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[dahy-op-ter] /daɪˈɒp tər/
Optics. a unit of measure of the refractive power of a lens, having the dimension of the reciprocal of length and a unit equal to the reciprocal of one meter.
Abbreviation: D.
an instrument, invented by Hipparchus, to measure the apparent diameter of the sun or moon or to estimate the size or elevation of distant objects.
Also, especially British, dioptre.
Origin of diopter
1585-95; < Latin dioptra < Greek: instrument for measuring height or levels, equivalent to di- di-3 + op- (for ópsesthai to see) + -tra noun suffix of means
Related forms
dioptral, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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diopter in Medicine

diopter di·op·ter (dī-ŏp'tər)
Abbr. D.
A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length measured in meters.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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