Corrective lenses

A corrective lens is a lensworn on or before the eye, used to treat myopia, hypermetropia, astigmatism, and presbyopia. The most common types of corrective lenses are spectacle lensesand contact lenses. Intraocular lensesare also beginning to become common. Myopia (short sightedness) requires biconcave or diverging lenses, whereas hypermetropia (long sightedness) requires biconvex or converging lenses.

In some cases, mild farsightedness can be treated with simple magnifying lensesor "reading glasses". However, an optometristmay need to prescribe a dioptrefor both eyes or each eye, allowing lenses to be custom ground to the patient's specific needs. Usually, the dioptre (or "prescription") is equal for both eyes; in some cases, however, the two eyes may need different prescriptions.

Patients with presbyopia or other disorders of accommodationoften benefit from bifocals, or lenses with separate sections ground to different prescriptions for different circumstances. Typically a person with myopia would have one section of a prescription lens that has a certain diverging power while another section of the lens would have a lower diverging power for close-up work. Similarly a person with hypermetropia would have one section of the lens with a certain converging power and another section with a greater power for close-up work.

See also

• Glasses
• Contact lens
• Intraocular lens
• Monocle
• Pince-nez
• Lorgnette

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Corrective+lenses Wikipedia article Corrective lenses.