View Video Astigmatism may be one of the most misunderstood words in the English language! To illustrate what astigmatism really is, compare an egg to a ping-pong ball, or a football to a basketball. Because they are not perfectly round, the egg and football have lots of astigmatism, whereas the ping-pong ball and the basketball have none. Similarly, two round surfaces in the eye are responsible for focusing light: the clear outer window of the eye called the cornea and the lens, which resides just behind the colored part of the eye (the iris). If one or both of these surfaces are not perfectly spherical or round, we say that astigmatism is present. The usual site of this irregularity in the eye is the cornea. It is a normal variant and, if present, may be considered one of nature’s imperfections. Rarely is astigmatism caused by lid swelling such as chalazia, and corneal scars, or by keratoconus (a rare condition in which the cornea becomes misshapen and pointed rather than smooth and rounded).