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Eyeglass Prescriptions - Topic Overview

Prescriptions for glasses have two main components: shape and power.

The shape of a lens determines the type of correction.

  • Concave, or minus, spherical lenses are thicker at the sides than in the middle to correct nearsightedness (myopia).
  • Convex, or plus, lenses are thicker in the middle than at the sides to correct farsightedness (hyperopia) or presbyopia.
  • Cylindrical (toric) lenses are curved more in one direction than another to make up for irregularities in the cornea camera.gif that cause astigmatism.
  • Convex lenses or bifocals refocus the image on the retina when people with presbyopia lose the ability to focus on close objects around age 40.

The power of a lens determines the amount of correction. It is specified in diopters. The higher the number of diopters, the more vision correction the lens provides.

WebMD Medical Reference from Healthwise

Last Updated: October 16, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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