1. A unit of measurement of the refractive power of a lens or curved mirror, equal to the reciprocal of the focal length in meters.
Usage: Chiefly British spelling; American English uses 'diopters'.; Used in optics and optometry.

Examples

• The prescription for her glasses was +2.5 dioptres in each eye.
• A lens with a focal length of one meter has a power of one dioptre.
• The optometrist measured the refractive error in dioptres.
• High myopia may require lenses of -8 dioptres or stronger.
• Contact lens prescriptions are also written in dioptres.