@ MikeJ,

Quote - I think the reason that you can see the iris from the side in a real eye better is due to refraction through the cornea and not because the iris is convex.

Possibly , but I still think a real iris is slightly convex, plus I'm no good at material nodes, and I'm not sure whether refraction would cure the highlight/shadows problem. A morph was a much simpler solution for me, but I'd also be interested to see what the node nerds can come up with.