1. A unit of measurement of the refractive power of a lens, equal to the reciprocal of the focal length in meters.
Usage: Also spelled 'diopter' in U.S. English; Commonly used in ophthalmology 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 refractive power of one dioptre.
• The optometrist measured the patient's vision correction in dioptres.
• Stronger corrective lenses have higher dioptre values.
• The contact lens was prescribed at -3.0 dioptres to correct myopia.