Keratoconus is a progressive eye disease in which the normally round cornea thins and begins to bulge into a cone-like shape. The cornea is the clear, central part of the surface of the eye, which is responsible for most of the eyes focusing power. In patients with keratoconus, the cone-shaped cornea deflects light and causes distorted vision.
Keratoconus often begins to develop between the teen years and the early 20s, although it can develop at any age. Changes in the shape of the cornea occur gradually, usually over several years. Patients with keratoconus often experience blurred and distorted vision, nearsightedness, and sensitivity to light.