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Visual stress resource centre Reading with visual stress

Dyslexia and Visual Stress
Factsheet 1: Visual Stress,  coloured overlays and tinted lenses.

What is Visual Stress?

Visual stress describes the discomfort some people feel when viewing text on a page of print or on a screen: sometimes after ten or fifteen minutes; sometimes immediately. Symptoms vary, but can include headaches and migraines (especially when working at the computer), sore eyes and eyestrain, and words or letters blurring or appearing to "jump" or move on the page. Visual stress can also cause fatigue and nausea when reading, and is a common, and often undiagnosed cause of educational failure and under-achievement.

Many people suffer unknowingly from visual stress (see Reading through Colour below), so it is worth checking out anyone experiencing reading difficulties or discomfort, especially after prolonged exposure to print or VDU. Sometimes a simple five minute experiment with different coloured overlays is all that is necessary, as the symptoms can often be alleviated by just changing the background colour of the text - although a thorough examination by an optometrist is also important, to check that there are no underlying eye problems. VISS, a computerized Visual Stress screening programme developed in association with the psychology department of Hull University, is a useful tool for identifying Visual Stress sufferers.

Visual stress is also termed Meares-Irlen Syndrome, Scotopic Sensitivity, or (in the USA) Irlen syndrome.

Reading through Colour

Research has shown that around 20% of the population suffer to varying degrees from visual stress, and could improve their reading by reading through a coloured overlay. When a person has the right tint, a number of aspects of reading can improve, including attention span, reading speed, fluency and comprehension.

Scientists have not yet agreed on the reasons behind the beneficial effects of reading through colour; only that they do exist, and that it is important to find the correct colour for each individual.

What about writing?

Writing on white paper can also cause problems. In the educational sphere, we have found that children scoring 4 or 5 out of 20 on a spelling test have improved their spelling score by 10 marks when switching to paper matching the colour of the tinted overlay they are using for reading. We supply A4 refill pads "Tinted for Visual Comfort" in 7 pastel colours.

Visual Stress and Dyslexia: are overlays a cure?

Although many dyslexic people experience visual stress, they are not the same thing: not all dyslexics suffer from visual stress, and not everyone experiencing visual stress is dyslexic. There is however a high correlation between dyslexia and Visual Stress: it seems that about three times as many Visual Stress sufferers are dyslexic than not. Coloured overlays are NOT a "cure" for Dyslexia.  In the years following the discovery (in 1980) of the benefits of reading through colour there were some commercial interests that took the "Dyslexia Cure" line, and there is still one website that promotes the use of overlays as a "cure". These claims have resulted in adverse publicity and consequent suspicion of a "quack remedy" that is unfortunately still shared by many people today. Crossbow do not subscribe to that view. Spectacles do not cure short-sightedness: they simply adjust its effects. It is the same with coloured overlays and VDU screen tinting software.


What is a coloured overlay?

A  coloured overlay is a semi-transparent overlay to be placed over text based materials.  Each overlay has a specific tint colour which can improve a number of aspects, including attention span, reading speed, fluency and comprehension.

When using a coloured overlay, the text should be positioned with the sheet over the page to avoid reflections from the surface of the overlay caused by lighting. The overlays have a matt coating on one side, which most users prefer. The overlay should not be creased, and it is a good idea to keep it in an envelope when it is not in use, although users should nevertheless feel free to touch the overlay when reading. Coloured overlays should simply be seen as a type of reading aid, like ordinary glasses, that makes the words clearer for some people. Alternatively reading rulers can be used instead of full page overlays.

What are reading rulers, and are they better than coloured overlays?

Reading rulers are less intrusive than larger overlay sheets, easier to handle, cheaper, and provide additional tracking support. They are particularly useful when referring to a printed document while word-processing. Many people prefer them. Research comparing reading rulers with A4 overlays has shown that the size of the overlay does not make any difference to reading speed.

Tinted Lenses

Coloured lenses can also be used: they have to be prescribed accurately following a specialist assessment. They are much more costly than overlays, but can be of greater value as the wearer experiences the benefit when reading from boards, posters and screens, as well as from printed pages, eliminating the glare from the page he or she is reading or writing on. Against that is the fact that sometimes colour preferences seem to change, which means another assessment and another pair of coloured glasses. A directory of Local Specialist Opticians who prescribe tinted lenses can be found on  Crossbow do not endorse or recommend any individual Optometry practices.

How long should overlays be used before tinted lenses are considered?

There are many factors involved. First, are the overlays obviously beneficial? If so, only a short trial period, say six weeks, is necessary, particularly if headaches have been reduced but not eliminated, and if something like untidy writing continues to be a problem and tinted paper is not practical. Under these circumstances glasses may further reduce the headaches and may well improve the handwriting. If, on the other hand, the response to overlays is less marked, it seems sensible to take a little longer before considering coloured glasses. Coloured glasses are more expensive than overlays, and it may be wise to wait before incurring the cost.

Some of this information has been adapted from the Essex University FAQ page on Visual Stress.  Click  here  for more information about coloured overlays and visual stress.

Are glasses always the same colour as overlays?

Often, but not necessarily.  For example, a person may choose a yellow overlay and benefit from blue lenses. The colour of the lenses can only be assessed by optometrists or orthoptists who use a device called the Intuitive Colorimeter ®, or by the use of a very large number of coloured trial lenses. Other methods of selecting coloured lenses may be less likely to select the best colour.

Why can glasses be a different colour from overlays?

When you wear glasses everything you see is coloured, but you are often unaware of the colouration because you adapt to it and make allowances for it (for example, the colour of light from a normal household light bulb is very yellow in comparison to daylight, but you are never aware of this). When you use an overlay only part of what you see is coloured and the eyes are adapted to white light. The way that the brain processes what you see in the two circumstances is very different.

© Crossbow Education Ltd 2013