Iridology is the term used to describe the study of markings in the human iris and how they correlate to the fitness of the body. Dr. Bernard Jensen, a well-known iridologist, stated that iridology could be used to discern and locate different stages of tissue inflammation and inherent weaknesses in the body.

While some, like Jensen, believe that iridology is not a diagnostic tool, many believers in and practitioners of iridology think the opposite. Iridology used to be synonymous with iridiagnosis, but changes in legality concerning whom may identify and ‘diagnose’ ailments (namely licensed doctors) and an evolving understanding of the powers of iridology have resulted in the creation and widespread use of the term ‘iris analysis’. This newer term and the related mindset suggest that iridologists are capable of locating certain problems or potential problems (such as a weakness in the lungs), but are not capable of diagnosing what, exactly, is or could cause the problem (such as lung cancer, or asthma)[3]. It is also important to note that iridologists do not always discover an actual problem, but may show what diseases and problems a person may be susceptible to, allowing the person to take proactive measures against said weaknesses[1].

History of Iridology

Iridology is considered to have two founding fathers: Dr. Ignatz von Peczely and Reverand Nils Liljequist. Both lived in the 1800s, and became interested in how the iris can reflect ailments of the body through personal experience. Peczely, as a child, accidentally broke an owl’s leg, and observed how the colours in its irises changed as it healed. Liljequist noted the changes in his own irises after taking drugs to combat an illness. Peczely and Liljequist independently created iris charts denoting which sections of the iris correspond to which parts of the body, and while the two men never knew of the others’ work their charts turned out to be strikingly similar[3].

Bernard Jensen (1908-2001) contributed greatly to the iris charts commonly used in iridology today and was a well-known practitioner and advocate of iridology. The Jensen iris chart was slightly modified by his student and daughter-in-law, Ellen Tart-Jensen (Ph.D., D.Sc.), resulting in one of the most widespread iridology charts used today. These more modern charts are highly detailed; Bernard Jensen’s original iris charts have a total of 166 different named areas between the left and right iris charts[3].

The methods of iridology have changed over time as technology progresses. In the 1800s iris examination was mostly conducted through direct, unmagnified observation, whereas nowadays many iridologists have access to high quality cameras and devices that allow for the observation of the iris at several times magnification. Newer, more widespread technology has greatly aided in the observation of minute details in the iris, and is indirectly responsible for the vastly more detailed iris charts common today[3].
Jensen chart revised colour.jpg
Jensen Iris chart, as modified by Ellen Tart-Jensen

But is Iridology Based on Science?

Well-known iridologist Bernard Jensen notes that iridology is “an interpretive art as well as a science”, but how scientific is that science? Iridology implies, and sometimes outright states, that the iris charts so instrumental to this practice were created through scientific observation and study, but there are no studies that show that a specific part of the iris corresponds to a certain part of the body. Some studies do show a correlation between a change in the colour of the eye and certain types of ailments or disease[10], but nothing to the detail and specificity that iridology is based on. Different iridologists may also have developed different charts, as there is no completely universal understanding of which exact part of the iris corresponds to every part of the body[3].

Several studies show that the predictive power of iridology is either nonexistent[7,8] or much less accurate than modern methods of diagnosis[11]. This suggests that there problems with the concept and application of iridology in relation to its ability to accurately predict and allow the discernment of physical ailments.

Why Iridology is a Pseudoscience

Unscientific versus Pseudoscientific

While the terms pseudoscientific and unscientific both refer to theories that should not be considered scientific, they are two distinctly separate terms. Unscientific theories and experiments involve inadvertent mismeasurements, miscalculations and similar forms of unintentionally bad science, whereas pseudoscience is generally defined as a collection of beliefs that are mistakenly presented or thought to be based on the scientific method, or that hold the same status as scientific truths[5]. Iridology appears, at first glance, to be partly an unscientific theory, as the mistaken correlations between the iris charts and actual ailments in a person’s body could be due to the inescapable human error that comes with finding correlations through observation. However, other parts of iridology are plainly not scientific at all, such as the fact that there is no one universal set of iris charts, and iridologists may develop their own charts that hold different parts of the body to be correlated to different sections of the iris. Despite these facts, iridology still attempts to pass itself off as a science, and as such should be examined using the criteria that demarcates science from pseudoscience.

Scientific verus Pseudoscientific

There is some debate in how to accurately and demarcate science from pseudoscience in an unbiased way. I believe the best demarcation criteria are a mix of Thagard’s and Popper’s views. Thagard notes that demarcation criteria needs to concern three elements: theory, community of advocates, and historical context, and suggests more specific criteria for latter two, which, while very subjective, seem logical.

Thagard's Criteria

Thagard suggests that a theory should be considered pseudoscientific if: it is less progressive than alternative theories over time; has several problems unsolved by the community of advocates; and practitioners and advocates show little effort towards solving said problems, evaluating the usefulness of their theory in relation to others, and are biased in considering confirmations and disconfirmations. These criteria make sense, as scientific theories are always evolving and/or being tested for error, and good scientific experiments are set up to avoid bias. Iridology, on the other hand, has several unsolved problems, including a low accuracy in correctly identifying bodily ailments and no common consensus over iris charts and which exact part of iris relates to which part of body, a problem which shows little progression (other than advancements in technology allowing for a more detailed viewing of the iris) since the conception of Iridology. Supporters of iridology have put little effort towards solving problems or evaluating the theory, and seem to deliberately ignore the problems in Iridology’s ‘science’; most iridology sites simply have brief, scientific-looking background on iridology and have no references to studies proving its usefulness. This deliberate miscommunication of the validity of the science behind Iridology also shows how advocates of Iridology appear to be biased when considering confirmations and disconfirmations, especially since there are several scientific studies showing how inaccurate iridology is[7,8]. Studies also show that, even in the rare case where iridology is shown to significantly (and not by random chance) predict a physical ailment, Iridology is far less accurate than more scientifically respected methods of detection [11].

Popper's Criteria for Testing a Scientific Theory

While Thagard suggests that pseudoscience should be examined with consideration to the three elements mentioned above, he never gives a conclusion on the best criteria when examining the actual theory of a possible pseudoscience. While it has its flaws, I believe Popper’s four ways to test a theory from The Logic of Science are satisfactory for this purpose.

Popper suggests that a theory should be tested for internal consistency, if its logical form is valid, how it compares to other theories, and whether the empirical applications of its derived conclusions are true. The only one of these criteria that Iridology appears to meet is Popper’s test of concerning its logical form, as its founding theory (that different parts of the iris reflect the state of different parts of the body) could be empirically derived and can be empirically tested. Iridology certainly does not appear to be internally consistent, as it states that different parts of the body are distinctly represented in a specific part or parts of the iris, and yet different iridologists may use different iris charts which can result in contradictions such as one iridologist may have the heart where another has the wrist. Iridology compares negatively with other scientific theories and methods of analyzing and diagnosing physical ailments, which have been shown to be far more accurate than Iridology. Lastly, Iridology resoundingly fails Popper’s final test of the empirical applications of the theory’s derived conclusions.

Falsifiability and its Flaws

Popper’s final test is, put simply, a test of a theory’s falsifiability, and whether it should be falsified or not. Falsifiability does have several know issues, mostly stemming back to a debate of when one can confidently say that a theory is falsified, or when enough evidence has been presented that is contrary to what a theory predicts to definitively say a theory is not true. Duhem, in particular, notes several ways to still claim a theory is true even with contrary evidence (although only some of these ways are applicable to Iridology), as the testing of a theory is actually a test of all the auxiliary hypothesis a theory relies on in addition to a test of the theory itself. If a piece of evidence appears to falsify a theory then those that believe in the theory may alter some of the auxiliary assumptions used to support the theory (if they are trying to uphold the possibly falsified theory), or otherwise state that the experimenters did not account for other possible variables that could change the conditions and outcome of the experiment. An example of this last case would be a test of the theory that the acceleration of a free-falling body is constant; if an experiment shows this theory to be false, it could always be argued that the body being tested was not actually free-falling, but had some force we are unable to recognize with our level of technology and understanding acting upon it[4].

In the case of Iridology, believers could amend the strong theory that specific locations in the iris reflect, and can be observed to reflect, the state of specific parts of the body to a weaker claim that the iris is only capable of accurately reflecting a small number of bodily locations and states, and these reflections are minute and difficult to accurately note. As such, Iridologists would still hold the same fundamental hypothesis while modifying it just enough to account for the potentially falsifying observations. This would also match with some (if not the majority) of experiments concerning the validity of iridology, in that it can be used to identify some bodily ailments, but not with anywhere near the same accuracy as more accepted scientific methods[11].

Iridologists could also argue that their theory holds true, but the experimental results that show its lack of significant predictive power are being misinterpreted in some way. Duhem notes that, as in the free-falling body example, results may be interpreted differently based on how a term is defined and viewed. In his example, there was a dichotomy between the ‘real’ meaning of a free-falling body (namely, one without any known forces acting upon it) and the symbolic one (one that falls at a constant acceleration, as given by the theory). Someone who believes in the latter meaning will always assume that there was some force acting on the body to cause it to fall with an acceleration that was not constant when someone who believes in the former meaning will see that there was no known force acting on the body, and thus the theory was proven wrong. Iridology does not have such a clear-cut example of this; however they could argue that their theory is true in a few ways based on the definition of Iridology as the study of correlations between marks in the iris and different stages of tissue inflammation and inherent weaknesses in the body (as noted in the introduction).

The experiment that was run by Karsten Münstedt et al. to test whether Iridology could be used to accurately diagnose cancer could be said to be invalid because Iridology cannot determine specific ailments, only bodily weaknesses; nowhere in the study did the experimenters mention testing the subjects for other weaknesses in the parts of the body to be tested for tumors. An experiment by T. J. Buchanan et al. sought to discover if there was any difference detectable by a computer in the irises of people who had coronary heart disease, asthma, ulcerative colitis, or psoriasis versus those who did not could be said to have the same experimental flaw as the experiment by Karsten Münstedt et al.. Buchanan’s experiment could also be argued as invalid due to the fact that the data was computer analyzed; the computer may not have been set to pick up the various differences that Iridologists claim to be able to spot in the iris, nor know how they relate to one another and the state of the various parts of a person’s body.

While falsifiability and empirical testing of a theory does not give completely conclusive results, Duhem notes that we also need to use our “good sense” to judge the outcome of experiments. While this is a far more subjective method to judge observations and experimental results, there does seem to be some truth to this notion. Iridology, we can note, has far more experiments showing its unreliability or simply that it does not work at all. While it is true that several of these experiments should have taken the time to test whether the subjects used had other ailments of the parts of the body used in the experiment, it is also important to note that in at least one study the results were similar to those that would occur from pure guessing (i.e. completely random chance), giving little impression of some unknown or overlooked pattern in the data [7]. The main general objection Iridologists could offer to these experiments is simply that the correlation between the iris and ailments of the body is not fully understood and thus sometimes wrongfully analyzed, in which case this theory has no business being used to analyze patients and provide a basis for their medical treatment.

In Conclusion

Iridology fails all of Thagard’s criteria concerning the community of advocates for and historical context of a theory for demarcating a scientific theory from a pseudoscientific theory, and fails all but one of Popper’s criteria for testing the form of a scientific theory. Popper’s final criteria, that concerning falsifiability, has its difficulties but can still be used to show that Iridology should not be given the same status as scientific theories due to the many gaps between what the theory postulates and the actual observed applications of the theory. Iridology presents itself as a (at least partially) scientific theory which has been proven true and useful in analyzing whether a person should be seeking medical help or therapy, but has no even potentially concrete evidence to back this claim. As such, Iridology should be considered a pseudoscience.

Possible Consequences of Relying on Iridology

Consulting an Iridologist without also visiting a licensed doctor could potentially be very hazardous. Because Iridology has a very low accuracy for correctly identifying bodily ailments, they may diagnose a client with an ailment they do not have, which could result with them buying medicine of some sort which they do not need. Iridologists may also fail to recognize an ailment that contemporary checkups would identify, causing it to be left untreated until it potentially worsened considerably and the symptoms became more evident.

However, Iridology, if it is accurate, could also be used to identify and pre-emptively treat a bodily weakness before it can develop into anything serious, as Iridology can supposedly recognize weaknesses in the body before they develop into actual problems. This side of Iridology would give similar information as a medical history, letting a client know what they are susceptible to and what symptoms to look out for. This use of Iridology would avoid the hazards of prescribing actual unnecessary medicine, and could be beneficial depending on what is recommended (more exercise, healthier diet, etc.).

Given that Iridology has been proven to be very inaccurate, someone interested in gaining more information about their heath would be far better off visiting a licensed medical doctor. Visits to an Iridologist can only tell a person what parts of their body may have ‘inflamed tissues’ (the exact cause and treatment of which would have to be determined by a medical doctor) and ‘inherent weaknesses’ that many of us already known from our medical histories, and as such should be considered a waste of time and money.


Iridology, as a theory that fits all of Thagard’s criteria for a pseudoscience and does not fit most of Popper’s criteria for logically testing a theory, should be seen as a pseudoscience with little applicable value. The theory of Iridology, in its most broad sense, has been shown to have some truth, however the hypothesis that the health of many parts of the body can be determined through close examination of a person’s irises has little basis in observations and no empirical evidence supporting it. Unless a widespread test of all parts of the body and how (or if) their health affects specific parts of the iris is preformed that discovers a significant correlation between the different parts of the body and the irises, Iridology’s supposed analytic abilities will never be scientifically supported. The eye may be the window to the soul, but as of yet provides little insight to the body.


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