Keratoconus (KC) is a noninflammatory conical protrusion of the central part of the cornea of still unknown etiology and poorly explored pathogenesis. By now a great number of theories and hypotheses on both etiology and pathogenesis of KC have been suggested: genetic, metabolic, immunological, endocrinological, ecological, etc. There are plenty of reports and research results supporting either of the theories and evidencing the link of KC to other diseases. Nevertheless, the question of the underlying reason for keratoconus development remains unresolved.