What is Visual Stress?
Visual stress is thought to be the most common visual reason for reading difficulties (see link to letter from Professor Bruce Evans) and describes unpleasant visual symptoms when viewing text, especially for long periods of time. Alternative names may be used to describe this condition including, Meares-Irlen Syndrome, Irlen Syndrome and Scotopic Sensitivity Syndrome.
The prevalence of visual stress has been reported as occurring in 5 – 20% of the population (British Dyslexia Association 2012), many of which suffer unknowingly or may be misdiagnosed. In people with dyslexia this is thought to be higher at around 35-40% (Wilkins 2003).
British Dyslexia Association: Eyes and Dyslexia. Available from; http://www.bdadyslexia.org.uk/about-dyslexia/further-information/eyes-and-dyslexia.html accessed 22/2/2012
Wilkins, A. (2003). Reading Through Colour: How coloured filters can reduce reading difficulty, eye strain, and headaches.
What are the symptoms?
- Distortions of the text
- Words or letter move
- Words or letters go blurry or fuzzy
Visual stress has a major impact on reading skills, effecting how quickly an individual is able to recognise words and the fluency in which they are able to read long passages of text and the ability to comprehend text.
The wider issues
Visual Stress may result in children struggling through school if the condition is left unnoticed. There can also be a wider impact of visual stress on a child’s psychological well-being. Parents who took part in helping to develop the information for this website described how their child’s condition led to feelings of low self-esteem and self-confidence through school as they felt they were not as clever as the others in their class. It was not their intelligence but the effects of visual stress that made it difficult for them to learn.
It is important for children to get assessed from age seven onwards for their condition as simple interventions such as the use of coloured lens glasses can help alleviate these symptoms.
How do coloured lenses help?
Coloured lenses assist children in reading anything from printed pages to boards and signs. They help remove any glare the child receives from the text, reduce fatigue when reading, increase reading fluency and comprehension. Some say that the colour of the glasses is dependent on the individual and may change in time which is why it is important to receive an individual specialist assessment. Others feel far few colours are needed.
The Science of Reading Difficulties
Irlen (1991) suggests that it is a sensitivity to certain wavelengths of light that distort the perception of the environment. Wilkins (2003) suggests some people have an abnormal visual cortex which causes them to be hypersensitive to coarse contrast strips, as is the case in written text. He feels this interferes with control of accommodation and convergence, which leads to distortions and apparent text motion. Harris proposes that the two eyes perhaps transmit visual information differently therefore causing information to arrive from one eye to arrive in the visual cortex later than the other eye. Stein proposes that reading difficulties are caused by deficits in the visual magnocellular system. Magnocellular cells (M-cells) are neurons in the brain which are found in the thalamus (at the top of the brainstem, between the cerebral cortex and midbrain) within the magnocellular layer of the lateral geniculate nucleus. These cells form part of the visual system. When we scan the text on the page the images move about the retina. It is only during brief fixations on the words that visual forms can be interpreted. The visual magnocellular system plays an important role in reading as it responsible for stabilising brief fixations and in directing eye movement between them. This is therefore essential in helping us identify letters in their correct order. Therefore children with reading difficulties often have unsteady eye control which results in the letters ‘jumping’ around the page affecting their ability to identify the order of the letters (Stein, 2003).
There are varying views surrounding the causes of visual stress which is why there are different approaches to the provision of the coloured lenses. Take a look at the links listed in the “Do coloured lens work” of this website for more in-depth perspectives.
Crossbow (2010) ‘Dyslexia teaching and learning aids, visual stress and phonics resources’. Available at http://www.crossboweducation.com/What%20is%20Visual%20Stress.htm Accessed: 3rd April 2012
Harris (2002) Paper presenttaion. The City University Course on Specific learning Difficulties. City University; London.
Irlen (1991) Reading by Colours. New York; Berkeley:2005.
Lucid (2004) ‘What is Visual Stress?’ Available at: http://www.lucid-research.com/visualstress.htm Accessed 3rd April 2012
Stein, J. (2003) ‘Visual Motion Sensitivity and Reading’ Neuropsychologia 41 pp.1785-1793
Wilkins, A. (2003). Reading Through Colour: How coloured filters can reduce reading difficulty, eye strain, and headaches. John Wiley & Sons: Chichester.