- The focusing power of a lens is measured in dioptres.
- Refractive error is measured in dioptres, and myopia is designated with a minus sign.
- The difference between the focusing powers of these two axes, measured in dioptres, is the astigmatism.
late 16th century (originally denoting an alidade): from French, from Latin dioptra, from Greek, from di- 'through' + optos 'visible'. The term was used in the early 17th century to denote an ancient form of theodolite; the current sense dates from the late 19th century.
Definition of diopter in:
- The British & World English dictionary