Keratoconus (from Greek: kerato- horn, cornea; an konos cone), is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve. Keratoconus can cause substantial distortion of vision, with multiple images, streaking and sensitivity to light all often reported by the patient. Keratoconus is the most common dystrophy of the cornea, affecting around one person in a thousand, and it seems to occur in populations throughout the world, although some ethnic groups experience a greater prevalence than others. It is typically diagnosed in the patient's adolescent years and attains its most severe state in the twenties and thirties.