Helen Irlen identified a syndrome defined as 'scotopic sensitivity' which it was claimed could be responsible for the inability of some people to read fluently and the symptoms of which could be ameliorated by the wearing of prescribed coloured lenses. The literature to date presents a confused and inconsistent picture concerning the use of the lenses. The literature (much of which is unpublished and difficult to obtain) is critically reviewed. Recent experimental evaluations of the lenses do not support the use of the lenses as a useful intervention for children with reading disabilities.