Astigmatism is a refractive error in which light rays fail to come to a single focus on the retina because of differing amounts of refraction in the various meridians of the eye. Astigmatism is usually considered corneal astigmatism or lenticular astigmatism. With astigmatism, the power of the eye is different in one direction compared to other direction, 90 degrees away. An eye with astigmatism may be shaped more oblong, like a football, rather than round, like a basketball.

Signs and Symptoms

Astigmatism usually causes vision to be blurry at distance as well as near. Patients with astigmatism often feel tired after reading and find that letters and words appear to be slanted. Squinting and tilting the head seems to improve vision distortion caused by astigmatism.

Causes

Astigmatism is caused by the cornea having an oblong shape, like a football, instead of spherical shape, like a basketball. A cornea with astigmatism has two curves, one flat curve and one that is steep. Light is then focused at two points instead of one. One point of focus may be in front of the retina and the other behind. This causes images to appear distorted in addition to appearing blurry. Astigmatism may also be caused by an irregularly shaped crystalline lens. This condition is termed "lenticular astigmatism."

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