Refract on the cornea doesn't work well in Poser because it turns dark. I'd use reflection only with transparency on the cornea.

The ring is likely the reflection (and then refradtion) of the white of the eye just adjacent. Adjust the refract bias if you think you need to use refraction :).

Because the cornea is part of the figure, and because you can't turn off/on shadows by that particular part on the figure, the refract on the cornea is going to make a shadow on the iris.

Laurie