2003). Increased ROS levels lead to enhanced oxidative stress, which is considered to be the initiating step of various microvascular complications of diabetes (Ha and Lee 2000). The results of the present study suggest that high glucose caused significant increases in protein carbonyl, 8-OHdG and MDA, and impaired the activities of antioxidative enzymes (GPx, CAT and SOD) in Müller cells. It was shown that the ROS level in Müller cells was directly increased by high glucose treatment, which was consistent with previous studies (Rösen et al. 2001; Brownlee 2005; Rolo and Palmeira 2006). This evidence concerns the gene CAT and diabetes mellitus.