Iridology: Prince Charles may like it, but the evidence shows it’s bogus

Ignaz von Peczely (1826-1911) was a Hungarian physician who entered the history books for one of the most bizarre ideas in all alternative medicine: he came up with the idea of iridology (or iris-diagnosis). It happened after he saw streaks in the iris of a man he happened to be treating for a broken leg, and after he witnessed similar phenomena in the iris of an owl whose leg had been broken. Based on such clues, von Peczely became convinced that, by observing the iris of a person, he was able to distinguish between healthy organs and those that are over-active, inflamed, or distressed.

Iridology became internationally known when US chiropractors and subsequently other alternative practitioners in Europe began adopting this method in their clinical practice. In the US, few insurance programmes cover iridology but, in some European countries, they tend to pay for this diagnostic technique. In Germany, for instance, 80 per cent of the Heilpraktiker (non-medically qualified health practitioners) are said to employ iridology as a diagnostic tool.

In essence, iridologists claim to be able to identify medical conditions or predispositions to disease through abnormalities of pigmentations in the iris. The current popularity of iridology makes it, I think, necessary to ask whether this method is more than hocus pocus.

My systematic review tried to achieve just that; it was aimed at critically evaluating all available tests of iridology as a diagnostic tool. Four case control studies were included; these are investigations where iridologists were asked to tell by looking at the iris of individuals whether they did or did not have a certain pre-defined condition. The majority of these studies found that iridology is not a valid diagnostic method. I therefore concluded: ‘The validity of iridology as a diagnostic tool is not supported by scientific evaluations. Patients and therapists should be discouraged from using this method.’

The review was conducted in 1999 and since its publication several further studies have emerged. One German team conducted a study investigating the applicability of iridology as a screening method for colorectal cancer. Digital colour slides were obtained from both eyes of 29 patients with histologically confirmed colorectal cancer, as well as from 29 healthy control subjects. The slides were presented in random order to the experienced iridologists who did not know to which group of individuals each slide belonged.

The iridologists correctly detected 51.7 per cent and 53.4 per cent of the slides. The likelihood of a correct diagnosis was thus no better than chance, and the authors concluded: ‘Iridology had no validity as a diagnostic tool for detecting colorectal cancer in this study.’

A study from South Africa sought to determine the efficacy of iridology in the identification of moderate to profound sensorineural hearing loss in adolescents. A controlled trial was conducted with one experienced iridologist who was blind to the actual hearing status of the participants and was asked to analyse their irises. Fifty hearing impaired and 50 normal hearing subjects took part in the study. A 70 per cent correct identification of hearing status was obtained with a false negative rate of 41 per cent compared to a 19 per cent false positive rate.

The authors of this investigation concluded: ‘Iridological analysis of hearing status indicated a statistically significant relationship to actual hearing status. Although statistically significant sensitivity and specificity rates for identifying hearing loss by iridology were not comparable to those of traditional audiological screening procedures.’

Finally, a German study tested the value of iridology for detecting common cancers. One hundred and ten subjects were enrolled; 68 subjects had histologically proven cancers and 42 participants were cancer-free. All subjects were examined by an experienced iridologist who was unaware of their medical details. The iridologist identified the correct diagnosis in only three cases. The authors of this paper concluded: ‘Iridology was of no value in diagnosing the cancers investigated in this study.’

Based on these results, iridology is clearly not a valid or useful diagnostic tool. First, the method is implausible: there is no anatomical or physiological basis for its assumptions. Second, the available clinical evidence does not support its usefulness as a diagnostic tool.

In other words, iridology is bogus. This statement is in sharp contrast to the information consumers currently receive about the method on countless websites, books and articles. Even Prince Charles, with his book Harmony: A New Way of Looking at Our World, has joined the chorus of quacks who are out to misguide us. This is what His Royal Highness wrote about iridology:

I have also learnt from leading experts how we can understand a great deal about the causes of ill health through more traditional methods of diagnosis – for example, through examination of the iris…

This is not to say that modern diagnostic techniques do not have a role, but let us not forget what we can gain by using the knowledge and wisdom accumulated over thousands of years by pioneers who did not have access to today’s technology.

In fact, an over-reliance can often mean that the subtle signs of imbalance revealed by the examination of the eyes, pulse and tongue are totally missed… Why persist in denying the immense value of such accumulated wisdom when it can tell us so much about the whole person — mind, body and spirit?

Perhaps you think that none of this really matters all that much. Who cares whether iridology is bogus or not? However, I would argue that, for at least two reasons, it does matter a great deal.

— Bogus methods cost money that could be better spent elsewhere.
— False positive and false negative diagnoses can put lives at risk.

Edzard Ernst, emeritus professor at the University of Exeter, is the author of A Scientist in Wonderland and the awardee of the John Maddox Prize 2015 for standing up for science. He blogs at edzardernst.com.


  • Jo Brodie

    One of the things that has surprised and amused me on iridology websites is that so few of them mention Wilson’s disease. This is a condition in which copper builds up in the tissues causing all sorts of problems, but it can also cause the appearance of rings around the iris which are often unmistakeable. False positives / negatives (and other confirming blood, biopsy or genetic tests) aside, I thought it was quite funny that no-one really mentions it – as it would seem to be one thing that iridologists (or anyone who’s spent five minutes looking at Google images) MIGHT have a tolerable chance of spotting 😉 [No I am not really suggesting that iridologists can diagnose Wilson’s disease].

    Some quacks even offer online iridology readings – you send them some money, a webcam snapshot of your iris (or live via a Skype consultation) and they email you a report. I’m in the wrong job!

    In the UK anyone making any health claims for iridology is at odds with the Advertising Standards Authority and Committee of Advertising Practice (CAP). Their guidance points out that “CAP has
    seen no evidence to prove that it works and practitioners should limit
    themselves to claims of availability only” – which is pretty damning 🙂
    https://www.cap.org.uk/Advice-Training-on-the-rules/Advice-Online-Database/Therapies-Iridology.aspx

  • westlondoner11

    And bizarrely, iridology has spread to veterinary practice – there are iridologists who specialise in dogs or horses. What a ludicrous way to earn a living.

  • Bravo to Ernst and the other scientists who have irrigated this iridology nonsense into the light of reason of the 21st century. What worries me is that socially powerful people choose to influence others to believe in it and choose to blindsight themselves to the evidence that it is bogus. This is why we need an independent institute for veracity.