In their editorial, Henderson and colleagues  request a “more balanced” approach to advocacy of coloured overlays.
One of the more recent studies of the effects of coloured overlays is an investigation by some of the authors of the editorial themselves . In it they recruited 46 undergraduate students, 16 of whom had received a “formal diagnosis of dyslexia” (sic) from an educational psychologist. The basis on which the controls were recruited is not stated, and no control overlay was used. Based on the prevalence of visual stress in dyslexia of about 30% [3,4], it is likely that only about 5 of the dyslexic sample had visual stress. The researchers did not carry out an eye examination, so it is also possible that some of the participants had other visual problems. Nevertheless, in common with 25 of the other 26 published studies investigating the effects of coloured overlays on reading rate, a significant increase in rate with a coloured overlay was obtained, the colour chosen individually according to the manufacturers published methods. Reading speed was assessed by reading aloud paragraphs comprising 10 lines of 15 randomly ordered common words , an assessment that avoids variability due to comprehension and prevents guessing from context. The authors also measured the comprehension of short passages (about 300 words) of prose, which were read silently, and followed by five comprehension questions read aloud by the examiner. Participants were permitted to look back at the text while answering the questions.
In their discussion, the authors ignore the improvements in reading rate they obtained, and concentrate instead on their failure to observe any effect of the overlays on comprehension. Given the methods by which comprehension was measured, any effect of the overlay would have been lost in the variability associated with (1) comprehension of the text, (2) memory for the text and (3) visual search of the passage. We might expect reading rate to be increased when the visual clarity of text is improved, be that improvement the result of an overlay or indeed refractive correction. We would not necessarily expect an effect on comprehension, however, given that comprehension is determined by many non-visual factors. It is not justifiable to infer, as the authors do, that their failure to observe an effect of overlays on comprehension means that overlays are of questionable use. Furthermore, the authors fail to cite an earlier demonstration in 1995 that the effects of overlays in improving the rate of reading connected prose are measurable only after several minutes of reading .
Overlays are cheap, and occasionally the benefits associated with their use are dramatic. It therefore makes sense for dyslexia charities to increase the public awareness of their possible benefits.
Readers interested in the above issues are referred to an up-to-date, balanced, and independent review by Uccula et al .
1. Henderson LM, Taylor RH, Barrett B, Griffiths PG (2014) British Medical Journal 349, g5160
2. Henderson LM, Tsogka M and Snowling MJ (2012) Questioning the benefits that coloured overlays can have for reading in students with and without dyslexia. J Res Spec Educ Needs, 13, 57-65.
3. Kriss I, Evans BJW (2005) The relationship between dyslexia and Meares-Irlen Syndrome. J.Res.Reading 28, 350-364.
4. Singleton C, Henderson LM. (2007) Computerized screening for visual stress in children with dyslexia. Dyslexia 13 (2), 130-151, 2007
5. Wilkins AJ, Jeanes RJ, Pumfrey PD, Laskier M (1996) Rate of Reading Test: its reliability, and its validity in the assessment of the effects of coloured overlays. Ophthal.Physiol.Opt. 16, 491-497.
6. Tyrrell, R., Holland, K., Dennis, D. and Wilkins, A.J. (1995) Coloured overlays, visual discomfort, visual search and classroom reading. J.Res.Reading, 18(1), 10-23.
7. Uccula A, Enna M, Mulatti C (2014) Colors, colored overlays, and reading skills Front. Psychol., 29 July, doi: 10.3389/fpsyg.2014.00833
Competing interests: I developed the Intuitive Overlays while working for the Medical Research Council, and was until recently in receipt of an Award to Inventors based upon royalties the Council receive from sales. This arrangement has now ceased.