|Claims||Patterns, colors, and other characteristics of the iris hold information about a patient's systemic health.|
|Related scientific disciplines||Medicine|
|Original proponents||Philippus Meyeus|
Iridology (also known as iridodiagnosis or iridiagnosis) is an alternative medicine technique whose proponents claim that patterns, colors, and other characteristics of the iris can be examined to determine information about a patient's systemic health. Practitioners match their observations to iris charts, which divide the iris into zones that correspond to specific parts of the human body. Iridologists see the eyes as "windows" into the body's state of health.
Iridologists believe they can use the charts to distinguish between healthy systems and organs in the body and those that are overactive, inflamed, or distressed. Iridologists believe this information demonstrates a patient's susceptibility towards certain illnesses, reflects past medical problems, or predicts later health problems.
As opposed to evidence-based medicine, Iridology is not supported by quality research studies and is widely considered pseudoscience. Iris texture is a phenotypical feature which develops during gestation and remains unchanged after birth. The stability of iris structures is the foundation of the biometric technology which uses iris recognition for identification purposes.
Iridologists generally use equipment such as a flashlight and magnifying glass, cameras or slit-lamp microscopes to examine a patient's irises for tissue changes, as well as features such as specific pigment patterns and irregular stromal architecture. The markings and patterns are compared to an iris chart that correlates zones of the iris with parts of the body. Typical charts divide the iris into approximately 80-90 zones. For example, the zone corresponding to the kidney is in the lower part of the iris, just before 6 o'clock. There are minor variations between charts' associations between body parts and areas of the iris.
According to iridologists, details in the iris reflect changes in the tissues of the corresponding body organs. One prominent practitioner, Bernard Jensen, described it thus: "Nerve fibers in the iris respond to changes in body tissues by manifesting a reflex physiology that corresponds to specific tissue changes and locations." This would mean that a bodily condition translates to a noticeable change in the appearance of the iris. For example, acute inflammatory, chronic inflammatory and catarrhal signs may indicate involvement, maintenance, or healing of corresponding distant tissues, respectively. Other features that iridologists look for are contraction rings and Klumpenzellen, which may indicate various other health conditions, as interpreted in context.
The first explicit description of iridological principles such as homolaterality (without using the word iridology) are found in Chiromatica Medica, a famous work published in 1665 and reprinted in 1670 and 1691 by Philippus Meyeus (Philip Meyen von Coburg).
The first use of the word Augendiagnostik ("eye diagnosis," loosely translated as iridology) began with Ignaz von Peczely, a 19th-century Hungarian physician. The most common story is that he got the idea for this diagnostic tool after seeing similar streaks in the eyes of a man he was treating for a broken leg and the eyes of an owl whose leg von Peczely had broken many years before. At the First International Iridological Congress, Ignaz von Peczely's nephew, August von Peczely, dismissed this myth as apocryphal, and maintained that such claims were irreproducible.
The German contribution in the field of natural healing is due to a minister Pastor Emanuel Felke, who developed a form of homeopathy for treating specific illnesses and described new iris signs in the early 1900s. However, Pastor Felke was subject to long and bitter litigation. The Felke Institute in Gerlingen, Germany was established as a leading center of iridological research and training.
Iridology became better known in the United States in the 1950s, when Bernard Jensen, an American chiropractor, began giving classes in his own method. This is in direct relationship with P. Johannes Thiel, Eduard Lahn (who became an American under the name of Edward Lane) and J Haskell Kritzer. Jensen emphasized the importance of the body's exposure to toxins, and the use of natural foods as detoxifiers.
Critics, including most practitioners of medicine, dismiss iridology given that published studies have indicated a lack of success for its claims. To date, clinical data do not support correlation between illness in the body and coinciding observable changes in the iris. In controlled experiments, practitioners of iridology have performed statistically no better than chance in determining the presence of a disease or condition solely through observation of the iris.
It has been pointed out that the premise of iridology is at odds with the fact that the iris does not undergo substantial changes in an individual's life. Iris texture is a phenotypical feature that develops during gestation and remains unchanged after birth. There is no evidence for changes in the iris pattern other than variations in pigmentation in the first year of life and variations caused by glaucoma treatment. The stability of iris structures is the foundation of the biometric technology which uses iris recognition for identification purposes.
Scientific research into iridology 
Well-controlled scientific evaluation of iridology has shown entirely negative results, with all rigorous double blind tests failing to find any statistical significance to its claims.
In a study published in the Journal of the American Medical Association, three iridologists incorrectly identified kidney disease in photographs of irises and often disagreed with each other. The researchers concluded: "iridology was neither selective nor specific, and the likelihood of correct detection was statistically no better than chance."
Another study was published in the British Medical Journal which selected 39 patients who were due to have their gall bladder removed the following day, because of suspected gallstones. He also selected a group of people who did not have diseased gall bladders to act as a control. A group of 5 iridologists examined a series of slides of both groups' irises. The iridologists could not correctly identify which patients had gall bladder problems and which had healthy gall bladders. For example, one of the iridologists diagnosed 49% of the patients with gall stones as having them and 51% as not having them. Dr Knipschild concluded:, "...this study showed that iridology is not a useful diagnostic aid." Iridologists defended themselves and attacked the study's methodology.
Edzard Ernst raised the question in 2000: "Does iridology work? [...] This search strategy resulted in 77 publications on the subject of iridology. [...] All of the uncontrolled studies and several of the unmasked experiments suggested that iridology was a valid diagnostic tool. The discussion that follows refers to the 4 controlled, masked evaluations of the diagnostic validity of iridology. [...] In conclusion, few controlled studies with masked evaluation of diagnostic validity have been published. None have found any benefit from iridology."
Regulation, licensure, and certification 
In Canada and the United States, iridology is not regulated or licensed by any governmental agency. Numerous organizations offer certification courses.
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