This is a photo-realistic eyeball model.
The iris will need to be adjusted depending on your model, along with
the eyeball transparency ramp.
I have also included the maps so the iris colour can be adjusted in photoshop
or your preferred photo editing software.
Please use refraction on your lights and render settings for best results.
Render with Mental Ray.
P.S If you would like to have control over the pupil, attach a cluster to the
verts on the iris and hey presto.