Keratoconus is a gradual change in the shape of the cornea (the clear layer in front of the iris and pupil) that causes it to become irregular and cone-shaped.

The condition usually begins between the ages of 10 and 25. Both eyes are usually affected, causing major changes in vision and requiring frequent changes in prescription for eyeglasses or contact lenses. The cause is unknown, but people are more likely to develop keratoconus if they have any of the following:

• Another family member who has keratoconus
• A tendency to develop many allergies (sometimes called atopy)
• A tendency to vigorously rub their eyes
• Lax eyelids
• Certain connective tissue disorders (for example, Ehlers-Danlos syndrome, Marfan syndrome, and osteogenesis imperfecta)
• Down syndrome
• Disorders that are apparent at birth and cause poor vision (for example, Leber congenital amaurosis, retinopathy of prematurity, and lack of an iris in the eye)
• Obstructive sleep apnea

Contact lenses often correct the vision problems better than eyeglasses, but sometimes the change in corneal shape is so severe that contact lenses either cannot be worn or cannot correct vision. In severe cases, corneal transplantation (see Transplantation: Corneal Transplants and Why They Usually Work) may be needed to restore vision. The insertion of corneal ring segments (objects that change the shape of the cornea to help correct refraction) seems to improve vision by allowing people to better tolerate wearing contact lenses. Corneal ring segments prevent certain people from needing a corneal transplantation. Ultraviolet light treatments that stiffen the cornea have had positive results and may become more common.

Last full review/revision November 2012 by Melvin I. Roat, MD, FACS