Attached Link: http://www.renderosity.com/mod/freestuff/search.php?section_id=-1&query=eye+texture&sort=relevancy&use_age=no&older_age=&older_units=day&newer_age=&newer_units=day&username=§ion_selector%5B0%5D=-1

Use image textures for the iris and sclera.  There are lots of them in the Poser freestuff that you can cut down and use on your own UV maps.  There may even be a tutorial on eye painting in the poser tutorials, though I'm having trouble finding one right now.