I think this will be very challenging. You can track a white shape over pupil and iris but then you will have to add mattes for they eyelid movement unless their eyes are always wide open and seen from the same angle.
Or probably a lot easier, you could try messing with the Levels of the eye until it looks right. That will ruin every thing else in the scene so you will have to add as mask to the eye so the levels filter only effects the eyes.
Hope this helps and best of luck.
Stephen Smith
Utah Video Productions
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