The Vision Thing:

Optometric Factors in the Assessment of the Information Technology Needs of Students with Dyslexia

Introduction

In assessing the information technology [IT] needs of students with dyslexia, optometric factors can play an important role in underpinning the justification for and allocation of a computer. This essay aims to explore the optometric correlates of dyslexia, in particular Meares-Irlen Syndrome, and the role of computers in helping to overcome the associated visual and literacy problems. The main focus of this essay is to illustrate the way in which the computer monitor, in generating a colour picture, mimics the way in which the human eye processes light and consequently can provide an appropriate medium for proof-reading as the user has more scope to change the background colour. I will discuss the optimal type of monitor for students with Meares-Irlen Syndrome and its consequent role in the compensatory strategies of such students. In addition, I will highlight the role of the assessor in referring students for an eye examination and the subsequent complementary role of the IT Trainer and/or IT training programme in ensuring that the user continues to utilise the optimal monitor and typeface settings in an appropriate manner.

The Optometric Correlates of Dyslexia

Phonological factors are currently acknowledged to be the main causes of dyslexia. The phonological model of dyslexia defines it in terms of difficulties associated with converting phonemes (‘smallest meaningful segment of language) into symbols (letters).¹ The mental activity associated with reading can be divided into word identification, phonological processing, and cognitive reasoning. A deficit in phonological processing will reduce a person’s ability to convert symbols into sounds (reading) and/or sounds into symbols (writing) thus preventing them from exhibiting their true cognitive ability and preventing them from producing written work commensurate with their underlying ability. However, there is a cluster of ‘symptoms of perceptual distortion and visual discomfort with which reading is sometimes associated’². It is important to note that there are a number of key visual skills required for academic work and conversely there are a number of visual anomalies, which have an association with reading skills. Research has shown that people with dyslexia have been found to have a number of associated visual anomalies as follows:

Ocular Accommodation: This is the process whereby ‘the shape of the lens inside the eye is changed to increase its power’³. This serves to keep the eye in focus during near vision which takes place naturally but places the greatest strain on the focusing system. [Reading comfortably for sustained periods requires the amplitude of accommodation to be substantially greater than that predicted for clear vision at the viewing distance]. Accommodative problems can result in a difficulty changing focus between the board and a textbook in a classroom context. Research has revealed that the average amplitude of accommodation of a group of children with dyslexia was significantly reduced compared with a control group of good readers.⁴

Visual Acuity: This refers to the angular sub-tense of the smallest size of detail that the eye can resolve and it is usually expressed in degrees which refer to the testing distance (six metres in the United Kingdom and 20 feet in the United States, hence 20/20 vision). Fluctuations in visual acuity e.g. myopia can affect a student’s ability to read from the board in a classroom situation but the general consensus is that is has little effect on specific learning difficulties.

Binocular Vision: Binocular vision refers to the ability of the two eyes to work together in a co-ordinated way and problems in this area are relatively common. A subtle weakness in the co-ordination between the two eyes (binocular instability) is especially common in people with dyslexia. Binocular vision anomalies can contribute to a reading difficulty and symptoms include eyestrain, headaches, blurred vision, double vision and perceptual distortions.

Ocular Dominance: This relates to the concept of a dominant eye and tests of ocular dominance were once used to determine whether an individual was ‘crossed dominant’ (sighting eye on the opposite side to the dominant hand) as crossed dominance was thought to be related to reading difficulties. However, ‘its relevance to dyslexia appears to be overstated and a possible cause of confusion is that at least three different types of ocular dominance: sighting, motor, and sensory dominance, have been reported’⁵. It is not known which, if any, of these types of ocular dominance is most relevant for reading and the general consensus seem to be that ‘sighting dominance is largely irrelevant to the assessment and treatment of reading and spelling problems’⁶. A recent test of motor ocular dominance or ‘visual dyslexia’, the Dunlop Test, is widely agreed to be unreliable, although there is growing evidence that ‘many children with dyslexia have some form of binocular instability’⁷.

Eye Movements: Saccadic eye movements are the visual system’s basic method of acquiring information from any visual scene in which the observer and the target are relatively stationary. During reading, the eyes typically fixate on a group of letters for about a quarter of a second whilst the information is assimilated and then make a saccadic eye movement to the next group of letters. Occasionally smaller backwards saccades (regressions) occur to aid comprehension. Thus, the saccadic movements are influenced by both the layout of the text and by the reader’s comprehension. It is difficult to determine whether ‘atypical eye movements are the result of poor reading skills or whether they are underlying causes of the poor reading’⁸. A large body of research on saccadic eye movements has been inconclusive and the results are often contradictory. Some research findings on pursuit eye movements (eye movements that occur in pursuit of a slowly moving target) reveal that people with dyslexia often exhibit saccadation of their eye movements for target speeds where this does not usually occur. However, pursuit eye movements are not used when reading. Another ocular motor function, ‘tracking skills’, is used to describe subjective estimates of ocular motor function in relation to reading performance. Moreover, the term is vague and can be accounted for by ‘lapses of concentration by the subject’⁹.

Transient Visual Sub-System: We have dealt with the control of the eyes by the brain (motor visual functions) above but it is important to realise that the optical image formed in the eye is heavily processed before it reaches consciousness. The components of the processing of the visual image are described as sensory visual factors. The transient visual sub-system is an early warning system for detecting the coarse details of moving or changing objects in our field of view and up to 75% of people with specific reading difficulties have a deficit of this system. There are no validated clinical tests of treatment for this condition and ‘it is not clear whether treatment would be helpful’¹⁰.

Behavioural Optometry: Behavioural optometry is a sub-discipline of optometry originating in the USA and the term covers a broad range of activities whereby optometrists take account of the whole person and his/her environment. It should be noted that many of the methods used have not been thoroughly validated with research and the benefits that some children seem to derive from these methods ‘may be explained as placebo effects’¹¹.

Meares-Irlen Syndrome: Some people experience visual perceptual distortions when they look at certain materials, particularly text. The distortions of text include blurring, movement of letters, words doubling, shadowy lines, shapes or colours on the page, and flickering. These distortions are characteristic of a condition that is often referred to as Meares-Irlen Syndrome, Irlen Syndrome or Scotopic Sensitivity Syndrome. Meares suggested that some children’s perception of text and reading disabilities ‘are influenced by print characteristics’¹². She found that in some cases the white gaps between words and lines masked the print and caused perceptual anomalies, such as words blurring, doubling and jumping. Coloured filters (either coloured sheets placed on the page - overlays - or with coloured glasses) are an effective treatment and it is claimed that the required colour differs from person to person and is very specific. Wilkins took this research a step further by developing the Intuitive Colorimeter, which enabled a double-masked randomised placebo-controlled trial [RCT].¹³ An RCT confers scientific validity on a treatment or intervention. Children experiencing Meares-Irlen Syndrome were tested with the Intuitive Colorimeter to determine the precise colour of filter that most improved their perception of text. The optimal and control tints were each worn for a period of four weeks, in random order, and the children reported significantly fewer symptoms with their optimal rather than their control tints.

The cause of the visual distortions is not known but it has been hypothesised that the distortions are due to a dysfunction, perhaps hyper-excitability, of nerve cells in the visual cortex (an area of the brain at the back of the head). Evans suggests that ‘lines of print on a page can cause pattern glare which can trigger symptoms of eyestrain and visual perceptual distortions … and this mechanism is probably responsible for at least some symptoms of “visual stress” with reading’¹⁴. Wilkins notes that ‘some areas of the visual cortex are sensitive to specific colours and this could account for the benefits from specific coloured filters’¹⁵. ‘Current knowledge suggests that the image captured by the eye is processed in modules that keep certain aspects of spatial information at least partially independent of information concerning colour’.¹⁶ It should be noted that Wilkins observed that a large number of the individuals tested had a history of migraine in the family and this seemed to correlate with the idea of pattern glare resulting in visual distortion. Migraine is known to have subtle effects on vision and Wilkins noted the similarities between the physiological mechanisms that induce seizures in patients with photosensitive epilepsy and those responsible for photophobia in migraine. In essence, the perceptual distortions are attributed to a hyper-excitability within the visual system, neurones firing inappropriately as a result of a spread of excitation. Coloured filters are thought to reduce the excitability by redistributing the excitation within the neural network of the cortex so as to avoid localised areas of hyper- excitability. Thus, Wilkins confirmed Meares’ observation that some people’s reading is affected by print characteristics and he observed that the effects of colour depend critically on typography: ‘colour has its greatest benefit with text that is small and closely spaced. With conventional text the effects on reading speed take time to appear, and do so only when the reader is beginning to tire’¹⁷.

It is estimated that Meares-Irlen Syndrome affects ‘10% of unselected schoolchildren’ and probably a higher proportion of people with dyslexia and individually prescribed coloured filters are an effective treatment for people with the condition¹⁸. However, it is recommended that ‘suspected sufferers should have a detailed eye examination before coloured filters are used’¹⁹.

The Study Aids and Strategies Assessment provides an ideal opportunity for assessors to determine which students with dyslexia experience visual anomalies and/or the symptoms of Meares-Irlen Syndrome. All assessors should be aware of the main symptoms of Meares-Irlen Syndrome which include the following visual distortions:

1. glare from the page;

2. page appears to shimmer;

3. headaches when reading;

4. sore eyes when reading;

5. movement/blurring of print;

6. seeing patterns and shapes on the page.

Assessors should also be aware of some of the indicators of Meares-Irlen Syndrome during the assessment, which include:

1. student continually rubbing eyes;

2. excessive blinking;

3. student confirms poor concentration especially when reading;

4. inefficient reading is confirmed e.g. slow reading and/or poor comprehension;

5. student confirms that he/she finds difficulty in keeping place when reading.

Assessors should also note that, in the case of students whose statement of special educational needs has been prepared in accordance with the 1993 Education Act, a description of vision is often included under the ‘medical advice’ component of the statement. It should be borne in mind that in the majority of cases the only vision test to have been performed is distance visual acuity (see above) and as was noted this is virtually irrelevant to reading performance. Often, a student will confirm that their vision is ‘normal’ because this is what is stated in the statement of educational need and/or because they have had a recent eye-test at an optician’s. The assessor must be aware that these tests invariably refer to visual acuity alone.

Studies have shown a high prevalence of ocular anomalies in patients presenting with the symptoms of Meares-Irlen Syndrome and the responsible assessor should recommend that students be referred to an eye care practitioner who is skilled in the assessment of people with reading difficulties prior to providing coloured overlays/spectacles.

Subsequent to the assessment by the eye care practitioner, the assessor should refer the student for a further detailed eye examination to determine which coloured filter is the most appropriate i.e. has the optimal effect. It is important to realise that the degree of precision in the choice of colour is critical for obtaining the best results and that the precision available for lenses is far greater than for overlays (as there is a wider range of colours available for lenses). In addition, it is essential to realise that the appropriate colours for use in glasses is not the same as that in overlays. Wearing glasses all the time makes the user unaware of the coloration because the user adapts to the colour and makes allowances. When a subject uses an overlay only part of what is seen is coloured and the eyes remain adapted to white light. The way that the brain processes what one sees in these two circumstances is very different. It is important for the student being assessed to realise that the colour of his/her spectacles may differ from the colour required for a coloured overlay and/or the settings of a computer monitor.

Although there are a number of optometric factors correlated with dyslexia, there is little evidence to indicate a direct causal link. Evans states that ‘the evidence for visual factors causing reading difficulties is rather less compelling than the argument that phonological factors are major causes of reading problems’²⁰. It is important to realise that phonological factors are in most cases more important in the aetiology of dyslexia. However, he concludes that ‘optometric and psychometric assessments of people with reading difficulties are complementary, not exclusive’²¹.

Bibliography

Evans, B.J.W, (due to be published in Autumn 2000), ‘Visual Factors in Dyslexia’.

Evans, B.J.W., Drasdo, N., and Richards, I.L. (1994), ‘Investigation of accommodative and binocular function in dyslexia’, Ophthalmic and Physiological Optics, 14.

Evans, B.J.W. (1993), ‘Dyslexia: the Dunlop Test and tinted lenses’, Optometry Today, 33.

Meares, O. (1980), ‘Figure/ground, brightness contrast, and reading disabilities’, Visible Language, 14.

Moseley, D. (1988), ‘Dominance, reading and spelling’, Bulletin of the Audiophonology University Franche-Comte, 4.

Microsoft Encarta 99 Encyclopaedia, 1993-1998, ‘Colour’.

PC Pro (July 1999), ‘The Cathode Ray Tube’.

Shaywitz, S. (1996), ‘Dyslexia’, Scientific American, November 1996

Stanley, G. (1991), ‘Glare, Scotopic Sensitivity and Colour Therapy’. Vision and Visual Dysfunction 13 – Vision and Visual Dyslexia (Edited by John F Stein).

Wilkins, A.J. (1996), ‘Helping reading with colour’, Dyslexia Review, 7(3).

Wilkins, A.J., Evans, B.J.W., Brown, J., Busby, A., Wingfield, A.E., Jeanes, R., and Bald, J. (1994), ‘Double-blind placebo-controlled trial of precision spectral filters in children who use coloured overlays’, Ophthalmic and Physiological Optics, 14.

Wilkins, A. (1991), Vision and Visual Dysfunction 13 – Vision and Visual Dyslexia (edited by John F Stein).

Mr Patrick Mulcahy

CCPD and NLRAC Assessor