Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists)
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Ophthalmic Physiol Opt · Jul 1999
Clinical TrialBoth 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. ⋯ 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 clinically reliable guide to optimal lens colour.