1. A retinal image analysis method including: (i) defining an optic disc for a retinal image; (ii) automatically tracing one or more vessels of the retinal image, each vessel comprising a group of vessel segments including a root segment and a plurality of daughter segments connected to the root segment in a vessel binary tree in which at a plurality of branching points one of said vessel segments branches into two said daughter segments; (iii) automatically displaying an image comprising the one or more traced vessels; (iv) using the vessel segments to calculate automatically a plurality of parameters; and (v) outputting the plurality of parameters; wherein the plurality of parameters comprise a parameter characterizing the group of vessel segments, the parameter being a fractal capacity dimension of the image.