The authors are independent and have no financial ties to 'visual-stress' treatment. It is also striking how measured they are in their conclusions. The weaknesses of the data are acknowledged as are other possible interpretations. This contrasts with the 'spin' put on the data in some of the papers that have been reviewed elsewhere in this blog.
A key aspect of the precision tinting hypothesis is that the choice of colour that ameliorates symptoms in the putative disorder 'visual stress' should be constant and repeatable. Otherwise, why would anyone spend hundreds of pounds on an assessment leading to the prescription of Precision Tinted Lenses (PCTs) if re-testing one month later were to show that a perceptibly different colour was required? This paper appears to show that the choice of colour is not repeatable and in as short a period of as one month, a significantly different colour may be needed.
The study
Twenty-six participants with 'visual stress' and no other uncorrected visual or ocular anomalies were recruited for the study. A difficulty in conducting this kind of research is that the criteria for diagnosing 'visual-stress' are an ever shifting target. In this case, they were..
i)Symptoms of visual discomfort or distortion while reading
ii)Alleviation of symptoms with a coloured overlay
Although it was not an inclusion criterion, two-thirds of participants had previously been diagnosed with visual stress and had been using overlays for a prolonged period. In addition, table 1 shows that most subjects increased their reading rate on the Wilkins Rate of reading test with their chosen overlay.
The authors, who are always measured in their conclusions, acknowledge that their criteria may have over-diagnosed 'visual-stress.' However, they also observe that 'no standard diagnostic criteria are available, quoting a review written by Professor Evans. The diagnostic criteria used in this study are as rigorous as many of the previously published studies on visual stress.
Subjects were tested first with Intuitive Overlays according to published method. For some reason, starting with rose, until the overlay that best ameliorated their visual symptoms was found. Subsequently, participants were tested with the Intuitive Colorimeter which is a light tight box in which hue and luminance can be varied independently, while the subject views strings of random letters arranged to look like words. First, the participant indicated which of the 12 hue settings made the 'text' more or less comfortable to read compared to white light. Hues were then compared against each other to find the best, and then the saturation of the preferred hue was reduced to find the minimum that would ameliorate symptoms. Finally, the brightness was adjusted to an optimal setting. In all, there are 288 possible lens colour settings from which the participant chose one.
Participants were tested on a second occasion one month later....
Results
Looking at the data for overlays. On the second occasion of testing, 11 subjects chose a completely different overlay and 3 subjects chose a similar but different colour. Because one-third of subjects were already using overlays it seems likely that they already knew their chosen colour. Consequently, this part of the study is open to bias. Even so, it is striking how many participants chose a completely different colour on the second occasion of testing.
The most interesting data relates to the Intuitive Colorimeter. Because subjects did not receive their chosen lens at the first testing session and because they had not been previously exposed to PCTs these results are less vulnerable to bias. All subjects chose a different colour on the second occasion of testing that was separated by at least 3 just noticeable differences (JNDs). That is, the different colour would have been plainly perceptible. The average was 9 JNDs. This is a telling statistic because above 6 JNDs symptoms should worsen according to the existing theory.
Conclusions
The results of this study are not compatible with the precision tinting hypothesis. If the colour required to ameliorate 'visual stress' is not stable there is little point in prescribing PCTs. The study also opens up other lines of research. What does influence the choice of colour? It has already been shown the gender has an effect. Maybe test order has an effect and I would be surprised if there are no priming effects. That is, the way the information is presented prior to testing or what colours participants are exposed to before testing, might influence the participants chosen colour.
These results have to be seen in the context of another recent study from a psychophysical laboratory at Imperial College described in the blog post of September 2015 that showed that PCTs did not improve contrast sensitivity function in the range of spatial frequencies that are said to be aversive in 'visual stress'.
Criticisms
It is a little churlish to criticise this study when it is such a breath of fresh air and it has to be good to have some new and independent researchers involved in this area. Anyway.....
1)'Visual stress appears to be accepted as an established disorder like blood pressure, diabetes or myopia for example. In fact, in spite of over 20 years of research, it remains a putative disorder that has yet to be properly defined. It is championed by only a few scientists and so far, at least, it has failed to achieve main stream acceptance. For example, there is no ICD10 code for Meares-Irlen Syndrome. A qualifying sentence in the introduction would have been appropriate.
2) Cortical hyper-excitability is a speculative neuro-scientific theory with weak theoretical underpinnings and a poor evidence base. In my opinion, it is given undue prominence.
3) Reference 9 in the paper refers to proposed diagnostic criteria for 'visual stress'. The paper 'A Delphi study to develop practical diagnostic guidelines for visual stress' will be reviewed in a future blog. Two of the three authors had a financial interest in the treatment of visual stress. Twenty-six practitioners who were frequent prescribers of PCTs and thus also had a financial interest were invited to take part in the study. This is not a credible process because the panel of a Delphi study is supposed to represent a range of voices; this one did not. For this reason, I do not think this paper should be cited as a credible source of information or at least it should carry some kind of 'health warning.'
Perhaps these criticisms are petty and they are very much my personal view. They certainly do not detract from the paper which should be read by anyone with an interest in 'visual-stress.'
