Dioptre
UNIT OF OPTICAL POWER
Diopter; Diopters; Dioptry; Dioptres; Dpt (unit); Dioptrie
A dioptre (British spelling) or diopter (American spelling) is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dioptre = 1 m−1. It is normally used to express the optical power of a lens or curved mirror, which is a physical quantity equal to the reciprocal of the focal length, expressed in metres.