Keratoconus is a progressive eye disease in which the normally spherical cornea thins and begins to bulge into a cone-like shape. The cornea is a clear organ that lies in the central portion of the surface of the eye. In patients with keratoconus, the cone-shaped cornea cannot focus light rays properly and causes distorted vision.
Keratoconus often begins to develop in adolescent years. A variant called pellucid marginal degeneration (PMD) affects patients in older years. Changes in the shape of the cornea occur gradually, usually over several years. The cause of keratoconus is largely unknown. Some genetic links which have been identified. While most people with keratoconus are otherwise healthy, patients with Down’s syndrome, connective tissue diseases, and certain retinal conditions are at higher risk of developing keratoconus. Allergic eye disease associated with eye rubbing is present in about 30% of patients with keratoconus.