This is actually in the free tutorial section at thegnomonworkshop.com, but I thought I would spread the word about this excellent tutorial. It’s for Maya and Mental Ray, but many of the concepts and techniques can be brought over to Blender.
WARNING: NOT DIAL-UP FRIENDLY AT ALL! And you may have to wait in a download line, but it’s worth it. Creating Believable Eyes: By Alex Alvarez. It’s the third one down the page and is in 4 parts, all Quicktime format. Unfortunately you have to register with the site to download. Please don’t be discouraged by that, I believe this resource is worth it! Close to 4 hours of instruction is given.