A high-resolution human eye and cornea model with Cycles materials (or at the least, my first valiant attempts at them). Doesn't use OSL shaders or other experimental Cycles features, so GPU rendering should be possible.
Base polycount of around 1350 quads. Render preview made at 2 subsurf levels, 4 light bounces and 500 samples/px.
Includes this list of extras:
A deform cage, useful for reshaping the eye to fit characters with alien, toon, or other non-human faces. Deformed eye can still rotate as a sphere.
Pupil dilation shape keys, driven by a custom bone.
A "Pixarize" shape key that will sink the iris to a concavity, for a Pixar-like eye.
Two parent Empties. One rotates just the eye (assign your tracking constraints to this one), while the other moves/rotates/scales the whole kit and boodle.
Painless importing into other .blends. Append the Object Group "eye_package" to bring in everything needed.
Full credit for the included textures and bump map goes to the user "arexma", who gave us some excellent BI eyes back in the day before he dropped off the Blend Swap radar. (View the source .blend here.) You may need to adjust the UVs if you substitute your own textures.