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Irlen Spectral Filters or Irlen Lenses, are coloured overlay filters or person specific tinted lenses worn as glasses or contact lenses that are intended to help people with the supposed perceptual processing difficulty known as Irlen Syndrome, formerly known as Scotopic Sensitivity Syndrome. For individuals who suffer from Irlen Syndrome, the brain is sensitive to specific wavelengths of light, resulting in difficulties with print clarity and stability and discomfort when performing visually intensive activities such as reading. Irlen Syndrome affects approximately 50 percent of individuals with reading difficulties and dyslexia, 33 percent of those with attention difficulties such as ADHD, 33 percent with autism, up to 50 percent of those who have suffered a traumatic brain injury, whiplash or concussion, and approximately 12-14 percent of the general population. Standardised diagnostic procedures have been developed to individualise the colour selection. The treatment is based on the idea of the scotopic sensitivity syndrome. In the past, critics have called the syndrome and the treatment controversial and have suggested it is based on what they call insufficient research. However, current research on the topic includes placebo controls, longitudinal studies, and cutting-edge brain mapping technology, all of which support the use of color to alleviate the symptoms associated with Irlen Syndrome.
Scotopic Sensitivity Syndrome 
Scotopic sensitivity syndrome, also known as the Irlen Syndrome', is said to be a visual-perceptual defect related to difficulties with light source, glare, luminance, wavelength and black/white contrast. According to Irlen, these difficulties lead to reading problems, eye-strain, headaches, migraines, and other physical difficulties that can be alleviated by the use of person specific tinted lenses, known as Irlen Spectral Filters, worn as glasses or contact lenses.
The syndrome has six characteristics:
- eye strain
- poor visual resolution
- a reduced span of focus
- impaired depth perception
- poor sustained focus
The scotopic sensitivity syndrome is diagnosed by interviewing the client and by observing responses to certain visual tasks such as interpreting geometric figures and reading.
History and research 
The idea of page based distortion was initially suggested in 1980 by Olive Meares, to improve the reading ability of people with a learning disability, specifically a certain type of dyslexia. Later this was taken further by psychologist Helen Irlen. The proposition by Irlen was made at the Annual Meeting of the American Psychological Association in 1983. At that time, there was little research made on the effect of tinted lenses. Irlen gained notable publicity demonstrating the efficacy of her method on television. Tinted lenses became a commercial success, and testing and prescribing centers were opened throughout USA.
There has been research on the efficacy of using Irlen filters and lenses since the 1990s. A recent[when?] review of 62 studies published in peer-reviewed journals found 56 studies with positive findings, 45 with positive results for particular reading skills, and 11 showing improvements in accommodation facility, eye movements while reading, and reduced headaches/migraine.
Diagnosis of Irlen Syndrome and treatment with Irlen Spectral Filters has been reviewed by the USA Medical Board[which?], and has been determined as not the practice of medicine; it has also been reviewed by various USA Boards of Optometry[which?] and has been found not to be the practice of optometry. Binocular and accommodative anomalies may occur in conjumction with the syndrome, but are not considered to be the underlying physiological basis of the condition.
Other purposes 
According to Irlen, the lenses can be used to treat a wide variety of problems that are associated with light sensitivity, discomfort and distortions. According to proponents[who?], tinted lenses have helped people with a head injury, concussion, whiplash, perceptual problems, neurologic impairment, memory loss, language deficits, headaches and migraine, autoimmune disease, fibromyalgia, macular degeneration, cataracts, retinitis pigmentosa, complications from an eye operation, depression, chronic anxiety and others[which?]. It has also been claimed[by whom?] that a treatment for scotopic sensitivity syndrome could help a number of incarcerated individuals and delinquent children.
The Irlen method has been criticised[by whom?] for being put to the market prior to serious research. According to Helveston, the scotopic sensitivity syndrome and its treatment has, as a phenomenon, resulted in classic group behaviour and has the characteristics of a fad with a charismatic personality as a leader and the supporting evidence being mostly anecdotal. A 2004 study by Professor Arnold Wilkins at Essex University, though, shows that this may not be the case. The syndrome is however, associated with a growing array of possibly diverse conditions, as well as worldwide franchise according to critics.
Research does however point quite consistently to a genuine underlying problem relating most likely to the central nervous system of those diagnosed with the syndrome. Even critics such as Helveston do not dispute this (rather their concern seems based on the way the condition has been "claimed" and "marketed" as opposed to its existence). It appears the severity of the Syndrome can diverge quite widely though.
See also 
- International Dyslexia Association (2004). "Controversial therapies". IDA Information Packet: 1–20.
- Chouinard, BD, Zhou, Cl, Hrybousky, S, Kim, ES, Commine, J. (2011). "A functional neuroimaging case study of Meares-Irlen syndrome/visual stress (MISViS)". Brain Topography, Nov: 29.
- Huang, J., Zong, X., Wilkins, A., Jenkins, B., Bozoki, A., Cao, Y. (2011). "fMRI evidence that precision opthalmic tints reduce cortical hyperactivation in migraine". Cephalagia: June 14.
- Noble, J., Orton, M., Irlen, S., Robinson, G. (2004). "A controlled field study of the use of coloured overlays on reading achievement". Australian Journal of Learning Disabilities, 9: 14–22.
- Robinson, G. L., & Foreman, P. J. (1999). "Scotopic sensitivity/Irlen syndrome and the use of coloured filters: A long-term placebo controlled and masked study of reading achievement and perception of ability". Perceptual & Motor Skills, 89(1): 83–113.
- Whiting, P., Robinson, G.L., & Parrot, C.F. (1994). "Irlen coloured filters for reading: a six year follow up". Australian Journal of Remedial Education, 26, 13-19.
- Wilkins, A. (2002). "Coloured overlays and their effects on reading speed: a review". Opthalmological and Physiological Optics, 22: 448–454.
- Wilkins, A.J., Evans, B.J.W., Brown, J.A., Busby, A.E., Wingfield, A.E., Jeanes, R.J., & Bald, J. (1994). Double-masked placebo-controlled trial of precision spectral filters in children who use coloured overlays. Ophthalmological & Physiological Optics, 14. pp. 365–370.
- "Testing & Treatment". Irlen Institute. Retrieved 15 January 2013.
- Meares, O. (1980). Figure/ground, brightness contrast and reading disabilities. Visible Lang. 14, 13-29
- Silver, Larry B. (2004). "Theme editor's note". IDA Information Packet: 12.
- Evans; Patel, Wilkins, Lightstone, Eperjesi, Speedwell, et al. (1999). "A review of the management of 323 consecutive patients seen in a specific learning disabilities clinic". Ophthalmological and Physiological Optics 19 (6): 454–466.
- Scott; McWhinnie, H., Taylor, L., Stevenson, N., Irons, P., Lewis E., Evans, M., Evans, B., & Wilkins, A (2002). "Coloured overlays in schools: orthoptic and optometric findings". Ophthalmological and Physiological Optics 22: 156–165.
- Helveston, Eugene M. (2004). "Tinted Lenses". IDA Information Packet: 12–13.
- Irlen Institute: FAQ
- Irlen patent summary
- LDRC: Irlen filters and learning disabilities (review article)
- ACNT: Irlen colored filters (review article)
- Musatcha.com Irlen Filter - Freeware software color filter
- Colour in the treatment of Visual Stress