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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: june 5, 2023

author: healthwise staff
clinical review board
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