In case you missed it, I published a post on the dubious existence of dyslexia this weekend. A few people have been in touch via Twitter to tell me about the remarkable effect of Irlen lenses and that their miraculous success is clear evidence of the existence of dyslexia. Well, despite their apparent impact on some people’s ability to read, I’m not so sure it has much of a bearing of on whether we can agree that dyslexia definitely exists.

I have a good friend who wears plain, very pale yellow spectacles when reading. She is dyslexic and convinced that she’s unable to read any but the simplest of texts without them. With her glasses on, she can read even academic texts absolutely fluently. She’s tried many different colours, all of which, apparently, helped about equally; she plumped for yellow simply because she liked yellow.

These lenses (basically ordinary spectacles with colour tinted glass lenses), or coloured overlays (clear but colour-tinted plastic sheets) seem sometimes, as in this case of my friend, have instant and stunning effects on the ease of reading. Sometimes the effect is small and sometimes there is no effect at all. Some assert that it is ‘dyslexics’ who are helped by these lenses, or overlays. However, Wilkins et al (2001) report finding that around half of ‘normal’ students in their three samples experienced reading as easier, and did it better, through coloured overlays; some individuals improved by over thirty per cent. They found that “A substantial proportion of children reported symptoms of visual stress…‟ (ibid. p. 50) and it was particularly these children who improved most, and most reliably, when using their preferred colour overlay. Symptoms of ‘visual stress’ included letter movement, text blurring and uncomfortable brightness. Almost a third of those who noticed improvement were still voluntarily using their overlay at the end of the school year, eight months after being introduced to it.

Well and good, but Ritchie (2010) finds that “the evidence for the efficacy of coloured filters is insufficient to recommend the treatment.” He goes on to say:

The existence of visual stress as a diagnostic entity has also been questioned (Royal College of Opthalmologists, 2009). This thesis first describes the various theoretical perspectives behind the use of coloured filters, and provides an in-depth review of the current evidence. A combined crossover study and randomised controlled trial of the coloured filters used by the Irlen Institute, the major proponent of the treatment, is then described. This experiment, which set out to avoid the methodological problems observed in previous trials – most importantly, double-blinding was employed – failed to find any evidence of visual stress, or for the statistically or clinically significant benefit of coloured overlays for reading rate or comprehension on two separate reading tests, in a sample of 61 Primary School-age children with reading problems. This was despite 77% of the sample having been diagnosed with visual stress by an Irlen diagnostician and prescribed coloured overlays.

Clearly, something is going on, and when it works, it really works. But nobody seems to know why. Wilkins et al (2001) speculate that as ‘visual stress’ is reportedly more common among migraine and epilepsy sufferers they may all be due to a “hyperexciteable visual cortex”. Why not?

Scotopic sensitivity syndrome (or Meares-Irlen syndrome) is a syndrome of the visual system. As such it’s not specific to literacy although it is capable, apparently, of dramatically affecting it. But, for ‘dyslexia’ to have any meaning it must be a syndrome which is specific to literacy – not a syndrome relating to sight in general. Although the sometime success of Irlen lenses or coloured overlays at alleviating reading difficulty  has some significance,  but leaves the dyslexia debate approximately where it was before they came along.

Does that help?