I designed the separate cover for the cornea because we want to use refraction, not transparency. But - without transparency, the cornea shadows the iris and so the iris gets no light.

My solution was a separate cover prop, and then turn of cast shadows for that. Thus the iris is fully lit even though completely covered.

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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)