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:

    • Farsightedness
    • Nearsightedness

    Causes, incidence, and risk factors

    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.