Northside Health Library


Astigmatism

Definition

Astigmatism is a type of refractive error of the eye. Refractive errors cause blurred vision and are the most common reason why a person goes to see an eye professional.

Other types of refractive errors are:

Causes

People are able to see because the front part of the eye is able to bend (refract) light and point it to the back surface of the eye, called the retina.

Changes in the length of the eye, or the shape of either the lens or the cornea make it more difficult for the eyes to focus light. If the light rays are not clearly focused on the retina, the images you see may be blurry.

With astigmatism, the cornea (the clear tissue covering the front of the eye) is abnormally curved, causing vision to be out of focus.

The cause of astigmatism is unknown. It is usually present from birth, and often occurs together with nearsightedness or farsightedness.

Astigmatism is very common. It sometimes occurs after certain types of eye surgery, such as cataract surgery.

Symptoms

Astigmatism makes it difficult to see fine details, either close up or from a distance.

Exams and Tests

Astigmatism is easily diagnosed by a standard eye exam with refraction test. Special tests are not usually required.

Children or others who cannot respond to a normal refraction test can have their refraction measured by a test that uses reflected light (retinoscopy).

Treatment

Mild astigmatism may not need to be corrected.

Glasses or contact lenses will correct astigmatism.

Laser surgery can help change the shape of the cornea surface to correct astigmatism, along with nearsightedness or farsightedness.

Outlook (Prognosis)

The right glasses or contact lenses, or laser vision correction can usually correct vision to normal.

Possible Complications

Uncorrected astigmatism in only one eye may cause amblyopia.

When to Contact a Medical Professional

Call for an appointment with your health care provider or ophthalmologist if vision problems worsen, or do not improve with glasses or contact lenses.

References

Olitsky SE, Hug D, Smith LP. Abnormalities of refraction and accommodation. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 619.

White PF, Scott CA. Contact lenses. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. St. Louis, Mo: Mosby Elsevier; 2008:chap 2.9.

Kramarevsky N, Hardten DR. Excimer laser photorefractive keratectomy. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. St. Louis, Mo: Mosby Elsevier; 2008:chap 3.4.


Review Date: 7/28/2010
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.
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