youre a drawing machine! ^^
on the last studies, you could add bigger/more reflections to those eyes, it should bump them up a lot (making them more 3d/ballish) and there for more realistic and alive. also a good idea to play with the iris... darker on the inner and outer edges, lighter in the middle (also darker on top of the iris, lighter in the bottom due to the shadow from upper eyelid) look around at a few examples and study the shadows/highlights and reflections http://www.bostonherald.com/blogs/sp...bionic-eye.jpg)
otherwise, good stuff, keep it up!