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Refraction test

Definition

The refraction test is an eye exam that measures a person's prescription for eyeglasses or contact lenses.

Alternative Names

Eye test - refraction; Vision test - refraction; Refraction

How the test is performed

This test is performed by an ophthalmologist or optometrist. Both of these professionals are often called "eye doctor."

You sit in a chair that has a special device (called a phoroptor or refractor) attached to it. You look through the device and focus on an eye chart 20 feet away. The device contains lenses of different strengths that can be moved into your view. The test is performed one eye at a time.

The eye doctor performing the test will ask if the chart appears more or less clear when different lenses are in place.

How to prepare for the test

If you wear contact lenses, ask the doctor if you need to remove them and for how long before the test .

How the test will feel

There is no discomfort.

Why the test is performed

This test can be done as part of a routine eye exam. The purpose is to determine whether you have a refractive error (a need for glasses or contact lenses).

For people over age 40 who have normal distance vision but difficulty with near vision, a refraction test can determine the right power of reading glasses.

Normal Values

If your uncorrected vision (without glasses or contact lenses) is normal, then the refractive error is zero (plano) and your vision should be 20/20.

A value of 20/20 is normal vision. This means you can read 3/8-inch letters at 20 feet. A small type size is also used to determine normal near vision.

What abnormal results mean

You have a refractive error if you need a combination of lenses to see 20/20. Glasses or contact lenses should give you good vision. If you have a refractive error, you have a "prescription." Your prescription is a series of numbers that describe the powers of the lenses needed to make you see clearly.

If your final vision is less than 20/20, even with lenses, then there is probably another, non-optical problem with your eye.

The vision level you achieve during the refraction test is called the best-corrected visual acuity (BCVA).

Abnormal results may be due to:

Other conditions under which the test may be performed:

What the risks are

There are no risks.

Special considerations

You should have a complete eye examination every 3 to 5 years if you have no problems. If your vision becomes blurry, worsens, or if there are other noticeable changes, schedule an eye examination immediately.

After age 40 (or for people with a family history of glaucoma), eye examinations should be scheduled at least once a year to test for glaucoma. Anyone with diabetes should also have an eye exam at least once a year.

People with a refractive error should have an eye examination every 1 to 2 years, or whenever their vision changes.

References

American Academy of Ophthalmology Preferred Practice Patterns Committee. Preferred Practice Pattern Guidelines. Comprehensive Adult Medical Eye Evaluation. Available at http://one.aao.org/CE/PracticeGuidelines/PPP_Content.aspx?cid=64e9df91-dd10-4317-8142-6a87eee7f517. Accessed February 26, 2013.

Scott CA. Testing of refraction. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. Philadelphia, PA: Elsevier Mosby; 2008:chap 2.8.


Review Date: 2/7/2013
Reviewed By: Franklin W. Lusby, MD, Ophthalmologist, Lusby Vision Institute, La Jolla, California. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.
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