Detecting the optic disc in retinal images by means of a geometrical model of vessel network

We present here a new method to identify the position of the optic disc in retinal fundus images. The method is based on the preliminary detection of the main retinal vessels by means of a vessel tracking procedure. All retinal vessels originate from the optic disc and then follow a parabolic course towards retinal edges. Thus, a geometrical parametric model was proposed to describe the direction of these vessels and two of the model parameters are just the coordinates of the optic disc center. Using samples of vessels directions (extracted from fundus images by the tracking procedure) as experimental data, model parameters were identified by means of a simulated annealing optimization technique. These estimated values provide the coordinates of the center of optic disc. A Matlab® prototype implementing this method was applied to a set of 40 images of both normal and pathological subjects. In all these images, the optic disc position was correctly identified, even in rather difficult pathological situations. An extensive validation on a set of 81 images (STARE project data set) is currently in progress to assess the robustness of the proposed technique.