Astigmatism

Astigmatic eyes have corneas that are shaped more like a football then like a round ball. This causes the lightrays to bend differently across the corneal surface. As a result, the lightrays do not intersect in one sharp focus point but rather form several focus points, either before or behind the retina. Images are defocused and slightly distorted.
 

Astigmatism is a very common refractive (focusing) error. The cornea is unevenly shaped, and bends and scatters light in different directions, which causes objects to look distorted and appear blurry. It occurs when the front curvature portion of the cornea is shaped somewhat oval (like a football) rather than round (like a soccer ball). The two different curves in such a corneal surface each bend light rays to a separate focus point. Astigmatism correction makes all the rays of light focus at the same distance so that they all fall correctly on the retina.

Astigmatism can occur alone as the sole optical error, or may occur together with either myopia or hyperopia. It can be corrected by glasses, contact lenses (hard or soft), and laser treatment.