I. Introduction
Retinal vascular lesions may reveal hypertension, diabetes, atherosclerosis and other cardiovascular diseases. At the same time, the retinal blood vessels are the only blood capillary of our body that can be observed directly and non-invasively. The change of retinal vascular may directly reflect the degree of diabetes and cardiovascular disease. Therefore, the detection and extraction of blood vessels in retinal images has important significance. In addition, due to individual differences, retinal vascular morphology will vary and has no reproducibility. And retinal vascular is located inside the human eye, its structure is less susceptible to external factors, so it has be widely applied in the fields of personal identification. national security and so on.