Liz Lewis and David Pointon,
Lorna Scott, Orthoptics
Dr Bruce Evans,
MRC Applied Psychology Unit,
Prof. Arnold Wilkins, Visual
There is now scientific research to
show that both coloured filters (worn as spectacles) and coloured plastic
sheets laid over text (known as overlays) can help some children to read.
This article is for parents and
teachers whose children continue to have difficulty reading after their vision
has been checked by an optometrist (ophthalmic optician).
What are coloured overlays?
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?
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. Each individual seems to need a different
colour, so it is important to assess the effects of a wide range of colours.
What proportion of children can benefit?
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?
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.
What are visual perceptual distortions?
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 Visual Stress (previously Meares-Irlen Syndrome, Irlen Syndrome or
Scotopic Sensitivity Syndrome).
How can visual perceptual distortion be spotted?
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.
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 (fuzzy)?";
"Is the page too bright, not bright enough or just about right?" ; “Does it hurt your eyes to look at the page or is
it OK?”. Reports of movement, blurring and glare are more likely in children
who benefit from overlays.
How are visual perceptual distortions caused?
cause of the distortions is not known with any certainty. Some authors have
hypothesised that the distortions are due to a dysfunction, perhaps a
hyper-excitability, of nerve cells in the visual cortex, an area of the brain
at the back of the head. Individuals with migraine, and those with migraine in
the family, are particularly susceptible to the distortions.
What is Visual Stress (Meares-Irlen
term Visual Stress is sometimes used to refer to the collection of symptoms and
signs of visual fatigue when reading that are reduced when colour is used as
therapy. Other terms are Meares-Irlen
syndrome, Irlen syndrome or Scotopic
Sensitivity Syndrome (
What are the symptoms of Visual Stress?
of the main symptoms are:
(onset of symptoms varies and may depend on lighting
conditions, style of text and quality of paper).
What are the signs of Visual Stress?
of the signs may be:
Which texts show a benefit from colour?
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. If the text is closely
spaced, the benefit is more immediate. Books with large text are less of a
problem, and may not need an overlay.
Which children benefit?
children who benefit may be good readers who tire quickly, 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?
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
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?
traits run in families and visual perceptual distortions are no exception.
Does visual perceptual distortion cause writing to deteriorate?
visual perceptual distortions that people experience can affect all aspects of
visual function, but they are more likely when the visual material has many
similar contours (letters). Text is unlike natural scenes in that it is
composed of many identical elements. These are at their most confusing in small
closely spaced printed text, but they also occur in handwritten work.
Do children need coloured overlays or coloured glasses permanently?
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 then
makes the distortions less distracting.
Can overlays or glasses harm the eyes?
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.
Should coloured glasses be worn all the time?
our view, children should be free to wear the glasses if they find it helpful
to do so. They should not becoerced into wearing them
if they would not otherwise do so, or bullied and teased so that they refrain
from wearing them. The response to colour is subjective and individual, and the
wearer is the best person to judge whether there is any benefit.
Should children with binocular difficulties who are undergoing orthoptic eye exercises or other medical treatment continue
to use overlays?
our opinion, overlays can be used regardless of any simultaneous eye exercises
or medical treatment. However, since visual perceptual distortions can
sometimes be caused solely by binocular vision problems, it is often sensible
to have these corrected first. If the distortions remain then coloured filters
need to be tried.
How long should overlays be used before coloured glasses are considered?
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.
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
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.
Are coloured glasses necessary?
who persist in using their overlay usually find coloured glasses more
convenient to use. Glasses can help with writing, whereas overlays cannot. The
degree of precision in the choice of colour is critical for obtaining the best
results, and the precision available with lenses is far greater than with
overlays. Perhaps for this reason glasses often give better results.
Are glasses the same colour as overlays?
is essential to realise that the appropriate colour for use in glasses is not
the same as that in overlays. 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 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 optimal colour.
Why are glasses a different colour from overlays?
you wear glasses everthing 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.
What is the best method for combining overlays?
best method is that which most efficiently covers the largest number of
Intuitive Overlays used in recent research4 were
scientifically developed so that similar colours can be combined two at a time
in a simple yet thorough way. If these overlays are used and all suggested
combinations are tried, a wide range of colours will have been efficiently and
How reliable is the choice of overlay colour?
tested a second time, individuals may sometimes choose a different colour, but
it is usually a similar colour. The choice of colour may appear random, but it
What does one do if a child reports a large range of colours beneficial, but
cannot make a consistent choice?
colours should be compared side by side. If the choice remains unreliable, then
one of the chosen colours should be given a trial for a period of a week,
followed by one of the other colours.
Do children change their preferred colour?
sometimes seem to change their preferred colour. The reason for this is not
Does it matter if the child still sees areas of white page around the overlay?
of white page may well affect the choice of colour. The conditions of the test
should resemble those under which the overlay will be used. If neighbouring
white pages are unlikely to be encountered when the overlay is used, they
should be avoided during the test procedure.
Would it help children to work under lighting that is not fluorescent?
are usually overlit by fluorescent and natural light.
Care must be taken to avoid glare by shielding work surfaces from direct
sunlight. Complaints of glare from fluorescent lighting should be taken
seriously; they usually result from real rather than imagined problems. In 80%
of classrooms fluorescent lighting emits high-frequency invisible flicker that
can affect some people, particularly those with migraine. If headaches are
attributed to fluorescent lighting, the individual should be seated where the
fluorescent light is "diluted" by daylight or the relatively steady
light from filament lamps.
Can adults be affected?
Although some people seem to "grow out" of the condition, many do
not. The distortions may be less pronounced when reading becomes fluent and
text ceases to be a meaningless collection of confusing shapes. Sadly, visual
perceptual distortion is often not recognised in children and many sufferers
enter adulthood without ever having been treated.
What do I do to find out if colour might help?
you should obtain an optometric examination. You should find an optometrist who
has an interest in reading difficulties (see below). The optometrist should
assess binocular (orthoptic) function.
you should obtain an examination with coloured overlays. The examiner should
have an Asessment Pack of overlays. Several different
packs are on the market with varying numbers of colours. The pack should
include a wide range of at least 10 colours.
is not sufficient to try the coloured sheets available from stationers, because
the colours are not subtle or varied enough.
examiner should listen to the client’s description of the distortions, and use
this description when trying to decide whether a particular colour reduces the
way of assessing benefit is for the examiner to administer the Wilkins Rate
of Reading Test. The test consists simply of a passage of
randomly ordered words that the client is required to read aloud as rapidly and
as accurately as possible. The words are all very commonly used and are
therefore familiar to most children, even those whose reading is very poor. The
words are arranged in random order so that the person cannot guess what words
come next. The text is printed in small closely spaced lettering so that any
visual difficulty is maximised and affects reading speed after only a short
period of reading.
rate of reading words on this test is usually more than 10% higher with the
chosen overlay than without in children who will subsequently make frequent use
of their overlay.
How can I find an optometrist who has specialised in reading difficulties?
(previously called ophthalmic opticians) can be found in most town centres.
Optometrists examine eyes to assess their health and to determine whether
glasses or eye exercises are needed. A small but growing number of optometrists
have specialised in assessing people who have reading difficulties. A list of
optometrists who prescribe coloured lenses can be obtained from the Society for Coloured Lens Prescribers.
needs teachers and educational psychologists also often know of local
optometrists who have specialised in this subject.
What tests should I expect the optometrist to do?
precise routine will vary from one optometrist to another but the basic eye
test includes refraction (tests of lens focus), acuity (ability to see small
objects), tests of the health of the eyes, and basic tests of ocular motor
function (how well the eye muscles work together). There are other tests that
are not always included in the examination but are generally thought to be
particularly important for children with reading difficulties. You can ask an
optometrist whether they would do these tests before you book an appointment.
all optometrists who have specialised in this subject have an Intuitive
Colorimeter, but all should know of a colleague who they can refer you to if
this further testing is needed.
Will there be a charge for these tests?
NHS pays optometrists a small fee for carrying out a basic eye examination. As
the tests listed above are of a specialist nature most optometrists have to
charge a private fee for the detailed investigation of people with reading
Where can I find out more?
following books provide a review of research in this area and a theoretical
explanation for the effects of colour
- for eyecare professionals : Wilkins, A.J. Visual Stress,
Oxford University Press: Oxford, 1995.
- for teachers and parents as well as eyecare
professionals : Wilkins,
A.J. Reading through Colour, Wiley: Chichester, 2003.
- for teachers and parents as well as eyecare
professionals with an interest in dyslexia : Allen, P.A., Evans, B.J.W. and Wilkins,
A.J., Vision and Reading difficulties, 2011