A unit of measurement of the refraction of a lens.
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.
A dioptric, a unit of measurement for the power of refraction or “strength” of a lens, determines its magnifying capability. A lens with a higher dioptric value indicates a stronger lens. Lenses that converge parallel light rays have a positive dioptric number and are employed to correct farsightedness. On the other hand, lenses that cause light rays to diverge possess a negative dioptric number and are used to correct nearsightedness, also known as myopia.