
208 Image Analysis and Modeling in Ophthalmology
12.3.2 Precise Segmentation
The standardized protocol to compute the AVR states that the vessel widths must be mea-
sured in several circumferences centered at the optic disc center. Moreover, their radii
must be a multiple of the optic disc radius. For these reasons, a rough location of the optic
disc is not enough and a precise segmentation is needed.
Since we are looking for the center and the radius of the optic disc, the circular Hough
transform is one of the best choices for this stage [19]. The aim of this feature detector is the
location of circles in the input image using a voting strategy ...