[visionlist] prism diopters

[Ben Backus]

Thank you everyone for your thoughts and suggestions.

Masahiro had the answer I was hoping for! The centrad is the answer!

On Thu, May 3, 2018 at 6:07 PM, 石井 雅博 <m.ishii at scu.ac.jp> wrote:

> Hi,
>
> Some optometrists use centrad that is a unit of angular measure equal
> to 1/100 of a rad or about 0.57 deg.
>
> - - - - -
> Masahiro Ishii
> School of Design, Sapporo City University
> phone 011.592.5390
> www.scu.ac.jp/profile/masahiro-ishii/
> 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?
>
> Thanks,
> Ben
>
> 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
> and
> Associate Professor, SUNY College of Optometry, New York, NY
>
>
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