Scotopic sensitivity syndrome, also known as Visual Stress, Irlen Syndrome, and Asfedia, is a condition relating to the interaction of the central nervous system and the eyes at a physiological level with light. It manifests itself most notably in terms of reading, although the symptoms of the condition can be more general than this. The condition does attract some controversy not in terms of its existence per se, but in the efficacy of reputed methods of treatment. Some experts whilst accepting the existence of the symptoms, question whether this is a homogeneous condition, or if one or more co-morbidities around another core condition, are not being confused with a homogeneous one. The condition is however recognised as a homogenous condition by an international body of expert opinion. Similar symptoms were separately described by two people working individually, each unaware of the other's work. In the early 1980s New Zealand teacher Olive Meares described the visual distortions some individuals reported when reading from white paper, while American therapist Professor Helen Irlen wrote a paper about the use of coloured overlays aiding the reading abilities of some people. 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 also tried by Orthoscopics franchise in the UK, with wide color coverage and tints manufactured by Hoyato match. Other commercial organisations have produced sets of therapeutic tints, although most have not received scientific evaluation.