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Diopter

The diopter is a unit of measurement used to describe how well a person sees.

Farsightedness is measured in positive diopters, and nearsightedness is measured in negative diopters. Astigmatism is measured in diopters that can be either positive or negative.

With diopters, the farther a measurement is from 0, the more severe the refractive error. For example, if a person has -4 diopters of nearsightedness, it means that the farthest point you can see clearly is one-fourth of a meter (about 10 inches) from your eye.

By Healthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Specialist Medical Reviewer Christopher J. Rudnisky - Ophthalmology
Last Revised July 6, 2009

WebMD Medical Reference from Healthwise

Last Updated: July 06, 2009
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