# Diopter

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## 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

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.

## Diopter

the unit of focal power of a lens and other axially symmetrical optical systems. It is indicated by the symbol D; 1 D is equal to the power of a lens or spherical mirror with a main focal length of 1 m. Focal power, expressed in diopters, is the reciprocal of the principal focal length in meters. The power of a converging lens is taken as positive, and that of a diverging lens, negative. The focal power of eyeglasses is given in diopters. Eyeglasses for nearsighted persons have negative focal power (negative number of diopters); those for farsighted persons have positive focal power.

## Diopter

a simple device for fixing the direction to an object—that is, sighting. It consists of two metal plates (the ocular and object diopters) fastened to the ends of an alidade or to a divided circle. The ocular diopter has a small circular hole or narrow slit, and the object diopter has a sight or small fine hair stretched at a certain distance from the ocular diopter. The diopter is used by turning it until, upon looking through the ocular diopter, the object diopter is projected on the object to be sighted. With a sufficient distance between the ocular and object diopters, the accuracy of sighting can be 2-5 minutes of arc. The diopter was described by Heron of Alexandria (c. first century A.D.) and was extensively used earlier in geodetic instruments. At present it is found only in some compasses.

## 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.
References in periodicals archive ?
Other great features include the click diopter, staged, locking eyecups, a shoulder harness, a lifetime warranty, and weighs in at just 37.
In addition to the expanded diopter range and Hyperopic Toric CE Mark approval, STAAR Surgical also designed several enhancements that increase physician ease of use of the Visian ICL during implant.
The company will begin shipping the Crystalens HD in the additional diopter steps on July 16, 2009.
Food and Drug Administration's (FDA) Ophthalmic Devices Panel of the Center for Devices and Radiological Health (CDRH) voted 8-3 late Friday afternoon to recommend that the STAAR Implantable Contact Lens (ICL) be approved with conditions for use in correcting myopia in the range of -3 diopters to -15 diopters and reducing myopia in the range of -15 diopters to -20 diopters.
15 minutes daily use of the mask improves blood circulation, boosts eye health, enhances cellular metabolism and reduces diopters.
The Food and Drug Administration warned that the implants are only for mildly nearsighted people, whose vision is formally diagnosed as ``minus 1 diopters to minus 3 diopters.
0 diopters as compared to the current range which starts at -5.
Therefore, the average treatment time for correcting four to five diopters of nearsightedness or farsightedness is just eight to ten seconds, about the time it takes to pour a cup of coffee.

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