Anuraag Singh

Strabismus- misalignment of the visual axis.

Visual axis - line of vision extending from the point of fixation to the fovea

Anatomical axis - is a line passing from the posterior pole through the centre of the cornea .

Orthophoria -perfect alignment of the visual axes

It is the angle formed between visual axis and the anatomical axis

As the fovea lies just temporal to the anatomical axis, a light shown into the cornea will cause reflex (on the visual axis) just nasal to the center of the cornea in both eyes (+ve angle kappa = 5°).

In high myopia the, the fovea lies nasal to the optical axis. So, the corneal reflex lies temporal to the center of the cornea simulating esotropia.

Negative angle kappa (myopia) leads to pseudo-esotropia.

Large positive angle kappa (hypermetropia) leads to pseudo-exotropia.

Heterophoria - (latent squint) tendency of the eyes to deviate. Ocular alignment maintained with effort.

Heterotropia - (manifest squint) which is present at all times

Esophoria- latent squint inwards turning of the eyes

Esotropia- manifest squint inwards turning of the eyes

Exophoria- latent squint outwards turning of the eyes

Exotropia- manifest squint outwards turning of the eyes

Hyperphoria/hypertropia- latent/manifest squint upwards turning of eyes

Hypophoria/hypertropia- latent/manifest squint downwards turning of eyes

Horizontal muscles :-

Medial rectus- Its sole action in the primary position is adduction.

- occulomotor nerve supply

Lateral rectus- Its sole action in the primary position is abduction

-abducens nerve supply

Vertical muscles

Superior rectus- Primary action elevation (secondary actions are adduction and intorsion.

- Oculomotor nerve supply

Inferior rectus - The primary action is depression ; secondary actions are adduction and extortion.

- Oculomotor nerve supply

Superior oblique - The primary action is intorsion

- secondary actions are depression and

abduction.

- oculomotor nerve supply

Inferior oblique - The primary action is extorsion

- secondary action are elevation and abduction .

- oculomotor nerve supply

Listing plane is an imaginary coronal plane passing through the centre of rotation of the globe. The globe rotates on the X,Y and Z axes of Fick which intersect in Listing plane .

The globe rotates left and right on the vertical Z axis.

The globe moves up and down on the horizontal X axis.

Torsional movements (wheel rotations) occur on the Y (sagittal ) axis which traverses the globe form front to back (similar to the anatomical axis of the eye )

Intorsion occurs when the superior limbus rotates nasally and extorsion on temporal rotation .

Ductions

Monocular movements around the axes of Fick.

They consist of adduction, abduction elevation, depression, intorsion and extorsion .

They are tested by occluding the fellow eye and asking the patient to follow a target in each direction of gaze.

Versions

Binocular, simultaneous, conjugate movements

( in the same directon ) .

VERGENCES

Vergences are binocular, simultaneous disconjugate or disjunctive movements.

Convergence is simultaneous adduction.

Divergence is outwards movement from a convergent position.

Positions of gaze:-

Six Cardinal positions of gaze are those in which one muscle in each eye has to move the eye into that position as follows:

Dextroversion

Levoversion

Dextroelevation

Levoelevation

Dextrodepression

Levodepression

Nine Diagnostic position of gaze are those in which deviations are measured. They consists of the six cardinal postions ,the primary position, elevation and depression .

Antagonist - muscles of the same eye moving the eye in opposite direction (medial and lateral rectus)

Synergists- muscles of the same eye moving it in the same direction (superior rectus and inferior oblique causing elevation)

Yoke muscles- muscles of both eyes moving the eyes in same direction; medial rectus of both eyes

Sherrington’s law- increase in innervation to one muscle causes decreased innervation to its antagonist (medial and lateral rectus)

Hering’s law- equal innervation flows to yoke muscles in eye movement ( medial rectus of both eyes)

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?

Is there a history of toxin or medication exposure?

1.Objective methods

2.Subjective methods

1.Objective methods:-

Hirschberg corneal reflex test

Krimsky’s test

Bruckner test

Cover uncover test

Alternate cover test

Prism bar cover test

Synoptophore

2.Subjective methods:-

Maddox rod test

Maddox wing test

Maddox tangent

Double maddox rod

Maddox double prism

Hess screen

Red green glass test

Diplopia field

Used as initial screening test for strabismus.

Amount of deviation: note location of corneal light reflex 1 mm = 7° or 15Δ

Corneal reflex at border Corneal reflex at limbusof pupil = 15° = 45°

This test is used to centralize the corneal reflection in squinting eye as compared to the reflex in fixing eye.

Results are expressed in prism diopter (PD).

Convenient test for quick evaluation of the angle of strabismus, especially in the abnormal fixation of the squint eye.

Performed by using direct ophthalmoscope to obtain a red reflex simultaneously in both eyes.

Deviated eye will have a lighter and brighter reflex than the fixing eye.

Bruckner test positive for left eye esotropia

1.Cover test:-

To detect a heterotropia

Procedure:-

1.The patient fixates a straight ahead target

2.If a right deviation is suspected , the examiner covers the fixing left eye

Note any movement of the right eye to take up fixation

No movement indicates orthotropia

Adduction of right eye indicates right exotropria

Abduction of right eye indicates right esotropia

Down movement indicate right hypertropia

Upward movement indicate right hypotropia

Test is repeated on opposite eye

Detects heterophoria

Procedure:-

Patient fixates a straight ahead distant target

Examiner covers the right eye and after 2-3 seconds removes the cover

No movement indicates orthophoria

If the right eye had deviated while under cover ,a re-fixation movement is observed on being unconvered.

Aduction ( nasal recovery) of right eye indicates exophoria and abduction ( temporal recovery ) indicates esophoria.

Upward or downward movement indicates a vertical phoria.

The test is repeated for the opposite eye

Dissociation test

Reveals total deviation when fusion is suspended

Procedure:-

Right eye is covered for several seconds

Occluder is quickly shifted to opposite eye for 2 seconds ,then back and forth several times

Note the recovery as the eyes return to their pre-dissociated state

A patient with well compensated heterophoriawill have straight eyes before and after the test.

A patient with poor control may decompensate to a manifest deviation

The prism cover test measures the angle of deviation

It combines alternate cover test with prisms

Procedure:-

The alternate cover test is performed first

Prism of increasing strength placed in front of one eye with base opposite the direction of deviation

Alternate cover test is performed continously as stronger prisms are used

Amplitude of refixation gradually decreases

End point reached when no movement is seen

To ensure maximum angle is found , prism strength is increased until movement is observed in opposite direction

Then reduced again to find neutral value

Angle of deviation equals the strength of the prism

A translucent occluder is used.

Covering both eyes with translucent occluderspermits a quick preliminary determination of whether an esotropia is of refractive –accommodative or non-accommodative origin.

Consists of

Chinrest

Forehead rest

Two cylindrical tubes with mirrored right angled bend and +6.50 D lens in each eyepiece.

This optically sets the testing distance as equivalent to 6 m.

Tubes are placed horizontally and supported by a column

Distance between the tubes can be adjusted -correspond accurately to the pt’s IPD.

The axis of tube is in line with the center of rotation of the eyes.

Adjustments for vertical separation of targets and cyclorotational adjustments

Illumination system

Increase or decrease stimulus luminance

Deviation is measured by moving the arms of the synaptophore into the position that images of the target fall on the respective foveal areas.

Horizontal deviations are compensated for by moving the synaptophore arms, vertical deviations by elevating or depressing the synaptophorepictures.

It can measure horizontal,vertical and torsional misalignments simultaneously.

It can be used for grading the binocular vision

1.First grade ( Simultaneous perception )

Tested by introducing two dissimilar but not mutually anatagonistic pictures , such as lion and a cage.

2.Second grade ( fusion )

Ability of two eyes to produce a composite picture from two similar images, each of which is incomplete in one small different detail

3.Third Grade ( stereopsis )

Ability to obtain an impression of depth

Superimposition of two pictures of same object taken from slightly different angles

It is based on the principle of dissociation

Maddox Rod consists of a series of planocylinder lenses about 3 mm in diameter, mounted in a trial frame lens.

A spot of light viewed through the Maddox Rod appears as an elongated streak.

The Maddox Rod is often colored usually red.

Used to find out presence of heterophoria or heterotropia

Easy for patient to understand

Easy to administer

Very useful for vertical deviations.

Reduce room illumination.

Maddox Rod is placed in front of one eye

Measuring horizontal deviations maddox Rod axes are placed horizontal which produces vertical streak

Measuring vertical deviations maddox Rod axes are placed vertical which produces horizontal streak

Patient initially views with both eyes open

Maddox Rod is placed horizontally (vertical streak) in front of right eye

With strabismics, the Maddox Rod is best placed over the fixating eye

Ensure that patient can see white light and streak simultaneously

Ask if the streak is to the right or to the left of the light

Same procedure is followed except maddox rod is placed with its axes vertically producing horizontal streak of light

If the horizontal streak of light is above the fixation light it indicates presence of hypo deviation

If the horizontal streak of light is below the fixation light it indicates presence of hyper deviation

It is based on the principle of dissociation

Instead of maddox rod a red glass is used

Tangent scale is used

Procedue

1.Patient is asked to fix the white light

2.Through the red glass light looks like a red spot

3.In orthophorics red spot overlaps white light

4.In deviation red spot can be either on left or right of white light.

For amount of heterophoria in near fixation

A vertical arrow is presented to one eye and a horizontal tangent scale to the other to give the measurement of the horizontal phoria .

A horizontal arrow and vertical scale are used to measure the vertical imbalance.

Scales are mounted at the fixed viewing distance of 1/3m.

Quantitative determination of cyclodeviation

Red and white maddox rods are placed in the trial frame. Red before RE and white before LE.

Direction of glass rods is aligned with the 90° mark of trial frame

Screen contains a tangent pattern ( 2D projection of a spherical surface ) printed on dark grey background.

Red lights ( can be individually illuminated ) indicate the cardinal positions of gaze

Each square represents 50 of ocular rotation.

Procedure :-

1.Patient seated 50cm from screen wearing red-green goggles ( red in front of right ) and holds a green pointer.

2.Examiner illuminates each point in turn which is used as point of fixation.seen only with right eye ( becomes fixating eye )

3.Patient asked to superimpose their green light on red light , so plotting the relative position of left eye.all points are plotted.

4.The goggles are then reversed and procedure repeated.

5.The relative positions are marked by the examiner on a Hess chart and connected with straight lines.

In orthophoria two lights more or less superimpose in all nine positions of gaze.

Suppression is an acquired cerebral function used by the patient to avoid confusion and diplopia.

Patient may not be aware of suppression

Suppression scotoma is present in tropias. It prevents diplopia.

Tests for suppression :-

1.Worth four dot test

2.Prism 4 PD base out test

3.Red glass test

4.Synoptophore

It consists:-

Self illuminating panel of

1.Two green

2.One red

3.One white

Generally done at 6m

Patient wears a red green glass :; red in front of right eye.

When the patient looks through green glass the patient can see only green spots and white spot looks light green.

While looking through red glass he can only see the red spot and white spot looks pink.

When a normal patient looks with both eyes open, he sees two green, one red and one mixture of red and green.

In case of left supression ,the patient will see two red lights.

In case of right supression ;sees three green lights.

If the patient sees five lights in presence of ocular deviation, patient has diplopia and normal retinal correspondence.

A patient with deviation and normal vision should experience diplopia unless he is ignorig or suppressing it.

Procedure:-

Patient fixes a white light

A red glass put in front of deviated eye

Patient become aware of second image as a red light

If there is deep suppression only white light will be visible

Special slides used to detect suppression

Depth of suppression can be measured by altering the illumination of the slides.

Normal retinal correspondence :- when anatomically corresponding areas of two eyes correspond to each other.

In abnormal retinal correspondence :- an extra foveal area of squinting eye and fovea of fixing eye have a common visual direction.

It’s a crude method of retaining binocular vision in squint.

More developed in microtropia

1.Bagolini striated glasses

2.Worth four dot test

3.After image test

4.Synoptophore

Bagolini striated glasses:-

Bagolini glasses – plane

- on one surface multiple parallel

lines etched

Procedure:-

Glasses mounted o trialframe

Done at 33cm or 6m

Spot of white light seen

Both eyes are kept open

Lens in right eye set at 45o axis

Lens in left eye set at 135o axis

Patient sees only one slanting line – other is suppressed

Lines cross each other (perfect cross), eyes are straight and have central fixation - NRC

Deviation + perfect X - ARC

Shining vertical light thrown on fovea of right eye

Similar (intensity and size ) horizontal light thrown on fovea of left eye

Light thrown for 20 seconds

Patient looks at fixation point

Interpretation:-

1.Perfect cross with central gap – central fixation with NRC

2.Vertical after image shifted to right – ARC with right exotropia with central fixation

3.Vertical after image shifted to left – ARC with right esotropia with central fixation

1.Uniocular or binocular Uniocular diplopia disappear on closing affected

eye Binocular diplopia disappear on closing either eye

2.False and true images False image – formed in deviated eye at a point

other than the macula.- blurred as compared to true image- may be separated from true image- distance may vary at different

positions of gaze and head- may be tilted-

Crossed diplopia – false image projected across the midline

False image formed in direction opposite to displacement.

Seen in Paralysis of adductors- MR,SR,IR

Uncrossed diplopia – false image do not cross midline

Seen in paralysis of abductors- LR,SO,IO

Qualitative tests for Stereopsis:

Lang’s 2 pencil test

Synoptophore

Quantitative tests for Stereopsis:

Random Dot test

Titmus Fly Test

TNO Test

Lang’s Stereo Test

TNO random dot test consist of seven plates of randomly paired red and green dots which are viewed with red-green spectacles.

Within each plate the dots of one colour forming the target shape are displaced horizontally in relation to their paired dots of other colour.

Frisby stereotest consist of three transparent plastic plates of varying thickness.

On the surface of ach plate are printed four squares of small randomly distributed shapes

One of the squares contains a hidden circle,inwhich the shapes are printed on the reverse of the plate.

Lang stereo test doesn’t require special spectacles

Targets are seen alternately by each eye through the built in cylindrical lens

Displacement of the dots creates disparity

Can often be used in very young children who may reach out to touch the pictures.

Titmus test consist of 3D polaroid vectograph

Two plates in form of booklet viewed through Polaroid spectacles

On the right is a Large fly

On the left is a series of circles an animals

1.Fly is a test of gross stereopsis, useful for young children

Fly should appear stand out from the page ,child is encouraged to pick up the tip of one of its wings between finger and thumb.

In absence of gross stereopsis fly will appear as ordinary flat photograph.

In book is inverted the targets will appear to be behind the plane of the page

2.Circles comprise a graded series which tests fine depth perception.

Each of the nine squares contains four circles

One of the circle in each square has a degree of diparity and will appear forward of the plane in presence of normal stereopsis

3.The Animals consist of three rows of animals , one of which appear forward of the plane of refrence.