I'm posting a very simple tutorial on how to model and apply shaders to get realistic eyes, the "windows of your character's soul". A lot of times, bad eyes can "kill" your character literally, even if it has the most perfect modeling of the world. The importance of the eyes is exactly this: give life to your character. Therefore, don't underestimate this very important step of CG character construction... if not, you've only created "puppets".
There is a quite big camber in the cornea, in the iris area. That irregularity, that all of us have, can become a great problem for a CG character. When rotating the eye, this area unfortunately would invade the eyelids faces, causing strange results. For that reason, I decreased this camber to avoid a probable future problem.
Create a sphere with few segments (in this case, 8):
If you prefer, delete the half and use a NURMS/Symmetry (MAX) or CPS Script (MAYA):
Here, we see the approximate size proportion of the iris in relation to the eye. It occupies an area a little larger than 2/4 of the height but not 1/3. Create 2 new loops according to the indications in red, exactly where the iris borders will be:
Here, the perspective view, after a small polygon "relax":
Model the small camber until getting a close result of this (side view):
We will transform the extremity triangles...
...in quads, cutting the mesh this way:
SubD wire version...
...shade mode. Observe that the camber is minimum, different than it happens in the real eye:
Here are the initial proportions maintained after the completion of the first part, the cornea: