Scotopic sensitivity syndrome

Scotopic sensitivity syndrome

Scotopic sensitivity syndrome, also known as Irlen Syndrome and Visual Stress Syndrome, approximating in some ways to Meares Irlen syndrome, and 'Visual Stress', refers to visual perceptual disorder(s) affecting primarily reading and writing based activities. Its existence is not recognized as a homogenous condition by the American Academy of Pediatrics or the American Optometric Association, although its symptomatic occurrence is accepted by the latter and has never been contested by the former (see skepticism below). It is accepted as a homogenous condition however by a respected body of international expert medical opinion, and has been studied in the former Applied Psychology Unit, Cambridge University in the UK, and the Scottish Parliament has also funded a research and treatment centre at the Glasgow Caledonian University, for the associated condition of Meares/Irlen Syndrome.

Irlen syndrome is sometimes categorised as a form of dyslexia. However, bestselling autistic author, Donna Williams, in her book Like Colour To The Blind wrote about her experience of tinted lenses (Irlen filters) after being diagnosed with scotopic sensitivity. In this book she described the lenses as enabling her to have cohesive, unfragmented vision, able to see faces, bodies and objects as a whole for the first time and reducing the extremity of experiences such as meaning-blindness, face blindness, inability to learn to read facial expression and body language and the social consequences of these impairments. This led to a worldwide raised awareness of scotopic sensitivity as a sensory perceptual problem common in many (but not all) autistics and expanded awareness of the potential effects of Scotopic Sensitivity far beyond that of reading disability, also leading to awareness of the effects of fluorescent lighting on those with this perceptual disorder.

The condition was 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 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 often referred to it as Meares-Irlen syndrome. Testing for scotopic sensitivity were also taken up by optometrists, opticians, and orthoptists in UK hospitals, and by optometrists and opticians in private practice using a technique that used the Intuitive Colorimeter, developed under Medical Research Council license. An alternative approach is used by the Orthoscopics franchise in the UK, with wide color coverage and tints manufactured by Hoya to match. Other commercial organisations have produced sets of therapeutic tints, although most have not received scientific evaluation.

Two examples of how a sufferer may see text



Scotopic sensitivity syndrome is based on the theory that some individuals have hypersensitive photoreceptors, visual pathways, and/or brain systems that react inappropriately to some wavelengths of light. Vision occurs when photons are detected by the retina, initiating a biochemical process affecting the visual pathways and deep structures of the brain. A growing number of researchers are taking an interest in the view that inappropriate biochemical processing has the potential to cause physiological and/or visual perceptual problems. Many of these problems are grouped together under the label "scotopic sensitivity syndrome".

In simple terms, the theory is that some signals from the eye are not getting to the brain intact and / or on time. Although the eye might be functioning correctly, the brain receives what is like a double exposed picture where the location of items is confused. The brain tries to filter out the bad information and so the conscious mind receives a reconstructed image. That image may be of the items moving (the brain constantly changing its best guess of what is there), blurred outcomes (inability to form a view of what is there), gaps in wrong spots, and a variety of other minor errors. There may also be exhaustion (from the mental effort to unscramble) and sore eyes (from the eyes constantly seeking extra data to aid the process) The problem is worst where different colours do not all give a similar outcome. In nature you get a lot of consistent data but on a man made item (e.g. paper) there might only be limited colour sets. i.e. The condition does not generate practical problems where there is lots of redundant data for the brain to use. The pragmatic response by Irlen was not to try to fix the problem but to avoid it. By filtering out the light most likely to generate problem signals to the brain, she was able to improve the likelihood that the brain will correctly distinguish between good and bad information. It also seems likely that in some individuals, over time the brain learns which colours are the problem items and improves its ability to reconstruct an accurate image.

Scotopic sensitivity syndrome Symptoms

One or more of these symptoms may be related to the condition:

  • Eye-strain
  • Fatigue
  • Headaches (including migraine)
  • Nausea, including visually related motion sickness
  • Problems with depth perception (catching balls, judging distance, etc.)
  • Restricted field of view and span of recognition
  • Discomfort with busy patterns, particularly stripes ("visual stress" and "pattern glare")
  • Discomfort with extreme conditions of bright/dark contrast (i.e. backlighting)
  • Discomfort or difficulty reading (reading involves busy patterns, particularly stripes. People with strong symptoms of the syndrome find it very difficult to read black text on white paper, particularly when the paper is slightly shiny.)
  • Text that appears to move (rise, fall, swirl, shake, etc.)
  • Losing text content and only seeing rivers of white through the text
  • Words moving together becoming one unrecognizable word
  • Attention and concentration difficulties
  • Seeing the part and losing the whole
  • Epileptic seizure related to strobing or pattern glare


The use of tinted lenses in glasses and coloured overlay sheets has been prescribed by many doctors; however, the efficacy of such treatment is questionable. It has been felt to be efficient treatment by some, and inappropriate by others, because more conventional treatments are sometimes more appropriate.

The College of Optometry (UK) has specified guidelines for optometrists who use the colorimeter system. A society for colored lens prescribers [1] has been established to provide a list of eye-care practitioners with expertise in the provision of colored lenses for the treatment of visual stress.

The Promethean Trust, a Norwich-based charity for dyslexic children, has found that the use of a cursor has eliminated the need for colored overlays or lenses. The cursor is simply a piece of card or plastic, approximately the size of a business card, with a notch cut out of one corner. The reader (or the remedial teacher) uses this to track print from left to right, and at the same time the card prevents the eyes from wandering ahead. Although no formal research has been conducted, it is likely that most cases of visual confusion result from the eyes moving in mini-saccades when the reader encounters an unfamiliar word. This occurs as the reader subconsciously tries to scramble letters to achieve a 'fit' with a familiar word. This creates the subjective impression that the letters 'won't stay still'.

Irlen Method

The Irlen Method is a controversial system that is intended to improve reading difficulties associated with scotopic sensitivity syndrome using tinted lenses and overlays.[1]

Irlen Screener

"Irlen Screeners are certified to administer the first testing session and determine whether an individual will benefit from further evaluation for Irlen Spectral Filters." [2]

Irlen Diagnosticians

"Irlen Diagnosticians are certified to administer both testing sessions. During the initial testing session, an individual is screened to determine whether wearing Irlen Spectral Filters will make a difference and the amount of improvement for reading and other academic activities. In addition, during this session 12 other areas will be evaluated and recommendations made. Only Irlen Diagnosticians are certified to test and determine your customized spectral filter worn as Irlen glasses or contact lenses and conduct yearly rechecks." [2]

Intuitive Colorimeter

Developed by Arnold Wilkins, Ph.D., University of Essex, England, an alternative system for the identification of tint to reduce symptoms.

Lack of Scientific Proof

Skepticism surrounding scotopic sensitivity syndrome has evolved on several fronts:

  1. Whether it exists as a distinct, predictably identifiable disease with a reasonable pathophysiological mechanism;
  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 any scientific evidence or basis for the use of colored lenses (the treatment used for Scotopic Sensitivity Syndrome) [3]. 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 both the optometric and ophthalmologic communities.[4] Furthermore, many special education departments within universities also challenge the validity of SSS and Irlen lenses.[5] As outlined by the Macquarie University Special Education Centre[6]:

In a joint statement, The American Academy of Ophthalmology, American Academy of Pediatrics, American Association for Pediatric Ophthalmology and Strabismus and American Association of Certified Orthoptists firmly repudiated the use of lenses, stating that there was no scientific evidence supporting their use. The expense of such treatment is unwarranted and may divert resources from evidence-based reading interventions.[7]

Critics claim that the symptoms of those with Scotopic Sensitivity Syndrome are related to already known visual disorders.[8] According to a statement released by the American Optometric Association in 2004:[9]

There is evidence that the underlying symptoms associated with the Irlen Syndrome are related to identifiable vision anomalies, e.g., accommodative, binocular, and ocular motor dysfunctions, in many patients seeking help from colored lenses. Furthermore, such conditions return to normal function when appropriately treated with lenses, prisms, or vision therapy. When patients exhibiting the Irlen Syndrome were treated with vision therapy, their symptoms were relieved. These patients were no longer classified as exhibiting this syndrome, and therefore did not demonstrate a need for the colored overlays or tinted lenses.


Critics assert 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".


  1. ^ Irlens Lens Program - University of Newcastle, Australia
  2. ^ a b Irlen Institute, "Irlen Screeners", 2008.
  3. ^ American Academy of Pediatrics, 2009
  4. ^ Cotton M, Evans K (1990). "A review of the use of Irlen (tinted) lenses". Aust N Z J Ophthalmol 18 (3): 307–12. doi:10.1111/j.1442-9071.1990.tb00625.x. PMID 2261178. 
  5. ^
  6. ^
  7. ^
  8. ^ Solan H, Richman J (1990). "Irlen lenses: a critical appraisal". J Am Optom Assoc 61 (10): 789–96. PMID 2136527. 
  9. ^ "The Use of Tinted Lenses and Colored Overlays for the Treatment of Dyslexia and Other Related Reading and Learning Disorders". Retrieved 2009-10-13. 

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