There is a popular belief in systematic changes in the iris patterns, reflecting the state of health of each of the organs in the body, one's mood or personality, and revealing one's future. Practitioners skilled in the art of interpreting these aspects of iris patterns for diagnosing clients' health, personality, and mutual compatibilities, are called iridologists. Like palm-readers and fortune-tellers, iridologists will offer advice on all of these matters by inspecting your iris. If you are interested in this sort of thing, a chart showing how each individual organ of the body is somehow "connected" to a specific spot on each iris for diagnosis is shown here. How personality is determined is revealed here, and a more elaborate theory of interpersonal compatibility based on iris patterns is detailed here.
Some limited types of changes in iris appearance can occur and do have a scientific basis: (1) In the first few months of life, a blanket of chromatophore cells in the anterior layer of the iris establishes eye colour; until this pigmentation develops, babies typically - even if only temporarily - have blue eyes. (2) Some pharmacological treatments for glaucoma involving prostoglandin analogues are reported to affect melanin, and therefore iris pigmentation, when applied topically to the eye. Such possible changes in iris colour are irrelevant for the method of iris recognition described here, as imaging is done with monochrome cameras and using infrared illumination in the 700nm - 900nm band; melanin is almost completely non-absorbant at these wavelengths. (3) Freckles can develop over time in the iris, as elsewhere on the body. Again these are spots of melanin pigmentation, invisible in the infrared illumination used for iris recognition, so they neither help nor hinder in the identification of the iris pattern. (4) Elderly persons' eyes sometimes show a thin white ring surrounding the iris. This is an optical opacity that develops with age in the base of the cornea, where it joins the sclera.
As for the occult belief that iris patterns reveal the state of one's organs and so may change systematically over time, there have been five reviews published in medical journals reporting various scientific tests of iridology (Berggren, 1985; Cockburn, 1981; Worrall, 1984, 1985; Knipschild, 1988; Simon, Worthen, and Mitas, 1979), and they all dismiss iridology as a medical fraud. In particular, the review by Berggren (1985) concludes: "Good care of patients is inconsistent with deceptive methods, and iridology should be regarded as a medical fraud."