Astigmatism is a refraction error of the eye characterized by an aspherical cornea in which one axis of corneal steepness is greater than the perpendicular axis. Astigmatism causes difficulties in seeing fine detail, and can be often corrected by glasses with a cylindrical lens or by toric contact lenses.

Astigmatism occurs when either the cornea or the lens of the eye is not perfectly spherical. As a result, the eye has different focal points in different planes. For example, the image may be clearly focused on the retina in the horizontal plane, but in front of the retina in the vertical plane. Once diagnosed, astigmatism is corrected by wearing glasses with lenses having different radii of curvature in different planes. They are commonly called cylindrical lenses.

External links

• MedlinePlus article (http://www.nlm.nih.gov/medlineplus/ency/article/001015.htm)
• AllAboutVision.com article (http://www.allaboutvision.com/conditions/astigmatism.htm)

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