Furthermore, some studies showed that the vascular endothelial growth factor (VEGF) is the major angiogenic stimulus responsible for increase of vasopermeability, cell proliferation and angiogenesis in diabetic retinopathy (DRP). Evaluation of VEGF levels in the vitreous have indicated a role for VEGF in diabetic macular edema: vitreous samples of patients with diabetic macular edema contain elevated VEGF concentration and injection of VEGF in experimental studies led to breakdown of the blood-retina barrier.