Diagnostic Techniques for Strabismus Ramin Sahebghalam M D

Diagnostic Techniques for Strabismus Ramin Sahebghalam M. D Oculoplastic and Strabismus Fellowship 2011

Tests of Ocular Alignment

Tests of Ocular Alignment � Cover tests. � Corneal light reflex tests. � Dissimilar image tests. � Dissimilar target tests.

Cover Tests prerequisites � Eye movement capability. � Image formation and perception. � Foveal fixation in each eye. � Attention. � Cooperation.

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

Cover Uncover Test Prism and Cover Test

Cover-Uncover 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.

Alternate Cover Test Alternate Prism and Cover Test

Alternate Cover Test � The patient's right eye is covered while fixating a series of distant accommodative targets. � After 2 to 3 seconds, 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. �

Prism Under 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.

Light Reflex Tests � Hirschberg, � Krimsky and Modified Krimsky, � Bruckner, � Major amblyoscope.

Hirschberg Method 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

Krimsky 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 Test The Krimsky test is especially useful in: � Younger patients, � Patients unable to maintain concentration prolonged prism and alternate cover testing, � Patients with diminished central fixation or both eyes. for in one

Krimsky Method

Dissimilar Image Tests 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 Target 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.

Evaluation of Ocular Torsion � 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.

Evaluation of Ocular Torsion � Primary Etiology oblique muscle overaction (most common). � Secondary oblique muscle overaction ( most common : S. O paralysis). � Restrictive processes involving cyclovertical muscles: 1. Thyroid ophthalmopathy 2. Brown syndrome, 3. Blowout fracture 4. Local myotoxicity (retro or peribulbar injections) Ø Orbital displacement (plagiocephaly)

Plagiocephaly

Evaluation of Ocular Torsion � 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.

Measuring Objective Ocular Torsion � Fundus Photography (most accurate), � Blind spot mapping, � Indirect Ophthalmoscopy (easiest).

Measuring Objective Torsion Indirect Ophthalmoscopy Grading system for estimating abnormal torsion

Measuring Objective Ocular Torsion X

Measuring Subjective Torsion Double maddox rod test � Easily � Quick performed � Quantitative

Measuring Subjective Torsion Double maddox rod test

Measuring Subjective Torsion Lancaster red-green test � Provides a diagrammatic representation of horizontal, vertical and torsional strabismus in 9 diagnostic positions of gaze.

Measuring Subjective Torsion Lancaster 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.

Measuring subjective torsion Lancaster red-green test Method: � Test repeated in 9 diagnostic positions of gaze. � Examiner and the patient change flashlights and repeat the test.

Measuring subjective torsion Lancaster 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 Lancaster red-green test Recent onset V pattern ET , right hypertropia and subjective extorsion.

Measuring Subjective Torsion Lancaster red-green test Old V pattern ET & right hypertropia , no subjective torsion

Measuring Subjective Torsion Lancaster red-green test � 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 coveruncover test, then NRC is present. � If the two amounts are not equal, ARC is present � Superimposition of both targets on zero shows harmonious ARC.

Worth 4 Dot Test � 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 Monofixation syndrome 3° macular scotoma : � Far W 4 DT: no fusion @ 6 m � fusion begins @ 2. 5 m � Near W 4 DT: no fusion @ 2 m � fusion begins @ 0. 66 m �

Worth 4 Dot Test Strabismic patients who acquire deviation of 10Δ or more after having developed normal binocular vision reflexes � ET: � XT: When NRC: In both far and near tests: Homonymous diplopia (5 dots) Heteronymous diplopia (5 dots)

Worth 4 dot test Strabismic patients who acquire deviation of 10Δ or more after having developed normal binocular vision reflexes � Sees When ARC: 4 dots � Test must be done @ near � 5° suppression scotoma in ET (40 cm) � >5 ° suppression scotoma in XT

Special Motor Tests � � � Forced ductions, Active force generation, Saccadic velocity.

Exaggerated Traction Test forced duction for oblique muscles � 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.

One handed exaggerated traction test for the superior oblique muscle right eye N T E M P O R A L A S A L E F

Exaggerated Traction Test forced duction for oblique muscles Applications � 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.

Exaggerated Traction Test forced duction for oblique muscles 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.

Prism Testing for Prediction of Postoperative Diplopia � 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 Method 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.

Prism Testing for Prediction of Postoperative Diplopia � If Method 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?

Prism Testing for Prediction of Postoperative Diplopia what the patient my see: � 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):

Prism Testing for Prediction of Postoperative Diplopia � 9% of all adult patient with constant strabismus undergoing surgery will develop post op diplopia. � 0. 8% of such patients will develop constant diplopia.

Prism Testing for Prediction of Postoperative 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.

Predictive Values of the Test Temporary post-op diplopia Permanent post-op diplopia Sensitivity 100% Specificity 73% 67% Positive predictive value 28% 2% Negative predictive value 100%