Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and chromosomal disorders. It has been blamed on eye rubbing as is often seen in Leber congenital amaurosis and other ocular disorders as well as in atopic conditions and in individuals who have worn contact lenses for many years. Cause and effect in these situations is difficult to prove and it is likely that keratoconus is an etiologically heterogeneous disorder. Only keratoconus associated with single gene mutations are considered here.
Recent evidence suggests that corneal hydrops is strongly associated with mitral valve prolapse.