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Guidelines For Procedures

GUIDELINE FOR STRABISMUS ASSESSMENT

STRABISMUS ASSESSMENT

COVER TESTSCover tests help in establishing whether orthophoria or an ocular deviation is present,whether an ocular deviation is latent or manifest, the direction of deviation and the fixationbehavior.

Prerequisites

Patient should be co-operative enough to fixate

Should have sufficient vision to see the target

Should have Central fixation in both eyes

Latent nystagmus should not be present

Technique It should be performed with & without glasses at distance (6m) & at near (33cm). Patient isasked to fixate a 6/12 visual acuity symbol for distance & a toy or small picture for near withone eye while the other eye is covered with occluder.

Interpretations are made as follows:

Direct Cover test

It confirms the presence of a manifest squint

Patient is first asked to fixate on a point with both eyes open

Normal looking eye is covered while the movement of the uncovered eye isobserved

In the presence of manifest squint the uncovered eye will move in opposite directionto take fixation

No movement of uncovered eye indicates either no squint, or eccentric fixation or

no vision in deviated eye

Cover – uncover test

It establishes the presence & type of heterophorias (latent deviation)

One eye is covered with occluder & other is made to fixate an object

In presence of heterophorias, the eye under cover will deviate

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In presence of heterophorias, the eye under cover will deviate

After a few seconds the cover is quickly removed & the movement of the eye(whichwas under cover) is observed

Direction of the movement of the eyeball tells the type of heterophorias

Alternate cover test

Interrupts binocular fusion &reveals the total deviation (phoria+tropia)

The right eye is covered for about 2 seconds

The occluder is quickly shifted to the opposite for 2 sec, then back 7 forth severaltimes

After the cover is removed, the examiner notes the speed & smoothness of recoveryas the eye returns to their pre-dissociated state

A patient with a heterophorias will have straight eyes before & after the test hasbeen performed, whereas a patient with heterotopias will have manifest deviation

Prism Cover test

Precisely measures the angle of deviation

The alternate cover test is first performed

Prisms of increasing strength are place in front of one eye with base opposite thedirection of the deviation

The alternate cover test is continuously performed

As stronger prisms are brought in, the amplitude of ocular re-fixation movementsgradually decreases

The end – point is reached when ocular movements are negated; the angle ofdeviation then equals the strength of the prism

Diplopia charting

To diagnose paretic muscles

Equipment – red –green filter; streak light

Step –by- step procedure

Red filter in front of the right eye & green in front of left eye

The patient is asked to fixate the streak light with his paretic eye

The light is moved from primary position into all the other eight direction of gaze

For each direction the patient is asked to inform the examiner about the kind ofdiplopia he experiences & when the separation between the red & green light isgreatest (homonymous, heteronymous, or vertical diplopia.

The direction of greatest separation will identify the paretic muscles

Hess charting

The screen contains a tangent pattern printed onto a dark gray background

Red lights that can be individually illuminated indicate the position of the gaze ofeach of the extra ocular muscles

The patient is seated 50cm from the screen & wears red-green goggles, red in lensin front of the right eye, & holds a green laser pointer

The examiner projects a vertical slit of red light on to the screen from a red laserpointer, which is used as the point of fixation

The patient is asked to superimpose their horizontal slit of green light on to the redlight

In orthophoria the two lights should be more or less superimposed in all ninepositions of gaze

The goggles are then reversed & the procedure repeated

The relative position are connected with straight lines

Worth four-dot-test

The patient wears a red lens in front of the right eye, which filter out all colors

The patient wears a red lens in front of the right eye, which filter out all colorsexcept red

A green lens placed in front of left eye, which will filter out all colors except green

The patient then views a box with four lights; one red, two green & one white

Results

If all four are seen, normal fusion is present

If all four are seen in presence of 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 &green lights are seen, diplopia is present

If the green & red lights alternate, alternate suppression is present Synoptophore

This is an instrument for assessing strabismus & quantifying binocular vision

It can detect suppression &ARC

Procedure –

Free the optical tubes by releasing the central lock & the two tube locks, whichshould be turned inwards

Measure the IPD & set the pointer on the scale according, by means of the control

Adjust the height of the chin rest

Set all pointers at zero

Appropriate lenses into lens holder

Grades of binocular vision

First grade (Simultaneous perception) Tested by introducing 2 dissimilar but not mutually antagonistic picture, such as bird & cage The subject is asked to put the bird into the cage by altering the columns If the two pictures cannot be seen simultaneously, then either suppression or significantamblyopia is present

Second grade (fusion)It is the ability of the two eyes to produce a complete picture from two similar pictures eachof which is incomplete in one small different detail like two rabbits, one lacking a tail & theother lacking a bunch of flowers

Third grade (Stereopsis)It is the ability to obtain an impression of depth by the superimposition of two pictures ofthe same object which have been taken from slightly different angles like the bucket whichis appreciated in three dimensions

Force Duction Test

This test is done to differentiate between palsies & restrictions

Can be done under GA/LA

After proper anesthesia the globe should be grasped near the limbus with eitherplain forceps or Pierse forceps to avoid tearing of the conjunctiva

Preferably the globe should be held with the help of two forceps at right angle tothe axis in which restriction is to be tested

After grasping, the globe should be rotated passively towards the direction of actionof suspect weak muscle

FDT is labeled negative if no resistance is encountered during passive rotation. Itimplies paralysis of the muscle

Positive FDT is labeled if a resistance is encountered during passive rotation of theglobe. With a feeling of resistance if the examiner can rotate the globe no furtherthan the patient voluntarily can, the motility detect is purely due to mechanicalrestriction

restriction

Force generation test

Eyeball is stabilized with the forceps applied at the limbus under topical anesthesia& patient is asked to move his both eyes in the direction of the muscle to be tested

During this movement, the force generated by the contracting muscle of the eyebeing tested is transmitted through the forceps to the examiner’s fingers

From the feel of the transmitted for examiner can judge subjectively whether thecontracting muscle is weak or normal

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