Enola, with one of our cats a cornea shot would be a challenge but much, much easier than with humans. From the side the cornea is easily seen..however captured on film or sensor is a different matter.  Of course, all sort of nice eye shots could make the challenge and not only parts of eyes.  Eyes may imply  much to the viewer and I would expect a few rather expressive photos to be posted. 

Have you had opportunity to try the "monthly challenge" yet?  This is fun and often truly challenging.

                                                                                                                                                    TomDart.

PS Doug.  Valou's "perspective" is a good idea, too.