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I think that a toroid that's set back from the sclera by an appropriate amount would probably produce a more accurate image. If I interpret MikeJ's wireframes correctly, his iris isn't set back from the sclera, and there's no dent in the middle for the pupil, either.

Actually it's set back from the sclera ever so slightly. It's a separate mesh, not attached to the sclera.
No real dent leading down to the pupil, no. I didn't think it necessary being that the pupil is completely transparent, in essence not really there.
But I see what you mean now.