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<div dir="auto">Ben et al,</div>
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<div dir="auto">I would use Centrads-- they are 1/100 of a radian. They have tbe following advantages:</div>
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<div dir="auto">1. They are equal to Prism Diopters (that ODs use when thinking about angles) - becuz they only deal with small angles.</div>
<div dir="auto">2. Technically the Centrads are more accurate and are linear with angle.</div>
<div dir="auto">3. Centrads have been taught to ODs - at least they have heard the term.</div>
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<div dir="auto">Jim Sheedy</div>
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<div dir="auto"><i>Sent from my LG Mobile</i></div>
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<div dir="auto">------ Original message------</div>
<div dir="auto"><b>From: </b>Little, Julie-Anne</div>
<div dir="auto"><b>Date: </b>Fri, May 4, 2018 12:38 PM</div>
<div dir="auto"><b>To: </b>Ben Backus;visionlist@visionscience.com;</div>
<div dir="auto"><b>Cc: </b></div>
<div dir="auto"><b>Subject:</b>Re: [visionlist] prism diopters</div>
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<div style="color:rgb(0,0,0); font-size:14px"><font face="Calibri">Hi Ben</font></div>
<div style="color:rgb(0,0,0); font-size:14px"><font face="Calibri">Why not use Metre angles (MA)? </font><span style="font-family:Calibri; orphans:2; widows:2">This is useful as gives you a comparable metric with
</span><span style="font-family:Calibri; orphans:2; widows:2; background-color:rgb(255,255,255)">accommodation, and is the reciprocal of the viewing distance (m). </span><span style="font-family:Calibri; background-color:rgb(255,255,255); orphans:2; widows:2">So
2 MA = vergence at 50cm, 3MA = vergence at 33cm etc. Not a linear, but at least a dioptric scale.</span></div>
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<div style="orphans:2; widows:2"><span style="orphans:2; widows:2; background-color:rgb(255,255,255)"><font face="Calibri">Metre angles (MA) are calculated by dividing the Prism diopter value by the inter-pupillary distance of the person in cm.</font></span></div>
<div style="orphans:2; widows:2"><font face="Calibri">MA = Prism Diopters/IPD(cm)</font></div>
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<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt; font-size:11pt"><span style="font-size:10pt; font-family:'Gill Sans MT',sans-serif">________________________________________</span></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt; font-size:11pt"><span style="font-size:10pt; font-family:'Gill Sans MT',sans-serif">Julie-Anne Little PhD MCOptom FHEA FEAOO</span></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt; font-size:11pt"><span style="font-size:10pt; font-family:'Gill Sans MT',sans-serif">Senior Lecturer in Optometry</span></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt"><font face="Gill Sans MT,sans-serif"><span style="font-size:10pt">Ulster University, </span><span style="font-size:13.333333015441895px">Northern</span><span style="font-size:10pt"> Ireland, UK</span></font></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt; font-size:11pt"><span style="font-size:10pt; font-family:'Gill Sans MT',sans-serif"><a href="http://biomed.science.ulster.ac.uk/research-institute/vision-science/" style="color:rgb(149,79,114)">http://biomed.science.ulster.ac.uk/research-institute/vision-science/</a> </span></p>
<p class="MsoNormal" style="margin:0cm 0cm 0.0001pt; font-size:11pt"><span style="font-size:10pt; font-family:'Gill Sans MT',sans-serif">ORCID ID:<span style="background-color:white"> orcid.org/0000-0001-5242-8066</span></span></p>
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<span style="font-weight:bold">From: </span>visionlist <<a href="mailto:visionlist-bounces@visionscience.com">visionlist-bounces@visionscience.com</a>> on behalf of Ben Backus <<a href="mailto:ben@seevividly.com">ben@seevividly.com</a>><br>
<span style="font-weight:bold">Date: </span>Thursday, 3 May 2018 at 21:14<br>
<span style="font-weight:bold">To: </span>"<a href="mailto:visionlist@visionscience.com">visionlist@visionscience.com</a>" <<a href="mailto:visionlist@visionscience.com">visionlist@visionscience.com</a>><br>
<span style="font-weight:bold">Subject: </span>[visionlist] prism diopters<br>
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<div>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.<br>
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Is there any unit out there--or should we define a new one, the "constant prism diopter"--that is equal to 1/100 radians?
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<div>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?<br>
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Thanks,<br>
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Ben<br clear="all">
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<div dir="ltr">Benjamin T. Backus, PhD
<div>Chief Science Officer,<a href="https://seevividly.com" target="_blank"> Vivid Vision, Inc.</a>
<div>525 York St., San Francisco, CA 94110, USA<br>
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<div>Tel. +1-415-787-7830<br>
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<div>Associate Professor, SUNY College of Optometry, New York, NY</div>
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