diopter (redirected from dioptral)

dioptre (US), diopter

a unit for measuring the refractive power of a lens: the reciprocal of the focal length of the lens expressed in metres

---

diopter [dī′äp·tər]

(optics)

A measure of the power of a lens or a prism, equal to the reciprocal of its focal length in meters. Abbreviated D.

---

Diopter

A measure of the power of a lens or a prism. The diopter (also called dioptrie) is usually abbreviated D. Its dimension is a reciprocal length, and its unit is the reciprocal of 1 m (3.28 ft). See Focal length, Lens (optics)

The dioptric power of a prism is defined as the measure of the deviation of a ray going through a prism measured at the distance of 1 m. A prism that deviates a ray by 1 cm in a distance of 1 m is said to have a power of one prism diopter. See Optical prism

Spectacle lenses in general consist of thin lenses, which are either spherical, to correct the focus of the eye for near and far distances, or cylindrical or toric, to correct the astigmatism of the eye. An added prism corrects a deviation of the visual axis. The diopter thus gives a simple method for prescribing the necessary spectacle for the human eye.