Time to look at the second part of the eye we will need to create: the iris. This object will live inside the outer eye model and will be fully visible, so it has to look right. To help us, we will use another normal map.
Following Figure 11.12, start by creating a standard cylinder but make sure it has the same divisions as the outer eye. This way the vertices will match when we position it inside the eye.
Figure 11.12. Create the basic iris shape.
Divide the cap twice before deleting the back of the cylinder. We need only the flat front for our iris.
The central area will act as your pupil, so adjust its size appropriately. ...