Iridology (also iris analysis, iris diagnosis or eye diagnosis) is an alternative medical diagnostic method which assumes that human diseases can be determined by analyzing the tissue structures of the iris. It could neither be empirically substantiated nor theoretically substantiated.
From the perspective of their users, iridology is rarely used as the sole diagnostic tool and is therefore usually supplemented by other methods. In particular, it should serve to establish a basic assessment that could point to possible weaknesses in the organism.
Iris diagnostics should not be confused with iris recognition, which is similar to the fingerprint used to identify people, and makes use of the fact that the structure of the iris is different in each person.
Source: Wikipedia