[visionlist] prism diopters

石井 雅博 m.ishii at scu.ac.jp
Thu May 3 20:07:14 -05 2018


Some optometrists use centrad that is a unit of angular measure equal
to 1/100 of a rad or about 0.57 deg.

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Masahiro Ishii
School of Design, Sapporo City University
phone 011.592.5390
skype ishiitoyama

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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