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Eye Glasses and Contact Lenses

Lenses for correcting or improving vision:

Picture of a young girl trying on a pair of eyeglasses

There are two types of lenses prescribed for correcting or improving vision. These include:

  • eyeglasses (Also called spectacles.)
    Eyeglasses are the most common form of eyewear and are used to correct or improve many types of visual problems. Refractive errors can include nearsightedness or myopia (difficulty seeing far away), farsightedness or hyperopia (difficulty seeing close up), and astigmatism (blurring due to an irregularly shaped cornea). Eyeglasses perform this function by adding or subtracting focusing power to the eye's cornea and lens.
  • contact lenses
    Contact lenses are worn directly on the corneal surface. Like eyeglasses, contact lenses help to correct refractive errors and perform this function by adding or subtracting focusing power to the eye.

How to read an eyeglass prescription:

The lens power of eyeglasses is measured in diopters. This measurement reflects the amount of power necessary to focus images directly on to the retina. When looking at an eyeglass prescription, you will see the following abbreviations:

O.D. (Oculus Dextrus) refers to the right eye (sometimes the abbreviation RE is used for “right eye”).

O.S. (Oculus Sinister) refers to the left eye (sometimes the abbreviation LE is used for “left eye”).

Illustration of a pair of eyeglasses
Click Image to Enlarge

In addition, the eyeglass prescription may also contain the following measurements:

  • sphere - this number measurement reflects the extent of the nearsightedness (minus) or farsightedness (plus).
  • cylinder - this number measurement refers to the amount of astigmatism (an irregularly shaped cornea which causes blurring) in the eye.
  • axis - this number measurement describes the direction of the astigmatism in degrees.

Bifocal is additional power in the lens for close-up work, listed on the prescription as "add."

What are the different types of eyeglass lenses?

The type of lenses used in eyeglasses depends on the type of vision problem, and may include:

  • concave lenses - are thinnest in the center. Used to correct nearsightedness (myopia), the numerical prescription in diopters is always marked with a minus (-) symbol.
  • convex lenses - are thickest in the center, like a magnifying glass. Used to correct farsightedness (hyperopia), the numerical prescription in diopters is always marked with a plus (+) symbol.
  • cylindrical lenses - curve more in one direction than in the other and are used to correct astigmatism.

Picture of a young girl wearing trial eyeglasses to determine her prescription

Photograph used by permission of
the National Eye Institute, National
Institutes of Health

Eyeglasses for children:

Pick a frame that is impact resistant and request shatterproof (or polycarbonate) lenses. Other choices to consider are:

  • scratch-resistant coating on the lenses
  • spring-loaded frames that are less likely to be bent or warped
  • silicone nose pads that prevent glasses from slipping
  • cable temples (ear pieces that wrap around the ear) - recommended in children under 4 years. Straps may also be recommended to hold the glasses in place.

Facts about contact lenses:

Almost 30 million Americans wear contact lenses, half of whom wear daily wear soft lenses. In general, contact lenses can be divided into two main categories: rigid, gas permeable lenses and soft, water permeable lenses. Special silicone lenses have applications in infants.

Reading a contact lens prescription:

The prescription for contact lenses includes more information than what is available on the prescription for eyeglasses. Special measurements are taken of the curvature of the eye. In addition, your child's physician must determine if your child is an appropriate candidate for contacts.

The contact lens prescription usually includes the following information:

  • contact lens power (measured in diopters, like eyeglasses)
  • contact lens base curve
  • diameter of the lens

Eye care specialists are required by federal law to give you a copy of your contact lens specifications.

Click here to view the
Online Resources of Eye Care


It is important to remember the health information found on this website is for reference only not intended to replace the advice and guidance of your healthcare provider. Always seek the advice of your physician with any questions you may have regarding a medical condition. If you think you may have a medical emergency, call your physician or 911 immediately.

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