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.


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.

Posted in: Naturopathy, Science and Medicine

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20 thoughts on “Iridology

  1. Intraneural says:

    Steve, you say that using a homunculus model is prescientific. I understand your point for iridology, auricular therapy, etc. But is not the homunculus a valid way of looking at the sensory and motor cortex?

  2. cervantes says:

    Well yeah, intra, but that seems entirely beside the point.

  3. DevoutCatalyst says:

    How marginal an activity is this? NCCAM makes no mention of it.

  4. Intraneural says:

    Okay, just making sure my understanding of neuroanatomy was not outdated since this is not my area of expertise. Thanks

  5. DrRobert says:


    It’s actually pretty well used in the CAM world. Many chiropractors and “integrative medicine” doctors employ this ridiculous quackery in their practice. I’ve always wondered about this, because it’s bound to be that all of these quacks come to completely different conclusions on the same (likely healthy) patient.

    There’s a fantastic article on QuackWatch that is a “confession of an iridologist”:

    The iridologist essentially admits that they do nothing more than cold-read a patient (similar to how a psychic does. “Do you get headaches?” – if they answer yes, then “Oh I can see that here.” – if they answer no, then “Oh I can see that you don’t!”) The iridologist realized that depending on the quality of light and the angle of the light reflecting off the iris his readings were completely different. They also employ a lengthy “medical history” form which gives them most of the background they need to trick you with their woo.

    Te iridologist even describes one time when his colleague claimed to find something on the iris, then adjusted the patient’s back, and then the finding was gone. They’re absolutely nuts.

  6. The sensory strip on the cortex does map to a sensory map of the body, and the motor strip to the various muscles, and these are referred to as the motor and sensory homonculus. Of course, in these cases the anatomy is well worked out. This is not a system of medicine, however, just neuroanatomy.

  7. Bogeymama says:

    I remember a 3 year old in our practice getting a diagnosis of Lennox-Gastaut syndrome. The family was not happy with the prognosis given to them by “Dr Doom and Dr. Gloom” as they called them, so went to an iridologist who is also a DAN! naturopath in our community. The grandmother told me he saw lots of “electrical firing” in the girl, but of course, he knew the diagnosis ahead of time. Thankfully, she knew that the money spent there was useless, but it has not stopped them from fundraising for 10s of thousands of dollars for stem cell treatments in the Dominican, etc. These guys are such predators …

  8. Quill says:

    Fascinating that there is a “profession” out there which could be completely thwarted by Visine.

  9. Intraneural says:

    Nice one Quill! Thanks too Steve. We had a visiting professor lecture in my fellowship about auricular therapy and the homunculus on the ear. It was hysterical how he tried to equate the different germ layers in the ear that were connected by neurologic pathways to similar ones throughout the body. Apparently different nerve fibers from each area of the homunculus on the ear were wired to the corresponding area on the sensory cortex. The “proof” was one functional MRI study that seemed very poorly designed. I almost laughed a few times during this lecture and I know that my director knew how nonsensical I thought this was.

  10. Janet Camp says:

    I’ve always wondered if I could set myself up as a Phrenologist and get all the same people who do these other ridiculous modalities to pay me to interpret the bumps on their heads? Luckily skeptics prefer to spend their time (quite uselessly in many cases, sadly), attempting to debunk this kind of crap. Perhaps I could tell them that one of their “bumps” makes them very susceptible to pre-scientific notions and convince them they are victims!

    Not only is there reiki, iridology, and homeopathy, but also kinesiology–not the sports thing–and all kinds of “spiritual practices way beyond even Buddhism. One of the ones someone I know joined recently is something called Breema–a type of massage that goes way beyond relaxation in its claims. It’s “bodywork” along with a whole bunch of quantum-type mumbo jumbo that seems to appeal to the scientifically-challenged.

    Look at the link for a good laugh!

    Happy Solstice!

  11. cervantes says:

    It’s not exactly to the point I suppose, but of course there are various ways in which conditions in one part of the body or in one body system can be read from signs in another. For example, the retina can reveal hypertension, a Babinski reflex (in the big toe) after age 2 can signal neurological disease in the spinal cord, etc. Doctors are familiar with these various signs and use them routinely. But that’s a far cry from saying there is a “homonculus” mapped onto some particular body part.

  12. Anarres says:

    “This is what might have happened next: …”

    Oh man, this paragraph is brilliant, I love it XD

  13. Lytrigian says:

    This is not a system of medicine, however, just neuroanatomy.

    Oh man, what an idea.


    Neuroscience has proven that specific regions of the brain map to specific parts of the body. Therefore, all diseases can be cured by stimulating those parts of the brain corresponding to the ailing organs. This brings the body’s own healing power to bear on those organs, which then cures the disease without the use of toxic pharmaceuticals. External stimulation is necessary because a side effect of disease is the blockage of the usual signaling pathways that would otherwise be used for messages that result in the healing response. Once the body is aware of the problem, it heals itself.

    This is what the phrenologists of old were trying to accomplish, but they had limited understanding of the underlying anatomy. Now, thanks to SCIENCE, we can approach the problem much more effectively.

    Stimulation is applied by an array of electroacupuncture needles inserted into the scalp, carefully arranged so as to deliver focused bursts of electromagnetic radiation to the specific region of the brain corresponding to the organs in question.

    We may call this new scientific method of treatment CORTEXOLOGY.

    I could make so much money if I didn’t have a conscience.

  14. Quill says:

    @ Lytrigian: lol! Thanks a lot! Now my funny bone hurts.

    I guess I could combine iridology and cortexology by sticking a 9-volt battery to my tongue and having someone watch my eyes light up. I can almost guarantee it will stimulate -their- funny bone!

  15. Lytrigian says:


    If someone actually comes out with this in the next year or two, I’m going to demand royalties.

  16. Quill says:

    :-) Better start trademarking names, then. Start with cortexology and also include very fancy variations such as bioelectrodynamic corticostimulation, accucortical neurophysiological curation, and anything else you can think of. Also include some diagrams, perhaps one showing a bunch of acupuncture needles wired to a bunch of switches and blinking lights, a Diehard battery and all atop a special hat of some kind.

  17. Grant Jacobs says:

    Thanks for providing this summary of iridology.

    If you want an example of iridology causing harm, this case from New Zealand might be worth noting:

    (I’m happy to stand guilty as charged of promoting one of my own posts; I’ve added a link to the post above to the comments in the thread following my article for my readers.)

  18. Jan Willem Nienhuys says:

    The career of Péczely Ignác (1826-1911) was somewhat different. Péczely got wounded in the battle of Trnava (14 December 1848) during the Hungarian uprising of 1848-1849. Afterwards he had a series of small jobs, for example as high school teacher and as technician. But when he started to work in the homeopathic practice of his brother-in-law Gulyás János, he became famous as miracle healer. Homepathy was a new fad at that time. One of his patients was the poet Madách Imre. At that time he got the idea of eye diagnosis. The owl story is something he allegedly recalled when he was treating a patient with a black line in his iris. The story that the black line in owl’s eye vanished afterwards is new to me. The traditional version is that he found an owl entangled in a hedge and that the animal broke its leg when young Ignaz tried to get it out. At that moment, so the story goes, he saw the black line. Maybe. Maybe he just saw an effect of the third eyelid of the owl. There are stories that he tried to duplicate the effect by breaking the legs of rabbits.

    Péczely was considered a dangerous quack in his time, and he often had problems with the authorities. He decided to end all this by getting a medical degree. He attended medical school in Vienna for 4 semesters at the age of 36 and obtained his MD diploma (1868) without taking an exam (rather unusual at the time). The authorities asked him afterwards to stop with his fraudulent eye diagnosis and newspapers wrote critical articles about him. This merely increased his popularity. His book, Felfedezések a természet- s orvosi tudomány terén. Az idült betegségek. Utmutatás a szemekbőli kórisme tanulmányozásához (Discoveries in natural and medical science. Chronic diseases. Manual for eye diagnosis) was published in 1880.

    If you know Hungarian, consult

    Fritz Salzer, in Augendiagnose und Okkultismus (München, 1926) quotes a letter from a young physician named Albert Siegrist (deceased in 1926), a son of the respected homeopath Albert Siegrist (1835-1906) and a brother of the inventor of the contact lens August Siegrist (1865-1947). Albert junior had gone to Budapest on the request of his father, to check on Péczely in 1888 or 1889. In this letter to his father he describes the visit in detail and finishes: ‘Is Dr. P. an ordinary fraud or is he mad? Maybe a mixture of both, but I tend to believe the former.’

    Albert Jr. describes a large beautiful plaquette stating that P. is made into a an honorary member of the association of homeopathic doctors of Württemberg. Albert Jr. pretends he once had a bout of impotence, and immediately ‘doctor’ Péczely can see in his eyes that he has syphilis. When Albert says he has a chronic catarrh of the mucosa, P. sees a left lung catarrh, pericarditis, a swollen left adenoid etc. etc.

    Summarising: the owl story is made up, and iridology is one of the evil offshoots of homeopathy.

  19. joemcveigh says:

    I’d just like to point out that iridology is what diagnoses the problem, but Japanese Eyeball Poking is what cures it.

    And that… is the secret to eternal youth.

    (No worries, Grant. This is the second time I’m shamelessly linking to one of my own posts. It’s just so relevant again.)

    Thank you, Steven Novella. I can’t believe I didn’t know about the wonderful art of iridology. This will surely help me in my Japanese Eyeball Poking practice. Any iridologists out there, feel free to give me a call. Now hiring!

    (In all seriousness, SBM Editors, I couldn’t resist. I love this site, so please don’t kick me out. It’s Christmas for Ignatz’s sake!)

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