This is the shader for iris and pupil. It's exactly the same nodes as the sclera because we're using the EyeSurface for reflections. If we use sclera for reflections, then this will remain the setup for iris and pupil, but sclera will change quite a bit.

However - the node values here are NOT the same. I wanted the somewhat weak blue iris texture to be more exciting. So I boosted both saturation and value. And I didn't need the yellow tint.

I forgot to mention earlier - your eye scatters need to be in a different scatter group than your skin scatter. Assuming your skin is group 1, set the eye scatters to 2 as I've done here.

If you don't remember to make a different scatter group, then the skin will look blue around the eyeballs.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)