@ cobaltdream,

Have a look at my second image on the previous page, the bottom part of the image. It's only an anti-aliased preview, not a render, but I think it shows that the convex toroid section shape looks quite realistic, especially the way it catches the light. It should do, because it is not far from the shape of a real iris. Compare it to the default dish shape, or convex sphere section from the previous image.