Iris
From Tardis Wiki, the free Doctor Who reference
An iris was a body part. It was a flat, coloured, ring-shaped membrane behind the cornea of the eye, with a pupil in the centre.[source needed]
Heather had a star shaped defect on her left iris. (TV: The Pilot)
Regeneration could change the colour of the iris. (TV: The Parting of the Ways)
