I've tried the solutions given in How to find a circular object in the image glaucoma? to detect the ellipse, but the detection results are not quite what I wanted.
In glaucoma we have a cup to disk ratio terms in which I must looking for calculate between the diameter of the optic disk (VDD) and optic cup (VCD). optical disks showed with a red circle (red channel) and optic cup showed with a yellow circle (green channel). how about calculating the diameter between optic disk and optic cup? sorry my first question is not complete. i have already detect the optic disk with canny edge detection, but i have not found a way to calculate the diameter of optic disk and optic cup. How might I do that?