Iridology and Credulity

The NZ Herald’s Life & Style section has (once again) affirmed their dedication to credulity, in an article by Donna McIntyre extolling the supposed virtues of iridology in what reads like an advertisement for a naturopath called Peter Riddering, ND (Not a Doctor) – Iridology: What the eyes reveal

EDIT: It seems the article has been moved into the NZ Herald’s Health & Wellbeing section (a subset of Life & Style): Iridology: What the eyes reveal

The article’s contents consist mostly of quoting Mr Riddering talking about how iridology supposedly works. No attempt is made, of course, to provide evidence supporting the claims he’s making. In fact, it seems the closest thing to supporting evidence that is offered is an argument from antiquity:

Modern iridology dates back to a Hungarian doctor Ignatz Peczely in the late 1800s but Peter says the Mayans, Egyptians, Chinese and Incas were also aware of iris markings and their link to health.

I’d like to flesh out the history of iridology a bit more than was done in the Herald article. The story goes that a young Ignatz Peczely observed a dark fleck in the iris of an owl with a broken leg (some reports claim that he broke its leg himself). After the owl had recovered, he noticed that the owl’s iris no longer contained the dark fleck, but instead contained a few white lines in about the same place.

When he had grown up, Peczely apparently became a homeopath (a sure sign of a quack if ever there was one). In his misguided attempts to treat people, he apparently noticed a similar fleck to the one he once observed in the owl in a man who, apparently, also had a fracture. After this, Peczely started to create a “map”, based on his observations, detailing how he thought the iris acted as a map of the entire body.

This “homunculus approach” to diagnosis, where one particular body part is believed to act as a map of the rest of the body, is relatively common in fake medicine. For example, tongue diagnosis is central to the practice of traditional Chinese medicine (TCM). Reflexology, which is essentially the idea that pretty much anything can be cured by a foot or hand massage, is another example.

Now let me just stop here. Nothing I have said so far really matters when it comes to whether or not iridology is a valid method of diagnosis. The things I have described are red flags, but they are far from conclusive. The real problem is what happened after Peczely’s original observations. Here’s what should have happened:

After making his initial observations, Peczely should have developed a hypothesis that internal medical problems can be diagnosed by examining the iris. In order to determine whether or not his hypothesis was true, he should have set up and carried out a set of rigorous tests that were capable of disproving his hypothesis.

That is not what happened.

As far as I can tell, iridology is based off “maps” that have been created not via rigorous testing of falsifiable hypotheses, but as a result of singular observations coupled with confirmation bias. Iridology is simply not supported by anatomy or physiology, and has never been shown to be an effective method of diagnosis or recognised as a legitimate diagnostic approach. Despite this, Peter Riddering charges people $65/hour for iridology sessions.

As he mentions in the Herald article (perhaps the only useful piece of information in there):

naturopaths are not allowed to make medical diagnoses. If [Mr Riddering] does come across anything, he suggests client go to their doctor

The way I see it, if you’re worried you might be ill here are 2 of your options:

  1. You see Peter Riddering, not a doctor, who uses a bogus method of diagnosis and, if he finds anything, tells you to see a real doctor.
  2. You see a real doctor.

I have to admit, I really don’t see the appeal in the first option. It seems the only differences are that the first option…

  • costs more
  • essentially funds fake medicine
  • carries a greater risk of misdiagnosis
  • takes more time

I’m not a medical doctor, so I’m going to give you the only health advice I’m qualified to give: ask a medical doctor

Here are some evaluations of iridology I found via a very quick search on Google Scholar, along with relevant excerpts from their abstracts:

  • An Evaluation of Iridology by Allie Simon; David M. Worthen, MD; Lt John A. Mitas, II, MC

    Iridology had no clinical or statistically significant ability to detect the presence of kidney disease. Iridology was neither selective nor specific, and the likelihood of correct detection was statistically no better than chance.

  • Iridology: Not Useful and Potentially Harmful by E. Ernst, MD, PhD, FRCP (Edin)

    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.

  • Iridology: A critical reveiw by Lennart Berggren

    [Controlled] clinical trials and experiments conclusively show that iridology has no ability to detect disorders in other parts of the body; there are sufficient proofs that iridology is purely conjectural. Iridology is of no medical value and might even be a potential danger to people seeking medical care. It should be exposed as a medical fraud.

  • Changing belief in iridology after an empirical study by P. Knipschild

    My paper on iridology presented evidence against its validity as a diagnostic aid.

    Note that this article itself did not assess the validity of iridology, but instead how doctors’ beliefs change when confronted with evidence against it.

  • Iridology: A Systematic Review by Ernst E

    Conclusion: The validity of iridology as a diagnostic tool is not supported by scientific evaluations. Patients and therapists should be discouraged from using this method.

  • An investigation of the relationship between anatomical features in the iris and systemic disease, with reference to iridology by PhD T.J. Buchanan, PhD C.J. Sutherland, PhD R.J. Strettle, PhD T.J. Terrell, MSc A. Pewsey

    The results demonstrate that the diagnosis of these diseases [ulcerative colitis, asthma, coronary heart disease or psoriasis] cannot be aided by an iridological style analysis.

  • Can Iridology Detect Susceptibility to Cancer? A Prospective Case-Controlled Study by Karsten Münstedt, Samer El-Safadi, Friedel Brück, Marek Zygmunt, Andreas Hackethal, and Hans-Rudolf Tinneberg

    Conclusion: Iridology was of no value in diagnosing the cancers investigated in this study.

If you’re at all worried that I’ve cherry picked the studies that support my conclusions, the quoted articles were simply all the links on the first page of results when searching for “iridology” on Google Scholar.

It seems iridology simply does not work. Anyone who says otherwise is either ignorant or dishonest.

3 thoughts on “Iridology and Credulity

  1. Not only is it unsupported, it’s absurd on any basis. I mean, the iris in each person is as unique as their fingerprint and can be used in identification systems e.g. “The Iris is a protected internal organ whose random texture is stable throughout life (from the 1st year onwards) and can be used as an identity document or a password offering a very high degree of identity assurance.”

    Might as well shove a pile of entrails in a bowl, there’s nothing there to support their claims. Even worse, because iridology is bollocks, and their training bollocks they’d be budding Dunning-Krugers who don’t know what they don’t know and they’d miss things that would indicate actual pathology which can be identified by looking at the eye – such as the yellowing of the sclera caused by true juandice, anaemia from the paleness of the inner lid or even opthalogical conditions that may be developing like glaucoma.

    1. Thomas Lumley of Stats Chat noted when he wrote about this article ( that, in 2003, the Herald seemed to know perfectly well that photographs of the iris could be used incredibly reliably for identification purposes.

      It’s worth noting that during the lead-up to the unfortunate death of New Zealander Yvonne Maine in 2010, she was being treated by Ruth Nelson, an iridologist and naturopath. However, from the news stories it sounds as though it’s her naturopathy that failed her in treating Mrs Maine, who apparently refused to see a real doctor, and no one seems to specify whether she was able to accurately diagnose her with iridology. I wonder if she’d still have refused to see a doctor if there was no “alternative” quack for her to see instead.

      I think it’s just as concerning that such indications as you’ve mentioned must be misdiagnosed as opposed to being missed altogether. If a person is told by an iridologist they trust that a cloudy area of their eye is indicative of a susceptibility to liver disease then they would likely be less likely to bring the issue to someone who can give them the diagnosis and treatment they may require.

      It’d be interesting to investigate just how consistent diagnoses given by different iridologists are. It’d be a win-win for science-based medicine, in that either it’s found that they’re inconsistent and therefore clinically useless, or they’re consistent and can therefore be compared with diagnoses attained via proven methods in order to determine whether these consistent diagnoses are correct or clinically useful.

      A common claim of iridologists is that iridology only diagnoses “susceptibility to disease”. This claim, although lacking in supporting evidence, makes the reliability of iridology more difficult to prove or disprove. If diagnoses from different iridoligists are inconsistent that would be enough to draw a conclusion, but if they’re consistent (which wouldn’t surprise me, considering that iridological diagnosis seems to rely heavily on standard iris charts) then it’d presumably take larger epidemiological studies in order to tell if they really are reliably diagnosing susceptibility to disease.

      Of course, considering the lack of prior probability and the fact that the weight of the current evidence stands firmly against the claims of iridologists, it doesn’t seem at all like a worthwhile avenue for further research.

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