Here the pupil has exactly the same shader as the iris. This looks better. Of course, the color map should be drawn correctly with total black in the middle for this to work right. But the transition should be gradual, not abrupt.

My point here, again, is the pupil material zone serves no purpose at all.

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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)