The eye is made up of eyeball, pupil and eyelids.
The eyelids can be opened and closed and can be textured separately from the rest of the eye so that they can be made to seamlessly take on the texture of the rest of the face.
The pupil can either be round or a slit shape and can be adjusted in size.
The eyeball can take on it's own texture and can be rotated in it's socket to allow the eye to look around.