There are many medical pseudosciences that persist despite a utter lack of either plausibility or evidence for efficacy. Some practices emerged out of their culture of origin, or out of the prevailing ideas of a pre-scientific age, while others were manufactured out of the imagination of perhaps well-meaning but highly misguided individual practitioners. They were just made up – homeopathy, for example, or subluxation theory.
Iridology belongs to this latter category – a system of diagnosis that was invented entirely by Ignatz Peczely, a Hungarian physician who first published his ideas in 1893. The story goes that Peczely as a boy found an owl with a broken leg. At the time he noticed a prominent black stripe in the iris of one eye of the owl. He nursed the bird back to health and then noticed that the black line was gone, replaced by ragged white lines. From this single observation Peczely developed the notion of iridology.
Peczely’s idea was that the iris maps to the rest of the body in some way, and therefore the flecks of color in the iris reflect the state of health of the various body parts. This basic approach to diagnosis or treatment is called the homunculus approach – the idea that one part of the body maps to the rest of the body, including the organ systems. Reflexology, auricular acupuncture, and even straight chiropractic follow this approach.
This is what might have happened next: After publishing his initial observations, Peczely set out to test his ideas with well-designed observations that were capable of proving his hypothesis wrong. He carefully built a body of descriptive, but well-established, facts about the relationship between the iris and health. Later, anatomists discovered the underlying mechanism of this connection – a vast system of interconnectedness between the iris and the rest of the body. Further research built on the iris connection, and later medical scientists found more and more ways to exploit this fascinating aspect of anatomy and physiology.
Of course, this is not what happened. Peczely did not do any serious scientific research. Rather, he simply invented a pseudoscience, by drawing maps of the iris that were as much a product of his imagination as observation, and were largely the result of confirmation bias. He did not perform blinded studies, or produce the kind of evidence that could separate a real phenomenon from an imaginary one. Iridology, as his practice became known, is the N-rays of medical diagnosis. Further, no subsequent science has supported the plausibility or reality of iridology. There is no underlying anatomy or physiology that can explain how the iris would reflect the state of function of any other part of the body.
This, unfortunately, has not stopped iridology from surviving on the medical fringe for more than a century. The modern popularity of iridology, especially in the US, can be traced back to a chiropractor named Bernard Jensen. He published the book, The Science and Practice of Iridology in 1952. Iridology, or iris diagnosis, continues to be practiced by so-called alternative practitioners, including some chiropractors and naturopaths. It has never been recognized as a legitimate medical practice. For example, for $150 naturopath Frank Navratil will diagnose you from a digital image of your eyes.
Often the iris diagnosis (which can also be done by software analysis) leads to recommendations for supplementation, which are conveniently sold by the iridologist. Here is a description of how iridology is used by a proponent:
The iris reveals changing conditions of every part and organ of the body. Every organ and part of the body is represented in the iris in a well defined area. In addition, through various marks, signs, and discoloration in the iris, nature reveals inherited weaknesses and strengths.
By means of this art/science, an iridologist (one who studies the coloration and fiber structure of the eye) can tell an individual his/her inherited and acquired tendencies towards health and disease, his current condition in general, and the state of every organ in particular.
Iridology cannot detect a specific disease, but, can tell an individual if they have over or under activity in specific areas of the body. For example, an under-active pancreas might indicate a diabetic condition.
Other sites caution that iridology cannot diagnosis pregnancy, because that is a natural condition of the body, and also cannot diagnose prior surgery, as anything that happens under anesthesia will block the signals that would otherwise change the iris. In other words – iridology only tells you about the susceptibility for disease – it cannot actually diagnose a disease or any other verifiable condition. This reasoning is called special pleading – the invention of a special rationalization for each fact that might otherwise falsify a claim or belief. Iridology, apparently, can only discern those things that cannot be verified or falsified.
What you end up with is a medical cold reading – similar to what a mentalist does to create the illusion of mind reading or psychic powers. While “reading” the iris the iridologist can ask about certain health issues. If they are present, that is used to validate iridology. If absent, then the subject simply has a susceptibility for the missing problem.
Iridology lacks any plausibility and its history is that of a pseudoscience, not a legitimate practice. But still we listen to the best scientific evidence in determining whether or not iridology is real. Perhaps Peczely got lucky and made a correct observation despite his lack of scientific confirmation. If iridologists could demonstrate that their readings provide real information, then we would have to take their claims seriously.
In 2000 Edzard Ernst (not surprisingly) published a systematic review of iridology research. He concluded:
In conclusion, few controlled studies with masked evaluation of diagnostic validity have been published. None have found any benefit from iridology. As iridology has the potential for causing personal and economic harm, patients and therapists should be discouraged from using it.
As with N-rays, when blinding is introduced iridology is exposed as a complete fiction. Under controlled conditions iridologists cannot agree with each other as to diagnosis, and cannot distinguish healthy subjects of very ill subjects. Since the Ernst review I found one other well-controlled study of iridology, this one in cancer diagnosis. From the abstract:
One hundred ten (110) subjects were enrolled in the study: 68 subjects had histologically proven cancers of the breast, ovary, uterus, prostate, or colorectum, and 42 were control subjects.
All subjects were examined by an experienced practitioner of iridology, who was unaware of their gender or medical details. He was allowed to suggest up to five diagnoses for each subject and his results were then compared with each subject’s medical diagnosis to determine the accuracy of iridology in detecting malignancy.
Iridology identified the correct diagnosis in only 3 cases (sensitivity, 0.04).
Iridology was of no value in diagnosing the cancers investigated in this study
There are no well designed studies that are positive.
Conclusion: Iridology is bunk
Iridology is an excellent example of pseudoscience in medicine, displaying many of the core features. It was invented by one individual based upon a single observation. It follows a pre-scientific notion of biology – the homunculus model. It lacks any basis in anatomy, physiology, or any other basic science. Its practitioners are mostly “alternative” practitioners who use the technique as a cold reading. And the research clearly shows that iridology has absolutely no effect – it does not provide any useful information at all.
Anyone using or promoting iridology is, therefore, a pseudoscientific practitioner. Any profession that endorses iridology is not science-based and should be looked upon with suspicion.