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 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.

Credits

By Healthwise Staff
Primary Medical Reviewer Adam Husney, MD - Family Medicine
Specialist Medical Reviewer Christopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology
Last Revised October 16, 2012

Last Revised: October 16, 2012

Author: Healthwise Staff

Medical Review: Adam Husney, MD - Family Medicine & Christopher J. Rudnisky, MD, MPH, FRCSC - Ophthalmology

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

To learn more visit Healthwise.org

© 1995-2013 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.