"Besides repeated failures and an evidence vacuum, there is one other essential problem which iridology faces: iridologists agree that the markings of the iris change to reflect changing states of health. Yet the pattern of a person's iris, like their fingerprints, remains the same their whole life long, which is why, like fingerprints, the markings of the iris can be used for biometric identification." Skeptic Wiki (The Encyclopaedia of Science and Critical Thinking)