The risk factors for RVH are complicated, including (1) systematic factors: poor glucose control or hyperglycemia, high blood pressure, diabetic nephropathy and diabetic retinopathy stage; (2) local factors: high perfusion of retinal vessels, retinal neovascularizaiton, low postoperative intraocular pressure (IOP) and high level of vitreous vascular endothelial growth factor (VEGF); (3) treatment factors: intravitreal tamponade, laser photocoagulation; (4) other factors: direct and indirect forces on eyes, such as doing strenous exercise too early after surgery. This evidence concerns the gene VEGFA and diabetic retinopathy.