The article in Optometry Today relies on a familiar rhetorical device, which is used to position proponents of visual stress treatment in the centre ground of a debate. It appears that there are "zealots" who claim that visual factors cause dyslexia and "deviants" who say that vision is irrelevant to dyslexia. To be fair, the power point files use the word 'denier' rather than the inappropriate term deviant. That said, I do not think either word is ideal.
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A link is then drawn between this somewhat banal statement and a more contentious one - as if they were equivalent. This time the dichotomy is between those who believe visual stress is a major cause of reading difficulties and those who believe that it does not exist. In the centre-ground is the statement 'maybe visual stress can co-occur with dyslexia.' Well, that is isn't saying very much. Flat feet, eating burnt toast and dandruff may co-occur with dyslexia - so what.
With regard to whether visual stress exists: if you mean do some people find stripy patterns visually aversive? The answer is obviously yes. If you want to call that visual stress Then yes 'visual stress" exists. However, whether dyslexics are more likely to experience visual stress, whether this is a factor in their reading difficulties and whether coloured overlays and lenses ameliorate visual stress and whether that, in turn, aids the acquisition of reading is not clear - the evidence is lacking at every step of the chain.
It is worth asking whether 'visual stress' is a widely accepted disease label? The International Statistical Classification of Diseases and Health Related Problems (ICD10) does not list 'visual stress' as a recognised disorder and neither does the American Diagnostic and Statistical Manual of Mental disorders DSM 5. It would appear that the wider scientific community is not convinced that 'visual stress' is a real pathological entity.
That brings me to the problem with the word 'denier'. That term has come to be associated with extreme positions that go against the overwhelming scientific or historical consensus. For example, climate change denial or holocaust denial. I hope that the intention of Professor Evans was not to implant in the mind of his audience some kind of link between those who adopt a sceptical approach to his work, that is entirely appropriate, and extreme fringe views such as evolution or climate change denial. The picture of a fringe religious group (see picture above), that has no relevance to the subject under discussion, leads me to think that could be the intention. There is no scientific consensus around visual stress and for that reason, 'denier' is an inappropriate label.
The real difficulty I have with all this is not that I am offended, it is that the arguments presented are not scientific arguments at all. They appear to me to be kind of techniques politicians use. Claim that you occupy the centre ground, link a statement that everyone can believe with a more contentious one, and link your opponents to extremist views - in this case, deniers of mainstream beliefs for which there is overwhelming evidence.
According to the Optometry Today article "evidence suggests that visual stress occurs in one in five people with dyslexia." This statement is not backed by any reference. There have been no epidemiological studies using the current diagnostic criterion for visual stress (reading the Wilkins Rate of Reading Test -WRRT-15% faster with chosen overlay). So, in truth, we do not know what the prevalence VS is among dyslexics. I assume the figure of one in five is based on a problematic study that has been reviewed elsewhere in this blog in May 2015. The study was inadequately powered, dyslexics were drawn from dyslexia clubs and unlikely to be representative of the wider population of poor readers and they were not a 'naive' population in that some may have previously been exposed to visual stress assessments.
Even if you accept this figure, it is not enough to say that 'visual stress' co-exists with dyslexia; you would expect it to be over-represented among dyslexics. A condition that results in apparent movement and distortion of print would tip an individual with borderline phonetic skills into the dyslexia subgroup and dyslexics with 'visual stress' should be less amenable to treatment by conventional educational means. There are no high-quality studies that show a statistically significant difference in the prevalence of 'visual stress' among dyslexics and normal readers.
According to the final part of the article in Optometry Today, optometrists should consult the website of the Society for Coloured Lenses Prescribers (S4CLP). This organisation will be the subject of a future post. It certainly is not a source of impartial information.
Tracy Brown of Sense about Science says that "One reason quackery survives is that it wears so much of the garb of legitimate medicine and legitimate medical charities." While it would be unfair to describe visual stress treatment with coloured lenses and overlays as quackery, I think a similar argument can be applied to S4CLP which has the veneer of a regulatory body such as the General Optical Council or General Medical Council. In practice, it is nothing of the sort.
