The effect of coloured overlays and lenses on reading: a systematic review of the literature

Abstract

Purpose: There are many anecdotal claims that coloured lenses and overlays improve reading performance and there is a substantial literature on the topic of whether reading performance is enhanced through the use of colour. Here we present the results of a systematic review of this literature and examine the quality of the evidence concerning the assertion that reading can benefit from use of coloured overlays or lenses. Methods: We systematically reviewed the literature concerning the effect of coloured lenses or overlays on reading performance by searching the PsychInfo, Medline and Embase databases. Our searches revealed 51 published items (containing 54 data sets). Different systems are in use for issuing coloured overlays or lenses and we reviewed the evidence under four separate system headings (Intuitive, Irlen, Harris/Chromagen and Other). We classified each published item using the Cochrane Risk of Bias tool. Results: Although the different colour systems have been subjected to different amounts of scientific scrutiny, the results do not differ according to the system type, or whether the sample under investigation have been classified as having visual stress (or a similarly defined condition), reading difficulty, or both. The majority of studies are subject to ‘high’ or ‘uncertain’ risk of bias in one or more key aspects of study design or outcome. Studies at lower risk from bias offered less support for the benefit of colour on reading ability. Whilst many studies report improvements with colour, the effect size is generally small and/or similar to the improvement found with a placebo condition. We discuss the strengths and shortcomings of the published literature and, whilst acknowledging the difficulties associated with conducting trials of this type, offer some suggestions about how future trials might be conducted. Conclusions: Consistent with previous reviews and advice from several professional bodies, we conclude that the use of coloured lenses or overlays to ameliorate reading difficulties cannot be endorsed and that any benefits reported by individuals in clinical settings are likely to be the result of placebo, practice or Hawthorne effects.