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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.
A.D.A.M. Medical Encyclopedia.
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, incidence, and risk factors
People are able to see because the front part of the eye (cornea) is able to bend (refract) light and focus it onto the back surface of the eye, called the retina.
If the light rays are not clearly focused on the retina, the images you see may be blurry.
With astigmatism, the cornea 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.
Signs 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, but do not cure it.
Laser surgery can help change the shape of the cornea surface to eliminate astigmatism, along with nearsightedness or farsightedness.
Expectations (prognosis)
Astigmatism may change with time, requiring new glasses or contact lenses. Laser vision correction can usually eliminate, or greatly reduce, astigmatism.
Complications
In children, uncorrected astigmatism in only one eye may cause amblyopia.
Calling your health care provider
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, Plummer L, Stass-Isern M. Abnormalities of refraction and accommodation. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 612.
- 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: 9/3/2012.
Reviewed by: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington. 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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Comparison of two different methods of lens removal in cataract surgery, particularly relevant to lower income settings
As people get older, the lens in the eye can become cloudy ‐ this is known as a cataract. Age‐related cataract is the most common cause of blindness in the world. Visual impairment due to cataract can be cured by a surgical operation removing the cloudy lens and replacing it with a plastic lens which is known as an intraocular lens or IOL. A key question is: what is the best way of removing the lens, especially in lower income settings? This review considers two ways of removing the lens: manual small incision surgery (MSICS) whereby the lens is fragmented and extracted through a small incision and extracapsular cataract extraction (ECCE) which is the standard technique whereby the lens is removed through a larger incision. The review includes three randomised controlled trials that have compared these two methods. 953 people with age‐related cataract in India and Nepal were randomly allocated to MSICS and ECCE. The trial reports did not clearly describe some of the methods and in only one trial were people measuring outcomes masked to treatment group. Only two of the studies reported relevant data on visual acuity. People whose lens was removed with MSICS were more likely to achieve good functional vision, however, overall not more than 50% of people achieved good functional vision in the two studies. 1.2% of people enrolled in two trials had a poor outcome after surgery with best‐corrected vision less than 6/60. There was no evidence of any difference between the two groups with respect to this outcome. Surgically induced astigmatism was more common with the ECCE procedure than MSICS in the two trials that reported this outcome. In one study there were more intra‐ and postoperative complications in the MSICS group. One study reported that the costs of the two procedures were similar.There are no other studies from other countries other than India and Nepal and there are insufficient data on cost‐effectiveness of each procedure. Better evidence is needed before any change may be implemented. Future studies need to have longer‐term follow‐up (six months) and conducted to minimize biases revealed in this review with a larger sample size to allow examination of adverse events.
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