Treatment of Dyslexia - Coloured tinted glasses

Meares-Irlen Syndrome - Definition, Symptoms and Treatment with coloured tinted lenses

HISTORY - The Origins of Scotopic Sensitivity, Meares-Irlen Syndrome:

In the early 1980s, a teacher in New Zealand, Olive Meares, was the first to provide a detailed written account of the spatial distortions affecting text being read, by some individuals.  Olive Meares also reported that the effects she cited could be reduced or eliminated by the use of coloured paper or by using coloured plastic overlays.  The overlay being placed over the text to be read.

A psychologist working in California, Helen Irlen, wrote a paper describing symptoms similar to Olive Meares.  Ms Irlen, named the effects as Scotopic Sensitivity or Irlen Syndrome.  The syndrome was one in which reading is impeded by distortions of print. She reported that the distortions were positively effected if text was viewed through a coloured filter or overlay.  Ms Irlen went further and established a protocol for screening for scotopic sensitivity and a system for dispensing coloured overlays as a result of the assessment.

There followed a period of time during which the scientific community discussed these findings with a great deal of scepticism. The problem being that there was no satisfactory explanation as to why the treatment of visual distortion of text with coloured overlays should work.  Of course this did not mean that it did not work.  In fact medicine is littered with examples of treatments working first followed by an understanding of why much later.

Reports of benefit from colour came to the attention of Dr Arnold Wilkins of the Medical Research Council. Concerned that the benefit was a placebo effect, he recognised that if colour potentially gave benefit, the colour needed to be selected with precision and with the three aspects of colour, hue, saturation and brightness independent of one another. To allow this selection he invented what is today the intuitive Colorimeter and used this instrument to carry out scientific research.

Prof. Wilkins and colleagues of Essex University were amongst the first to apply scientific rigor to the study of scotopic sensitivity or Meares-Irlen Syndrome, as it had become known.  The Essex University team set up double blind placebo controlled trials and went on to establish a number of tools for screening for scotopic sensitivity and quantifying the effects of coloured overlays.  

The screening test is available to professionals and is know as the Intuitive Overlays Test.  Whilst the tool used to quantify the effects of overlays is also available to professionals and is known as the Wilkins rate of reading test.

In the past assessment for scotopic sensitivity was generally done by the Irlen Institute.  It was quite an expensive assessment and the overlays were also relatively expensive.  Now the Intuitive Overlays Test combined with the Wilkins rate of reading test has enabled practitioners who have been trained by the Institute of Optometrists to carry out an assessment and prescribe an overlay for use when reading.  This has rolled out the number of professionals who have these assessment skills and made the assessment and prescription of suitable overlays very much more affordable.

If you or your child is experiencing visual effects such as thus cited above: text wobbling, moving, flickering, blocking out, underlining, halo effects, head aches, a feeling of over brightness then it would be useful to have an assessment in this regard.

The Irlen Method has helped children and adults worldwide become successful rather than continue to experience enormous difficulties. In addition to dyslexia, patients with headaches, migraine and photosensitive epilepsy may benefit. This method has received international acclaim and Helen Irlen?s work has been included in professional journals, textbooks, National Geographic, TV shows such as 60 Minutes and Good Morning America, ABC World News With Peter Jennings, NBC News and has been the subject of many news broadcasts by the BBC and news shows in Ireland, Hong Kong, Netherlands, New Zealand, and Australia including their 60 Minutes.

Trial Tinted Lenses and Overlays

The Irlen Method provides a unique service for children and adults with reading, attention, and learning difficulties. But even good readers and gifted students can be helped. At least two million Americans are identified as learning disabled. Many more are labeled as "not trying hard enough" at school for a variety of reasons, including lack of motivation, attention deficit disorder, reading problems, or discipline problems.

Irlen Syndrome, also known as, Scotopic Sensitivity Syndrome (SSS) is a type of visual perceptual problem. It is not an optical problem. It is a problem with how the nervous system encodes and decodes visual information. Academic and work performance, behaviour, attention, ability to sit still and concentration can be affected. Individuals with this problem see the printed page differently, although they may not realize that they do. Having Irlen Syndrome keeps many people from reading effectively, efficiently, or even at all.

Individuals with Irlen Syndrome see the printed page differently from those with normal vision and must constantly adapt to distortions appearing on the printed page. They may be slow or inefficient readers, exhibit poor comprehension, suffer from strain, fatigue or headaches. It can affect their attention-span, energy-level, motivation, handwriting, depth-perception and, ultimately, self-esteem. Irlen syndrome sufferers may be labelled as underachievers with behavioural, attitudinal, or motivational problems. It is a complex and variable condition sometimes found to co-exist with other learning-disabilities.

What is Visual Stress?

Visual Stress is a visual perception problem which makes it difficult for affected individuals to see text clearly. The contrast between black text on a white background makes the letters appear jumbled, animated or blurred. It has been estimated that 11% of the population are affected. Some children initially thought to be dyslexic may be suffering from just Visual Stress.

The classic symptoms are:-

  • Words are moving around the page.
  • When I read I get a headache.
  • The words are blurred
  • The page is too bright and I cannot see the words clearly.

Look out for:-

  • Reading avoidance.
  • Skipping lines or words.
  • Loses place easily.
  • Difficulty understanding text.
  • Whilst reading -
    • "Words move"
    • Tires easily.
    • Eyes become red or start watering.
  • Whilst writing -
    • Poor spelling.
    • Makes mistakes when copying text.
    • Untidy work.
  • Others -
    • Difficulty catching a ball.
    • Poor distance judgement.
    • Clumsiness.



Children who are unaware that they have Visual Stress may come to believe that they must be stupid or slow as they fall below the reading standards of their friends and classmates. This can lead to frustration and lead to disruptive behaviour.

It is extremely important that Visual Stress is diagnosed as early as possible. Some people experience visual stress when viewing text for long periods. The symptoms vary from person to person, but can include headaches and migraines (especially when working at the computer), eyestrain, and experiencing instability of print when viewing text.

Visual Stress can also cause eyestrain and headaches in both adults and children and the non-drug treatment may be effective.

Often these symptoms can be alleviated through changing the background colour on which the text is superimposed. Where colour is proven to be beneficial, the condition is termed Meares-Irlen Syndrome.

What is the Meares-Irlen Syndrome?

Meares-Irlen Syndrome is characterised by symptoms of

  • asthenopia - or eye strain is an ophthalmological condition with nonspecific symptoms such as fatigue, red eyes, eye strain, pain in or around the eyes, blurred vision, headache and occasional double vision. Symptoms often occur after computer work, reading, or other activities that involve tedious visual tasks.
  • visual perceptual distortions when reading which are alleviated by the use of specific coloured filters or overlays.


Meares-Irlen Syndrome is a condition characterised by perceptual reading problems such as illusions of shape, colour or motion, combined with sore, tired eyes and headaches (asthenopia), the symptoms of which are alleviated by the use of coloured overlays over the page of text or by wearing tinted lenses9501, 9601, Eperjesi, 2000  Meares-Irlen Syndrome (MIS) is also referred to as Irlen Syndrome or Scotopic Sensitivity Syndrome. It may affect adults as well as children. The symptoms of the syndrome are also referred to by some as visual stress or visual discomfort.0201 Those affected often will not complain of such specific symptoms as they believe that everyone perceives printed pages in the distorted way that they do. Indeed, Meares (1980) found that the children she studied obviously believed that she saw exactly what they saw when looking at a page of print. Such symptoms can thus manifest as poor comprehension, slow and hesitant reading, skipping words, and trouble in copying or signs of inattention. A child could, therefore, be labelled as being lazy, unmotivated, inattentive  or  having a behavioural disorder such as Attention Deficit Disorder. The child may hide  problems by working extra hard just to obtain acceptable grades.

History of the Meares Irlen Syndrome

  • The symptoms of the syndrome were first reported in the scientific literature in 1980 by Olive Meares.
  • Helen Irlen subsequently developed a diagnostic technique for the condition and patented a set of coloured overlays and tinted spectacle filters to ease the symptoms.
  • Initially, there was controversy over Irlen?s claims as she failed to publish any peer reviewed research data as evidence for her treatment.
  • Subsequent research, including various double-masked, placebo-controlled trials have provided some, although not conclusive, evidence for this condition and the beneficial effect of coloured overlays and filters.
  • Various theories have been proposed to explain the syndrome, such as contrast sensitivity, retinal sensitivity, binocular and accommodative anomalies, a defective magnocellular pathway and cortical hyperexcitability.
  • None of these theories, however, fully explain the different and specific colour required to alleviate symptoms in different subjects.
  • Future research needs to address this fundamental issue rather than simply providing further evidence for the therapeutic effect of colour on affected subjects.
  • The relationship between Meares-Irlen Syndrome, migraine and photosensitive epilepsy is requires further investigation. One factor, however, that is not in dispute is the need for a complete optometric and orthoptic examination of any patient complaining of asthenopic or perceptual distortions to exclude visual or ocular motor problems that may cause similar symptoms to those reported in Meares-Irlen Syndrome.


    1.1. Description of Meares-Irlen Syndrome

    1.2. Symptoms of MIS
    The symptoms of MIS can include the following:
    ? blurring of print
    ? ?squashed up? print
    ? movement or wiggling of print
    ? words falling off the page
    ? letters changing or doubling
    ? letters fading or becoming darker
    ? patterns appearing on the page
    ? blobs of colour appearing or moving on the page
    ? streams or rivers of light running down or across the page
    ? nausea, discomfort or pain from the glare from the page
    ? eye strain and headaches
    More general symptoms can include
    ? light sensitivity to glare, sunlight, headlights, streetlights
    ? inefficient reading
    ? slow reading rate
    ? attention deficit - restlessness when reading or writing
    ? strain and fatigue when reading

    How Common is Mearles-Irlen Syndrome?

    In a study conducted in a Kent primary school during 1996, Wilkins et al. identified 19% of 8-11 year olds that benefited from coloured overlays.

    Jeanes et al 9701 screened 93 primary schoolchildren aged 5-11 from a Cambridge school as well as 59 secondary schoolchildren from Kent, aged 11-12. Fifty-three per cent had initial perception benefit. Ten months later, 14% of the primary schoolchildren and 9% of the secondary schoolchildren were still using either a coloured overlay or tinted glasses.

    Additional studies would suggest that about 30% of children find coloured overlays useful but only 5% of all schoolchildren have a severe degree of Meares-Irlen syndrome.

    In 2002, a study was conducted to investigate the prevalence of Meares-Irlen syndrome in the adult population. From a sample of 113 university students, 34% showed a 5% improvement in reading speed with a coloured overlay.0201 These results were comparable to those found with children, suggesting that up to one third of the general population may suffer from MIS to some degree.Reports of the prevalence of MIS undoubtedly vary depending on the criteria used to diagnose the condition. There is probably a continuum of the syndrome with many people having only mild symptoms and fewer suffering to a severe degree (Evans, 2004c).

    Specific Learning Difficulties, underachievement and Merles-Irlen Syndrome

    Specific learning difficulties occur when a person has a particular problem with any aspect of learning which is not commensurate with the person's intelligence or due to lack of opportunity.

    The commonest specific learning disability is dyslexia with a prevalence of approximately 5%. Dyslexia has been described as an unexpected problem in learning to read and spell in people who seem otherwise capable and intelligent.


    The British Psychological Society states that dyslexia is evident when accurate and fluent word reading and/or spelling develops very incompletely or with great difficulty.9801

    Dyslexics may also experience difficulty

    • in understanding verbal language
    • in clearly expressing themselves either when speaking or writing.
    • Some may confuse left and right or
    • have problems with the concept of before and after,
    • and some dyslexics may have difficulty with organisational and planning tasks Eperjesi, 2000

    Dyslexia is a lifelong problem, caused by some form of brain dysfunction although the mechanisms are not fully understood. A phonological processing deficit is generally thought to be a major factor in dyslexia (Evans, 2004A) and manifests as a problem associating letters with the constituent sounds of speech.0301

    Visual problems are not the cause of dyslexia although they can contribute to reading difficulties and many dyslexics have visual deficits such as binocular instability and accommodative insufficiency (Evans, 2004b).

    Irlen, in 2005,  suggested that 46% of those with reading problems or learning disabilities have MIS and 65% of dyslexics have the condition.

    Dyslexic children tend to report more visual symptoms than good readers, although, as with MIS, some do not as they assume everyone has the same experience. Many of the symptoms suffered by dyslexics are similar to those caused by MIS - such as headaches when reading, blurring, moving text, double vision, or skipping words or entire lines.

    Many symptoms of MIS can also be indicative of visual problems, such as blurring or double vision. It follows that no single symptom or even group of symptoms can  be used to definitively diagnose a condition such as MIS or dyslexia.

    For MIS, the essential discriminating factor seems to lie in the treatment. If symptoms of eyestrain and visual perception distortions are alleviated by using a coloured overlay or filter, then the patient is regarded as suffering from MIS.

    Dyslexics may well suffer from MIS in addition to dyslexia,  compounding their reading difficulties. Treatment of the MIS symptoms may not necessarily solve all of their reading problems.

    Optometric Correlates of Meares-Irlen Syndrome

    Optometric correlates are those eye-related problems that are strongly associated with MIS with one possibly influencing the other. Anyone suffering any sort of visual problem with reading requires a thorough optometric examination to correct any refractive errors.

    Binocular Instability

    Binocular instability is frequently associated with reading difficulties but can be easily treated with fusional reserve exercises, or if due to temporary poor health, then with prisms or spheres.

    Accommodative Anomalies

    Accommodation is the increase in power of the eye or change of focus in order to clearly see objects at closer distances by changing the curvature of the crystalline lens. Accommodation reduces with age as the crystalline lens loses elasticity - this is called presbyopia and generally necessitates the wearing of reading glasses to see close objects.




    The amplitude of accommodation is the maximum amount that the crystalline lens can accommodate. In young children this would be expected to be in the order of +15D. A reduced amplitude of accommodation or accommodative insufficiency can lead to blur and asthenopia when reading. In a study of 8-12 year-old schoolchildren, those that chose an overlay to help them with their reading and continued to use it for at least 4 months exhibited reduced amplitudes of accommodation (Scott et al., 2002) and Evans has also shown a strong link between reduced amplitudes of accommodation and MIS and dyslexia (Evans et al., 1995; 1996).
    Lag of accommodation is the difference between the accommodative response and the accommodative stimulus. Thus a poor accommodative response equates to a high accommodative lag and can contribute to accommodative infacility which is a slow or difficult accommodative response. Subjects often complain of blurred distance vision immediately after sustained close work. This can affect children copying work from boards into books and has been demonstrated in some dyslexics (Evans, 1998).
    Accommodative fatigue is the inability of the eye to sustain sufficient accommodation over an extended period of time. This will cause eyestrain, blur and headaches after sustained effort at near. Hence accommodative anomalies can produce similar symptoms to those reported in MIS but can be treated with exercises or spectacles (Evans, 1997).

    1.5.3. Convergence Insufficiency
    Convergence insufficiency is an inability to adequately converge the eyes or to maintain sufficient convergence for comfortable near vision. Convergence is essential for near vision and is linked to accommodation by the so-called near-triad of accommodation, convergence and miosis; the three responses that occur when looking at a near object and are all mediated by the third cranial nerve, the oculomotor nerve. Symptoms of convergence insufficiency are tired eyes, blurring, double vision and headache (Evans, 1997). This has been found in some studies of dyslexics but can be easily treated with convergence exercises (Evans, 1998).

    1.6. Visual Stress
    Visual stress can be defined as the inability to see comfortably without distortion or discomfort (Wilkins et al., 2004). Visual stress encompasses a variety of adverse effects caused when viewing particular visual stimuli. Such effects include pain or discomfort around the eyes, headaches, dizziness, nausea, seizures, and perceptual distortions such as movement, blur, flicker, and colour (Wilkins, 1995; 2003). Such symptoms are also referred to as pattern glare since they are particularly prevalent when viewing repetitive geometric patterns (Simmers et al., 2001a).
    According to Wilkins in his book, Reading Through Colour, ?If this kind of visual stress is treatable with coloured filters, the symptoms and signs are referred to as Meares-Irlen Syndrome? (Wilkins, 2003). In a case report of three patients referred with suspected MIS, Evans writes ?These people are often described as having visual stress rather than Meares-Irlen Syndrome, although it seems likely that the two conditions have much in common and may simply be different manifestations of the same condition? (Evans, 2005) and he goes on to collectively describe the conditions as Meares-Irlen Syndrome/Visual Stress or MISVS. Hence there appears to be confusion and inconsistencies in the terminology, with different researchers coining different names for perhaps the same condition.

    1.7. Migraine and Visual Stress
    Susceptibility to the effects of visual stress is extremely high in people who suffer frequent, severe headache or migraine. Those people who are susceptible to illusions induced by visual patterns tend to suffer more headaches than others and are more susceptible to pattern illusions on days when they have a headache or the day before (Wilkins, 1995).
    Migraine is differentiated from normal tension headache by symptoms of nausea and aggravation by physical activity. Many migraines are preceded by visual aura, consisting of perceptual distortions, flashing lights, zigzag lines and partial loss of vision. The visual nature of this aura suggests that the visual cortex is involved. There is some evidence that tinted glasses can reduce the frequency of headaches (Wilkins et al. 2002) thus suggesting a common mechanism for headache and visual stress.

    1.8. Photosensitive Epilepsy
    Epilepsy is a disorder of the brain in which abnormal neuronal activity results in recurrent seizures. Approximately 4% of epileptics suffer seizures in response to visual stimuli such as flashing or flickering lights or geometric patterns and shapes and this is referred to as photosensitive epilepsy (Wilkins, 1995).
    The brain activity of epileptics can be examined using the electro-encephalograph (EEG) which records the potentials from the brain using electrodes against the scalp. Any changes in neuronal activity from the norm on viewing particular visual stimuli can be recorded. Such recordings have shown that a flickering light will induce a characteristic response in a photosensitive epileptic, called a photoconvulsive response. Such experiments have shown that the patterns most likely to elicit photoconvulsive responses are striped with long line contours, i.e. those resembling grating patterns (Wilkins, 1995).
    Grating patterns frequently encountered in the everyday world can include wallpaper and soft furnishings, clothing designs, streams of sunlight shining through trees, the stair tread of escalators, brickwork and tiles, ventilation grills, ceiling panels and even printed text on a page. For those people susceptible to photosensitive epilepsy, such patterns are likely to be encountered on a regular basis throughout their daily lives. Flicker from televisions and other cathode ray tube appliances can also induce seizures. Could these visual patterns also be responsible for the symptoms of visual stress or MIS in non-epileptics? Are the visual stress symptoms a less intense form of photosensitive epilepsy?

    1.9. Description of Colour
    Colour can be described in terms of three perceptual properties, hue, value and chroma. Hue is the description of the appearance of a wavelength, i.e. 580nm has a yellow hue. It is commonly interchanged with the word colour, although colour actually refers to all three attributes of hue, value and chroma together. Value refers to the brightness or the amount of radiant energy perceived whereas chroma is the saturation or how vivid a colour appears.

    1.9.1. Chromaticity Diagrams
    Colours can be plotted on a two-dimensional diagram in terms of chromaticity coordinates which specify the proportions of three primary colours (red, green and blue) required to make up that colour. The Commission Internationale de l?Eclairage (CIE) x,y, chromaticity diagram is a mathematical manipulation of a chromaticity diagram such that there are no negative quantities. All physically realisable colours lie within a horseshoe-shaped locus with white in the centre and spectral colours along the perimeter (Fig. 1.1). These diagrams and colour coordinates will be considered in more detail later when discussing the research into the use of coloured overlays and tinted lenses for MIS.

    Figure 1.1. The CIE x,y chromaticity diagram. Image from: Periferiak/CIE-xy.jpg

    1.10. Diagnosis and Treatment of MIS
    Since the definition of MIS is somewhat arbitrary, in that the diagnosis of the condition depends upon whether the symptoms are alleviated by the use of coloured filters, the only sure way to diagnose MIS is by the use of coloured filters. However, the means by which different practitioners determine the precise colour of the filter differs.

    1.10.1 Irlen Differential Perceptual Schedule
    Helen Irlen?s book, Reading by the Colors, begins with a self-test of 14 questions:
    Do you skip words or lines when reading?
    Do you reread lines?
    Do you lose your place?
    Are you easily distracted when reading?
    Do you need to take breaks often?
    Do you find it harder to read the longer you read
    Do you get headaches when you read?
    Do your eyes get red and watery?
    Does reading make you tired?
    Do you blink or squint?
    Do you prefer to read in dim light?
    Do you read close to the page?
    Do you use your finger or other markers?
    Do you get restless, active, or fidgety when reading?

    If you answer yes to three or more of these questions, then Irlen suggests that you might be suffering from SSS (Irlen, 2005).
    In an Irlen clinic the diagnosis of SSS is based upon the results of the Irlen Differential Perceptual Schedule or IDPS. The first part comprises subjective responses to visual tasks such as counting the white spaces along the top and down the side of a striped cube in an illustration (Fig. 1.2) (Irlen, 2005).

    Figure 1.2. An example of a perceptual task used by the Irlen Method to diagnose SSS. Children are asked to count the number of white spaces along the top and down one side (Irlen, 2005).

    Next the patients are questioned about the nature of any visual distortions while observing lines of music and they also complete a questionnaire to identify the presenting symptoms (as above) (Solan & Richman, 1990). If the responses to the IDPS indicate the presence of SSS then a series of coloured overlays is used to determine which one is most effective at improving reading (Irlen, 2005).

    1.10.2. Coloured Overlays
    Different coloured overlays (acetate sheets) are placed over a page of print to determine which, if any, has the greatest effect on reducing the visual distortions experienced by the patient. The overlays are placed in turn over a page of text; different coloured overlays can be compared side by side and overlays can be superimposed on top of each other to produce a stronger coloured overlay (Fig. 1.3). If the text appears clearer with an overlay or a combination of overlays, then this is indicative of MIS and the chosen overlay will be prescribed to use whenever the patient feels the need.

    Figure 1.3. Comparison of a single overlay with a double overlay. Image from: http://www.essex.

    1.10.3. Rate of Reading Test
    Reading rate is measured with and without the chosen overlay to quantify any improvement in reading. A significant increase in reading speed, usually taken as 5%, with the overlay indicates a benefit to be gained from that overlay and hence is indicative of MIS (Wilkins et al., 1996).

    1.10.4. Intuitive Colorimeter
    The Intuitive Colorimeter (Fig. 1.4) systematically samples light of different colours illuminating a page of text. Controls on the side change the hue, saturation and brightness to determine the optimum colour? for reducing distortions for any particular individual. A positive response to testing with the Intuitive Colorimeter indicates that the subject may be suffering from MIS

    Figure 1.4. The Intuitive Colorimeter. Image from: wpe3.jpg.

    1.10.5. Tinted Lenses
    If a benefit is seen with coloured overlays, then specific coloured spectacle lenses can be prescribed to be worn as the patient feels necessary. The Wilkins method uses the Intuitive Colorimeter setting as an initial guide to the optimal tint which is then subjectively revised using a set of tinted trial lenses. The Irlen method uses a trial and error process of trying different coloured lenses, firstly singly and then in combination to ascertain the optimal tint. Precision tinted contact lenses are also available (Evans et al., 1999). One diagnostic criterion proposed by Evans for MIS is evidence of a sustained benefit from coloured filters (Evans & Joseph, 2002) which presumably could also be applied to the coloured overlays.

    1.11. Aim
    In the following chapters, I shall review the evidence for the existence of Meares-Irlen Syndrome and discuss the theories that have been put forward that relate to its cause.


    2.1. Olive Meares
    Olive Meares, a teacher in a New Zealand reading clinic, was the first person to publish a report about the use of tinted overlays to assist with reading difficulties. Meares questioned several children about the print they were reading and she discovered that when reading black print on white backgrounds, many children perceived the words to move or wobble, or the spaces between words to form streams of white which detracted from the black print and made reading very difficult. These children preferred small print similar to that produced in adult books rather than the larger print designed for children because ?the white doesn?t glare at you so much?. One child who used a dirty perspex sheet over his page and another that preferred reading reverse type copy, or white words on a dark grey background, prompted Meares to try tinted perspex overlays to assist with reading. She postulated that the brightness contrast of black-on-white print was a major contributing factor towards reading disabilities. (Meares, 1980).

    2.2. Helen Irlen
    In 1983, an American psychologist, Helen Irlen, presented a paper to the annual convention of the American Psychological Association, describing how some of her students used coloured acetate sheets to reduce visual distortions when reading (Wilkins, 2003). Irlen coined the term Scotopic Sensitivity Syndrome (SSS) for this perceptual problem and explains in her book, Reading by the Colors, first published in 1991, that she developed the theory of SSS over a ten year period working as coordinator of an adult learning disability programme funded by the federal government. Between 1981 and 1983, Irlen interviewed more than 1500 adults with reading problems. One subgroup of individuals emerged who all had good phonetic skills, adequate decoding skills and sight vocabulary but still found reading immensely difficult. This group complained that the letters and words ran together or moved, the white spaces formed rivers down the page and the words became black lines. These distortions got worse with prolonged reading making comprehension of the words difficult if not impossible. One day, one of the students produced a red overlay that she had used four years earlier in vision training exercises. Another student put the coloured acetate sheet on her page and found that the distortions had stopped. After trying out many different coloured sheets, Irlen found that 31 out of her 35 students reported that the distortions were much reduced and reading was easier with a coloured overlay. It seemed that the colour necessary to help a student was particular to that student and everyone had different optimal colours (Irlen, 2005). Irlen then spent the following years developing diagnostic techniques and patenting a set of coloured overlays and coloured lenses or filters. She founded the Irlen Institute for Perceptual and Learning Difficulties in California to offer her patented treatment of Irlen Filters to SSS sufferers. Today there are Irlen Clinics in most US states and across the world, with more than eight thousand certified Irlen screeners working in the educational system in the USA, Canada, Australia, England and New Zealand (Irlen, 2005).

    2.2.1. Scepticism Against Irlen?s Claims
    Irlen?s early claims of discovering a syndrome which she called Scotopic Sensitivity Syndrome that could be treated with her patented Irlen Filters were met with much scepticism. The name itself caused controversy. Scotopic vision is mediated by rod photoreceptors and comes into play in dim illumination as rods are 1000x more sensitive to light levels than cones. Rods are not found in the fovea which is the area of the retina responsible for high acuity visual processing such as reading. The name ?Scotopic Sensitivity? implies an increased sensitivity of the rod receptor system. However, since the visual problems reported by SSS sufferers occur when reading, it is the cone photoreceptors and hence photopic vision that is in use and not scotopic vision. The name Scotopic Sensitivity is therefore a misnomer. Irlen defends this name as describing a syndrome as one in which individuals ?perceive the world around them in a distorted way as a result of a sensitivity to certain wavelengths of light? (Irlen, 2005).
    Even more controversial, certainly up to 1990, was the lack of published research data in peer reviewed scientific journals validating Irlen?s claims. Irlen filters were being widely publicised in the media as a successful treatment for reading disorders, but eyecare professionals had no evidence upon which to base any judgements (Helveston, 1990). Despite this lack of scientific proof, Irlen had patented her filters and was charging sizeable sums of money for the treatment (Coyle, 1995) utilising so-called trained Irlen screeners who were not qualified as eyecare professionals (Evans et al., 1999). Irlen was claiming that this new syndrome was unrelated to vision anomalies and that the symptoms of SSS remained undetected by standard visual and medical examinations, psychological evaluations or other school related tests (Solan & Richman, 1990). Irlen seemed to base this assumption on the fact that all of her clients had received an eye examination within one year of the Irlen testing and hence had no vision problems. One study, however, that recruited 39 subjects from the general population, for an investigation of Irlen filters found that despite having had a recent eye examination, 95% of those who met the criteria for having SSS as defined by the Irlen screening protocol, did in fact have significant uncorrected refractive errors, binocular vision problems, accommodative disorders, ocular motor anomalies, or hysterical amblyopia (Scheiman et al., 1990).
    The evidence that was available to support Irlen?s claims tended to be anecdotal and certainly was not obtained under rigorous scientific conditions. Much of the evidence provided was in the form of questionnaires completed by those wearing the Irlen filters who reported that the filters helped. However, in such studies there were no control groups, no statistical analyses, and most importantly no consideration of any placebo effect (Evans & Drasdo, 1991). The placebo effect is when symptoms are alleviated in some way by an otherwise inert treatment due to the subject believing that the treatment works. Hence several years after Irlen?s initial claims regarding SSS, the consensus was that underlying vision problems were probably the cause of the symptoms of those individuals who were identified as Irlen filter candidates and that the therapy itself lacked credibility.

    2.3. Arnold Wilkins
    Arnold Wilkins was a scientist working for the Medical Research Council Applied Psychology Unit investigating photosensitive epilepsy in which specific visual stimuli precipitated seizures. Flickering light had been found to be epileptogenic as had certain visual patterns particularly stripes. Such patterns were also found to be ?uncomfortable to look at? for non-epileptogenic patients and were reported to cause various visual illusions of colour, shapes or motion. This effect became known as pattern glare. Susceptibility to such illusions seemed to be greater for those who suffered from frequent headaches, particular those suffering from migraine. This research led Wilkins to propose his theory of visual stress in which certain characteristics of visual stimulation can give rise to discomfort and seizures (Wilkins, 1995). Wilkins became intrigued about Irlen?s claims that coloured filters could ease symptoms of visual perception dysfunction as the symptoms reported in SSS correlated well with the symptoms reported in visual stress. Wilkins examined a selection of individuals who had supposedly benefited from the use of Irlen filters. Vision was compared using the coloured Irlen lenses, darkened, neutral density lenses that allowed the same amount of light through as the Irlen lenses, and clear lenses. Overall, the tinted Irlen lenses gave a modest improvement in the speed of visual search, fewer illusions and headaches and for some the lenses also improved acuity and muscle balance. However, this study again had no control over the placebo effect as the subjects were aware of the colour of the lenses they were wearing and being existing Irlen clients, they were presumably already convinced of the supposed benefits of those coloured lenses (Wilkins & Neary, 1991).

    2.3.1. Intuitive Colorimeter
    To overcome the placebo problem, Wilkins designed the Intuitive Colorimeter (Fig. 2.1) to illuminate text with coloured light in order to better study patients who reported benefits from using Irlen Filters. This instrument allowed the subject to systematically vary the hue, saturation and brightness in order to determine the optimum ?colour? for reducing visual distortions (Fig. 2.2) (Wilkins, 1995; 2002; 2003).

    Figure 2.1. Schematic diagram of the Intuitive colorimeter. Image from psychology/overlays/int_ colorim.gif

    Figure 2.2. The principle of the Intuitive Colorimeter. A transparent disc (large circle) is divided into three sectors to which are added a coloured filter, red, blue and green. The disc is free to rotate about a central axis and this axis can move horizontally. A circular beam of white light (small circle) passes through the disc and is coloured as a result. The proportion of red, blue and green light is dependent upon the position of the disc with respect to the beam of light. If the beam of light is centred upon the disc the proportions of red, blue and green are equal and white light is produced (a). if the disc is translated horizontally, the proportion of the three primary colours changes and so produces a different coloured light (b) and if the disc is rotated in a lateral position, the saturation of the colour is varied (c) (Wilkins et al. 1992b).

    In a revised model of the colorimeter, a beam of white light passes through a cylindrical filter assembly via a square aperture into a viewing chamber with matte white inner surfaces. The filter assembly is divided into seven sections, each with a different filter so as to transmit light of a different colour. The colours of the filters have hues evenly distributed in a circle around white in the CIE 1976 uniform chromaticity scale diagram (Fig. 2.3).

    Figure 2.3. The coloured filters of the Intuitive Colorimeter as shown on the CIE 1976 Uniform Chromaticity scale diagram. The concentric curves show the change in chromaticity as the hue control is altered, and the spokes show the change when the saturation control is altered (From Wilkins, 1995).

    The patient puts their head close to the viewing window and looks at a page of text within the instrument. Their entire visual field is coloured with light from the chamber which is initially white. The patient describes any distortions seen and then systematically compares the white light to a coloured light with increasing saturation until all possible colours have been viewed. Any beneficial colours can then be reviewed and the optimal saturation and brightness determined to ascertain the overall optimal colour (Wilkins, 2003).
    Whilst developing the Intuitive Colorimeter, Wilkins examined several children with reading difficulties. He found that many of them consistently chose very specific settings of the colorimeter which made the distortions in the text disappear. Wilkins then directly compared the results of his Intuitive Colorimeter with the Irlen method of prescribing tinted filters. In eight out of nine children, the colour appearance of the Irlen trial lenses closely agreed with the colour given by the colorimeter (Wilkins et al., 1992a). This seemed to support the claims of Irlen, and furthermore, indicated that the colour found by the colorimeter would provide a good indication of a potentially therapeutic colour for tinted lenses (Wilkins, 1995). However, further scientific based evidence was still required.
    2.3.2. Therapeutic Precision Tinting
    Irlen used a range of 150 different coloured filters in her treatment protocol (Scheiman et al., 1990). Wilkins subsequently developed a set of tinted trial lenses using a precise tinting technique that very closely approximated any colour that could be obtained in his colorimeter. Comments from many children during the developmental process indicated that the colour of any tinted lens needed to exactly match the colour chosen with the colorimeter or else the beneficial effects were reduced (Wilkins, 1995). Preliminary case studies indicated the benefits of tinted lenses for those with reading difficulties, photosensitive epilepsy and migraine (Maclachlan et al., 1993; Wilkins, 1995). Wilkins therefore conducted an open trial to investigate the long term use of his tinted lenses. The subjects presented with a variety of problems including reading difficulty, perceptual distortion of text, headaches, eyestrain and photosensitive epilepsy. They were assessed with the Intuitive Colorimeter and chose their preferred colour for reading. Tinted trial lenses were selected and the optimal tinted lenses determined. The lenses incorporated any necessary refractive correction and the subjects were instructed to wear the lenses as they wished. After approximately one year the subjects reported any benefits of their tinted glasses. 45 out of the original 55 subjects were still wearing their tinted glasses of which 44 reported improvement in their presenting symptoms (Maclachlan et al. 1993). This trial did not include a full optometric assessment, had no measurement of reduction of symptoms or control over placebo effects and so any reported benefits were impossible to quantify. However, the results gave Wilkins the impetus to conduct a multi-centre double-blind, placebo-controlled study.

    2.3.3. Coloured Overlays
    The Irlen Clinics use a set of seven overlays of turquoise, blue, green, yellow, peach, rose and gold (Tyrrell et al., 1995) which when plotted on a chromaticity diagram (Fig. 2.4) do not appear to sample colours systematically.
    Wilkins developed an alternative set of ten overlays of grey, yellow, lime green, mint green, aqua, blue, purple, pink, rose and orange called The Intuitive Overlays (Wilkins et al., 2001) and which systematically and evenly sample the colour space as shown in Fig. 2.5 (Wilkins, 1993; Jeanes et al., 1997).

    Figure 2.4. The chromaticity coordinates of the seven Irlen coloured overlays in the CIE 1976 Uniform Chromaticity Scale Diagram. The large black dots represent the seven overlays and the small dots represent the paired combinations. The cross represents white. Image from Jeanes et al., 1997.

    Figure 2.5. Chromaticities of the nine coloured Intuitive Overlays (inner ring of white circles) and the grey overlay (central point) when in contact with a white page. The chromaticities of double overlays of the same colour are shown by the outer ring of circles, and the crosses represent double overlays of neighbouring colours. From Wilkins, 2003.
    The overlays can be superimposed upon one another giving a more saturated colour, and in order to sample the colours systematically it is only necessary to combine overlays with another of the same or similar colour as shown in Fig. 2.6. The overlays are glossy on one side and matte on the other to reduce reflections, although when uppermost, the matte surface can reduce clarity (Wilkins, 2002).

    Figure 2.6. Part of the Intuitive Overlays Record Sheet showing the different colours of the overlays (inner ring) and the combinations to try when testing (outer ring).

    Several placebo-controlled studies showed that coloured overlays had beneficial effects on reading; one colour gave the best results whereas other colours gave little or no benefit and the optimal colour was particular to each individual (Jeanes et al., 1997; Evans et al., 1999; Lightstone et al., 1999; Wilkins et al., 2001; Bouldoukian et al., 2002). However, the colour of an overlay was not necessarily a good indication of the colour of an optimal tint for glasses (Lightstone et al., 1999). When using an overlay the eyes are adapted to the ambient light, whereas when wearing tinted glasses the entire visual field is coloured accordingly and the eyes adapt to that colour (Jeanes et al., 1997). This adaptation involves a mechanism known as colour constancy whereby the brain adjusts for effects of incident lighting and so still recognises the ?correct? colour of objects regardless of the spectral content of the illuminating light. This mechanism underlies the precision of the Intuitive Colorimeter in predicting correct tints for glasses as the entire visual field is illuminated in the chosen colour.
    Waldie and Wilkins supposedly investigated whether the optimal colour of an overlay changed with increased size but found no difference in reading speed using overlays which covered the entire page, overlays which covered the text only and left the margin white or overlays covering the text with a margin in a complementary colour (Waldie & Wilkins, 2004). However, to properly answer this question they should have compared overlays covering the page with much larger overlays covering the entire visual field.
    Overlays are used to assess the likelihood of a subject benefiting from tinted glasses without incurring the expense of precision tinted lenses (Wilkins et al., 1994) and may even be preferred by some patients when reading rather than constantly wearing a coloured pair of spectacle lenses as some children have reported teasing at school because of their tinted glasses.

    2.3.4. Double-masked, Placebo-controlled Trial
    The gold standard in clinical trial design is the randomised, double-masked, placebo-controlled study. Subjects are randomly assigned to the therapeutic or control group and are unable to distinguish between the two protocols hence controlling for any placebo effect, and neither the investigators nor the subjects know which group is which.
    Wilkins used a double-masked, placebo-controlled cross-over trial to ascertain whether the reported benefits of tinted lenses were due solely to placebo effects (Wilkins et al., 1994). Schoolchildren selected from those suffering from headaches, asthenopia or reading difficulty were all assessed with coloured overlays to determine which colour best reduced the visual distortions. Only those children who then used their chosen overlay consistently for at least 3 weeks were eligible for the study. The Intuitive Colorimeter was used to provide two chromaticities, one of maximal benefit at eliminating visual distortions and another which reduced the distortions but did not eliminate them. Two pairs of tinted glasses were produced for each subject, an experimental pair with the optimal tint, and a control pair with the sub-optimal tint. The glasses were sent to the children, one pair at a time randomly selected by the tinting laboratory, to be worn for at least one month. Due to the nature of the colorimeter test procedure, the children were unable to tell which lens colour was their chosen optimal tint and hence the placebo effect was controlled for. The children kept diaries to record episodes of eyestrain and headaches. After both trial periods, 71% of days on which the experimental glasses were worn were recorded as symptom-free as compared to 66% of symptom-free days with the control glasses; 22 of the 52 children said that they preferred the experimental glasses with 26 preferring the control and 4 having no preference. The difference between the two tints for each subject was very small, corresponding to approximately six times the just noticeable difference in colour. The authors postulated that this could explain the fact that both pairs were deemed beneficial and maybe the subjects were unaware of slight differences in symptoms when wearing the different glasses (Wilkins et al., 1994). A greater clinical effect would perhaps have been seen with a greater difference in tints between the experimental and control glasses but this would have weakened the double-masked design of the trial. In a later study, it was shown that 6 just noticeable differences from the optimal tint reduced any benefit in reading to less than 5% of the maximum (Wilkins et al., 2005a) although the reduction in visual symptoms was not quantified.
    A similar, double-blind, randomised, controlled trial with cross-over design was used on adult migraineurs to compare the effectiveness of precision tinted lenses in the prevention of visually precipitated headache (Wilkins et al., 2002). Optimal and control tints were selected with the subjects wearing each pair for a period of six weeks. Again the difference in chromaticities of the two tints differed by only six times the just noticeable difference. A marginally significant improvement with the optimal tint was noticed but only 17 subjects completed the trial. A more significant result would likely be achieved with more subjects. Optometric testing on these subjects revealed that the only significantly different factor was the migraineurs? susceptibility to pattern glare which improved with the optimal tinted lenses (Evans et al., 2002). This lent weight to the hypothesis that migraine and MIS were related conditions with a common cause of pattern glare.

    2.3.5. Rate of Reading Test
    Wilkins designed a specific reading test in order to accurately compare the speed of reading in children with and without coloured overlays or tinted lenses. The test maximises visual stress by using small, closely spaced text, but requires minimal reading ability hence is suitable for poor readers. The test comprises a passage of randomly ordered simple words selected from the 110 most frequent words in children?s reading books, with the same 15 words rearranged on each of ten lines. The words have to be seen correctly to be read as they cannot be guessed from context. The text is printed in Times 9 point print and made to resemble stripes by reducing the horizontal spacing between words. The test is scored by noting errors on a score sheet (Fig. 2.7) and by measuring the time taken to read the passage with and without a coloured overlay. Different versions are available with the words in different orders (Wilkins et al., 1996).

    Figure 2.7. The score card for the Rate of Reading Test showing an enlarged version of the test, with each word numbered and annotations showing if words or lines were omitted or mixed up.

    The test has a high test - retest reliability and Wilkins also showed that increases in the rate of reading with the coloured overlays is correlated with improvements using overlays on a test requiring silent reading for comprehension and so the Rate of Reading Test can be used as a measure of typical reading tasks (Wilkins, 2002).
    A study comparing the optimal colours of overlays and lenses measured the reading rate under four conditions of no colour, chosen overlay, lenses matching the chosen overlay and lenses matching the optimal colorimeter setting. The results confirmed that both overlays and tinted lenses increased reading speed provided that the colour was optimal for that subject whereas lenses matching the overlay colour had a much reduced effect showing that the optimal colour of overlays and tints were not identical. Furthermore, since the subjects were unaware that one set of lenses matched their overlay colour and one matched the colorimeter setting, it gave credence to the earlier double-masked, placebo-controlled cross-over trial for precision tinted lenses (Lightstone et al., 1999). These results were corroborated by a randomised controlled trial in 2002 (Bouldoukian et al., 2002) which concluded that in appropriate patients, individually prescribed coloured overlays can cause an increase in reading performance as well as a reduction in symptoms.


    3.1. Contrast
    In 1980 when Olive Meares published her report of reading disabilities in the journal Visible Language, she suggested that the maximum brightness contrast of black print on a white page was a major factor in the problems children had with reading (Meares, 1980). It seemed that the stark white background overpowered the page and the glare interfered with the perception of the black lettering. This effect was eliminated by the use of reverse-type print, i.e. white print on a dark grey page. The glare of the white background was also reduced by the use of smaller print or by using a dirty or tinted perspex sheet (Meares, 1980). Meares gave no indication that particular coloured tints were of benefit, she just reported that reducing the extreme brightness contrast on the pages of children?s books was beneficial.
    A study into the prolonged use of coloured overlays by schoolchildren reported a significantly improved rate of reading with a preferred coloured overlay as compared to a grey overlay which reduced the contrast by an equivalent amount as the coloured overlay. Jeanes et al. therefore concluded that the effect of coloured filters was not solely due to a reduction in contrast (Jeanes et al., 1997). However, this study also failed to show a significant difference between the rate of reading with a preferred overlay and that of a complementary colour so apparently disproved the whole theory.
    Lovegrove reported that although poor readers had normal visual acuities, they suffered from subtle visual deficits in their contrast sensitivity function across spatial frequencies as compared to good readers (Lovegrove et al., 1980). Contrast sensitivity is a measure of the minimum contrast required for detection of an object against a background or of a grating pattern (Norton et al., 2002). At stimulus durations equivalent to the fixation periods occurring in reading, the good readers showed a peak contrast sensitivity at 4 cycles per degree which was not exhibited by the poor readers and Lovegrove postulated that these differences were cortical rather than retinal, being due to variations in the two visual processing channels that process spatial information (Lovegrove et al., 1980). This became one of the pivotal pieces of research from which the transient pathway deficit or magnocellular deficit arose (see section 3.4).

    3.2. Retinal Sensitivity
    Irlen described SSS as a dysfunction that occurred once the image was focussed on the retina (Scheiman et al., 1990; Solan & Richman, 1990). According to Solan and Richman, Irlen postulated that the discharge rate of retinal receptor cells was subject to random variation in certain individuals resulting in visual oscillations and fluctuations in the number of light quanta absorbed. Hence the visual dysfunction was associated with an excessive sensitivity of the retina to certain frequencies of the visible light spectrum. The Irlen filters supposedly reshaped the spectral band by attenuating only specific frequency bands predetermined to be problematic (Solan & Richman, 1990). No scientific or clinical evidence was presented to back up this hypothesis. Indeed, Moseley analysed the spectral absorption characteristics of the Irlen overlays and blue tinted lenses and found no evidence that specific wavelengths were attenuated but that they acted as an overall absorber of visible light (Evans & Drasdo, 1991).

    3.3. Ocular Motor Anomalies
    Binocular and accommodative anomalies can cause symptoms similar to those reported in MIS (Evans et al., 1999). In the early 1990s many sceptics of Irlen?s proposals believed that visual problems were the underlying cause of the symptoms reported by those purported to be suffering from SSS and treatment could be effected by traditional optometric or orthoptic therapy (Scheiman et al., 1990). Subsequent trials involving detailed optometric assessment strongly indicated that uncorrected refractive error was not the cause of MIS (Evans et al., 1995), although several studies have shown that children with MIS tend to have poor vergence reserves suggesting that binocular instability may be a correlate of MIS (Evans et al., 1995; 1996; Scott et al., 2002). Slightly reduced amplitudes of accommodation have also been found in MIS and in dyslexia (Evans et al., 1995, 1996; Scott et al., 2002) as has reduced stereoacuity (Evans et al., 1996). If an accommodative mechanism were responsible for MIS, it might be expected that those with reduced amplitudes of accommodation would have optimal filters in bluer tints than the control filters since blue light has a shorter focal length than red light. No evidence was found to support this (Evans et al., 1996), and Ciuffreda et al., reported that Irlen filters had no effect on steady-state accommodation at near (Ciuffreda et al., 1997). Evans and Wilkins argue that any ocular motor defect is unlikely to explain the beneficial results seen with specific tinted lenses (Evans et al., 1995; 1996) and Evans advocates treating any ocular motor dysfunction first and then only if symptoms persist, consider using coloured filters (Evans et al., 1999). Simmers et al. investigated the accommodative response of tinted lens wearers with their prescribed tinted lens, a tinted lens of complementary colour, a neutral density lens and no lens. Although they showed no specific differences between the prescription tinted lens and the other lens types, they did notice significant fluctuations in accommodation in the no lens condition which they postulated to be indications of visual stress either as a result of, or a cause of perceptual distortions (Simmers et al., 2001b).
    Abnormal saccadic eye movement has also been proposed as a cause of reading difficulties as the eye movements involved in reading are primarily saccades and those with reading disabilities, especially dyslexia have been shown to exhibit abnormal saccades (Biscaldi et al., 1998). This is, however, probably an effect of the problem rather than a cause as poor comprehension of specific words necessitates rereading those words (Evans, 1998; 2004b). Attentional problems may also be a factor in abnormal eye control as many dyslexics are also diagnosed as suffering from attention deficit/ hyperactivity disorder (ADHD) (Iovino et al., 1998; Evans, 1998).

    3.4. Magnocellular (Transient Pathway) Deficit
    The human visual system is composed of at least two parallel pathways, the parvocellular or P-pathway and magnocellular or M-pathway. These two pathways originate in the retina with different retinal ganglion cells that have different receptive fields. Parvocellular ganglion cells or midget class cells have small cell bodies and short dendrites with thin axons and little myelin and project to the small-celled parvocellular layers of the dorsal lateral geniculate nucleus (dLGN). The magnocellular or parasol class cells have large cell bodies with large dendritic trees, wide, heavily myelinated axons and project to the large-celled, magnocellular layers of the dLGN (Figs. 3.1, 3.2).

    Figure 3.1. Human ganglion cells: midget parvocellular cells with small cell bodies and small dendritic trees and parasol magnocellular cells with large cell bodies and large dendritic trees. Image from

    Figure 3.2. The projections of parvocellular and magnocellular retinal ganglion cells in the dLGN. Image from

    The two pathways differ in four important physiological properties. P cells are colour-opponent and sensitive to high spatial frequency, low temporal frequency and high contrast (low contrast sensitivity) such that the P-pathway is responsible for high acuity, colour and slow, sustained responses whereas M cells are monochromatic and sensitive to low spatial frequency, high temporal frequency and low contrast giving low acuity, fast, transient responses (Wilkins, 1995). Hence P cells, which are concentrated in the central retina are responsible for detecting detailed form and colour as opposed to M cells which have a more uniform location across the retina and detect global form and motion. The two cell types also differ in their projections to the visual cortex with the P cells projecting to layers 4Cβ of V1 and then via the blob and interblob regions (Fig. 3.3) through V2 to V4 and V5 respectively. The blobs are sensitive to colour but not orientation whilst the interblobs are sensitive to orientation but not colour. M cells meanwhile project to 4Cα which in turn projects to 4B of V1 and then via V2 to V5 (Baker, 2000). Regions of the extra-striate cortex appear to be specialised for specific functions. Area V4 is selectively activated by colour whereas V5 or middle temporal (MT) cortex is selectively activated by motion. Although there are connections between the magno and parvo pathways, and the cellular properties do overlap to some extent, on the whole the magno pathway projects from the retina to areas of the cortex sensitive to motion and the parvo pathway projects to areas coding for colour and form.

    Figure 3.3. Projections of M and P cells of the dLGN to the primary visual cortex V1. Image from

    Subsequent to Lovegrove?s study on contrast sensitivity (Lovegrove et al., 1980), other perceptual studies examining aspects of the visual system have shown that dyslexics appear to have defects in processing of fast and transient visual information with high contrast sensitivity and low spatial frequency (Livingstone et al., 1991) although attempts by some research groups to replicate those results failed (Victor et al., 1993; Johannes et al., 1996) and others have found no evidence of a low spatial frequency contrast sensitivity defect in MIS subjects (Evans et al., 1996; Simmers et al., 2001a). Dyslexics are characteristically poor at spatial tasks such as telling left from right or map reading, and at temporal tasks such as daily organisation or telling the time. It was these properties that led to the proposal of a magnocellular deficit in poor readers whereby those affected are unable to properly process fast incoming sensory information (Stein & Walsh, 1997).
    Anatomical evidence was provided by Livingstone et al., who compared five dyslexic brains with five control brains and found smaller cell bodies and greater disorganisation of the magnocellular layers in the dLGN of the dyslexic brains although the parvocellular layers appeared similar in the two groups (Livingstone et al., 1991).
    Chase demonstrated that reading is impaired under red light (Chase et al., 2003) and proposed that this impairment is of M-pathway processing of low spatial frequencies as found in text. Chase therefore concludes that coloured filters that cut out longer red wavelengths will enhance reading performance (Chase et al., 2003). This would suggest that colours chosen for overlays and lenses would always be of shorter wavelengths but one study of overlay usage showed that rose was one of the most commonly chosen colours (Wilkins et al., 2001). Chase suggests that some poor readers with impaired M-pathways may learn to use their P-pathways more for reading and hence would be unaffected by red light whereas others continue using the M-pathway and so remain susceptible to red light impairment (Chase et al., 2003).
    Stein argues that some of the reasons the magnocellular system is so important in reading is that it helps to control eye movements by stabilising the brief fixations on words and directing the movements between fixations (Stein & Walsh, 1997; Stein, 2003) as well as being pivotal in controlling the direction of attention. With an impaired magnocellular system, visual attention is unfocussed with unstable eye control and hence letters appear to move around making reading difficult (Stein, 2003).
    Stein maintains that a deep yellow filter or overlay helps dyslexics by improving eye movement control, contrast and motion sensitivity (Stein, 2003). He argues that in daylight the magnocellular system receives summed input from all three types of cone photoreceptor in proportion to their retinal density suggesting that the peak sensitivity of the system is at yellow wavelengths. If the magnocellular system is defective in poor readers, then using a yellow filter should rebalance the system. However, such yellow filters do not so much increase yellow wavelengths as cut out blue wavelengths, suggesting that dyslexics may be more sensitive to blue light which inhibits visual function. Indeed Stockman et al. have shown that S-cone input does inhibit magnocellular function. Hence a yellow filter helps those with defective magnocellular function by reducing the inhibitory S-cone input (Stein, 2003). Conversely, Stein also found that 10% of children with reading problems were not helped by yellow but by deep blue filters but on further examination he discovered that those children seemed to have impaired S-cone input so a blue filter would reduce the L and M cone input and thus restore the normal balance (Stein, 2003).
    Stein also proposes that a weak magnocellular system has benefits as indeed many dyslexics are gifted in other areas. He argues that reading ability is strongly hereditary and that without a benefit any serious genetic deficiency would have been selected out. One particular gene site linked to reading problems has been discovered on chromosome 6 and is situated within the MHC immune regulatory region. This could also explain why many dyslexics seem to suffer from autoimmune disorders and inflammatory disorders. However this tendency to inflammatory disorders seems also to confer a protection against high blood pressure and possibly also cancer (Stein, 2003). It has also been shown that the MHC system has a role in the control of development of magnocells hence a defective gene in this location could account for a weakened magnocellular system in dyslexics. One mechanism suggests antibodies against developing magnocells are transported across the placenta during foetal development (Stein, 2003). Another gene site associated with poor reading has been found to be involved in polyunsaturated fatty acid metabolism and magnocells are particularly sensitive to polyunsaturated fatty acid deficiency. Hence Stein advocates a diet rich in essential fatty acids as found in oily fish (Stein, 2003).
    Migraineurs exhibit reduced contrast sensitivity proportional to the duration of their disease suggesting that recurrent attacks of migraine may damage the visual system (Wilkins, 1995) and may indicate a common magnocellular deficit mechanism between migraineurs and dyslexics. However, McKendrick and Badcock showed a similar loss of function in both M- and P-pathways in migraineurs indicating non-selective visual dysfunction (McKendrick & Badcock, 2003). Other studies have showed that some poor readers have good magnocellular function whereas some good readers have poor magnocellular function (Stein, 2003). Stein, however, argues that researchers should be wary of confusing absence of evidence with evidence of absence of a role of the M-system in dyslexia, adding that any weakness of evidence between magnocellular function and reading is perhaps due to an inability to measure the magnocellular function accurately enough (Stein, 2003).
    The biggest argument against a magnocellular deficit theory is that, despite the various models, not one accounts for the large range and specificity of colours that are found beneficial by those suffering from MIS.

    3.5. Cerebral Hyperexcitability
    Wilkins has proposed a theory of visual stress to explain the similar symptoms and benefits seen with coloured filters in those purportedly suffering from MIS, migraine and photosensitive epilepsy. Certain visual stimuli that seem to provoke migraine also provoke photosensitive epileptic seizures and those visual stimuli include geometric patterns, particularly stripes, which can also occur in pages of text. Such repetitive striped patterns seem to induce pattern glare or visual stress which are the same symptoms as reported in MIS.
    Much of Wilkins? evidence for a hyperexcitability mechanism comes from studies of photosensitive epileptic patients. Epileptiform EEG activity tends to occur under binocular conditions and since the visual pathway is monocular up until the primary visual cortex, this suggests that epileptic seizures are triggered in the visual cortex (Wilkins, 1995). Furthermore, orientation and line length of geometric patterns can affect the likelihood of seizure (Wilkins, 1995), and these visual parameters are coded for within the visual cortex. The visual cortex is arranged into hypercolumns, whereby each 2mm cube of hypercolumn is devoted to one particular area of visual space and comprises overlapping ocular dominance columns and orientation columns with interspersed blob and interblob regions sensitive to wavelength and orientation respectively (Fig. 3.4). Hence there is substantial evidence for a cortical basis to pattern-induced epilepsy.

    Figure 3.4. Hypercolumns in the visual cortex. Image from

    In some patients, epileptiform responses are more pronounced when visual patterns are presented in only one half of the visual field (Wilkins, 1995) and migraineurs who suffer headache on only one side of the head report asymmetric visual illusions when looking at aversive visual stimuli (Wilkins et al., 2004). Due to the passage of neurones along the primary visual pathway, with the crossing-over of nasal fibres at the optic chiasm, the left cerebral hemisphere receives the image of the right visual field and vice versa (Fig. 3.5). This observation of asymmetric epileptogenic susceptibility indicates a differential excitability of the two cerebral hemispheres and indeed the two hemispheres seem to act independently in triggering epileptic responses (Wilkins, 1995).
    A minimum area of the visual cortex needs to be stimulated to elicit an epileptogenic response (Wilkins, 1995) and seizures are also more likely if the visual pattern is moving in some way so as to induce a rhythmic cortical excitation. Stationary patterns are more epileptogenic than patterns drifting in one direction due to the constant microsaccades or miniature movements that the eyes make during fixation whereas vibrating or phase-reversing patterns are highly epileptogenic (Wilkins, 1995). This then suggests that epileptogenic seizures are somehow triggered by the rhythmic, synchronised cortical excitation of a critical area in one or both visual hemispheres.

    Figure 3.5. The primary visual cortex showing the decussation of retinal nasal fibres at the optic chiasm. Image from

    The drug sodium valproate is used in the control of visually induced seizures and is thought to affect the inhibitory neurotransmitter GABA or γ-aminobutyric acid which is found in the brain (Wilkins, 1995). In 1978 Sillito proposed that complex cell orientation selectivity was dependant upon GABA-mediated inhibition from a network of interneurones. It was suggested that pyramidal complex cells sample excitatory inputs from a number of columns with different orientation selectivity and the purpose of the inhibitory interneurone connections was to compensate for this lack of precise sampling (Sillito, 1978). Wilkins thus postulated that a strong localised excitation as found when viewing a particular oriented visual pattern could deplete the local availability of inhibitory GABA which in certain individuals could then lead to over-excitation or hyperexcitability (Wilkins, 1995).
    But how does this account for the different specific colour preferences of the subjects? Colour representation in the V2 area of the cortex has been shown to be spatially organised in a systematic order (Xiao et al., 2003) rather than in an opponent manner. Wilkins thus infers that different coloured stimuli are processed in different parts of the cortex (Wilkins et al., 2005b) allowing for coloured overlays or lenses to change the pattern of excitation thus reducing hyperexcitability and relieving symptoms (Wilkins, 1995; Evans et al., 1996; Wilkins et al., 2004).
    Several lines of evidence suggest a common mechanism for photosensitive epilepsy and migraine: the visual patterns that induce seizures in epileptics can also induce perceptual distortions in others, particularly those with a history of migraine; magnetic stimulation of the visual cortex in migraineurs stimulates visual phenomena; functional magnetic resonance imaging (fMRI) of migraineurs shows increased blood oxygenation level-dependent (BOLD) responses when viewing aversive visual patterns; and anti-epileptic drugs have been shown to have anti-migraine effects (Wilkins et al., 2004; Griffin et al., 2006). Furthermore, preliminary results have shown that the BOLD response in area V3 of the visual cortex is reduced when wearing optimally tinted spectacles (Wilkins et al., 2004).
    Wilkins also suggests that MIS is related to migraine and photosensitive epilepsy by pattern glare. The mechanism of cerebral hyperexcitability, therefore, accounts for a range of symptoms with increasing severity from visual discomfort and MIS through migraine to photosensitive epilepsy (Evans et al., 1994).


    4.1. Discussion
    In 1980 Meares suggested a rethink of children?s book design was necessary to reduce the maximum brightness contrast of the black print on a white page. Today, not much has changed. In 2002 Wilkins commented that typographical practice needed to change as it would be preferable to design children?s reading materials to minimise distortions in the first place rather than find individual solutions for each affected child. This is still true and really ought to be passed on to book designers and publishers.
    Lighting is another contributory factor to poor reading. Many schools use fluorescent lighting which has been shown to cause headaches due to the flicker that occurs as a result of the modulation of the current flowing in the lamp (Wilkins, 2005). Depending on the design of the lamp, the flicker can be more or less noticeable and some individuals seem especially sensitive to such flicker. It has been suggested that flicker of fluorescent lighting at 100Hz affects saccadic eye movements and accommodation and that symptoms of SSS increase under fluorescent lighting (Evans & Drasdo, 1991). However, such symptoms are not reported only under conditions of fluorescent lighting and so although such environmental conditions may exacerbate any visual distortions, it is unlikely to be the primary cause. It would be beneficial to many children, however, to do away with such flicker and indeed modern lighting systems do not flicker. The problem is the cost of replacing existing lighting systems although this should be balanced against the reduced running costs of the new system.
    Regardless of the environment, it cannot be denied that many people, adults and children, suffer from perceptual illusions when reading or viewing certain geometric patterns. It is also very difficult to ignore the evidence that many of these people find relief from the symptoms by using either coloured overlays or coloured filters.
    Irlen?s initial claim of her revolutionary treatment for a previously unrecognised disorder without scientific evidence caused much scepticism among the ophthalmic community, and rightly so. However, some studies contradicting her claims are themselves flawed in design. One study conducted by Sheryl Menacker set out to determine if tinted lenses caused a measurable improvement in the reading rate of dyslexic children. She found absolutely no significant trend for coloured lenses but she only used four different colours - red, blue, yellow and green, on 24 children (Menacker et al., 1993). Therefore one of the main claims of Irlen, that the colour was highly specific for each individual, was totally ignored.
    Subsequent research by others has, in part, begun to justify some of Irlen?s proposals, although many of these studies also have flaws. Many studies used subjects who were existing overlay or filter users and so there will always be the chance of unwanted placebo effects because these subjects in the main desperately want the treatment to work. They may well give biased good results for both the experimental and control lenses in any subjective test. Many of the tests are subjective and so impossible to quantify - one person?s slight improvement on symptoms could be another person?s great improvement.
    Despite criticism of Irlen?s early studies for not including full optometric assessments to check for any refractive or ocular motor problems, many of the later studies also did not include such examinations. A case report by Bruce Evans in 2005 highlighted the need for careful optometric and orthoptic examination in practice to exclude other possible causes of perceptual distortions prior to considering MIS (Evans, 2005) and this should be a fundamental component of all studies investigating the condition.
    The number of subjects studied in different experiments varies greatly. Some studied as few as 5 (Simmers et al., 2001b; Wilkins et al., 2005a), some more than 300 (Evans et al., 1999). Since results are generally presented as percentages, they do need to be considered together with the total number of subjects. An apparent benefit seen in 50% of subjects would be more significant in a total sample of several hundred rather than just six subjects!
    The selection criteria for subjects can also have a bearing on the final results. There is no absolute definition of dyslexic or reading disabled person so similar studies recruiting such subjects may vary hugely in the subject population dependent upon their specific selection criteria.
    Some published papers can perhaps exaggerate the findings of experiments and indeed of earlier studies. For example, in the first double-masked placebo-controlled trial of precision tinted lenses (Wilkins et al., 1994) the authors concluded that there was on average a greater reduction in symptoms with the experimental glasses that could not be due solely to any placebo effect. The results actually showed 71% of days were symptom-free with the experimental glasses as compared to 66% with the control glasses and no statistically significant differences found in the reading analysis; but 42% of the children preferred the experimental glasses with 50% preferring the control. At best these results show a potential benefit of tinted lenses worth further investigation. However, in subsequent papers, these results are described as ?a clear reduction in headaches? (Wilkins, 1996), ?clinical benefits? (Wilkins et al., 1996), ?significantly reduce symptoms? (Evans et al., 2002; Bouldoukian et al., 2002), ?improvements in symptoms? (Scott et al., 2002). Interestingly, Wilkins was a co-author for all of these papers. Therefore caution must be employed when reviewing the literature - original results need always to be considered, rather than reports of results.
    Irrespective of these minor design flaws or over enthusiastic accounts of results, it seems apparent that certain individuals certainly have a sensitivity to visual perceptual problems which can be alleviated by the use of colour. There is most likely a continuum of the syndrome, ranging from very mild symptoms to severe reading impairment. It is also very likely that MIS is associated with migraine and photosensitive epilepsy but whether these three conditions are also just variants of one disorder is not yet clear. The exact relationship between MIS and dyslexia is also not yet defined. Certainly some dyslexics appear to be helped by coloured filters, but whether there are two subsets of dyslexia, one affected by colour and one not, or whether these individuals simply suffer from two unrelated conditions cannot be confirmed.

    4.2. Conclusions
    The Chambers English Dictionary definition of syndrome is a ?concurrence, especially of symptoms; a characteristic pattern or group of symptoms; a pattern or group of actions, feelings, observed happenings, etc., characteristic of a particular problem or condition?. Meares-Irlen Syndrome is characterised by visual perception disorders and a benefit from colour. As such, this disorder is indeed a syndrome by definition.
    The most plausible explanation for the condition from the available evidence seems to be cortical hyperexcitability with the coloured filters redistributing visual excitation so as to alleviate symptoms. However, with current knowledge, this does not totally explain the specificity for particular colours shown. Therefore, how can we totally discount an alternative theory of some sort of magnocellular deficit which also does not account for the colour specificity seen in MIS. It may well be that a combination of these two theories is involved, but perhaps also with an as yet undiscovered element. The research must go on.



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  5th November 2011

The above was abstracted from a dissertation by Joanna Clair Lawrence BSc Optometry.

At one time it appeared on the web and we began to summarise it, find the references and link to them.

Two things happened.

  1. The original work was removed from the web.
  2. Some of the links to the references were also removed from the web

We have decided to leave the page as it is and hope that it will assist readers interested in Meares-Irlen Syndrome.

The details of the original dissertation are: Meares-Irlen Syndrome - Does It Exist? 2007 Lawrence JC  City University London, Department of Optometry and Visual Science.

We are also aware of -