Recent studies have suggested that one possible cause of keratocouns involves increased degradation of the corneal extracellur matrix. Most studies have examined corneas from patients with bilateral, sporadic keratoconus. In this report, both corneas from a 70-years-old man with a history of familial keratoconus and clinical signs of unilateral keratoconus were examined for gelatinase activity. Our results demonstrated a qualitative (three additional activity bands of 88, 92 and 100 kDa molecular weights) and quantitative differences (an appareent increase in overall amounts) in the gelationolytic enzyme profiels of the affected keratoconus corneas, and cultured kearatocytes. In addition, gelatinolytic enzymes were4 more readily extracted from the affected cornea compared with controls. These data lend support to the hypothesis of a heterogeneous etiology for keratoconus and to previous suggestions that this disorder may be related to an alteration in extracelluar matrix degradation.