AMBLYOPIA

I. Introduction: This laboratory will introduce you to various amblyopia diagnostic and therapeutic approaches, including various anti-suppression therapy techniques.

 

II. Acuity Determination: Find a partner and try the Flom Psychometric Series. See Lab Guide for specifics.

Now, lets turn our attention to Toby, a nine year old patient who is in your office and has a Hx of "lazy eye". O.D. acuities were 20/20 (uncorrected). Responses were rapid and confident. O.S. acuities were very difficult to obtain. Toby would repeat letters, reverse sequence and miss several letters on at least three lines of acuity. Final acuity levels were estimated at 20/70 &emdash;1 O.S.

 

1. What characteristics is Toby demonstrating that are consistent with amblyopia O.S.?

  • Toby demonstrated Crowding Effects, gradual slope to threshold acuity
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    2. Organize the following acuity tests in order of difficulty for Toby (from least difficult to most difficult)

  • - 5 whole Snellen chart - 1 electrodiagnostics (VER)

    - 6 Flom psychometric series - 2 sine wave grating

    - 3 Snellen chart/single letter - 4 Snellen chart/single line

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    III. Fixation status:

    A. Try the visuoscope ("Euthyscope"). Watch it, the unit does get HOT! Once again, follow the directions provided in the lab handout 8.1. Judge whether fixation is central or eccentric; steady or unsteady.

  • For Toby: you consistently find the foveal light reflex to the right of the center of the "bulls eye" on O.S. On the Euthyscope, displacement of the foveal light reflex is 6 circles. O.D. has steady central fixation. Toby foveates the target, then saccades to the eccentric position.
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    3. What is the direction and magnitude of eccentric fixation O.S?

  • 6D nasal steady eccentric fixation with initial foveation
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    4. What acuity would you predict from the magnitude of the eccentric fixation, O.S.?

  • 20/60
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    5. Would you expect this patient to have a strabismus? Why or why not?

  • YES! Most cases of eccentric fixation occur in strabismic amblyopes
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    6. Why is it important to describe the consistency of the eccentric fixation? What does the observation that Toby initially foveated the bulls eye before moving to an eccentric location mean to your prognosis?

    Without initial foveation of the bulls eye, it would indicate a very embedded eccentric fixation pattern. Poor prognosis 

    B. Now try the Haidinger Brush (entopic phenomenon) using our Handy Dandy MITT (monocular integrity tester and trainer) unit. Make sure the patient perceives the rotating "propeller" by having him/her move away and towards the MITT machine. What happens to the brush as your patient moves? Where is the brush centered if your patient looks to the right of the fixation target with their right eye? What type of eccentric fixation would that mimic?

    larger/smaller

    7. With the left eye, draw what you think Toby would perceive when attempting to fixate the central spot of the MITT unit?

  • . * (note: ignore vertical separation)
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