The ratio of the optic cap to disc (CDR) in retinal fundus images is one of the principal physiological characteristics in the diagnosis of glaucoma. Currently the CDR is manually determined which can be subjective and limits its use in mass screening. To automatically extract the disc, a variational level set method is proposed in this paper. For the cup, two methods making use of color intensity and threshold level set are evaluated. A batch of 73 retinal images from the Singapore Eye Research Centre was used to assess the performance of the determined CDR to the clinical CDR, and it was found that the threshold and variational level set methods produced 97% accuracy in the determined CDR results, an 18% improvement over the color intensity method. The results indicate potential applicability of the methods for automated and objective mass screening for early detection of glaucoma.
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