During normal vision, light first enters the eye through the cornea, then passes through the pupil and the lens where it is focused at a point on the retina at the back of the eye.
Astigmatism is caused by a deformity of the eye in which the shape of the cornea is more oval and asymmetric than the normal round shape. This deformity causes light to focus on points in front of and/or behind the retina instead of on the retina itself, causing images to be blurred or distorted.
People with astigmatism may also report frequent headaches or eyestrain. Astigmatism is a very common disorder, and it can occur with either nearsightedness or farsightedness.
Blurred or distorted vision caused by astigmatism can be improved by wearing glasses or contact lenses.