MOTOR EVALUATION OF STRABISMUS

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Gauri Shankar shrestha, M.Optom, FIACLELecturerSameer Bhaila, B.optom II year

Contents

Introduction Detection of phoria and tropia

Position of the globes Observation of head position

Determination of presence of deviation Measurement of deviation

Objective methodsSubjective methods

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BINOCULAR VISION Vision achieved by co-ordinated use of both

eyes. The image which arise in each eye separately

are appreciated as a single mental impression Mainly three mechanisms

a) Sensory

b) Motor

c) Central

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Motor Mechanism Concerned with maintenance of two eyes in

correct positional relationship at rest and during movement.

Motor mechanism includes following factorsAnatomical or static factor

Structure of orbits and their contents

Physiological or dynamic factors

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Physiological factor

a) Postural reflex Movement of eyes co-ordinate during the movement of head relative to body or body relative to space.Independent of visual stimuli.

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b) Psycho-optical reflexDependent on visual stimuli.Fixation reflexRe-fixation reflexConjugate reflexDisjunctive or vergence fixation reflexCorrective fusional reflex

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c) Kinetic reflexMaintenance of two eyes in their correct relative positions within orbits as a result of a controlled accommodation convergence relationship.Accommodative convergenceConvergence induced accommodation

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HETEROTROPIA: A manifest strabismus

HORIZONTAL- esotropia or exotropiaVERTICAL- hypertropia or hypotropiaTORSIONAL- incyclo or excyclodeviationCombined horizontal, vertical and/or

torsional

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Concomitancy

Concomitant strabismusThe deviation does not vary in size with

direction of gaze or fixating eye Noncomitant strabismus

The deviation varies in size with direction of gaze or fixating eye

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Observation of head posture

Patient with comitant horizontal heterotropias have normal head position.

Head position in nystagmus Possibility of head to turn into null direction

Patient having high U/L amblyopia turn their head away from amblyopic eye

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Abnormal head positions common in connection with incomitant and paretic deviations

Purpose: relieve the paretic muscle sufficiently so that binocular single vision can be obtained.” -

Bielschowsky

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Observation of head posture

Abnormal head position take either the form of tipping the chin up or down, a face turn or a head tilt to one shoulder.

Patient with A and V pattern deviation tend to carry head with chin depressed or elevated.

Patient with right lateral rectus paresis turn face to right.

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Subjective Tests Diplopia test

Red Glass test Tangent screen Maddox Rod Maddox Wing Maddox double rod test

Haploscopic test Lancaster R-G test

Von Graefe method

Measurement of Deviation

Objective tests Prism and cover testMajor AmblyoscopeCorneal reflection

tests Hirschberg Method Krimsky’s Method

Ophthalmoscopy

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OBJECTIVE TESTS

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Determination of presence of deviation COVER TEST

Differentiates The deviation is latent or manifest The direction of deviation The fixation behavior Whether visual acuity is significantly

decreased in one eye

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Factors to be specified during a cover testFactor specified Choices

Type of deviation Phoria or Tropia

Frequency (if strabismic) Constant or Intermittent

Laterality (if constant strabismic)

Unilateral or Alternating

Magnitude In prism diopters

Direction Eso, Exo, Hypo, Encyclo, Excyclo or combination

Comitancy Comitant or Incomitant

Refractive correction In Diopters

Test distance In meters16

PRISM and COVER TEST

There will be no movement of the eyes

when the selected prism

causes the image to fall on the

fovea.

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Inaccuracy can be caused by

1. Inaccurate fixation due to blind eye2. Presence of eccentric fixation3. Inappropriate positioning of prism4. Effect of refractive correction

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MEASUREMENT with the MAJOR AMBLYOSCOPE

Consists of 1.Chinrest2.Forehead rest3.Two tubes carrying targets seen

through an angled eye-piece one for each eye

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SYNAPTOPHORE

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Use Artificially performs cover tests Measure subjective and objective angle of deviation Measures horizontal, vertical, oblique deviation Measures fusion ranges Measures the grades of BSV Measure ARC, Suppression, stereopsis, Horror

Fusionis, measure foveal scotoma Useful in visual training

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CORNEAL REFLECTION TESTS (Hirschberg Method)

Estimation/ measurement of the deviation by observing the first purkinje image

Especially preferred when:In young children, unable to maintain fixation for a

longer than a momentThe amount of deviation cannot be determined by

the prism and cover test or by any subjective tests.

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1mm of decentration of the corneal reflection =7° of deviation of the visual axis

Hirschberg

1 mm displacement ~7 or 15

Brodie 1987

1mm displacement~20-22 Hasebe at al 1998

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Krimsky’s method

Prism is used to change the position of the corneal reflection in the deviating eye.

Amount of prism needed to reposition corneal reflection in the deviating eye to the normal position

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OPHTHALMOSCOPY

Fovea – 0.3 dd below a horizontal line extending through the geometric center of optic disc.

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Excyclotortion Incyclotortion

SUBJECTIVE TESTS

Based on Diploscopic principleHaploscopic principle

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DIPLOSCOPIC TEST

Determination of the subjective localization of a single object point imaged on the fovea of the fixating eye and on extra-foveal retinal area in the other eye

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Red glass test Tangent screen Maddox rod

Maddox wing Double Maddox rod Bagolini Striated lenses

Red glass test

A red glass is placed in front of one eye. Pt fixates a small light source and states whether the

red light is to the right or to the left and above or below the white light.

If the white fixation light is in the center of the maddox cross, pt must state the numbers near which the red light is seen.

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Tangent screen test

A green Maddox rod is held before the pt’s right eye while the left eye views a scale of red trans-illuminated number.

The white light at the center of the scale produces the streak, while the red numbers and green colored rod eliminate the additional streaks

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Maddox rod

Consists of small glass rods (a series of plano-convex cylinders in red or white) causes an astigmatic elongation of the fixation light

Produce a vertical or horizontal streak to measure the horizontal and vertical deviation.

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Vertical rod to measure the vertical deviation

Maddox rod is oriented vertically in front of one eye and a measuring prism in other

Starting with 8 or 10 prism base up or base down prism the amount of prism power is gradually reduced until pt reports the horizontal streak goes through the spot

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Horizontal rod to measure lateral phoria

Uses horizontally oriented distance test chart having a spot light in center and numbers or letters extending on either side

Horizontally oriented Maddox rod is placed in front of one eye and the pt is asked to report the position of the vertical streak, the number letter or through the spot.

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H G F E D C B A 0 1 2 3 4 5 6 7 8

Maddox rod on RE

If light streak pass through numbers

Uncrossed diplopia- esophoria through letters

Crossed diplopia- exophoria

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H G F E D C B A 0 1 2 4 5 6 7 8

H G F E D C B A 0 1 2 4 5 6 7 8

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Maddox wing

For amount of heterophoria in near fixation (1/3m) 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.

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MADDOX WING

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Maddox double rod test

Quantitative determination of cyclodeviation Red and white maddox rods are placed in the trial

frame in front of each eye. Direction of glass rods is aligned with the 90° mark of

trial frame

A spot light is shown, for which the pt sees horizontal streaks.

If one line appears slanted toward the nose, excyclotropia is present.Maddox rod is turned until the red line is seen

parallel with the white line. E.g. toward the 100° mark of the right trial frame, 10° right exotropia is present

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Bagolini striated glasses

Produce an image of a streak of light, perpendicular to the axis of striations when viewing a spot light.Prism can be added to shift the streaks of light

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HAPLOSCOPIC TESTS

Two test objects rather than one are presented to the patient

Visual field of two eyes are differentiated and dissociated by presenting different target with major amblyoscopeEach eye with different color filter Polaroid projection

Lancaster test / R-G test

Uses a window shade type of screen (ruled into squares of 7cm) so that at distance of 2m each square subtends approx 2°

Pt wears red green reversible goggles 2 projectors are used Red with examiner Green patient Image formed by projector are linear and measured

In NRC, Separation of the streaks on the screen = deviation of the

visual axes

Titling of streak indicates presence of cyclotropia

Tilt of the retinal image is opposite to the tilt of the horizontal line as seen by the observer.

Von Graefe Method

The method of phoria measurement in which a dissociating prism is placed in front of one eye and a measuring prism in front of the other eye

The dissociating prism should be strong enough to cause diplopia

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A base down prism is placed in front of one eye causes the image on the retina to be displaced downward, below the macular area, so the object that formerly was seen straight ahead is then seen as being displaced upward

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Measuring lateral phoria

Target: vertical line of 20/20 letters A vertical prism of 7/8 pd is placed in front of one

eye A base in prism as the measuring prism in other eye Pt is asked to report when the two columns of letters

are on the same level. Prism power is reduced until the patient reports

alignment.

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Measuring vertical phoria

When dissociating for the vertical phoria measurement, base in prism is used

Eyes are able to make much larger fusional convergence movements than fusional divergence movements.

15pd BI in one eye and a measuring prism BU or BD in other eye

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Target: a horizontal row of 20/20 letters on the chart at 6m or 40cm.

Pt is asked to report when the two rows of letters are on the same level.

Prism power is reduced until the patient reports alignment.

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Hess Screen Test:

Hess chart of Left VI CN Palsy:

Contraction of left chart and expansion of rightLeft chart - marked underaction of lateral rectus and mild overaction of medial rectusRight chart - marked overaction of medial rectus

Diplopia Charting:

Diplopia Charting:…

References

1. Binocular vision and ocular motility- Gunrter K Von Noorden

2. Primary care optometry- Theodore Grossvenor

3. Clinical orthoptics-Fiona J. Rowe4. Clinical visual optics-Bennett & Rabbetts5. Internet

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Thank you...