Keratoconus is a progressive disease that results in what is known as ectasia, which is
a steepening and thinning of the cornea. Patients experience vision loss due to progressive
irregular astigmatism, typically in both eyes, although the condition can be very asymmetric.
The prevalence of keratoconus is estimated to be between 1 in 375 to 1 in 2000 individuals
and typically presents in the second decade of life. How and why keratoconus
develops is still largely unknown, but genetic factors and heredity are known to play a
role. Additionally, there have been multiple associations made between keratoconus and
various systemic conditions, and these associations could serve as clues to the pathogenesis
of keratoconus. Some of these systemic associations have been corroborated by multiple
controlled studies, while others are only suggested by small observational studies. In this
review, we aimed to summarize the evidence for the most frequent systemic associations of
keratoconus.
