diag tests for strabismus 1390 2011

Diagnostic Techniques forStrabismus

Ramin Sahebghalam M.DOculoplastic and Strabismus Fellowship

2011

Tests of Ocular Alignment

Cover tests. Corneal light reflex

tests. Dissimilar image tests. Dissimilar target tests.

Tests of Ocular Alignment

Eye movement capability. Image formation and perception. Foveal fixation in each eye. Attention. Cooperation.

Cover Testsprerequisites

Cover-uncover test, Alternate cover test, Prism and cover test. Prism and cover–uncover test, Prism under cover test.

Cover Tests

Cover Uncover TestPrism and Cover Test

An absence of movement of an eye when the other eye is covered occurring in both eyes, means that the patient does not have a heterotropia

It does not differentiate between orthophoria and heterophoria.

Cover-Uncover Test

Alternate Cover TestAlternate Prism and Cover Test

The patient's right eye is covered while fixating a series of distant accommodative targets.

After 2 to 3seconds, the right eye is uncovered , cover rapidly is moved to the other side and left eye is covered.

The patient whose eye moves on alternate cover has either a heterophoria or heterotropia.

Differentiation between the two requires the cover–uncover test.

Alternate Cover Test

A temporal horizontal shift is esophoria or esotropia,

A nasal shift is exophoria or exotropia, The movement of the eye downward is

hyperphoria or hypertropia . If both eyes make movements downward, it

is called dissociated vertical deviation.

Alternate Cover test

Is used to measure the size of DVD, Base down prism is place on the eye, Cover is place in front of prism, Prism power is increased until no movement

of the eye can be seen after removing the cover.

Prism Under Cover Test

Hirschberg, Krimsky and Modified Krimsky, Bruckner, Major amblyoscope.

Light Reflex Tests

A light reflected in the deviated eye:

Nearer the pupillary center than the margin: 5°,

At pupillary margin : 15°, Midway between pupillary margin and

limbus it is 25°, At the limbus it is 45° to 60°, and beyond

the limbus it is 60° to 80°.

Hirschberg Method

Each 1-mm deviation of light reflex represents 7° or 15 Δ of deviation.

Brodie’s rule: 1 mm=21 Δ (using flash photographs with millimeter rulers included for standardization, Brodie estimated a Hirschberg ratio of 21 prism diopters/mm, this angle correlates highly with that derived from alternate prism and cover testing).

Hirschberg Method

Hirschberg Method

Traditional: center the displaced light reflex by putting appropriate prism over deviated eye.

Modified: hold the prism over fixating eye (easier to read).

Krimsky Method

The Krimsky test is especially useful in: Younger patients, Patients unable to maintain concentration for

prolonged prism and alternate cover testing, Patients with diminished central fixation in

one or both eyes.

Krimsky Test

Krimsky Method

Dissimilar image tests are based on the patient's response to diplopia created by 2 dissimilar images.

Maddox rod test, Double Maddox rod test, Red glass test.

Dissimilar Image Tests

Are based on the patient's response to the dissimilar images created by each eye viewing a different target; the deviation is measured first with one eye fixating and then with the other.

Lancaster red-green projection test, Hess screen test, Major amblyoscope test.

Dissimilar Target Tests

Torsional strabismus occurs when the eye is abnormally rotated about the visual axis.

Malfunction of the vertical rectus and oblique muscles is responsible.

Evaluation of torsion is mandatory in vertical strabismus, whether or not the patient complains of torsional diplopia.

Evaluation of Ocular Torsion

Evaluation of torsion is not possible with external landmarks.

While the actual axis of rotation is close to visual axis, it is easier for most examiners to visualize the fovea moving relative to the optic nerve.


Primary oblique muscle overaction (most common).

Secondary oblique muscle overaction ( most common :S.O paralysis).

Restrictive processes involving cyclovertical muscles:

1. Thyroid ophthalmopathy2. Brown syndrome,3. Blowout fracture4. Local myotoxicity (retro or peribulbar injections) Orbital displacement (plagiocephaly)

Evaluation of Ocular TorsionEtiology

Plagiocephaly

Anatomic (objective) torsion refers to anatomic rotation of eye.

Subjective torsion refers to the patient’s perception of rotation.

Comparison of anatomic and subjective torsion can help determine the time of onset of cyclovertical strabismus.


Fundus Photography (most accurate), Blind spot mapping, Indirect Ophthalmoscopy (easiest).

Measuring Objective Ocular Torsion

Measuring Objective TorsionIndirect Ophthalmoscopy

Grading system for estimating abnormal torsion

Measuring Objective Ocular Torsion

X

Easily performed Quick Quantitative

Measuring Subjective TorsionDouble maddox rod test

Measuring Subjective TorsionDouble maddox rod test

Provides a diagrammatic representation of horizontal, vertical and torsional strabismus in 9 diagnostic positions of gaze.

Measuring Subjective TorsionLancaster red-green test

Measuring Subjective Torsion Lancaster red-green test

Method: Patient is seated 1 meter from screen with

head straight, wearing anaglyphic goggles. Room darkened. Examiner projects the red streak obliquely

on the center of scale ( primary position).

Measuring Subjective Torsion

Lancaster red-green test

Method: The streak is rotated upon patients

command to be seen vertical. The patient is asked to place the green

streak in the same place as the red streak. The actual location of projected streaks is

manually recorded.



Method: Test repeated in 9 diagnostic positions of

gaze. Examiner and the patient change

flashlights and repeat the test.

Measuring subjective torsionLancaster red-green test

Interpretation: The Lancaster red-green test is interpreted as

if the two streaks are direct projections from the foveas:

Left side of the plot indicates the left gaze and the right , right gaze.

If the red streak is rotated clockwise, the right eye is extorted, if the red streak is upper, the right eye is upper. If the red streak is on the right, there is exotropia and vice versa.

Measuring subjective torsion




Recent onset V pattern ET , right hypertropia and subjective extorsion.



Old V pattern ET & right hypertropia ,no subjective torsion

The examiner can read the amount of subjective deviation directly from the screen.

If this degree is equal to formerly measured objective deviation (measured in cover-uncover test, then NRC is present.

If the two amounts are not equal, ARC is present

Superimposition of both targets on zero shows harmonious ARC.



Possible in children who can count to five. If the visual acuity can be determined, so

can the Worth 4 dot response. The test is performed with ordinary room

illumination to provide the usual peripheral vision clues.

Results should be reported as suppression or fusion.

Best at detection of suppression.

Worth 4 Dot Test

Distant Worth 4 dot test. Near Worth 4 dot test.

Worth 4 Dot Test

3° macular scotoma : Far W4DT: no fusion @ 6 m fusion begins @ 2.5 m Near W4DT: no fusion @ 2m fusion begins @ 0.66 m

Worth 4 Dot TestMonofixation syndrome

When NRC: In both far and near tests: ET: Homonymous diplopia (5 dots) XT: Heteronymous diplopia (5 dots)

Worth 4 Dot Test Strabismic patients who acquire deviation of 10Δ or more after having developed normal binocular vision reflexes

When ARC: Sees 4 dots Test must be done @ near

5° suppression scotoma in ET (40 cm) >5 ° suppression scotoma in XT

Worth 4 dot test Strabismic patients who acquire deviation of 10Δ or more after having developed normal binocular vision reflexes

Forced ductions, Active force generation, Saccadic velocity.

Special Motor Tests

This test places obilque muscles on maximum stretch by simultaneously retroplacing, torting and rotating the globe.

Forced duction of rectus muscle are best done by pulling the eye forward to put these muscles on maximum stretch.

Exaggerated Traction Testforced duction for oblique muscles

One handed exaggerated traction test for the superior oblique muscle right eye

EF

NASAL

TEMPORAL

Intraoperative assessment of completeness of an oblique muscle weakening procedure is the most useful application of this test.

The test must be done before and after oblique tenotomy and disinsertion.

The test can confirm the diagnosis of oblique muscle overaction.


Applications

Deciding over tuck or recess in SO paresis. Differentiation of IO paresis and Brown. The test helps differentiate hyperdeviation

causes: inferior oblique overaction, DVD, rectus contracture.


Applications

Is investigated in adult patients with constant starabismus.( a study on 424 patients by Kushner B.J, Archive of Ophthalmo,vol 120, Nov 2002)

Prism Testing for Prediction of Postoperative Diplopia

Patient wears appropriate correction. Patent fixes to an accommodative Snellen

optotype near to his vision threshold in better eye.

Neutralize the deviation by placing prisms over the deviating eye and ask the patient if he sees double.

Then remove the first prism and introduce increasing rotary or bar prisms, begin with 0 and overcorrect the deviation by 5 to 10 .


Method

If the patient sees double in any of the former stages, then he/she is asked about type of diplopia:

Cross or uncross ? Sharp, or shadowy ghost images? What is the distance between the two

images?


Method

Does not see double in any test :no risk. A shadowy ghost image in far periphery :

(ARC):very low risk of temporary or constant post- op diplopia.

Intense and close together:a little risk. Unable to subjectively localize the second

image (lost or confused localization):


what the patient my see:

9% of all adult patient with constant strabismus undergoing surgery will develop post op diplopia.

0.8% of such patients will develop constant diplopia.


28% of patients with positive pre-op prism test will develop temporary post op diplopia.

2% of such patients will develop permanent post-op diplopia.


Temporary post-op diplopia

Permanent post-op diplopia

Sensitivity 100% 100%

Specificity 73% 67%

Positive predictive value

28% 2%

Negative predictive value

100% 100%

Predictive Values of the Test

diag tests for strabismus 1390 2011

Documents