked
onto the back surface which is revealed only
when the screen is illuminated.

Interpretation of Hess/Lee's Screen Test
• The two charts are compared.
• The smaller chart indicates the eye with the paretic muscle.
• The larger chart indicates the eye with the overacting muscle.
• The smaller chart shows its greatest restriction in the main
direction of action of the paretic muscle.
• The larger chart will shows its expansion in the main direction of
action of the yoke muscle.
Changes with time: These are useful as a prognostic guide.
• Secondary contracture of the ipsilateral antagonist.
• Secondary inhibitional palsy of the antagonist of the yoke muscle

Lee’s screen records of right superior
oblique palsy

Motor Examination
The examination of motor status includes:
• Head posture
• Measurement of ocular deviation
• Limitation of ocular movements
• Fusional vergences.

Head Posture
Head posture has three components:
• Chin elevation or depression (vertical)
• Face turn to the right or left side (horizontal)
• Head tilt to the right or left shoulder
(torsional).

Common causes for abnormal head posture are:
• Incomitant squint, which is either paralytic or
restrictive.
• Concomitant squint with A or V pattern, e.g. chin up in
V exotropia or A esotropia
• Nystagmus cases with null position.
• One-eyed persons and hemianopic patients who take a
head posture to center their gaze in the available field.
• Other common causes are refractive errors in the form
of wrong cylinder axis or under corrected spectacles.
• Causes of ocular and non-ocular torticollis is presented

Causes of ocular and non-ocular
torticollis

Measurement of Deviation
Light Reflex Tests
Hirschberg test:
• A pen torch is shone into the eyes from arm’s length and the
patient is asked to fixate upon the light. If the eyes are deviated,
the light reflex falls on different locations instead of the center.
• Slight symmetric nasal displacement is normal and it is caused by
the physiologic positive angle kappa.
• Temporal displacement of the light reflex indicates esotropia; nasal
displacement indicates exotropia and inferior displacement
hypertropia.
• Displacement of light reflex to the pupillary margin indicates a
tropia of 15 degrees, mid iris 30 degrees and limbus 45 degrees

The orientation of the corneal reflex provides a
comprehensive diagnosis of the type of strabismus. The
decentration provides a representative idea about the
magnitude of the strabismus (Hirschberg’s test)

Krimsky test:
• It is a modification of the
Hirschberg test. A prism is placed in
front of one eye with the apex
towards the deviation, a pen light is
then one into both eyes and the
patient is asked to fixate on the
accommodative target juxtaposed
to the penlight.
• The prism is then increased or
decreased until the reflex becomes
symmetrically centered in the pupil.
• Placing a prism over the fixing eye
in a patient with tropia causes both
the eyes to move towards the apex
of the prism, which moves the
deviated eye in the primary
position.

Bruckner test:
• This test is performed by using the direct
ophthalmoscope to obtain a red reflex from both eyes
simultaneously.
• In patients with strabismus, the test shows asymmetric
reflexes with the brighter reflex coming from the
deviated eye.
• This also helps in identifying any pathology that
changes the normal red reflex, including
anisometropia, gross retinal pathology, large retinal
detachment and corneal, lenticular and vitreous
opacities.

Angle kappa
• Angle kappa is the angle between the line of sight and
the anatomic orientation of the eye or
corneal/pupillary axis.
• The line of sight is the line from the fixation target to
the fovea.
• The corneal /pupillary axis is a line from the center of
the pupil which is perpendicular to the cornea.
• Positive angle kappa is associated with the outward
turning of the eye.
• Negative angle kappa is associated with the inward
turning of the eye.

• Most normal patients have a physiologic positive
angle kappa.
• Pathologic positive angle kappa occurs when the
macula is pulled or displaced temporally in
diseases like retinopathy of prematurity and
Toxocara canis retinal scar in the temporal
periphery.
• A negative angle kappa is due to nasal macular
displacement secondary to a retinal scar between
the optic nerve and the fovea.

Cover Tests
• These tests are based on the patient’s ability to
fixate, and both eyes should have central fixation.
• They allow the examiner to differentiate tropia
from phoria, assess the degree of control of
deviation, and note fixation preference and
strength of fixation of each eye.
• Attention and cooperation are required and both
eyes should not have any gross motility defect.

Cover-uncover test
• This test is done to detect a heterotropia, without
dissociating an existing phoria.
• It should be performed both for near and distance.
• The test is performed by covering and then uncovering
one eye while observing the fellow eye for a tropia
shift as the eye takes up fixation.
• If there is no shift of either eye after covering and
uncovering each eye, there is no manifest deviation
and the eyes are straight.
• covering one eye produces a refixation shift, then a
manifest tropia is present.

Alternate cover test
• This test is done to dissociate binocular fusion in order
to determine the full deviation, including any latent
phoria.
• Alternately each eye is occluded and refixation
movement of uncovered eye to midline is observed.
• No shift in the alternate cover test indicates
orthophoria.
• A refixation shift to cover/alternate cover test indicates
that strabismus is present, either a tropia, phoria or a
tropia with phoria.
• Presence of a phoria only is an indication of binocular
fusion

Prism-alternate cover test
• This test determines the amount of prism
necessary to neutralize the full deviation
including any latent phoria, by quantitating the
shift associated with alternate cover testing.
• A prism is placed in front of the deviating eye
with the apex towards the deviation.
• Alternate cover testing is then performed with
the prism in place, the prism is changed (either
increased or decreased) depending on the
refixation shift

Simultaneous prism cover test
• It is used to measure the tropia component of
the monofixation syndrome without
dissociating the phoria and is therefore used
in patients with small angle strabismus.
• A prism and occluder is presented
simultaneously in front of either eye and this
process is repeated until there is no shift of
the deviated eye when the fixing eye is
covered.

Measuring incomitant deviations:
• When measuring patients with restrictive or paralytic
deviations the primary and secondary deviation should be
considered.
• In accordance with Hering’s law, the deviation is larger
when the eye with limited duction is fixing (secondary
deviation) than when the “good eye” fixes (primary
deviation).
• While measuring a deviation with prisms, the eye without
the prism is considered the fixing eye and the eye with the
prism is the non-fixing eye, irrespective of the fixation
preference or presence of amblyopia.
• This is because the eye without the prism must come to the
primary position to take up fixation.

Different Aspects of Measurement
• Deviation measurement with distance and near
fixation Evaluation of Strabismus to determine sub
type:
– Esotropia–(basic/convergence excess/divergence
insufficiency type)
– Exotropia–(basic/convergence insufficiency/
divergence excess type)
• Deviation measurement with and without glasses
• Deviation measurement in 9 gaze positions
• Deviation measurement in up gaze of 25 degree and
down gaze of 35 degree for determining A-V patterns

• Deviation measurement with right and left
eye fixing, especially in incomitant squints.
• Deviation measurement with subjective and
objective method to determine the type of
correspondence.
• Deviation measurement after prolonged cover
to differentiate a true divergence excess type
from a simulated divergence excess exotropia.

Measuring the AC/A Ratio
• AC/A ratio is the amount of change in convergence for
a specific amount of change in accommodation.
• Accommodation is the increase in lens power to clearly
focus at near. It is measured in diopters.
• The number of diopters of accommodation needed to
focus at a specific point is the reciprocal of the fixation
distance in meters.
• For example if the fixation target is at 1/3rd meter
then an emmetropic patient has to accommodate 3.3
diopters to put the image into focus.

• The two most useful methods for measuring
the AC/A ratio are:
1. Heterophoria method
2. The lens gradient method.

Assessment of Ocular Movements
• Ductions test single eye movements and are
examined with one eye occluded, while
versions test binocular eye movements.
• Both horizontal and vertical ductions are
quantified with a graded 0 to minus 4 scale,
with minus one limitation meaning slight
limitation and minus four limitation meaning
severe limitation with inability of the eye to
move past midline.

• Evaluation of versions include eye
movements through all 9 cardinal gaze
positions.
• Abnormal versions can be noted on a scale of
+ 4 through 0 to – 4, with 0 indicating normal
movement, + 4 indicating maximum
overaction, while – 4 indicates severe
underaction.

Diagrammatic representation of
binocular ocular movements

Assessment of Torsion
• Torsion refers to rotation of the eye about its visual axis.
• Intorsion occurs when the 12 o'clock meridian is rotated
nasally, and extorsion occurs when the 12 o'clock position
is rotated temporally.
• The vertical rectus and oblique muscles are responsible for
the torsional status of the eye.
• Malfunction of these muscles causes characteristic
alterations in the torsional position.
• Objective (anatomic) torsion refers to the anatomic
rotation of the eye about the visual axis.
• Subjective torsion refers to the patient’s perception of
rotation that may result from anatomic torsion.

Anatomic torsion
• It is the actual torsional position of the eye, not
dependent on the patient’s subjective response.
• It is helpful to compare the relative position of the
fovea and the optic nerve.
• The actual axis of the rotation of the eye is close to
the visual axis at the fovea.
• A horizontal line through the fovea intersects the
inferior half of the optic nerve.
• The eye is considered abnormally extorted if the
horizontal line through the fovea passes below the
lower margin of the optic nerve and abnormally
intorted if this line was above the center of the disk.

Methods of Measuring Objective
Torsion
• Indirect ophthalmoscopy: Indirect ophthalmoscopy
provides a simultaneous view of the optic nerve and
fovea and is the most convenient way for the examiner
to objectively assess torsion. The inverted view
however can be a source of confusion.
• Fundus photography: The main advantage of using
fundus photography to grade torsion is that a ruler or
protractor can be placed over a still photograph to
accurately determine the amount of torsion.
• Blind spot mapping: This was one of the first methods
to demonstrate abnormal ocular torsion.

Methods of measuring subjective
torsion
• These methods require the patient to assess
the torsional orientation of a target. The two
methods most frequently used are the double
Maddox rod and the Lancaster red green test.

Fusional Vergences
• The measurement of vergences is important ,it
determines the capability of the motor system to
cope with an induced misalignment of visual
axes. Vergence amplitudes are tested in three
planes:
1. Horizontal: Convergence and divergence
2. Vertical: Sursumvergence and deosumvergence
3. Torsional: Incyclovergence and
excyclovergence.
• Measurement can either be done with prisms or
the synoptophore.

Horizontal Vergences
Near point of convergence: The simplest way to measure
convergence is to bring a point drawn on paper closer to
the eyes, till the point becomes double. This in the near
point of convergence. The point at which it becomes
blurred is the near point of accommodation.
• Normally, the near point of convergence is 8 to 10 cm.
• Apart from the patient describing the diplopia, the outward
deviation of the eye is also looked for.
• Near point ruler, Royal Air Force binocular gauge and
Livingstone gauge are instruments based on this principle.
• Convergence and divergence for near (33 cm) and distance
(6 m) can be measured with the help of a prism bar or
rotary prisms.

• Using base-out prisms, the convergence
amplitudes can be measured and using base-in
prisms, the divergence amplitudes are measured
and similarly vertical oriented prisms can be used
for measuring vertical vergences.
• Normal convergence is 35 to 40 PD for near and
14 to 20 PD for distance.
• Normal divergence is 15 to 20 PD for distance and
5 to 8 PD for near.

Assessment for Extraocular Muscle
Paresis/Paralysis
• Park’s Three Step Test
• Tests of Muscle Function
• Field of Binocular Fixation.

Park’s Three Step Test
• Step 1: The hypertropic eye in the primary (straight
ahead) position is identified. This implies that either
one of the two depressors of the hypertropic eye or
one of the elevators of the hypotropic eye is paralysed.
• Step 2: The patient is then asked to look horizontally
towards the right and then the left. The examiner
observes in which position the vertical deviation is
more. deviation increases in the direction of action of
the paralyzed muscle, the likely two of the four
muscles identified in Step 1 are delineated.

Step 3 (Bielchowsky head tilt test):
• the patient’s head is tilted towards each shoulder and
the position in which the vertical squint increases is
noted.
• on tilting the head towards one shoulder the eye on
the same side intorts and the other eye extorts, the
ipsilateral synergist of the paralyzed muscle will try to
intort or extort the globe since the muscle also has a
vertical action, that vertical effect will be more
prominent in the paralyzed eye. This delineates the
actual cyclovertical muscle that is paralysed.

• the Park’s three step test is not useful in
multiple vertical muscle palsy, like the third
nerve palsy where many muscles are
simultaneously affected, restriction due to
restrictive or myopathic causes and old cranial
nerve palsy.

Tests of Muscle Function
Passive forced duction test:
• It can be performed under topical anesthesia or in the
operating theater under general anesthesia.
• After proper anesthesia the globe should be grasped near
the limbus with either forceps without teeth or Pierce
forceps to avoid tearing of the conjunctiva.
• globe should be held at right angles to the axis in which the
restriction is to be tested.
• After grasping, the globe should be rotated passively
towards the direction of action of the suspected weak
muscle, while the patient is asked to look in the same
direction so as to avoid the effect of tonic innervational
factor.

Interpretation of results:
Negative: If no resistance is encountered during
passive Evaluation of Strabismus rotation and the
examiner can rotate the globe to its whole extent,
it implies that the motility defect is clearly caused
by paralysis of the weak muscle.
Positive: If resistance is encountered during
passive rotation of the globe, it can be due to the
combined mechanical restriction and agonist
muscle weakness.

Exaggerated traction test: It is a modified forced
duction test which is performed to estimate the
tightness in superior and inferior oblique
muscles.
Forced generation test: In this test, the eyeball is
stabilized with the forceps applied at the limbus
and patient is asked to move both his eyes in the
direction of the muscle to be tested against
resistance provided by the examiner who tries to
stabilize the eyeball in the primary gaze position.

Field of Binocular Fixation
• The normal field of binocular fixation is 50 degrees downwards
and 45 degrees in all other directions.
• With the head fixed, an object is moved along the arc of an arc
perimeter like the Lister’s perimeter.
• Bowl perimeters like the Goldmann’s perimeter can also be
used.
• The patient indicates when the single object appears double.
• The area of binocular single vision is opposite to the direction in
which the binocular motility is impaired.
• the field of binocular fixation represents the extreme limits of
conjugate movement of the eyes in all directions in the absence
of any movement of the head. This can be charted in a manner
similar to the charting done for Hess charts.

Approach to Paralytic Strabismus
• Paralytic strabismus, is a form of incomitant
strabismus, resulting from primary or secondary
inadequacy of extraocular muscle action due to
neural dysfunction.
• Incomitancy is synonymously used with paralytic
squint
• it is important to clarify that causes of
incomitancy (gaze dependant variation of
deviation) range from paralytic strabismus to
restrictive etiology to alphabet pattern
strabismus

• Paralytic strabismus can be congenital or
acquired. It presents with limitation of ocular
movement, strabismus, abnormal head posture
or diplopia.
• The following terms are commonly used when
referring to a case:
1. Paresis: This refers to weakness of the muscle,
when some movement is possible.
2. Paralysis: This refers to complete loss of
muscle function, when no movement is possible.

AIMS OF INVESTIGATION
• To establish type of limitation: Neurogenic, myogenic
or mechanical (restrictive).
• To diagnose which muscles are underacting or
overacting
• To differentiate congenital/ long standing cases from
those of recent onset.
• To find and treat the cause of palsy if possible.
• To provide a permanent and repeatable record so that
progress can be assessed.
• Approach to a patient with paralytic strabismus
include:

HISTORY
• Onset and duration: Most acquired cases are acute in
onset. In long-standing cases or congenital cases,
symptoms may be less marked and intermittent due to
intervention of suppression or other abnormal
sensorineural adaptations.
• Binocular diplopia: Presence of binocular diplopia,
intermittently, or in a specific gaze is strongly
suggestive of muscle palsy. Presence of diurnal
variation suggests myasthenia gravis. Compensating
factors like a particular head posture any should be
noted.

• Photophobia: Symptoms of photophobia may be present
in patients with associated pupillary abnormalities,
difference in pupil size of the two eyes may be noted by a
conscious patient. Drooping of eye lid may be present
additionally in cases of third nerve involvement.
• Abnormal eye movements: A few patients or parents may
describe abnormal eye movements as ‘eyes that do not
move together’.
• History suggestive of etiology: Trauma, fever, diabetes
mellitus, hypertension, forceps delivery, and surgical
trauma could be etiological causes of paralytic strabismus.
• Others: Symptoms suggestive of other cranial nerve
dysfunction should be enquired .

OBSERVATION OF THE PATIENT
• In children the following should be observed
while taking history and during the preliminary
examination:
• Abnormal head posture (AHP)
• Eye alignment
• Eye movements
• Facial asymmetry
• Difference in pupil size
• Ptosis or lid retraction
• Any difficulty in speech, hearing or locomotion.

SENSORY EVALUATION
• Haploscopic/ Suppression tests
• Diplopia tests
-Diplopia tests using a red filter in front of the right eye
and a green filter in front of the left eye. A streak is
projected on to the screen and the patient’s response is
noted as to the distance between the two images in various
gaze positions and tilt or torsion if any
– Maddox rod is placed in front of the right eye and white
light shone into the eye and similar responses
– Worth four dot test is a good screening test for the
presence of diplopia
• Stereoacuity.

TESTS FOR ASSESSMENT
OF OCULAR DEVIATION
Cover tests:
• The specific information to be derived from cover tests in
cases of paralytic strabismus is:
– The direction of deviation (horizontal, vertical or
torsional)
– Presence of incomitance by comparison of deviation in all
nine gaze positions by means of an alternate cover test.
– Greater magnitude of secondary deviation compared to
primary deviation is revealed on comparison of the extent
of the deviation, with either eye fixing. In accordance with
Hering’s law, the deviation is larger when the eye with
limited ductions is fixing (secondary deviation).

(A) Patient with left
third nerve palsy
fixating with her right
eye (normal eye)
(B) The patient can
take up fixation with
the left eye (affected
eye). Note that the
primary deviation is
much more than the
secondary deviation

– Prism cover test is used objectively to
measure the horizontal and vertical deviation.
Cyclotropia cannot be measured by this
method. Measurements should be taken in all
nine positions of gaze by either moving the
patient’s head or moving the target

Harm’s tangent screen:
• This is the most effective way of measuring cyclotorsion. It
can be measured in ninenpositions of gaze with the head
turned or tilted depending on the information required.
• It consists of a large screen measuring 2.9 meters each
way, with a chess board pattern.
• There is a fixation light in the center that can be converted
to a line when assessing torsion. A helmet with a fixation
device is worn by the patient who projects a green ring on
the screen.
• The test uses subjective diplopia perception to measure
deviation. This creates maximum dissociation between the
two eyes

Maddox rod
• It provides an entirely subjective method of
measuring horizontal, vertical and torsional
deviations.
• It is useful to measure small deviations; which are
sometimes difficult to see on prism cover test.
• It is an excellent way of detecting and measuring
torsion in an observant patient. It may be very
useful to assess cases of acquired palsies
especially superior oblique palsy.

EXAMINATION OF OCULAR TORSION
Subjective Tests
Subjective tests are those whereby the patient’s active
co-operation is required for the appropriate
interpretations of the test.
Double Maddox rod test:
• Two Maddox rods, one red and the other white, are
placed in front of the two eyes with the axes vertically.
If the patient has vertical strabismus, the lines will be
seen one above the other.
• If there is no vertical separation, a 4D base-down prism
is placed in front of one of the rods to displace one of
the lines upwards.

• A patient without any cyclotropia will see two
parallel lines one above the other.
• Patient with cyclotropia will see one horizontal
line and one tilted line.
• He is then instructed to rotate the Maddox
rod corresponding to the tilted line such that
the two lines become parallel to each other.
• The axis of this rod gives the degree of
cyclodeviation .

Lancaster red-green test :
• It provides a diagrammatic representation of torsion in all nine
positions of gaze.
• The patient is seated 1 meter from screen, with red green goggles,
red in front of right eye .
• The examiner projects a red streak on the screen, slightly obliquely,
which is rotated until it appears straight to the patient.
• The patient is then given the green flashlight to project it next to
red streak. The actual positions of light bars are recorded using red
ink for right and green ink for left eye.
• The test is repeated for all nine positions of gaze. The procedure is
repeated with examiner projecting green light and left eye fixing.

Bagolini striated glasses:
• The apparatus consists of a pair of trial frames, a spotlight and two
plano glasses each marked with fine striations which produce a line
image of the spotlight.
• The principle of the test is similar to Double Maddox rod test.
• The glasses are placed in the trial frame with the striations being
vertical so as to produce a horizontal line image.
• The patient will see two lines one above the other in presence of
vertical strabismus.
• If there is no vertical separation, a small prism is used to separate
the lines.
• If the lines appear tilted to the patient, cyclotropia is present. The
amount of cyclotropia can be recorded by asking the patient to
rotate the glass till the lines are parallel

Bagolini striated glasses test.
• A, both eyes are aligned with
each other (lines are parallel).
• In position B, there is
misalignment, which is
corrected by rotating the
Bagolini lenses to such
position, where the lenses
become parallel.
• C, The extent of this rotation
gives a measure of the
cyclotropia

Major amblyoscope:
• The patient is asked to superimpose the slide
with the red cross in a slide with a white cross
within the surround so that all the lines are
parallel.
• Torsion is adjusted by rotating the slide with the
tilted image and the amount of adjustment is
recorded in degrees.
• Measurement can be recorded by fixing the eye
in all nine positions of gaze. It provides a
repeatable record of cyclotropia in all gazes.

Objective Tests
• These tests are dependent on the examiner’s
observations. A combination of subjective
and objective evaluation is required to reach
an appropriate conclusion.

Indirect ophthalmoscopy:
• The anatomic torsional position of the eye is considered
normal when a horizontal line drawn through the fovea
passes through the inferior one third of the optic disk. This
is seen on indirect ophthalmoscopy, as passing through the
superior one third of disk.
• Evaluation of Strabismus If the horizontal foveal line is
displaced superiorly, the eye is extorted, and if it is
displaced inferiorly, the eye is intorted.
• Similarly when displaced ½ disk diameter below the
junction of superior and middle thirds of the optic disk, eye
is considered to have 4+ intorsion.
• .

Guyton’s grading for degree of torsion
on indirect ophthalmoscopy
• Each additional 1/8th
displacement of fovea
beyond normal range is
graded as +1, +2 .
• Guyton’s grading
system helps quantify
the torsion. If the
foveal line is displaced
half disk diameter
above the superior disk
border, the eye is
considered to have
+4extorsion

Fundus photography:
• Fundus photographs of the posterior pole can be used
to measure the amount of torsion.
• To measure torsion, a horizontal reference is obtained
by aligning the edge of the film with a straight edge.
The angle between the horizontal reference and a line
joining the fovea to optic disk center can then be
measured with a protractor (optic nerve head- foveal
angle)
• The main advantage of this method is that a ruler or a
protractor may be placed over a still photograph to
accurately determine the amount of torsion.

OCULAR MOTILITY ASSESSMENT
the ocular movements assessed in paralytic
strabismus are:
• Ductions
• Versions.
Ductions are defined as monocular eye
movements, tested with one eye occluded.
Versions are binocular conjugate eye
movements

• Details to be noted when testing for ocular motility:
– Motility must be checked in nine positions of gaze and
recorded as movement being full, limited or excessive.
- The muscle action is graded, with 0 denoting normal
action, -1 to -4 denoting increasing grades of
underaction and +1 to +4 denoting overacting muscle.
– Easy fatiguability should be rule-out by repeated
testing, especially in suspected cases of myasthenia
gravis.

– Any discomfort on ocular movement,
suggestive of mechanical restriction or
inflammatory lesion.
– A change in the palpebral fissure size, as in
Duane’s retraction syndrome should be noted.
– A change in position of globe, for example
globe retraction sometimes accompanies
mechanical restriction

• As per Hering’s Law of equal innervation, the contralateral
yoke muscle of the affected paretic muscle overacts as the
innervation flowing to both muscles is equal and as the
paretic muscle requires more innervation, the yoke muscle
overacts.
• As there is no abnormality in the innervation of muscles in
the case of restrictive strabismus, the classical yoke muscle
overaction is not observed in restrictive strabismus.
• Overaction of the ipsilateral antagonist muscle as per
Sherrington’s Law may also not be observed in restrictive
strabismus because a fibrosed muscle can neither contract
nor relax and hence the underaction may persist on both
instances.

Hess and Lees screen:
• The plotted charts aid in the diagnosis of ocular
motility defect, measure the deviation, and
provide a repeatable record of the condition.
The screen is based on the principle of:
• Foveal projection
• Hering’s and Sherrington’s laws of innervations
• Dissociation of eyes by means of
complementary colors (Hess screen), or a mirror
(Lees screen).

Interpretation
The charts of the two eyes are compared for the position, size and
shape.
• The higher field belongs to the higher eye, as the test is based on
foveal projection.
• Smaller field belongs to the eye with primary limitation of
movement.
• Inward displacement of dots indicates underaction of the muscle
being plotted.
• Outward displacement of dots indicates overaction of the muscle
being plotted.
• Equal sized fields indicate symmetrical limitation in both eyes
suggesting a non paralytic etiology, or rarely a longstanding
paralytic strabismus with development of muscle sequelae.
• Sloping fields denote A and V patterns.

SUPPLEMENTARY TESTS
Bielschowsky Head Tilt Test
• Purpose: To determine the paretic cyclovertical
muscle.
• Principle: All the cyclovertical muscle have designated
primary, secondary and tertiary actions. Based on
these 3 levels of actions and taking into consideration
that the deviation is maximum in the area of
functioning of the affected paretic muscle, the ocular
motility of the eyes are tested in the primary position,
the horizontal gaze, and then with the head tilted to
bring forth torsional movements, in an effort to
delineate the affected muscle.

• Method: The patient fixes a mid-distance
target, the examiner notices the eye position;
then the head is tilted maximally (30 degrees)
towards either shoulder. The amount of
hyperdeviation in either position is compared

Interpretation:
• Both, a right SO palsy and a left SR palsy will present with right eye
hyperdeviation, or left hypodeviation.
• When the head is tilted towards the right shoulder, the right eye is
normally intorted by the right superior oblique and superior rectus.
• The depressing action of superior oblique is balanced by the
elevating action of superior rectus.
• If there is a superior oblique palsy, the unopposed action of the
superior rectus will result in hyperdeviation of right eye.
• In case of a left SR palsy, there will be minimal difference in vertical
deviation on right head tilt. This helps in determining the fault
muscle based on physiological principles. This now forms an
essential component of the Park’s-Helveston 3-step test.

Parks-Helveston 3-Step Test
• This test is performed to simplify diagnosis of
vertical muscle palsies
• Method
Step 1: Cover test is performed in primary
position to note which eye is hypertropic
Step 2: Alternate cover test is performed in
dextroversion and levoversion to assess the
direction of greater vertical deviation
Step 3: Bielschowsky head tilt test is performed,
noting the degree of hypertropia in either
position

• Step I: Primary gaze position:
The hypertropic eye is noted.
In this example, there is right
sided hypertropia. This
indicates:
1. Paralysis of the right eye
depressors:
a. RIR,
b. RSO.
2. Paralysis of the left eye
elevators:
a. LSR
b. LIO.
Thus, 4 out of 8 muscles that
could have been affected are
eliminated

• Step II:
The eyes are moved in
dextroversion and
levoversion. The direction
where the right hypertropia
increases is noted. In this
case, the right hypertropia
increases in right gaze. This
indicates that the paralyzed
muscle is a dextrovertor. The
dextrovertors in the 4
muscles delineated above
are:
a. RIR
b. LIO.
Thus 2 out of 4 muscles
delineated are eliminated

• Step III:
The head is tilted and the
increase in the right hypertropia is
noted. In this case, the right
hypertropia increases on the left
head tilt. This indicates:
1. Both the RIR and the LIO are
extortors of the eye.
2. In the left head tilt position,
the right eye of the patient is
extorting and the left eye is
intorting
3. the deviation is maximum in
the sphere of action of the
paralyzed eye. The extortor that
comes into action in a left head
tilt is the extortor of the right eye;
hence the RIR is the paralyzed
muscle.

• Depending on the clinical interpretations of
this test findings, the isolated palsy of any of
the 8 cyclovertical muscles can be delIneated
• This test does not provide accurate
information when there is multiple
extraocular muscle palsy, some of which may
be affecting the cyclovertical muscles also.
• Useful in the scenario of isolated
cyclovertical extraocular muscle palsy

DIAGNOSING RESTRICTION VERSUS
PARALYSIS OF MUSCLES
Saccadic velocity measurements:
• saccadic velocity can help differentiate restriction from
paresis by observation.
• The patient is instructed to look at two separate targets
held horizontally apart to test horizontal saccades or
vertically to test vertical saccades.
• It is important to bring the eye to a field where the
muscle has maximal function.
• For example, to check for lateral rectus function, the
eye should be in adduction, so that patient can
maximally demonstrate abducting power by generating
a lateral saccade.

• An optokinetic nystagmus drum may be used in
very young children unable to follow instructions
• The rectus muscles are the major movers of the
eye and are responsible for saccades. Thus,
saccades are an indicator of rectus muscle
function.
• Strabismus associated with limited ductions and
diminished saccadic velocity is suggestive of
rectus muscle paresis.

• Ocular restriction is associated with a normal,
but shortened saccadic movement as the eye
stops abruptly when restriction is met,
sometimes termed as ‘dog on a leash’ pattern.
• Quantitative assessment of the saccades is
possible using electro-oculography, infrared
scleral reflection technique and scleral search
coil technique.

• Measurement of horizontal and vertical saccadic movements will
provide an idea of rectus muscle function.
• EOG can be used to record this at any age. It is inexpensive and
repeatable.
• In ocular muscle paresis or paralysis saccadic speed is reduced,
mildly to markedly and can be used to monitor recovery.
• It is not useful for superior oblique palsy diagnosis as it is extremely
difficult to elicit isolated torsional saccades.
• Saccades are unaffected in muscle restriction such as thyroid
ophthalmopathy.
• By inducing OKN response or vestibular nystagmus, saccades can be
studied in a child. It is also useful in complex and confusing
disorders.
• It can be also used in lost or slipped muscles after strabismus
surgery.

Forced duction test (FDT):
• This procedure can be done as an outpatient
procedure under topical anesthesia or can
also be performed intraoperatively.
• Topical anesthetic like proparacaine is applied
to that area of the conjunctiva that would be
grasped for the test.
• This can be with proparacaine eye drops or
with a cotton tipped applicator soaked with
proparacaine.

• Tooth or Pierce Hoskin’s forceps are used to
firmly grasp the Tenon’s tissue close to the
limbus at both locations, perpendicular to the
desired direction of movement.
• This helps prevent corneal abrasions, should
the forceps slip.
• The eye is rotated in “paretic” direction. If
there is resistance to passive rotation of the
eye, a restrictive disorder is diagnosed.

• When performing FDT for recti muscles, the globe
should be protracted to stretch the recti.
• This maneuver helps identify a tight rectus muscle.
• For testing obliques for restriction, the opposite holds
true.
• If restriction is worse with retropulsion, it is secondary
to periocular adhesion or a tight oblique muscle.
• It is important to note that a positive FDT does not
exclude the presence of a co-existing palsy. In fact
most cases of long standing rectus palsy will have
contracture of the antagonist muscle leading to a
positive FDT.

Forced generation test (FGT)
• This test helps measure active muscle force and
is useful for diagnosing rectus muscle palsy.
• It can be done only in a co-operative, alert
patient.
• The patient is asked to look in the direction of
action of the paretic muscle while a sterile
cotton swab is held just beneath the limbus on
that same side.
• The amount of force generated by the paretic
muscle is compared with that generated in the
normal contralateral eye.

IOP changes on eye movement
(Jampolsky’s test)
• It is an indirect means of estimating
generated muscle forces when ocular
movements are limited by a tight muscle.
• Intraocular pressure increases as the eye
forcibly attempts to move against the
restriction.
• This differential intraocular pressure test can
be used in co-operative children. A change of
more than 6 mm Hg is considered significant.

Palpebral fissure changes on eye
movements:
• Restrictive strabismus may cause changes in the
palpebral fissure as the complete extraocular muscle
fascial system and the connective tissues of the orbital
adnexa and eyelids may be leashed together.
• This is usually not seen in paralytic strabismus as the
condition is predominantly neural. in certain cases, like
complete third nerve palsy, there may be a component
of pseudoproptosis and eyelid lag because of relative
lack of tone of the affected muscles
• conclusion of the above tests, the clinician must be
able to say if the incomitant strabismus is paralytic,
myogenic (myopathic) or restrictive.

MEDICAL INVESTIGATIONS
• A sudden onset, painful complete third nerve palsy is suggestive of
intracranial aneurysm, hence immediate neuroimaging is
warranted.
• Multiple cranial nerve palsies, generalized CNS disease, and
progressively worsening symptoms are a warning sign of an
enlarging intracranial lesion and again urgent neuroimaging is
warranted.
• If symptoms and signs are suggestive of myasthenia gravis,
tensilon test, ice test, acetylcholine receptors (ACH) receptor
antibodies, and electromyography (EMG) may be indicated.
• Isolated palsy in over 45 years age group is suggestive of
microvascular etiology. Hence, regular overview of blood pressure,
complete blood count (CBC), erythrocyte sedimentation rate (ESR),
blood sugar and serum lipids.

PRINCIPLES OF MANAGEMENT
• The surgical intervention for paralytic strabismus
is usually undertaken 6 months after the
stabilization of the deviation, giving sufficient
time for spontaneous improvement.
• If central fusion disruption is present as in some
patients due to palsy after head trauma, the
prognosis for realignment is guarded.
• Decision to surgically intervene may need to be
modified if the paralysis is associated with a
progressive neurological disorder.

• Aims of surgery vary with the patient’s clinical features and severity
of the palsy.
• For instance in total third nerve palsy the goal of surgery is good
alignment in the primary position.
• if the palsy is partial, the aim is not only to restore alignment but
also to center the diplopia free field of binocular single vision.
• In patients with sixth nerve palsy to improve abduction surgically in
the presence of severe abduction limitation.
• In fourth cranial nerve palsy, surgery is undertaken to eliminate
abnormal head posture which may be a head tilt or a chin down
position as seen in bilateral superior oblique paralysis.
• The surgical goals should be explained to the patient preoperatively.

Treatment of Symptom Producing
Palsies
Conservative
Prisms
• These are prescribed in elderly patients to avoid
morbidity associated with surgery
• Patients unfit for surgery comprise another indication
• Small deviations which may be overcorrected
surgically.
• The prescription of prisms is always preceded by a trial
prism for 4 to 6 weeks to ensure that the patient is
comfortable.

The aims of surgery in both congenital and
acquired palsy are
• To overcome symptoms
• To restore concomitance as far as possible.
• To enlarge the field of BSV, especially in the
primary position gaze.
• To overcome or decrease the need for abnormal
head posture
• To obtain a less noticeable deviation.

Indications of surgery in congenital
and acquired palsies
Congenital Palsies
Children
Indications for surgery:
• Unsightly head posture
• A manifest strabismus is present with evidence of sensory and
motor fusion, indicating that binocular single vision could be
restored.
• Decompensating deviation.
Adults
• Adult patients with long-standing or congenital palsies can be
treated conservatively using relieving prisms or with surgery.
• Treatment is indicated only if symptoms are present.

Acquired Palsies
Management comprises investigation and
treatment of the cause.
• A period of observation to allow time for
spontaneous recovery and treatment of the
underlying condition is required.
• A period of 9 to 12 months is necessary in
neurogenic palsies.
• The patient must be medically stable before
surgery is performed and ocular movements
must have been static for at least 3 months.

• Binocular single vision should be maintained by means
of prisms if possible. It can prevent the development
of suppression and amblyopia in children.
• Occlusion is indicated to avoid troublesome diplopia.
• Botulinum toxin may be used to prevent contractures
of the ipsilateral antagonist muscle of the paralysed
muscle.
• Further treatment and surgical options can be
considered if recovery does not take place.
• Recovery is not always full but patients with residual
diplopia on extremes of gaze learnt quickly to move
their heads to maintain binocular single vision (BSV).

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.
• Muscle Resection Recession
MR 1-1.5 degree 2-2.5 degree
LR 1-2 degree 1-2 degree

• The maximum limit allowed
- MR -resection - 8 mm
- MR -recession - 5.5 mm
- LR -resection - 10 mm
- LR -recession - 8 mm

EVALUATION OF A SQUINT PATIENT (4).pptx

EVALUATION OF A SQUINT PATIENT (4).pptx

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