NOS3 and diabetes mellitus: Nitric oxide (NO) metabolism is closely related to the NADPH system because excess O2•− production can induce uncoupling of endothelial nitric oxide synthase (eNOS); this might result in endothelial dysfunction and neovascularization eventually, since NO helps maintain ocular hemodynamics by protecting the endothelial cells of vascular beds and nerve fibers against pathogenic processes, e.g., diabetes and glaucoma [36,37].