nurbs sphere> rough out eye shape> deatch the front of the eye from the rest> duplicate the main eye shape and scale it down the the white bit (whaterver its called)> make the cross section of iris and pupic (which will just be a space inside the eye)> revolve the profile and detatch the pupil from the iris> you can then add matterials seperately to each section and parent it all under one group. To be honest its not allways necessary to do this much work on the eye.