Did you every try to model an eye with Blender? This is a nice tutorial for professional looking eyes from César Salcedo.
César starts by modling the eyeball using a reference. You will see that the modeling is done in a few simple steps to produce a great looking eye model.
After that he sets up the lights and then he does the UV-mapping for the eye to prepare it for texturing.
The node setup for the textures is rather complex, I extracted the images so you could try to reproduce it, the links to the textures are added below the video:by