·Diabetic retinopathy(DR)is one of important eye diseases that may cause blindness.Its occurrence and development is related to blood glucose level,duration of diabetes,environment and genetics.Nitric oxide(NO)is an important vasoactive substance which correlate with capillary occlusion,microcirculation disturbance,endothelial cell proliferation in DR.Nitric oxide synthase(NOS)is now accepted as a key enzyme of NO synthesis.The functions of NO and NOS on genetic polymorphism to DR are summarized in this review.·