<Tr> <Th> Frequency </Th> <Td> ~ 1 in 2,000 people </Td> </Tr> <Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> Keratoconus (KC) is a disorder of the eye which results in progressive thinning of the cornea . This may result in blurry vision, double vision, nearsightedness, astigmatism, and light sensitivity . Usually both eyes are affected . In more severe cases a scarring or a circle may be seen within the cornea . </P> <P> While the cause is unknown, it is believed to occur due to a combination of genetic, environmental, and hormonal factors . About seven percent of those affected have a family history of the condition . Proposed environmental factors include rubbing the eyes and allergies . The underlying mechanism involves changes of the cornea to a cone shape . Diagnosis is by examination with a slit lamp . </P>

Refraction defect due to irregularities of the surface of the cornea or lens