Astigmatism is a defect in vision caused by a lack of symmetry in the cornea of the eye. The eye forms images by focusing light that enters the eye onto the retina. If the cornea is misshapen, the image formed may be blurred.

The cause of astigmatism is unknown. It is usually present from birth, and sufferers are often near or farsighted. People with the condition may wear glasses or undergo laser eye surgery. Tests for the condition may involve looking at an image like the one below. Lines in one direction may appear fainter or more blurred than oin another direction.