Vision and Visual Stress

Visual Stress, what’s that?

The specific learning difficulty Dyslexia and a condition described as ‘Visual Stress’ are often wrongly thought to be connected or even the same thing and in fact they are completely different issues but they may co-exist.

‘Dyslexia’ is a specific learning difficulty that is caused primarily by a difficulty processing speech sounds. This may include having difficulty discriminating, blending and recalling speech sounds and/or having slow recall of the sounds that are attached to letters. This can also present as the individual being slow to retrieve words from their long term verbal memory.

Sarah Cowell, Dyslexia Assessment and Tuition
Sarah Cowell, Dyslexia Assessment and Tuition

Some children find that when they read, words blur and/or appear to move. This is obviously distressing and it also impacts on their reading rate and accuracy. As the child involved has always seen words this way, they may not realise that this is in fact unusual and so they may not necessarily even mention it to their teacher or parents. If the child’s parents or carers are aware of their child’s difficulty, they rightly take them to an optician who may discover another causal factor such as, for example, astigmatism. Corrective lenses will be prescribed or/and eye exercises and with time all is well.

But this is not always the outcome. The child may continue to have difficulty reading due to visual distortions even whilst wearing their prescribed glasses or they may have not been prescribed corrective lenses at all and so nothing has changed.

Research has suggested that the distortions people experience whilst reading text on white ground, if not found to be due to another cause, may be the result of hyperexcitability in the visual cortex. This propensity tends to be referred to now as, ‘Sensory Visual Stress’ or simply ‘Visual Stress’. This may be remediated by taking away the glare of the white ground and changing it to ground to another colour; not all people who are affected are remediated by the same colour.

Sarah Cowell, Dyslexia Assessment and Tuition
The concept of Visual Stress has been controversial from the outset, but many optometrists and behavioural optometrists now assess visual stress using a ‘colorimeter’ which is a machine created by Professor Arnold Wilkins in 1993 at the UK Medical Research Council’s, Applied Psychology unit. This machine works out the precise colour that will best support the individual involved. And if this proves to be helpful, the individual may opt to have a pair of glasses made with coloured lenses which can be added to a corrective prescription if necessary.

As stated at the outset, coloured lenses or overlays are not a cure for Dyslexia. Dyslexia, although not curable, can be supported with specialist tuition and the use of assistive technology.

Individuals who come for a dyslexia assessment at my practice have to have had a recent regular vision test and if prescription glasses are needed, to have received them so that they are worn for the assessment. If in spite of this, the individual misses words out, or/and, has to track the text with their finger or/and rubs their eyes or appears to tire when they read, or they themselves when asked say that words appear to wobble on the page, or blur, a recommendation will be made that they should to be assessed by an optometrist or behavioural optometrist who carries out visual stress assessments after carrying out a full set of vision assessments. It is vital to check that an optometrist or behavioural optometrist will offer a comprehensive assessment and management of problems involving binocular vision (accommodation and convergence) disorders, and visual stress, in addition to the standard sight tests comprising refraction and ocular health assessment.