Astigmatism is an irregularity in the curvature of the cornea or lens that causes light traveling in different planes to be focused differently. The normal cornea or lens has a spherical curvature like the inside of a ball. In astigmatism, the cornea or lens has an elliptical curvature, like the inside of a spoon. As a result, some portions of an image are in focus on the retina, while other portions are blurred and vision is distorted.