Definition from Wiktionary, the free dictionary
See also Diopter
Alternative forms 
diopter (plural diopters)
- 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.
- (obsolete) Any lens system, such as a telescope.
- (obsolete) A theodolite or similar surveyor’s angle measuring device.
- (obsolete) An alidade.
- (obsolete) A surgical speculum.
- (obsolete) An instrument for drawing the skull by projections.
unit of measure
alidide — see alidide
speculum — see speculum
instrument for drawing skull