Oxidative stress caused by formation of free radicals leads to
retinal vasculature damage (Bursell and King, 1999; Bursell et al.,
1999). Moreover, these free radicals as reactive oxygen species
(ROS) are the strong stimulus for the release of proinflammatory
cytokines-interleukin 1b (IL-1b) and tumor necrosis factor
(TNF-a) which damage endothelial cells and play an important role
in the pathogenesis of DR (Gustavsson et al., 2008).