[visionlist] prism diopters

Ben Backus ben at seevividly.com
Thu May 3 15:14:00 -05 2018

 I'm helping to build some virtual reality vision tests for optometrists to
use. Generally optometrists want visual angle to be measured in prism
diopters (PD). But PD are not a nice unit: they are nonlinear. For example,
40 PD = atan(40/100) = 0.38 radian, but 40 * (1 PD) = 0.40 radian.

Is there any unit out there--or should we define a new one, the "constant
prism diopter"--that is equal to 1/100 radians?

Has anyone tried simply declaring that, for your use, 1 PD will be equal to
~0.573 deg? How did your optometrist friends react to that?


Benjamin T. Backus, PhD
Chief Science Officer, Vivid Vision, Inc. <https://seevividly.com>
525 York St., San Francisco, CA 94110, USA
Tel. +1-415-787-7830
Associate Professor, SUNY College of Optometry, New York, NY
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