Astigmatism (a-STIG-ma-tiz-um) is an eye condition that causes objects to appear blurry because the front part of the eye is misshapen.
The eyeball usually is round and nearly the same size as a ping-pong ball. The front part contains a clear layer of tissue called the cornea and also the lens that help to focus the light that enters the eye. When people have astigmatism, the cornea and/or the lens is misshapen, and their curved surfaces are unequal. If the curve is just slightly off shape, only objects at a distance may appear blurry. People with more serious astigmatism, however, may experience a distortion of all images.
Astigmatism is common and cannot be prevented. In research studies, almost 90 percent of people show some degree of astigmatism. Often the degree of astigmatism is different in one eye than in the other. However, the amount of astigmatism is so slight that for the vast majority of people, it does not affect their vision and needs no treatment.
As of 2016, the cause of astigmatism was unknown. It usually is present at birth and often is found in several members of the same family, which indicates that to some degree the trait is likely to be inherited. Surgically induced astigmatism can occur after a person undergoes eye surgery. It is much less common than natural astigmatism, but often creates a higher degree of vision problems for the individual.
Variations in the shape of the cornea or lens cause a person with astigmatism to see images that are out of focus when they reach the eye's retina * . The retina is made of layers of light-sensitive cells at the back of the eyeball that act like the film in a camera. The distorted image is projected onto the retina and transmitted to the brain for processing through the optic nerve.
The first signs of astigmatism are determined by how severely the cornea or lens is misshapen. In mild problems, people with astigmatism may find that they have headaches or tired eyes at times, or distorted vision at certain distances. In severe cases, people with astigmatism may have blurry vision that makes reading, playing sports, and other activities difficult. Astigmatism often is discovered during an eye exam in school, at the doctor's office during a check-up, or when a parent notices that a child is having trouble seeing clearly. Usually astigmatism does not worsen as a person gets older.
Astigmatism may be managed with prescription eyeglasses or special “toric” contact lenses. The latter are available in soft lenses and rigid gas-permeable (RGP) lenses, although some patients find that RGP lenses offer better visual acuity (sharpness). Both glasses and toric contact lenses help change the way that images are focused as they pass through the cornea and the lens, and both allow clear images to arrive at the retina.
Besides eyeglasses and contact lenses, astigmatism can be treated with refractive surgeries. One of the most common is the laser eye surgery called laser assisted in situ keratomileusis (LASIK), which reshapes the cornea and can correct both astigmatism and either nearsightedness or farsightedness. Other surgical options are conductive keratoplasty (CK), which uses heat rather than a laser to correct vision and is sometimes recommended for patients over 40 years of age, and astigmatic keratotomy (AK), which involves incisions to help reshape the cornea.
Some people with astigmatism report some improvement after doing various eye exercises, but exercise alone cannot eliminate the need for other means of vision correction.
See also Blindness • Farsightedness • Nearsightedness
Estenson, Joseph. Astigmatism—A Reference Guide. Washington DC: Capitol Hill Press, 2015.
Mimouni, M. et al. “Factors Predicting the Need for Retreatment after Laser Refractive Surgery.” Cornea 35, no. 5 (2016): 607–12.
“Astigmatism.” American Optometric Association. http://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/astigmatism?sso=y (accessed March 19, 2916).
Boyd, Kierstan. “What is Astigmatism?” American Academy of Ophthalmology. http://www.aao.org/eye-health/diseases/what-isastigmatism (accessed March 19, 2016).
American Academy of Ophthalmology. PO Box 7424, San Francisco, CA 94120-7424. Telephone: 415-561-8500. Website: http://www.aao.org
American Optometric Association. 243 N. Lindbergh Blvd., Floor 1, St. Louis, MO 63141. Telephone: 800-365-2219. Website: http://www.aao.org
National Eye Institute Information Office. 31 Center Dr., MSC 2510, Bethesda, MD 20892-2510. Telephone: 301-496-5248. Website: http://www.nei.nih.gov
* retina (REH-tuh-na) is the tissue that forms the inner surface of the back of the eyeballs; it receives the light that enters the eye and transmits it through the optic nerves to the brain to produce visual images.