I put this together this morning, intending, originally to post it on my blog, but I think it's better laid out this way. Which means I get to upload it here, so people can download it full size.
Please DO NOT repost this on other sites, redistribute it, etc. You may, however, link to it to your hearts content.
Provided, that is, you find it informative.
I painted this in Corel Painter, however, it should work just as well in Photoshop or whatever paint program you have, provided it works with layers and layer settings.
Please be aware: I paint eyes so often that it's like breathing for me. Sometimes I do things without even being aware that I've done it or how I did it... I tried to break everything down as simply as possible for this, but if you need clarification, don't hesitate to ask.
Eyeball model: me (image isn't stock) [link]