Sunday, October 26, 2008

Patterns of functional visual loss

taken from Liu Volpe and Galetta text p. 388
1. General observation of functionally blind-- may move into and bump objects without falling and hurting themselves; may not look at examiner speaking to them as a truly blind person might do; may wear sunglasses or mimic Stevie Wonder or other famously blind people.

2. Pupils-- should be abnormal except in cortically blind. A patient with total blindness and intact pupillary reflexes is likely to be functional. A complaint of photophobia with orbicularis oculi contraction to bright light is incompatible with an ocular cause of blindness.

3. OKN's- response is involuntary, but can be blocked by looking away from or beyond stimulus, or by excessive convergence.

4. Proprioceptive tests are performed by truly blind but not by functional. For example, looking at one's hand, bringing the tips of the fingers together from a distance, or signing one's name are better done by truly blind.

5. Mirror test-- a large mirror in front of a blind person, rocked, will produce an involuntary response if the patient is sighted and has better than hand motion vision..

6. Surprise-- atypical behaviors such as making faces, writing shocking words.

7. Evoked potentials-- a normal test can help, but an abnormal test can be ambiguous. My have in evoked fields, have characteristic hemifield loss from patient looking down.

2. Stereopsis-- requires binocular vision-- Titmus test
3. Placement of green lens should prevent visualization of Ishihara color plates


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