The controversy – a personal view.


It is appropriate to make the public aware of the use of colour in dyslexia, but the conflicting nature of the evidence base should be made patently clear.  These personal reflections on recent literature do not constitute a comprehensive review but are intended to draw out the arguments for and against the use of coloured filters.


To quote the Rose review “Identifying and Teaching Children and Young People with Dyslexia and Literacy Difficulties”:

“Visual stress is a term used to describe the experience of eye strain, difficulty in focusing, headaches, and illusions of colour or movement in written text. These experiences may become more marked when reading for prolonged periods. Estimates indicate that about 20% of the general population experience some degree of visual stress, but lighting conditions, type and size of font, and degree of background contrast all affect susceptibility and severity. Visual stress is not generally recognised as a medical condition, although many optometrists and hospital eye clinics will identify it and provide treatment. Visual stress has sometimes been referred to as 'visual dyslexia', but there is no evidence supporting a causal link between visual stress and dyslexia. Although there is some evidence of increased prevalence of visual stress in children and adults with dyslexia, it is important to note that assessment of visual stress and response to treatment is usually by subjective report. Where visual stress is identified or suspected, the most widely used intervention in schools is a tinted acetate overlay. Many schools used pastel coloured paper for worksheets and handouts to alleviate these problems. The use of buff-coloured paper, for example, can cut down on visual anomalies and can support reading fluency and text access. “


The use of colour to treat reading difficulties elicits strong views. Some experts are convinced that visual stress exists and precision tinted lenses are an effective treatment for this real condition and other experts remain unconvinced that the condition exists. 

In an editorial in the British Medical Journal entitled “Treating reading difficulties with colour”  Henderson, Taylor, Barrett and Griffiths (2014) argued that dyslexia is a verbal not a visual disorder, best dealt with by interventions that target phonological skills and letter knowledge. They assert that: “There are no validated diagnostic tests for visual stress and the symptom complex is vague, including frequent blinking, losing one’s place on the page, and “eye strain.” Indeed, there is little dispute that the symptom complex is difficult to define and overlaps with that of other disorders. Evidence suggests that the routine eye test does not identify visual stress.

The editorial takes the dyslexia charities to task for failing to make clear the conflicting nature of the evidence base. Dyslexia Action has responded. The BMJ editorial was criticised by Evans and Allen (2014) in a  reply published in the same journal. They regarded the literature cited as selective.

Some of editorial’s authors (Henderson Tsogka and Snowling, 2013) have questioned the benefits of overlays in a research article. In their study 46 undergraduate students were recruited, 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. Given the prevalence of visual stress in dyslexia it is likely that only about 5 of the dyslexic sample had visual stress.) No eye examination was conducted, so it is possible that some of the participants had other visual problems. Nonetheless, in common with many other studies using overlays, a significant increase in reading speed with a coloured overlay was obtained, the colour chosen according to the manufacturers published methods. The reading speed was measured using a passage of randomly ordered common words, read aloud (Rate of Reading Test). The authors also measured comprehension for connected prose.  They constructed a short test of comprehension:  passages (about 300 words) of prose, were read silently, and followed by five comprehension questions read by the examiner. Participants were permitted to look back to 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.  The authors omit to cite a report by Tyrrell et al in 1995, who studied the effect of overlays on reading using connected prose (school books).  This study showed that when reading connected prose the benefits of the overlay were measurable only after extensive periods of reading (due no doubt to the variability associated with comprehension).  After 15 minutes reading the children’s reading speed decreased when reading without the overlay.

Henderson et al argue that a failure to observe a benefit of overlays on reading comprehension indicates that they are of questionable value. This argument is itself perhaps questionable. Whereas we might expect reading rate to be increased when the visual clarity of text is improved, whether as the result of an overlay or indeed refractive correction, we would not necessarily expect an effect on comprehension because comprehension is determined by many non-visual factors. Given the methods by which comprehension was measured in the study by Henderson et al, any effect of the overlay is likely to 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.  One perhaps should not infer, as the authors do infer, that a failure to observe an effect on comprehension means that overlays are of questionable use.

A study by Richie et al. (2011) is widely cited as demonstrating that coloured filters are of no benefit.  This study used one individual trained using the Irlen methods (which are proprietary and differ from those described on this site) to identify individuals with visual stress. No improvement in reading speed with overlays was obtained on the Rate of Reading Test. Most other studies of coloured filters have demonstrated an improvement with overlays on this test, including the study by Henderson et al. The many studies have included those with single masked design and placebo controls, but none was double-masked (indeed it is difficult to mask the choice of overlays). It is possible that the masking used in this study reduced the effect of the overlays. It is also possible that the identification of individuals with visual stress was inappropriate, possibly over-inclusive: 77% of individuals selected by their teachers as “below average” readers were identified with Irlen syndrome. This is nearly twice the conventional estimates of the prevalence of visual stress in individuals with dyslexia and would have meant that many children did not have visual stress. Another possible explanation for the absence of any effect of overlays is that the study used the Irlen overlays, and these do not sample colour systematically even though a purple overlay has been added to the set.

There are papers by Harries et al (2015) and by Hall et al (2013) describing a comparison of two alternatives to the Colorimeter and Irlen systems for tinted lenses. In one of the two systems compared, different filters were given to the two eyes, and in the other all participants received identical blue or yellow filters. The studies did not include a control, so the broadly similar benefit reported for both systems could be due to placebo effects.

Some children will use an overlay for a short time, and then stop using it. This might be taken as evidence that overlays are of little value. Such an inference may or may or may not be appropriate. There is evidence that (in patients with multiple sclerosis) the use of an overlay for a two-week period increases reading speed not only with the overlay but also without. The “carry-over” effect suggests some generalisation of benefit. Perhaps individuals discontinue the use of overlays because they no longer need them, alternatively perhaps they never needed them.

There are position statements from the American Academy of Paediatrics, Council for Children with Disabilities, American Academy of Ophthalmology, American Association for Paediatric Ophthalmology and Strabismus, the Board of Certified Orthoptists and the Royal College of Ophthalmologists, all of which take the view that the evidence for the use of coloured filters to treat visual stress is inadequate at best.  None of these cite all the literature included in an independent and reasonably complete review of recent literature, which can be obtained here. The (British) College of Optometrists are less categorical and include a guideline according to which the prescription of coloured filters may be sanctioned. The websites of the Association of Optometrists and the British and Irish Orthoptic Association both provide links to training for the members, many of whom manage visual stress in their clinical practice. Many of those who have received training are members of the Society for Coloured Lens Prescribers.

Arnold Wilkins, 2015