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 c oloured sheets of plastic (overlays) are placed upon the page, or when colo ured lenses are worn. Overlays provide a surface colour whereas lenses mimi c a change in the colour of a light source, The neural mechanisms that unde rlie colour constancy ensure that the chromaticity of overlays and lenses i s processed differently by the visual system. We investigated (1) the relat ionship between the optimal colours of overlays and lenses, and (2) how rea ding 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(R) which sample chromaticity systematical ly and (2) the chromaticity co-ordinates of the lenses subsequently chosen using the Intuitive Colorimeter(R), a device providing a light source that can be adjusted in hue, saturation and luminance independently. The relatio nship between the chromaticities of the overlays and the lenses showed cons iderable variation. In a second study, patients attending the Specific Lear ning 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 randoml y ordered common words (Wilkins Rate of Reading Test): (1) with no colour, (2) with the chosen overlay, (3) with lenses matching the chosen overlay an d (4) with lenses matching the Colorimeter setting. The aids increased read ing rate significantly only in conditions (2) and (4). There was no signifi cant improvement when lenses matching the overlay colour were used, and und er this condition the reading rate was significantly poorer than in conditi ons (2) and (4). The colour of a lens will improve reading only if it is se lected under conditions that mimic a change in the colour of a light source : coloured overlays give no clinically reliable guide to optimal lens colou r. (C) 1999 The College of Optometrists. Published by Elsevier Science Ltd. All rights reserved.