Use of filters to treat visual-perception problem creates adherents and sceptics.

Patients who think they have a visual-perception dysfunction known as scotopic sensitivity-Irlen syndrome have trouble reading and may experience almost-constant headaches. Some find they are helped by coloured filters developed by a California researcher, Helen Irlen, who published a book on the subject called Reading by the Colors. Although Irlen has been criticized for not publishing scientific proof of the validity of her theories, her techniques have found some support, including some within the medical community.