All good suggestions above, and here is what I do when I want something quick and cheap. Turn down the brightness of the eyes material "white" color to match you scene ambience - this reduces the "glowing eye" syndrome. Set the highlight size to much smaller than the default, and play with highlight luminosity and hue a bit to capture your ambience - granted its not nearly as good a solution as the cornea prop, but if not too close-up it works. I rarely use the default Poser settings on eyes - they all look bad, but can be improved with a little experimentation.