The eye is sometimes said to provide a window into the health of a person for it is only with the eye that one can actually see the exposed flesh of the subject without using invasive procedures. There are a number of diseases, particularly vascular disease that leave telltale markers in the retina. The retina can be photographed relatively straightforwardly with a funds camera and now with retinal image processing there is much interest in computer analysis of retinal images for identifying and quantifying the effects of diseases such as cardio vascular diseases. A retinal image provides a snapshot of what is happening inside the human body. In particular, the ceremonial of the retinal blood vessels has been shown to imitate the cardiovascular condition of the body. Retinal images provide considerable information on pathological changes caused by local ocular disease which reveals diabetes, hypertension, arteriosclerosis, cardiovascular disease and stroke. Computer-aided study of retinal image plays a central role in diagnostic procedures. However, automatic retinal segmentation is complicated by the fact that retinal images are often noisy, poorly contrasted, and the vessel widths can vary from very small to very large. So in this survey we can review various segmentation techniques to improve the accuracy in blood vessel extraction.

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