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