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Asfedia, formerly known as Irlen's Syndrome and Scotopic Sensitivity (Syndrome), is a reading disability. Its characteristics include:

a) the inability to visually detect the edges of or properly "decode" black-colored text written or printed on a white background; and,

b) the inability to sustain 'decoding' for a significant length of time.

Both of these phenomena manifest themselves in a wide variation of intensity, giving rise to the uncertainty for so long associated with the diagnosis of dyslexia. The relationship between reading challenges and visual edge detection results from the fact that text can be understood as a series of vertical edges in a horizontal array. In order for the eyes to successfully and efficiently move (saccade) from one word to the next, the speed with which the brain can identify (detect) these vertical edges needs to be maximized. In individuals displaying poor reading speed and/or "reading stamina", this ability to detect edges is compromised.

In an attempt to both clearly identify this condition in all further work on the subject, and to reinforce the fact that it is just one part of a complex mixture, some asfedia sufferers created the following:

A - Arrythmic
S - Saccade &
F - Foveation during
E - Edge
D - Detection
I - Iterative
A - Arrays

The effects of the condition are ameliorated via the use of special coloured filters and overlays.


Two manifestations of the Lorem ipsum text transformed as a sufferer of Irlen Syndrome might see it.

Scotopic Sensitivity Syndrome, also known as Meares-Irlen Syndrome or Irlen Syndrome, is a broadly defined visual perceptual disorder affecting primarily reading and writing based activities. Because of this, it 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 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 like meaning-blindness, face blindness, inability to learn to read facial expression and body language and the social consequences of these impairments. This lead to a worldwide raised awareness of Scotopic Sensitivity as a sensory perceptual problem common in many (but not all) people with autism and expanded awareness of the potential effects of Scotopic Sensitivity far beyond that of reading disability, also leading to awareness of fluorescent lighting on those with this perceptual disorder.

The condition was jointly described by two people working individually, unaware of the work of the other person. In the early 1980s New Zealand teacher Olive Meares described the visual distortions some individuals reported when reading from white paper, while American psychologist Helen Irlen wrote a paper about the use of coloured overlays aiding the reading abilities of some people. Irlen named her findings "scotopic sensitivity", though the discussions and debates over the following years often referred to it as Meares-Irlen Syndrome. Testing for Scotopic Sensitivity were also taken up by ophthalmologists in UK hospitals using a technique called Colorimeter and an organisation run by ophthalmologists called Brain Power International also produced its own affordable self testing set of therapeutic tints for Scotopic Sensitivity, including a set specific to the autistic population.


Scotopic Sensitivity Syndrome is based on the theory that certain wavelengths of light interfere with the visual pathways between the eye and the brain.


  • Light sensitivity and contrast problems. 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.
  • Restricted field of clear vision
  • Poor depth perception
  • Attention and concentration difficulties
  • Context blindness and poor object recognition
  • Seeing the part and losing the whole


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 in treatment by some.

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. Irlens Lens Program - University of Newcastle, Australia


Skepticism surrounding scotopic sensitivity syndrome has evolved on several fronts:

  1. Whether SSS exists as a distinct, predictably identifiable disease with a reasonable pathophysiologic mechanism,
  2. Whether SSS is causally or incidentally related to dyslexia, autism, or other conditions, and
  3. Whether existing methods of SSS treatment of SSS are appropriate and effective.

The association of scotopic sensitivity syndrome and dyslexia has been challenged by many authors in both the optometric and ophthalmologic communities[1].

Tinted lenses and dyslexics--a controlled study. SPELD (S.A.) Tinted Lenses Study Group.

Gole GA, Dibden SN, Pearson CC, Pidgeon KJ, Mann JW, Rice D, Rooney KF, Hannell G, Fitzgerald BA, Kortman JY, et al.

SPELD Incorporated, Kensington, South Australia.

We have carried out a randomised prospective controlled trial of the effect of tinted lenses on the reading ability of 24 non-asthmatic dyslexic children aged between nine and twelve years. Reading ability was assessed using the Neale Analysis of Reading. After one school term, there was no significant difference in the change in reading age between treatment and control groups. After two school terms (approximately six months), only 11 children (44%) were still wearing the glasses. Of 381 suitable subjects for entry into the study, 208 were excluded because of a diagnosis of asthma (to avoid effects of medication on cerebral function). As a result, we may have excluded subjects who would have responded favourably to tinted lenses.

Critics claim that the symptoms of those with Scotopic Sensitivity Syndrome are related to already known visual disorders[2]. According to a statement released by the American Optometric Association in 2004[1]: "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."

A previous controlled study found the lenses not to significantly improve reading ability."[2]"


Critics assert that the term "scotopic sensitivity" is a misnomer given that the symptoms of "Scotopic Sensitivity Syndrome" reportedly occur during photopic conditions.

Related Subjects


  1. Cotton M, Evans K (1990). A review of the use of Irlen (tinted) lenses.. Aust N Z J Ophthalmol 18 (3): 307-12. PMID 2261178.
  2. Solan H, Richman J (1990). Irlen lenses: a critical appraisal.. J Am Optom Assoc 61 (10): 789-96. PMID 2136527.

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