STRABISMUSClassification and ExaminationDr.Puskar GhoshPGTBurdwan Medical College

Strabismus:

• It is a condition in which the visual axis of the two eyes does not meet at the point of regard.

• Greek word-”strabos”:crooked

• PHORIA:latent visual axis deviation,held in check by fusion.

• TROPIA:a manifest visual axis deviation.

• Intermittent Tropia:deviation may exist in only certain gaze positions or target distance.

• Visual axis (line of vision) : extending from the point of fixation to the fovea.

• Anatomical (Pupillary) axis:is a line passing from the posterior pole through the centre of the cornea .

• Angle kappa : is the angle subtended by the visual and anatomical axes .

+5˚ exotropic.

Extraocular muscles:

5.5

6.6

7.0

7.7

Movements of the eye:• Uniocularly-Duction• Binocularly-Version.-Same direction• Opposite direction-Vergence• Adduction-nasally horizontal• Abduction-temporally horizontal• Sursumduction or elevation-upward• Deorsumduction or depression-downward• Incycloduction• Excycloduction

Eye movements:Yoke muscles

For co ordinated eye movements one muscle of the each eye act togather.These are called yoke muscle.• Hering’s law,for a

binocular movement the corresponding muscle (yoked) receive equal and simultaneous innervation.

• Sherington’s law of reciprocal innervation,for any binocular movement the direct antagonist receives an equal and simultaneous inhibition of its innervation.

Binocular vision:• Definition:

It is the state of simultaneous vision with two seeing eyes that occurs when a person fixes his visual attention on an object of regard.

Correspondence:

Grades of BSV:

• Simultaneous perception

• Fusion

• Stereopsis

Ability to fuse points outside corresponding retinal area

Ability to fuse image projected in corresponding retinal pints

Ability of perception of depth

Binocular vision and Squint:• Confusion-due to different image viewed by two foveaImmediately checked by cortical or retinal rivalry mechanism.

• Diplopia-one object is perceived by one of the fovea of one eye and other

object is perceived by extrafoveal point of the other eye which has a different localization value in space.

Binocular diplopia-single image on closing one eyeMonocular diplopia-in astigmatism,neurological conditionsUncrossed diplopia-esodeviationCrossed diplopia-exodeviation

Adaptation Mechanisms:• Motor Adaptation:1. Fusion• Beyond fusional reserve-asthenopia

1. Head postures• Chin elevation or depression• Face turn • Head tilt

3. Blind spot mechanism: esotropia of 15˚,other image fallsOn blind spot-no diplopia.

Adaptation Mechanism:• Sensory Adaptation:• Supression:Confusion is takled by foveal rivalry which is

actually a suppression.extrafoveal image suppression is readily occurs if

the visual potential of the extrafoveal point is poor.

FacultativeObligatory• Anomalous Retinal Correspondence:It is the binocular functional adaptation to

strabismus at the cortical level.The fovea of the fixing eye develops a correspondence (binocular relationship) with an extrafoveal point of the other eye.

• orthophoria ; perfect alignment of the visual axes. Most individuals have heterophoria.

• Hypophoria/hypertropia; latent/manifest squint downwards turning of eyes

• Hyperphoria/hypertropia; latent/manifest squint upwards turning of eyes

• Exophoria; latent squint outwards turning of the eyes

• Exotropia; manifest squint outwards turning of the eyes

• Esophoria; latent squint inwards turning of the eyes

• Esotropia; manifest squint inwards turning of the eyes

Classification: Strabism

usConcomitant:deviation same in all gaze

Incomitant:inequal deviation

Horizontal1. Esotropia2. Exotropia

Vertical1. Hypertropi

a2. Hypotropi

a

Torsional1. Incyclotropi

a2. Excyclotropi

aUnderaction

Overaction

Restrictive

Paralytic

Neurogenic1. Supraneuclear2. Infraneuclear3. Neuclear

Myogenic

DIFFERENCE INCOMITANT CONCOMITANT

Age Late earlyMagnitude of squint Varies with eye

positionSame in all gazes

Diplopia Present Usually absentOnset Sudden GradualPrecipitating event Head injury RareHead posture Present AbsentSecondary deviation >primary =primaryOcular movement Restricted FullFalse projection Present AbsentMechanism Defect in efferent

pathwayDefect in afferent pathOr central mechanism

Sensory adaptation Rare frequentCyclotropia Usually present Absent (expt A,V

patterns)

Clinical Evaluation:• History:H/O present illness-• Age of onset• Duration of the squint• Chief Complaints:• Symptoms-• Asthenopia:• Uniocular• Binocular• Onset:• Recent onset squint manifested with • Diplopia• Past pointing• Vertigo• Prostration

• Diplopia:• Diplopia may not be complained of in case of

adoption of head posture• Or,when sensory adaptation occurs.• Decompensation of pre existing heterophoria-

diplopia of intermittent onset.• Recent onset acquired squint-sudden onset

diplopia.• Type of diplopia-horizontal,cyclovertical• Direction of gaze in which it predominant• Whatever BSV is retained

Cosmetic defects:• Whether the defect is Intermittent or constant• Whether unilateral or alternating• Head Posture.Precipitating factor:like injury,illness,shock.Past medical history• Developmental history (children with cerebral palsy)• H/O glass- Regularity of use Power of the glass Proper cycloplegia for correction for his age.• Use of prisms/convergence exercise/occlusion• Surgery for squint One or both eye Which muscle How much What Sx.

Birth History• Antenatal history-drugs taken/illness during

pregnancy• Gestational age & birth weight at delivery• Type and length/problem during labour.Family history

EXAMINATION:A. Visual Acuity:a) In Preverbal Children-• Fixation and following

• Comparison between behavior of the two eyes.• Fixation Behavior• 10∆ test

• Rotation test

• Preferential looking

a) Teller Acuity cards

b) Cardiff Acuity cards

• VEP

b) Verbal children:• 2 years:picture naming (crowded Kay picture)

•

• 3 years:matching the letter optotypes (Keelaer logMar)

• B.Refraction• C.Examination of Anterior and Posterior chamber Lid problems,ptosis,media opacities

Pupillary reflexes

Fundus

D.Tests for stereopsis:1. Synoptophore2. TNO test:480-15 sec of arc3. Frisby:600-15 sec of arc4. Lang:200-1200 sec of arc

Test for fusion:Synoptophore

E.Examinations of the Motor status:1. Head posture:• To be noted when pt is unconcious about it.• Eye is out of the field of action.2. Ocular Deviation• By ordinary mm scale• Synoptophore

• What to see? Direction Frequency Magnitude Comitancy Laterality AC/A ratio

Ocular Alignment tests:A. Cover Tests:• Prerequisites:Ability to fixate the targetHave central fixationNo gross/severe mobility defects

a. Alternate Cover b. Cover uncover testc. Prism Bar Cover tests

a

b

• Cover Uncover test for tropia:

• Prism Bar Cover test

Corneal light reflex tests:A. Hirschberg test:

B. Krimsky test

• A pen-torch is shone into the eyes from arm’s length and the patient asked to fixate the light.

• The distance of the corneal light reflection from the centre of the pupil is noted; each mm of deviation is approximately equal to 7° (one degree ≈ 2 prism dioptres).

placement of prisms in front of the fixating eye until the corneal light reflections are symmetrical

Hirschberg test

No obvious squint Manifest squintCover test(either

eye)Cover test(fixing eye)

Other eye moves for fixation

No movement

Remove cover

Squint remains momentarily then aligned

Intermittent

Cover other eye

No movement Movement fellow eye

Uncover test

Cover eye straighten

No movement

Immediate: latent

Sometime:intermittent

Alternate cover

Latent/intermitent

No movement

Microtropia

Next slide

• Cover Test(fixing eye)

Other eye remain deviated1. Blind eye2. Eccentric fixation3. Immobile4. Pseudosquint

Other eye moves for fixation

Remove cover

Eye deviate again

Eye remain straight,other eye deviates

Manifest constant squint Manifest alternating squint

Pseudosquint:1. Epicanthic folds-

esotropia 2. Abnormal

interpupillary distance-

short:esotropia wide:exotropia 3. Angle kappa Positive:exotropia Negative:fovea is situated nasal to the posterior pole (high myopia and ectopic fovea):esotropia

Subjective test of deviation:A. Maddox wing test

• Maddox rod test:

• Maddox Double PrismUsed in case of cyclodeviation

• Two prism of 4pd• Pt looks at a horizontal

line (other eye ocluded)

two lines,parellal but shifted vertically from each other.

• Pt opens other eye (not have double prism)

Line in between above two lines.

Motility Tests:• Versions towards the eight eccentric positions of

gaze are tested by asking the patient to follow a target.

• A quick cover test is performed in each position of gaze to confirm whether a phoria has become a tropia or the angle has increased and the patient is questioned regarding diplopia.

• Ductions are assessed if reduced ocular motility is noted in either or both eyes.

• The fellow eye is occluded and the patient asked to follow the torch into various positions of gaze.

Grading:• Adduction:• Normal-if nasal 1.3rd of the

cornea crosses the lower punctum

• Abduction:• Normal-if temporal limbus

touches the lateral canthus.• Oblique overaction-• Angle of adducting eye makes

with horizontal line as it elevates,abducts on lateral version to opposite side.

Near point convergence:nearest point on which the Pt. can maintain binocular fixationNear Point of accomodation:nearest point on which the eyes can maintain clear focus

RAF Rule

Fusional Vergence:• It determines the capability of the motor system

to cope with an induced misalignment of visual axes.If it is large,even a large angle squint remains latent.

• They may be tested with prisms bars or the synoptophore.

• An increasingly strong prism is placed in front of one eye, which will then abduct or adduct (depending on whether the prism is base-in or base-out), in order to maintain bifoveal fixation. When a prism greater than the fusional amplitude is reached, diplopia is reported or one eye drifts the other way, indicating the limit of vergence ability.

F.Examination of Sensory status:A. Test for supression-a) Worth 4 dot test:• Four dots-NRC/HARC• Five Dots-Esodeviation-uncrossed (red on right)Exodeviation-crossed

(red on left)Vertical-vertically displaced• Three green Dots-Supression

of Rt.eye.• Two red dots-Supression of

left eye.

b. Bagalini’s striated glass test:

Symetrical cross-NRC or ARC of Harmonious type

Asymetrical Cross-incomitant squint with NRC

Single line-supression of the other eye

Cross with gap-central supression scotoma

• C.4∆ Prism test:

In bifoveal fixation

In Microtropia

• D.After Image Testing:Flash-horizontal-REVertical-LEResponse:1. Cross-

NRC(irrespective of deviation)

2. Asymmetrical crossing-ARC

• Amount of separation depends on angle of anomaly.

Tests for Paralytic squint:A. Past Pointing:

Measurement of Deviation:• Diplopia charting:• Image is

separated by red green glass.

• To quantify the separation between the double image

• Maximum separation-field of action of paralytic muscle

• Hess/Lees charting:

Forced duction Test:

• Anaesthesia• Supine position• Lids retracted• Pt is asked to look in the

direction of the muscle being tested (to relax antagonist)

• Eye is held in the limbus• Rotated in the direction of

action of the muscle Moves freely-negative Restricted-positive Push posteriorly-false +ve for

recti,desired for obliques.

Park’s Three steps test: (for 4th nv palsy)• 1.Assess which eye is hypertropic in primary

position.

2.Any increase in hypertropia in horizontal gaze

3.Bielschowsky Head tilt test:to see if any increase of hypertropia on tilting of head to any side