Keratoconus corneas exhibited a 2.2-fold increase of catalase mRNA level (P < 0.01) and 1.8-fold of enzyme activity (P < 0.03); a 1.5-fold increase of cathepsin V/L2 mRNA (P < 0.03) and abnormal protein distribution; and a 1.8-fold decrease of TIMP-1 mRNA (P < 0.05) and 2.8-fold decrease of protein (P < 0.0001) compared with normal (physiologic) corneas.