Diopter meaning : A unit of measure of the power of a lens or mirror, equal to the reciprocal of its focal length in meters. Myopia is diagnosed and measured in diopters. The dioptre adjustment mechanism of a pair of binoculars. Any lens system, such as a telescope. A theodolite or similar surveyor’s angle measuring device. An alidade. A surgical speculum. An instrument for drawing the skull by projections.