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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 before the test and for how long.
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 Results
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 perfect vision, meaning you are able to 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 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:
- Astigmatism
- Hyperopia (farsightedness)
- Myopia (nearsightedness)
- Presbyopia (inability to focus on near objects that develops with age)
Other conditions under which the test may be performed:
- Corneal ulcers and infections
- Macular degeneration
- Retinal detachment
- Retinal vessel occlusion
- Retinitis pigmentosa
Risks
There are no risks.
Considerations
You should have a complete eye examination every 3 - 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 -2 years, or whenever their vision changes.
References
Katz M, Kruger PB. The human eye as an optical system. In: Tasman W, Jaeger Ea, eds. Duane's Ophthalmology. 15th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2009:chap 33.
Kaufman JH. Subjective refraction: fogging and use of the astigmatic dials. In: Tasman W, Jaeger Ea, eds. Duane's Ophthalmology. 15th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2009:chap 39.
Scott CA. Testing of refraction. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. St. Louis, MO: Mosby Elsevier;2008:chap 2.8.
Olitsky SE, Hug D, Smith LP. Examination of the eye. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 618.
American Academy of Ophthalmology Refractive Management/Intervention Panel. Preferred Practice Pattern Guidelines. Refractive Errors & Refractive Surgery. San Francisco, CA. American Academy of Ophthalmology, 2010. Accessed January 17, 2011.
American Academy of Ophthalmology Preferred Practice Patterns Committee. Preferred Practice Pattern Guidelines. Comprehensive Adult Medical Eye Evaluation. San Francisco, CA: American Academy of Ophthalmology, 2010. Accessed January 17, 2011.
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; and Franklin W. Lusby, MD, Ophthalmologist, Lusby Vision Institute, La Jolla, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
