Astigmatism

  • Definition

    Astigmatism is a condition that results in blurred, unfocused, or fuzzy vision. The cornea (the front surface of the eye) or lens (located behind the cornea) has an abnormal or irregular curve.
    There are two common types of astigmatism:
    • Corneal astigmatism—misshapen cornea
    • Lenticular astigmatism—misshapen lens
    Normal Anatomy of the Eye
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  • Causes

    The precise cause of astigmatism is unknown. It is often present at birth and may coexist with nearsightedness or farsightedness. Sometimes, it may occur after an injury or eye surgery.
  • Risk Factors

    Factors that may increase your chance of astigmatism include:
    • Heredity—a family history of astigmatism, eye disease, or disorders such as keratoconus
    • Eye surgery—certain types of eye surgery, such as cataract removal
    • A history of corneal scarring or thinning
    • A history of excessive nearsightedness or farsightedness
  • Symptoms

    Some people with astigmatism may have no symptoms. In those that have symptoms, astigmatism may cause:
    • Blurred or distorted vision, which may cause you to squint
    • Headaches
    • Lightheadedness
    Symptoms vary depending on the extent of the astigmatism.
  • Diagnosis

    Your eye doctor will ask about your symptoms and medical history. An examination of your eyes will be done.
    Tests to evaluate your eyes may include:
    • Visual acuity assessment test (VAT)—to assess distant vision
    • Refractor test
    • Keratoscope—to detect and measure the presence of corneal surface curvature
  • Treatment

    Treatment options may include the following:
    Corrective Lenses
    Corrective lenses, such as glasses or toric contact lens, are prescribed to offset the eye’s visual abnormalities or defects.
    Surgery
    To correct severe astigmatism, your eye surgeon might use special knives or a laser beam to correct the abnormal or irregular curve of the cornea.
    There are three types of surgical procedures that an eye surgeon might perform:
    • Photorefractive keratectomy (PRK)—laser beams are used to reshape the abnormal or irregular curve of the cornea
    • Laser-assited in situ keratomileusis (LASIK)—laser beams used to reshape the curve of the cornea by removing corneal tissue
    • Radical keratotomy (RK)—small incisions (cuts) are made partial thickness into the cornea
    • Laser-assisted subepithelial keratomileusis (LASEK)—not as commonly used, but it may benefit people with thin corneas, or those at high risk of an eye injury
  • Prevention

    There are no current guidelines to prevent astigmatism. See your eye doctor for regular check-ups.
  • RESOURCES

    Eye Smart—American Ophthalmology http://www.geteyesmart.org

    National Eye Institute (NEI) http://www.nei.nih.gov

    CANADIAN RESOURCES

    Canadian Ophthalmological Society http://www.cos-sco.ca

    The Canadian National Institute for the Blind http://www.cnib.ca

    References

    Condon PI, Mulhern M, et al. Laser intrastromal keratomileusis for high myopia and myopic astigmatism. Br J Ophthalmol. 1997;81(3):199-206.

    Goss DA. Refractive error changes in mixed astigmatism. Ophthalmic Physiol Opt. 1999;19(5):438-40.

    Holladay JT, Moran JR, et al. Analysis of aggregate surgically induced refractive change, prediction error, and intraocular astigmatism. J Cataract Refract Surg. 2001;27(1):61-79.

    Komaroff AL, ed. Harvard Medical School Family Health Guide. New York, NY: Simon and Schuster; 1999:423-425.

    Kymionis GD, Aslanides M, et al. Laser in situ keratomileusis for residual hyperopic astigmatism after conductive keratoplasty. J Refract Surg. 2004;20(3):276-278.

    Miller JM, Dobson V, et al. Comparison of preschool vision screening methods in a population with a high prevalence of astigmatism. Invest Ophthalmol Vis Sci. 2001;42(5):917-924.

    Pesudovs K. Autorefraction as an outcome measure of laser in situ keratomileusis. J Cataract Refract Surg. 2004;30(9):1921-1928.

    Taneri S, Feit R, et al. Safety, efficacy, and stability indices of LASEK correction in moderate myopia and astigmatism. J Cataract Refract Surg. 2004;30(10):2130-2137.

    Tobaigy FM, Ghanem RC, et al. A Control-matched comparison of laser epithelial keratomileusis and laser in situ keratomileusis for low to moderate myopia. Am J Ophthalmol. 2006;142(6):901-908.

    Varley GA, Huang D, Rapuano CJ, et al. LASIK for hyperopia, hyperopic astigmatism, and mixed astigmatism: a report by the American Academy of Ophthalmology. Ophthalmology. 2004;111(8):1604-1617.

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