Photographer Dani Diamond teach how you can easily retouch eyes with a natural look using Photoshop. This 14-minute Photoshop video tutorial gives some useful description of how to read light within the iris of the eye and other similar techniques.
“Unlike many videos out there I start off by explaining how the human iris reacts to light. Once acknowledged one may apply any method of editing out there in a natural manner.”
Here the final image: