An interesting combination use of motion tracking and the After Effects Bulge Effect, Joshua Lester demonstrates how to take some existing footage of an eye, and have it appear the the pupils are dilating.
This Quick Tip will show how to manipulate footage of an eye to create the illusion that the Iris or Pupil is dilating
This is a great example of how some simple tools and techniques can yield some great results, using the old-shool After Effects Point Tracker to track the eye and use that tracking data to drive the position of the bulge effect. Check out the tutorial for Simulating a Basic Dilating Iris in After Effects here.