Astigmatism is caused by asymmetric curvature of the cornea. Instead of being round like a marble, the corneal curvature is shaped like a football. Light is not sharply focused at any distance. Since the eye has 2 focal points, astigmatism most commonly occurs in either nearsightedness or farsightedness. Mixed astigmatism is an unusual type of astigmatism. In this case, one focal point is near and the other far.
