For the eyes, you need two have two eyeballs as separate polygon meshes or groups.
Location. The eyeballs should be in their sockets, obviously.
Orientation. The eyes should be looking forward towards positive Z and their line of gaze should be exactly parallel.
Cornea. Eyeballs should have inner and outer shell with a little bulge in the front for the cornea.
Eyelids and Sockets. The eye sockets should be modeled such that at least the inside of the upper and lower eyelid is present.
Lacrimal Gland. For realism, there should be lacrimal glands at the inside of each eye, but they're not mandatory.
