I'm having some trouble with this, and to fully explain I really ought to post an awful lot of screen shots; however I don't really want to expose other people's node set-ups, either to ridicule or copyright infringement.

I'll be experimenting further myself later on today, but in the meantime I thought this must be something that others have done and there may be some general pointers.

First picture: the character with the glasses made invisible. This is the materials from PDesign's Priscilla for V4, rendered in Poser 7. I should point out straight away that I've tried other commercial V4 materials with the same outcome, but not as yet something simpler. I've also tried simplifying the eye materials by removing nodes other than image maps, again the problem remains. One of the barriers I've encountered is that I don't really understand what V4's eye materials are doing, so I'm not sure where to start.