Those who cannot remember the past are condemned to repeat it.
– George Santayana

Science-based medicine is more than a set of methods or certain philosophy of medicine – it is an entire approach to what should be the core questions for any interventionist profession: is it real and does it work?

These are often deceptively difficult questions to answer. Fortunately we have at least a century of experience applying systematic methods to answering these questions within the context of medicine. This is a wealth of history from which to learn, full of cautionary tales and enlightening examples.

However, as Winston Churchill lamented, we tend to forget the lessons of the past leading to, “…the most thoughtless of ages. Every day headlines and short views.”

Part of the mission of science-based medicine (and skepticism in general) is to remember the lessons of the past as they relate to science and pseudoscience, and to constantly remind the public and our colleagues of these lessons.

The history of medicine is littered with ideas that did not pan out, worthless treatments, non-existent diseases, and frequent error. That is unavoidable, and acceptable as long as we constantly strive to correct and minimize those errors.

The primary lesson of the history of medicine is that new ideas need to go through a rigorous process of evaluation before they should be generally accepted and implemented. We are constantly examining and refining those rigorous methods. They include careful evaluation of possible mechanisms and overall scientific plausibility, coupled with clinical evidence designed to eliminate all forms of bias and illusion.

The alternative is to be overwhelmed by bias and illusion, which tends to lead us to false positives – confirmation of our cherished guesses, and even to entire systems of medicine based on fairy tales and imagination.

Many of these medical treatments or systems, after being discarded by science because they failed in rigorous evaluation, continue on as scientific zombies – unkillable, immune to evidence and reason, going through the motions of life without actually being alive.

Irlen syndrome

In my opinion, Irlen syndrome is one such scientific zombie. The idea was created in the early 1980s by Helen Irlen, a therapist. Some people also give credit for co-developing the idea to New Zealander Olive Meares, a teacher. As described on

The Irlen Method has been used for over 25 years to identify and help people with a type of processing problem called Irlen Syndrome, formerly known as Scotopic Sensitivity Syndrome (SSS). Irlen Syndrome is not an optical problem. It is a problem with the brain’s ability to process visual information. This problem tends to run in families and is not currently identified by other standardized educational or medical tests.

The notion is that the brain in some people with learning disabilities and other related problems has difficulty processing visual information, causing eye strain, mental fatigue, and poor performance on visual tasks, such as reading. This difficulty, however, is worse with certain frequencies of light, and if they can be filtered out with colored lenses the brain would have an easier time processing visual information, relieving symptoms.

It’s a bit of a far-fetched idea, but not a priori impossible. It does sound like the kind of overly simplistic idea a non-neuroscientist would think of. Regardless, sometimes naive guesses turn out to be correct, or at least contain a kernel of truth. We have had 25 years to test this idea scientifically – how has it fared?

Not very well, as you may have guessed. Reading through the literature, by 1990 the scientific community went from skeptical to outright rejection of Irlen syndrome. It never crossed the threshold of proving that it exists as a distinct entity. In medicine this can be tricky, as different diseases and disorders can overlap in their signs and symptoms. It is also easy to mistake many different disorders for one far-reaching disorder (which appears to be the case here).

The question is – is there anything unique to what is alleged to be Irlen syndrome? Does the concept add anything to our understanding of patients and how to treat them? Are there specific findings or tests that predict something about how a patient will respond to a treatment or the natural history of their illness? Without a specific feature, test result, or predictive value, it is likely that the alleged syndrome is an illusion rather than a genuine pathophysiological entity.

A 1990 critique concludes:

Furthermore, in the absence of any evidence that it is a separate and distinct entity, it appears that the scotopic sensitivity syndrome is, in fact, a symptom complex which results primarily from various refractive, binocular, and accommodative disorders. Some of the papers which support Irlen’s hypotheses provide reason to believe that there is a strong placebo effect.

Existing known eye disorders (listed above) explain the findings in patients diagnosed with Irlen syndrome. Further, when treated for these known eye conditions with established therapies, the patients improved and the findings used to diagnose Irlen syndrome resolved.

A 1991 review was not kind to the proponents:

Research on this is reviewed, and is also shown to have procedural irregularities which preclude firm conclusions. Owing to the poor quality of much of this research the claims of the protagonists of these therapies cannot be proved or disproved. A proposed new therapy is normally preceded by a valid theoretical hypothesis; this has been lacking in the present topic.

Another 1990 review focusing on treatments concluded:

Recent experimental evaluations of the lenses do not support the use of the lenses as a useful intervention for children with reading disabilities.

So – the syndrome does not appear to exist, the research is shoddy, and the specific treatments (colored lenses) do not appear to work. In a science-based world Irlen syndrome would have been pronounced dead in the early 1990s. The other possibility is that Irlen syndrome exists but the research was just inadequate, in which case the proper response would have been to do large rigorous trials to settle the question once and for all. We can jump ahead a decade to a 2002 review:

However, very little objective evidence has been provided to support anecdotal reports of improvements in visual performance. Many studies are flawed in that they lack controls for investigator bias, and placebo, learning and fatigue effects. Therefore, the use of tinted lenses in low vision remains controversial and eye care practitioners will have to continue to rely on anecdotal evidence to assist them in their prescribing decisions.

The research largely dries up there, except for some small physiological studies that I find unconvincing. One efficacy trial appears in PubMed after the 2002 review, a 2011 study:

The Irlen diagnostician diagnosed Irlen syndrome in 77% of our poor readers. We found no evidence for any immediate benefit of Irlen colored overlays as measured by the reading-rate test or the global reading measure.
Our data suggest that Irlen colored overlays do not have any demonstrable immediate effect on reading in children with reading difficulties.


Irlen syndrome is yet another example of a medical diagnosis and treatment that was promoted prior to adequate scientific evidence to establish that it is real, and treatments based upon the diagnosis are effective. A quarter of a century later evidence is still lacking, and what evidence we do have that is reasonably rigorous is negative.

The most parsimonious interpretation is that Irlen syndrome is not real. The label is being applied to a heterogeneous group of patient who have many other conditions. Colored lens therapy does not appear to work.

In my opinion, given that this is the status of Irlen syndrome after 25 years it is unethical to continue to promote and offer this as a treatment. The burden rests heavily on proponents to conduct large rigorous studies if they wish to persist in their claims, and then to abide by the results of those studies.

Otherwise Irlen syndrome (by its various names) will continue to exist as a medical zombie, alongside homeopathy, psychomotor patterning, acupuncture, subluxation theory, and other unkillable nonsense.

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the president and co-founder of the New England Skeptical Society, the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also contributes every Sunday to The Rogues Gallery, the official blog of the SGU.