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At Conway Phillips we offer a coloured overlay assessment to determine if patients can benefit from the use of coloured overlays when reading. Unfortunately this service is not available on the NHS.


We charge a private fee of £30 for this service. Coloured overlays cost £10 each. The following frequently asked questions have been provided by the Institute of Optometry and should help further explain about the use of coloured overlays.

What are coloured overlays?

Coloured overlays are sheets of translucent or transparent coloured plastic that can be placed over a page of a book so as to colour the text beneath without interfering with its clarity.

What do they do?

To book a coloured overlay assessment with Conway Phillips, call us today on 

01925 633 746

Coloured overlays reduce the perceptual distortions of text that children sometimes describe. They enable some children to read text more fluently and with less discomfort and fewer headaches. It is important to assess the effects of a wide range of colours because individuals do not all benefit from the same colour.

What proportion of children can benefit?

In several studies, children in county primary schools were - individually shown a passage of text covered in turn by a variety of coloured overlays, including grey or clear overlays for comparison. About 20% of the children found one or other of the colours improved the clarity of the text. They continued to use an overlay of that colour without prompting for more than three months. They read more quickly with their overlay, both before and after they had become accustomed to its use.

How should an overlay be used?

The reader should place the sheet over the page, when reading. The text should be positioned to avoid reflections from the surface of the overlay caused by lighting. The overlay should not be creased, and it is a good idea to keep it in an envelope when it is not in use. Pupils should nevertheless feel free to touch the overlay in order to point when reading. If teasing is a problem, it may help for staff to explain to the class that the use of overlays to correct sight is similar to the use of glasses. It may also be helpful to trim the overlay so that it is less conspicuous.

What are visual perceptual distortions?

Some people can experience distortions when they look at certain materials, particularly text. The distortions of text include blurring movement of letters, words doubling, shadowy lines, shapes or colours on the page, and flickering. These distortions are characteristic of a condition that some have called Meares-lrlen Syndrome, Irlen Syndrome or Scotopic Sensitivity Syndrome.

How can visual perceptual distortion be spotted?

Visual perceptual distortion should be suspected in children who have trouble learning to read, particularly if they report headaches and eye- strain from prolonged exposure to the page. If the child reports any illusory movement of the letters or words, or glare from the white paper, then treatment with coloured overlays or filters should be considered.


One possible question to ask is: 'After you have been reading for a while, do the words or letters do anything different?'. If open-ended questions such as the above fail to provoke reports of distortions, more direct questions can be given. The child can be shown a page of text, and asked the following questions: 'Do the letters stay still or do they move?'; 'Are the letters clear or are they blurred?'; 'Is the page too bright, not bright enough or just about right?'. Reports of movement, blurring and glare are more likely in children who benefit from overlays.

What is Meares-lrlen Syndrome?

The term Meares-lrlen syndrome is sometimes used to refer to the collection of symptoms and signs of visual fatigue when reading that are reduced when colour is used. Other terms are Irlen syndrome or Scotopic Sensitivity Syndrome (SSS)1. (The syndrome is not yet widely recognised by the medical and scientific communities, and there is no universal agreement on its name.) The symptoms of visual perceptual distortion in children with reading difficulty were first described by Olive Meares, but have been listed by Helen Irlen, as follows.

What are the symptoms of Meares-Irlen Syndrome?

Some of the main symptoms are:


• Glare from the page

• Headaches when reading

• Sore eyes when reading

• Movement/blurring of print

• Onset of symptoms varies and may depend on lighting conditions, style of text and quality of paper

What are the signs of Meares-lrlen syndrome?

Some of the signs may be:


• Rubbing eyes

• Excessive blinking

• Poor concentration

• Inefficient reading

• Difficulty in keeping place

Which texts show a benefit from colour?

Coloured overlays and coloured glasses can increase the speed of reading, although with conventional text the improvement may only be apparent after ten minutes continuous reading when the child would begin to tire were an overlay not used.3 If the text is closely spaced, the benefit is more immediate.

Which children benefit?

The children who benefit may be good readers, but more often they have difficulty reading. They usually suffer visual discomfort when reading and, when questioned, will often report perceptual distortions of the text. These distortions usually include apparent movement or blurring of the letters and words. Often there is a family history of migraine.

Does visual perceptual distortion relate directly to learning difficulties, or dyslexia?

Children with reading difficulty are more likely than others to report visual perceptual distortion, and to benefit from coloured overlays. A smaller proportion of good readers also show similar benefits. Individuals with dyslexia may have difficulties with visual perception, but usually also have difficulties of a linguistic nature which need to be addressed separately.

Why can children have 'perfect eye sight' and still experience distortion?

An optometrist (previously known as an ophthalmic optician) will report 'perfect eye sight' when someone can see a letter chart without needing refractive correction (glasses), and when there are no (orthoptic) problems of co-ordination between the eyes. The perceptual distortions may occur quite independently of any refractive error, although they are often, but not always, associated with a mild binocular vision difficulty (i.e. a difficulty in moving the eyes together, keeping the direction of gaze appropriately co-ordinated). In most cases the binocular difficulties do not appear to be the basis for the distortions.

Does visual perceptual distortion occur in families, and if so, why?

Many traits run in families and visual perceptual distortions are no exception. The genetic contribution is the subject of investigation.

Do children need coloured overlays or coloured glasses permanently?

It seems that children benefit most from colour if it is offered as soon as any reading difficulty is suspected, before the cycle of failure has begun. Many 7 year-olds appear to use coloured overlays for a year or two and then discard them as unnecessary. This may be because the acquired familiarity with text makes the distortion less distracting.

Can overlays or glasses harm the eyes?

Just as some colours are reported as being beneficial, others are often reported to be uncomfortable. Individuals sometimes show a marked aversion to these uncomfortable colours. Provided the appropriate colour is chosen, it seems unlikely that overlays can have any detrimental effect. The possible long-term effects of wearing coloured glasses are unknown at present.