Automatic detection and boundary estimation of the optic disk in retinal images using a model-based approach

A new method to automatically locate the optic disk and estimate its shape in color retinal images is proposed. Principal component analysis (PCA) is applied to the candidate regions at various scales to locate the optic disk. The minimum distance between the original retinal image and its projection onto "disk spaces" indicates the center of the optic disk. The shape of optic disk is obtained by an active shape method in which affine transformation is used to transform the shape model from shape space to image space. The effects of vessels present inside and around optic disk are not eliminated, but also incorporated in the processing. The proposed algorithm takes advantage of top-down strategy that can achieve more robust results especially with the presence of large areas of light lesions and when the edge of the optic disk is partly occluded by vessels.