A dioptre (or diopter) is a unit of measurement used to indicate the optical power of a lens or curved mirror. It is defined as the reciprocal of the focal length in meters; for example, a lens with a focal length of 1 meter has a power of 1 dioptre. Higher dioptre values correspond to stronger lenses. Dioptres are commonly used in optics, including eyeglasses and contact lenses, to correct vision.