Prescriptions for glasses
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Prescriptions for glasses
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 in middle age.
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
| Author | Robin Parks, MS |
| Editor | Kathleen M. Ariss, MS |
| Associate Editor | Michele Cronen |
| Associate Editor | Pat Truman |
| Primary Medical Reviewer | Kathleen Romito, MD - Family Medicine |
| Specialist Medical Reviewer | Carol L. Karp, MD - Ophthalmology |
| Last Updated | July 7, 2007 |
| Last updated: | July 07, 2007 |
|---|---|
| Author: | Robin Parks, MS |
| Reviewed By: | Kathleen Romito, MD - Family Medicine, Carol L. Karp, MD - Ophthalmology |
| Editors: | Kathleen M. Ariss, MS, Pat Truman |
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