Well, of course I'm guessing since I don't know what you have going.

If you are using Ambient Occlusion on the eyes, it is typical that the AO darkens them considerably. In a normal render, you'd probably boost the Diffuse_Value to compensate, trying to keep the overall brightness, while showing some of the AO effect to give the eye some depth.

When I say "boost" I mean simply that the current value is too high. With GC, even darkened eyes will not be dark anymore. You'd want to un-boost the diffuse reflection in such cases.

If you're not using AO, this could still be the case. It's just a matter of what half-assed workaround was being applied to make the eyes appear to be the correct brightness when viewed on a computer monitor. Such choices turn into over-compensation once the GC lens is applied.

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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)