Ever Wonder Why Patients Do This?


I’m sure there are many observations you have about interesting or seemingly odd things that patients do without apparent explanation.  Here’s one that puzzled me for a number of years.

Stereo Test Booklet

Ever wonder why you have a patient look at the stereo booklet, and they start to move the booklet around?  I’m not talking about moving the booklet inward, which increases the disparity and makes the target less demanding.  I’m talking about the patient holding the booklet at a fixed distance, but angling or tilting it around a vertical or horizontal plane, rocking the booklet back and forth to create motion.  Why would movement increase the ease of seeing the target?

The answer is that adding motion to disparity increased the ability of the individual to discern stereoscopic effects.  Here is a very nice, recently published study in the journal Strabismus showing that.

Strabismus Journal Cover

Motion-in-depth is perceived though two parallel and complementary mechanisms, detecting changing disparity over time and the recognition of intraocular velocity differences.  The patient tilting the booklet back and forth, sometimes rocking it to and fro, is manipulating both of these variables.  Creating new standardized tests for naturalistic stereoscopic 3D (S3D)  viewing would be welcome.

Equally if not important is the therapeutic angle.  We make a point of working on dynamic cues when we utilize motion parallax.  This is still largely done with old fashioned vectograms or relatively crude computerized targets.  Stimuli holding great promise for naturalistic viewing in the context of 3D gaming are on the cusp of release for clinical use.  One example is iCare.

iCARE

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