Health Information and Tools >  Eyeglass Prescriptions
Facebook Tweet Share

Main Content

Eyeglass Prescriptions

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 dioptres. The higher the number of dioptres, the more vision correction the lens provides.

Credits

Current as of: October 12, 2022

Author: Healthwise Staff
Medical Review:
Adam Husney MD - Family Medicine
Anne C. Poinier MD - Internal 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. Learn how we develop our content.