[visionlist] prism diopters

[Ebirch]

For angles up to 45pd the approximation of 2 pd per deg works pretty well.  See this excellent paper  by Irsch

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4502167/#!po=13.2353


Eileen Birch
Sent from my iPhone

> On May 3, 2018, at 10:14 AM, Ben Backus <ben at seevividly.com> wrote:
> 
> 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.
> 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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