While many studies report improvements with coloured lenses , the effect size is generally small and /or similar to the improvement found with a placebo condition .
Consistent with previous review s and advice from several professional bodies , we conclude that the use of coloured lenses or overlays to ameliorate reading difficulties can not be endorsed and that any benefits reported by individuals in clinical setting s are likely to be the result of placebo , practice or Hawthorne effects
PURPOSE There are many anecdotal cl aims and research reports that coloured lenses and overlays improve  reading performance .
Here we present the results of a systematic review of this literature and examine the quality of the evidence .
Both coloured overlays and coloured lenses can improve reading fluency, but their optimal chromaticities differ.
Some individuals read more fluently when the text is coloured : i.e. , when coloured sheets of plastic ( overlays ) are placed upon the page , or when coloured lenses are worn . Overlays provide a surface colour whereas lenses mimic a change in the colour of a light source . The neural mechanisms that underlie colour constancy ensure that the chromaticity of overlays and lenses is processed differently by the visual system . We investigated ( 1 ) the relationship between the optimal colours of overlays and lenses , and ( 2 ) how reading rate is affected by a particular colour in overlays and lenses .  In 100 patients we noted ( 1 ) the overlay(s ) chosen from among the 29 combinations of the 10 IOO Intuitive Overlays which sample chromaticity systematic ally and ( 2 ) the chromaticity co-ordinates of the lenses subsequently chosen using the intuitive Colorimeter , a device providing a light source that can be adjusted in hue , saturation and luminance independently . The relationship between the chromaticities of the overlays and the lenses showed considerable variation . In a second study , patients attending the Specific Learning Difficulties clinic at the Institute of Optometry , London , were given overlays to use for two months . Seventeen who derived benefit were examined using the  Intuitive Colorimeter .  Patients were asked to read aloud r and omly ordered common words ( Wilkins Rate of Reading Test ) : ( 1 ) with no colour , ( 2 ) with the chosen overlay , ( 3 ) with lenses matching the chosen overlay and ( 4 ) with lenses matching the Colorimeter setting . The aids increased reading rate significantly only in conditions ( 2 ) and ( 4 ) . There was no significant improvement when lenses matching the overlay colour were used , and under this condition the reading rate was significantly poorer than in conditions ( 2 ) and ( 4 ) . The colour of a lens will improve reading only if it is selected under conditions that mimic a change in the colour of a light source : coloured overlays give no clinical ly reliable guide to optimal lens colour
While many studies report improvements with coloured lenses , the effect size is generally small and /or similar to the improvement found with a placebo condition .
Consistent with previous review s and advice from several professional bodies , we conclude that the use of coloured lenses or overlays to ameliorate reading difficulties can not be endorsed and that any benefits reported by individuals in clinical setting s are likely to be the result of placebo , practice or Hawthorne effects
PURPOSE There are many anecdotal cl aims and research reports that coloured lenses and overlays improve  reading performance .
Here we present the results of a systematic review of this literature and examine the quality of the evidence .