A unit of the power of refraction (“strength”) of a lens; the greater the power, the stronger the lens. Lenses that cause parallel light rays to converge have a positive dioptric number and are used to correct longsightedness
(see hypermetropia). Those that cause divergence have a negative number and are used to correct shortsightedness (see myopia).
A term used in the measurement of the refractive or focusing power of lenses; one dioptre is the power of a lens with a focal distance of one metre and is the unit of refractive power. As a stronger lens has a greater refractive power, this means that the focal distance will be shorter. The strength in dioptres therefore is the reciprocal of the focal length expressed in metres.
n. the unit of measurement of the power of *refraction of a lens. One dioptre is the power of a lens that brings parallel light rays to a focus at a point one metre from the lens, after passing through it. A stronger lens brings light rays to a focus at a point closer to it than a weaker lens and has a higher dioptric power.
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