Not all eyes are perfect circles, sometimes they are more oval shaped. If a person has an irregular shape or curvature of the cornea (the clear part that covers the surface of the eye) or lens inside the eye then it results in an astigmatism which is quite common. In a round eye, or in an eye without astigmatism, the cornea and lens allow the light to focus at a single point on the retina. If there is an astigmatism, then the cornea or lens is more elliptical which causes the light either to focus before or after the retina. It is common to have astigmatism along with other vision conditions such as nearsightedness or farsightedness. Together, these vision conditions are called ‘refractive errors’ because they affect how the eyes bend or ‘refract’ incoming light. People with astigmatism tend to require a more specific prescription for glasses or contact lenses which allows light to bend properly on the shape of their eye. There is an added component of a prescription for glasses or contact lenses called the cylinder, which is customized to correct an astigmatism.