The activity of oxidant enzymes XO (6.2±0.9 U/L; P<0.01) and MPO (52.4±6.3 U/L; P<0.01) in the serum of patients with age-related cataract was significantly lower compared to patients with age-related cataract and HT (XO=9.0±1.2 U/L; MPO=77.3±8.4 U/L) and patients with HT and DM (XO=11.9±0.9 U/L; MPO=89.5±5.0 U/L). Here, MPO is linked to diabetes mellitus.