Attached Link: http://www.psalmons.co.uk/

There's a P5/P6 tutorial in the "Tips" section on how to improve eyes, though the details are for Daz's Millenium figures. But there's several little things you can do with shaders, rather than a texturemap. I don't 100% agree with the suggestions there; I'd give a slight red tint to the black of the pupil myself, and as a general rule I avoid the extremes of black and white so as to leave a little room for highlights and shadows.