Astigmatism is a type of refractive error of the eye. Refractive errors cause blurred vision. They are the most common reason why a person goes to see an eye professional.
Other types of refractive errors are:
People are able to see because the front part of the eye (cornea) is able to bend (refract) light and focus it onto the retina. This is the back inside surface of the eye.
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. This curve causes vision to be out of focus.
The cause of astigmatism is unknown. It is most often present from birth. Astigmatism often occurs together with nearsightedness or farsightedness. If astigmatism gets worse, it may be a sign of keratoconus.
Astigmatism is very common. It sometimes occurs after certain types of eye surgery, such as cataract surgery.
Astigmatism makes it hard to see fine details, either close up or from a distance.
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.
Astigmatism may change with time, requiring new glasses or contact lenses. Laser vision correction can most often eliminate, or greatly reduce astigmatism.
In children, uncorrected astigmatism in only one eye may cause amblyopia.
Call your health care provider or ophthalmologist if vision problems worsen, or do not improve with glasses or contact lenses.
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White PF, Scott CA. Contact lenses. In: Yanoff M, Duker JS, eds. Ophthalmology. 4th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 2.7.