COMITANT STRABISMUS

I. Introduction: This laboratory will introduce you to various techniques to asses sensory fusion abilities of patients with strabismus. We will use our friend Toby for this drill.

 

II. All About Toby:

Angle Determination: Toby is a 30Æ constant LEFT XT@ 7 meters and 40cm.

It appears from office visits, photographs and cover test that the strabismus is of early onset and unilateral.

Acuity Determination O.D.: 20/20

(BVA): O.S.: 20/30

Accommodation (DPU): O.D. 18D O.S.17 D

Accomm. Facility (+/-2.00) O.D. 15 c/m O.S. 14 c/m

 

What tests for ARC would become invalid if central fixation could not be ensured?

MOST AFFECTED: Hering Bielschowsky After-image test

- It turns out that Toby was just pulling your leg; he is really 20/20 in either eye.....BAD TOBY...BAD!!!

 

III. Sensory Fusion Tests For Toby

 

A. Bagolini Striated Lens test: As you follow the procedure for using the Bagolini striated lens test (attached), please consider the following about Toby.

1. Assume Toby has NRC, demonstrate how he may respond with this test

-Where would the light be in relation to the crossing streaks?

LIGHT WOULD BE BELOW THE CROSSING

-How much prism would be required to get a "perfect X"?

30 PRISM DIOPTERS BI

2. What would happen if Toby suppressed his left eye? Draw what it would look like.

- Parafoveal suppression?

- Large suppression zone?

 

3. Is the depth of the supression zone related to the size of the angle? NOPE!

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    4. Assume Toby has harmonious ARC, how he may respond now?

    -Where would the light be in relation to the crossing streaks?

    A "PERFECT CROSS" IN SPITE OF AN H=30 XT’

    -How much prism would be required to get a "perfect X"?

    ZERO!!….TRICK QUESTION!

    5. Assume Toby has typical unharmonious ARC, demonstrate how he may respond now?

    -Where would the light be in relation to the crossing streaks?

    THE CROSSING WOULD BE ABOVE THE LIGHT(S)

    -How much prism would be required to get a "perfect X"?

  • SINCE uARC HAS AN ANGLE OF ANOMALY (A) BETWEEN ZERO AND THE OBJECTIVE ANGLE (H), THE SUBJECTIVE ANGLE (S) MUST BE BETWEEN ZERO AND 30 PRISM DIOPTERS BI. BEST BET: 15-20 BI
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    6. Why is it important to test at various distances?

  • MANY CASES OF STRABISMUS MAY BE WORSE AT ONE PARTICULAR VIEWING DISTANCE OVER ANOTHER. FOR EXAMPLE: A DIVERGENCE EXCESS EXOTROPIA MAY HAVE NORMAL FUSION AT NEAR, BUT A 40 PRISM DIOPTER XT @ DISTANCE WITH RATHER DEEP hARC.
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    B. 4 Base Out Test: As you follow the procedure for using the 4 BO Test (attached), please consider the following about Toby.

     

    create your own Toby style supression zone by placing a polarized filter over O.S.

    1. What would be your expected result as the prism is placed over the RIGHT eye?

  • FOR TOBY: VERSION TO LEFT; NO CONVERGENCE
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    2. What would be your expected result as the prism is placed over the LEFT eye?

    FOR TOBY; NO MOVEMENT

     

    C. The Synoptophore: As you follow the procedure for using the synoptophore (attached), please consider the following about Toby.

     

    1. Assume Toby has NRC, demonstrate how he may respond with this test

    H = 30; S = 30; A = ZERO

    2. What would happen if Toby suppressed his left eye with a small superimposition target? What would you try to allow him to conquer suppression?

    1. lower illumination of dominant right eye

    2. raise illumination of non-dominant left eye

    3. flicker non-dominant left eye

    4. yell at patient!

     

    3. Assume Toby has harmonious ARC, how he may respond now

    H = 30; S = ZERO; A = 30

     

    4. Assume Toby has typical unharmonious ARC, how he may respond now

    H = 30; S = *15; A = *15

    *ANY VALUE BETWEEN 5 AND 25 IS O.K.

    D. Worth Four Dot Test: (red lens: O.D.) As you follow the procedure for using the Worth 4 Dot Test (attached), please consider the following about Toby.

     

    1. Assume Toby has NRC, demonstrate how he may respond with this test

    TOBY MAY:

    -SEE TWO RED LIGHTS

    -SEE 3 GREEN AND 2 RED LIGHTS

    2. What would happen if Toby suppressed his left eye? SEES TWO RED LIGHTS His right eye? ? SEES THREE GREEN LIGHTS 

    3. Assume Toby has harmonious ARC, how he may respond now?

    TOBY MAY:

    -SEE ONE RED LIGHT/TWO GREEN LIGHTS/ SPLIT TOP LIGHT BETWEEN RED AND GREEN

    -*SEE 2 RED LIGHTS

    * IF SUPPRESSION IS DEEP ENOUGH

    E. Hess-Lancaster Screen: As you follow the procedure for using the Hess- Lancaster test (attached), please consider the following about Toby. Assume the red lens is over O.D. and that Toby controls the green spot. You (the doctor) place the red spot on the "zero" (primary position)

    1. Assume Toby has NRC, demonstrate how he may respond with this test. He is a 30D exotrope.

    -He would place the green target to the (left / superimpose / right) of where you place the red target when attempting to superimpose

    -What would happen if Toby controlled the red light?

  • when attempting to superimpose, he would place the red target to the right of where you place the green target
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    2. Assume Toby has hARC, demonstrate how he may respond with this test.

    -He would place the green target to the (left / superimpose / right) of where you place the red target when attempting to superimpose

    -What would happen if Toby controlled the red light?

     

    TOBY WOULD superimpose

     

    E. Hering - Bielschowsky After Image Test: Instill an afterimage to each eye of your partner as described in this handout.

    1. Assume Toby has NRC, demonstrate how he may respond with this test

    PERFECT CROSS…NO MATTER THE SIZE OR DIRECTION OF STRABISMUS

    2. What would happen if Toby suppressed his left eye on this test? What would this say about the depth of suppression?

  • Horizontal (or whichever orientation presented OS) would be partially or completely suppressed. IT WOULD BE EXTREMELY DEEP SUPPRESSION OS
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    3. Assume Toby has harmonious ARC, how he may respond now?

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  • OD after-image (Vertical) would be shifted to the right (uncrossed). The separation would be equal to the magnitude of the strabismus @ that viewing distance. Assuming a 30D XT:

    @50cm separation = 15 cm

    @ 1 meter separation = 30 cm

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    4. What would the above result say about the depth of ARC?

    EXTREMELY DEEP

    5. Assume Toby has typical unharmonious ARC, how he may respond now?

  • OD after-image (Vertical) would be shifted to the right (uncrossed). The separation would be between a perfect cross (0; NRC) and H @ that viewing distance. Assuming a 30D XT:

    @50cm separation: > 0 < 15 cm

    @1 meter separation: > 0 < 30 cm

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