Irlen syndrome, occasionally referred to as scotopic sensitivity syndrome (SSS) or Meares-Irlen syndrome, very rarely as asfedia, and recently also as visual stress, is a proposed disorder of vision.
In 1980 New Zealand teacher Olive Meares described the visual distortions some individuals reported when reading from white paper. In 1983, American psychologist Helen Irlen wrote a paper about the use of coloured overlays aiding the reading abilities of some people. Similar symptoms were separately described by Meares and Irlen—each unaware of the other's work. Irlen, who was the first to systematically define the condition, named her findings "scotopic sensitivity", though in the discussions and debates over the following years some referred to it as Meares-Irlen syndrome.
There remains to this day stark controversy over whether non-Irlen-certified Meares-Irlen syndrome and the original Irlen syndrome are the same condition. Irlen syndrome, for example, seems to include a broader array of symptoms, including severe variants of the core condition. Basic testing for scotopic sensitivity was tried by optometrists, opticians, and orthoptists in UK hospitals, and by optometrists and opticians in private practice employing a technique that used the Intuitive Colorimeter, developed under Medical Research Council license. An alternative approach to correct Irlen syndrome was tried by Orthoscopics franchise in the UK, with wide colour coverage and tints manufactured by Hoyato match. Other commercial organisations have produced sets of therapeutic tints, although most have not received scientific evaluation.
The disorders have been studied in several institutions, including the Psychology Department at Essex University, the former Applied Psychology Unit, Cambridge University in England, and in the case of Meares-Irlen syndrome, Visual Unit at Glasgow Caledonian University in Scotland. the Visual Stress Unit offered non-commercial diagnostic and therapeutic services to individuals, and provided advice to the Scottish National Health Service.
In Australia, Irlen syndrome was researched by Paul Whiting at the University of Sydney. Whiting set up the first Irlen Dyslexia Centre in Australia, which operated in the Children's Centre at Sydney University for more than 15 years. Irlen syndrome was also studied in Australia by Greg Robinson (1944–2008) at the University of Newcastle. He was director of the Special Education Centre at the School of Education.
In the US, peer-reviewed literature on the topic suggests that much is unknown about the cause of these disorders, ranging from the 2011 study in a journal of the American Academy of Pediatrics, "Irlen Colored Overlays Do not Alleviate Reading Difficulties" and the 2012 study in the journal "Brain Topography", "A Functional Neuroimaging Case Study of Meares–Irlen Syndrome". The first, purely in relation to Meares-Irlen syndrome, finds that there is no evidence for one of the fundamental claims of therapeutic benefit; the second which focused primarily on Irlen syndrome found compelling evidence of unique brain function linked to the syndrome.
The College of Optometrists (UK) has specified guidelines for optometrists who use the colorimeter system. A society for coloured lens prescribers has been established to provide a list of eye-care practitioners with expertise in the provision of coloured lenses for the treatment of visual stress.
Treatment | Irlen Method
The Irlen Method uses coloured overlays and tinted lenses in the form of glass or contact lenses. The method is intended to reduce or eliminate perceptual processing errors; it is claimed the resultant retiming of visual signals in the brain improves the reading difficulties associated with scotopic sensitivity syndrome.
Skepticism relating to scotopic sensitivity syndrome's exact pathology has evolved on several fronts:
1. Whether it exists as a distinct, predictably identifiable disease with a reasonable pathophysiological mechanism, or whether a range of symptoms from other conditions are being placed under this convenient heading;
2. Whether it is causally or incidentally related to dyslexia, autism, or other conditions; and
3. Whether existing methods of scotopic sensitivity syndrome treatment are appropriate and effective.
A 2009 report by the American Academy of Pediatrics (AAP) does not believe that there is conclusive scientific evidence for the use of coloured lenses (one treatment used to relieve symptoms of scotopic sensitivity syndrome) although it acknowledges anecdotal evidence to the contrary. When discussing its scientific basis, the AAP mentions that "[t]he method used to select the lens or filter color has been highly variable, the color selection has also shown considerable variability, and the test-retest consistency has been poor" (p. 843).
The association of scotopic sensitivity syndrome and dyslexia has been challenged by many authors in the optometric and ophthalmologic communities. Furthermore, many special education departments at universities challenge the validity of coloured lenses as an effective treatment for the condition as outlined by the Macquarie University Special Education Centre.
Critics claim that the symptoms of those with Scotopic Sensitivity Syndrome are related to already known visual perceptual and neurological disorders. According to a statement released by the American Optometric Association in 2004:
As outlined by Hyatt, Stephenson and Carter (2009)
Scientific repudiation | Terminology
Critics maintain that the term "scotopic sensitivity" is a misnomer given that the symptoms of "scotopic sensitivity syndrome" reportedly occur during "photopic" conditions. The term "scotopic sensitivity" seems dubious, given that scotopic vision is the vision of the eye under low light conditions and as such vision is provided by rod cells on the retina, which have little or any role in colour vision; it does not make sense that a coloured lens or coloured overlay would have any impact upon "scotopic sensitivity syndrome". However, under low light conditions, the condition may exhibit itself in a distinctive manner (i.e. perceptions/visual disturbances of light, tones, and tracers that are not otherwise visually recordable or present).