[visionlist] prism diopters

Alessio Facchin alessio.facchin at unimib.it
Wed May 16 05:03:39 -05 2018

 Hi all,
1 Prismatic dioptre (PD) is defined as the deviation of 1cm at 1meter of
distance, so it's easy to practically construct an instrument for binocular
assessment, with a grid.
As an example, for 40cm each PD is separated by 4mm. See MIM card for
phoria assessment.

Yes, in it's nature (compared to degrees) this measure it's non-linear
because 100PD = 45°, but in the field of Optometry and Orthotics, values
are small, and usually they did not exceed 40PD. I think the best measure
for Optometrists remain PD for a simple use and comparison with other tests.

In a clinical practice PD is a standard for binocular test results, even
you can also use degrees for other uses, like field of view, test dimension
See: Scheiman, M., & Wick, B. (2014). *Clinical management of binocular
vision: heterophoric, accommodative, and eye movement disorders*.
Lippincott Williams & Wilkins.

Alessio Facchin PhD
Post-doctoral Research Fellow
Department of Psychology - University of Milano-Bicocca
Building U6 - Room 3109
Piazza dell'Ateneo Nuovo 1
20126, Milano, Italy
+39 02 6448 3863
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