Visual Stress
Visual Stress is a defect of vision which results in various distortions and symptoms of discomfort when trying to read passages of print and looking at certain striped patterns. Many different visual conditions can result in difficulties when reading and it is important that other possible causes are fully investigated before looking at visual stress.
One of the main distinguishing features of visual stress is the role played by carefully selected coloured filters which can ease the symptoms of distortion and discomfort. The optimum colour required is specific to each individual and may change over time. It can be achieved by using overlays, (transparent plastic sheets placed on a page of print,) or by coloured spectacle lenses, but because of the different modes of use, the colour needed for an overlay is very unlikely to be the same as that required in a spectacle lens.
It is important to note here that the existence of visual stress and its treatment with coloured filters remain controversial, due to a mixed body of evidence from research. Because of the subjective nature of the colour selection process, careful monitoring of the child’s use of an overlay over a period of time, (generally a full school term,) is necessary in order to be sure that colour is of benefit to the child. A recent Delphi study, which combines the knowledge and experience of experts in the field, provides practical guidelines for diagnosing visual stress.
Dyslexia and Visual Stress
Parents are sometimes confused about the relationship between dyslexia and visual stress; these are completely different and separate conditions. There is strong evidence that the major causal factor in dyslexia is a deficit of phonological awareness, and it is diagnosed by educational psychologists and certified specialist assessors. Dyslexia is not caused by any type of visual condition and so cannot be diagnosed or treated by optometrists.
Early research suggested that those with dyslexia were significantly more likely than those in the general population to suffer from visual stress. However, research over recent years seems to point to minimal correlation between the two conditions. It suggests that visual stress occurs in up to 20% of the population so up to 1 in 5 of those with dyslexia, (and those without the condition,) are likely to be helped with coloured filters.
Visual stress is a defect of vision and as such should only be diagnosed by a qualified optometrist. Some teachers and other educational professionals, particularly those involved in helping children who have special educational needs, regularly show coloured overlays to children with reading difficulties, but if they suspect visual stress they should always refer to an optometrist.
A full eye examination is necessary
There are many visual conditions which can cause difficulties when reading and more generally. Before investigating the possibility of visual stress other possible causes of the symptoms must be ruled out or addressed. It is important for all children, (as well as adults,) to have regular eye examinations, ( for which children will often be funded by the NHS.)
During the eye examination the optometrist will check many aspects of your child’s vision and discuss findings with you, together with any further investigations or treatment which may be necessary or helpful. Spectacles may be necessary. Sometimes a Special Investigation into visual problems relevant to reading will be advised, and this will generally include an overlay test to investigate the possibility of visual stress.
If an overlay of a particular colour is found to make reading easier it will be issued to be used wherever appropriate, (e.g., home, school, college.)
Where children are found to have visual problems such as visual stress, treatment of these can help them to read more comfortably and may improve their perception of text. This may help them benefit from teaching and contribute to an improvement in reading performance.
Adults
Most of the information above concentrates on assessment for children but it is important to remember that adults too can have visual stress and benefit from coloured filters. It is not uncommon for people to become aware of a problem only when further education or a new job presents greater visual demands. Sometimes when we are assessing a child the parent suddenly understands a problem they have also had, perhaps since childhood. People with photosensitive migraine, photosensitive epilepsy, multiple sclerosis and other neurological conditions can sometimes find that coloured lenses help to ease their visual symptoms.
For adults the investigative process can often take a different path, with a comprehensive extended eye examination often replacing the Special Investigation and a subsequent colorimetry appointment in place of the overlay assessment and trial.
Please see our website information on Our Special Investigation and Coloured Overlays and Colorimetry, and if you are concerned in any way about your child’s vision, (or your own,) please contact the practice for advice. Very often the starting point is a full eye examination.
(Please note that some services are available only at our Houghton Regis practice.)
