1. A method for optic disk detection in retinal images, comprising: extracting a vessel tree from a retinal image; locating an optic disk in the retinal image using the vessel tree; enhancing a contrast of the optic disk; removing vessels from the contrast enhanced optic disk; detecting a boundary of the optic disk with vessels removed by generating an edge map; projecting the edge map at a plurality of angles by using a radon transform; and estimating a radius and center of the optic disk using the projections, wherein locating an optic disk in the retinal image comprises: selecting first start and end points and second start and end points from different branches of the vessel tree; finding a shortest path between the first start and end points and a shortest path between the second start and end points; finding an intersecting point of the shortest paths at a root of the vessel tree; and defining the intersecting point as a location of the optical disk.