How can I find optic nerve in a retina image

I'm not using Matlab, but I've done recognition of some features using AForge.NET and can tell you that your case is not the so easy, due to several problems of your image: the lack of colors; the spot you are looking for is fuzzy, it's shape is very irregular due to oblique lighting showing shadows from some veins; there are other fuzzy spots in the image; they look different to your eyes but will confuse the standard recognition algorithms; there are long whitish veins which also can be detected as false positives.

You will need certain experimenting to "solve" this image. But the general way should be this: first, you perform contrasting transform to the picture, probably going to extreme. Then you perform blob analysis. If the blob detection algorithm has size discrimination (filtering out by size), especially in two directions (vertical, horizontal), you should use it. After blob detection, I'm almost sure you are going to have some false positives, so you will have to perform your own filtering to choose the right one. This problem is greatly simplified by the fact that you have only one object. Most likely, the sizes of this feature lie in a pretty narrow domain, do you can look at the convex hull instances of the detected spots and find one which is the "most rounded" with the sizes closest to the expected size.

Sorry if my advice is not definitive enough. I would need to conduct a good deal of research myself to resolve this kind of recognition, but I feel that it's quite possible.

—SA