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Dyslexia Specialists Since 1993

Visual Stress: What is it?

Visual stress describes the discomfort some people feel when viewing text for long periods. Symptoms vary , but can include headaches and migraines (especially when working at the computer), eyestrain, and words or letters appearing to "jump" or move on the page. Many people suffer unknowingly from visual stress (see below), so it is worth checking out for anyone experiencing reading difficulties, although a thorough examination by an optometrist  is also important, to check that there are no underlying eye problems.

Where there is no underlying problem and the symptoms can be alleviated through changing the background colour of the text, visual stress is also termed Meares-Irlen Syndrome or Scotopic Sensitivity. 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 is is important to find the correct colour for each individual.

What about coloured glasses?

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 in the classroom as the wearer experiences the benefit when reading from the boards, posters etc as well as from printed pages, and eliminate the glare from the page he/she is writing on as well as what he/she is reading. Against that is the fact that sometimes colour preferences seem to change, which means another assessment and another pair of coloured glasses, plus the fact that most children feel uncomfortable wearing them in public once they reach secondary school. For a list of some optomerists in the UK who prescribe coloured lenses click here.

Are glasses the same colour as overlays?

No. For example, a child 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 are glasses 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.

Visual Stress and Dyslexia

Although many dyslexic experience visual stress, they are not the same thing: not all dyslexics suffer from visual stress, and not everyone experiencing visual stress is dyslexic. Coloured overlays are NOT a "cure" for Dyslexia.

Will my local Optician know all about visual stress?

Maybe; maybe not. However an increasing number are prescribing coloured overlays and lenses. Check out our list on the link "local specialist Opticians" to find the one nearest you. This list is not exhaustive and is reviewed periodically, so it is always worth checking online anyway if we haven't got anyone listed near you.

How should a coloured overlay be used?

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 pupils should nevertheless feel free to touch the overlay in order to point when reading. It can be pointed out to the class if neccessary that  coloured overlays are a type of reading aid, like ordinary glasses, that make the words clearer for some people. Alternatively reading rulers can be used instead of full page overlays. (For more detail, see separate article: coloured overlays care and use.)

Are reading rulers better than coloured overlays?

Reading rulers are less intrusive than larger overlay sheets, easier to handle, cheaper, and provide additional tracking support. Many children and adults 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. For an abstract of the research on this topic. see Visual Stress and Coloured Overlays: does size matter?

How long should overlays be used before coloured glasses 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 untidy writing continues to be a problem. 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 see whether the child continues to use overlays without prompting for, say, a school term or longer, before considering coloured glasses. Coloured glasses are more expensive than overlays, and it may be wise to wait before incurring the cost.

Another factor to consider is the age of the child. It is often difficult to assess a child for coloured glasses below the age of 8.

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.