Visual Problems and Reading Difficulties

By Dr Sue Fowler

It would seem obvious that the visual system must play a part in explaining the difficulties suffered by some intelligent children learning to read. Unfortunately this is not the view of many experts, from psychologists to teachers who still believe that all the problems suffered by dyslexic children can be solved by improving their phonetic awareness and teaching them spelling rules. However, more than half the words in English are irregular and can't be sounded out. In order to read such words you must be able to visualise the word as a whole. It cannot be read by knowledge of its constituent parts. A child is not able to remember what a word looks like if every time he looks at it he sees the letters in a different order a different way round, blurred or double.

The part played by vision is particularly important in the early stages of learning to read when the child learns to recognise and remember the shape of the letters and to attach a name to the shape. The child has to learn that b is not the same as d, and that d is the same letter as D.

Some bright children with difficulty to read, have a very obvious history of intermittent hearing loss, and confused or delayed development of language. In these cases the teaching of phonics and spelling rules can be very successful. However, as the child progresses it may become clear that although they decode regular words easily, they still fail to recognise the visual shape of irregular words. The reason for this is assumed to be poor visual memory, but the underlying cause may be one of visual confusion disrupting the normal development of visual memory. Investigation of vision and eye movement control may give the answer and help both child and teacher. In contrast is the very bright, articulate child who finds reading very difficult, with no early warning signs of problems learning to talk. They learn to sound words out easily, but their progress is still slow, showing no visual recall of word shape at all. The sooner this child is asked to describe how he sees the letters move about, and is referred for visual assessment the sooner he will start to improve, and overcome his frustration. The child complaining of visual confusion learning to read has not necessarily been diagnosed as dyslexic, before visual investigation is carried out.

Reading is a complex visual task. It requires identification and localisation of the orientation of the lines of which letters are constructed, memory of what is seen, followed by association with meaning and language. If a word is to be read a clear image of its constituent letters must be formed on the retina, at the back of the eye. This information is then passed to the primary visual cortex at the back of the brain. Here the direction and orientation of the parts of the letters are further decoded and passed eventually forwarded to the angular gyrus, part of the temporal lobe of the brain. Here the pattern is matched to previously laid down visual and auditory engrams (memory patterns) of words previously seen, for recognition and meaning. Learning to read is, however, not just a process of recognition, but also of seeing the letters in the correct orientation and localisation in space, associated with meaning and language.

During reading, information about the letters and words is taken in during periods of fixation, when the eyes are kept still. Eye movements are then required to move the eyes to the next word, a saccade, or step movement of the eyes. The saccades are necessary to bring the fovea, the area of clearest vision in the centre of the retina, to the next target to enable clear definition of the word. Identification is not possible during the saccade when the images stream across the retina, producing blur. It is now thought that smooth pursuit; (following eye movements) play a large role in the control of fixation, by tracking the movement of the image to stabilise the fixation on the next group of letters. (Knowler 1990). Thus the accurate control of both saccadic and smooth pursuit eye movements are necessary for reading.

In order to know exactly where a letter is within a word, on a line of print, information about the position of the image on the retina, must be associated with signals, from the eye muscles denoting the direction in which the eyes are pointing at the time, in relation to the observer. When the two eyes are converged (pointing inwards towards the nose) as is necessary to focus on a near object, such as words on a page, this association is particularly difficult as both eyes are pointing in opposite directions, with respect to the head. Thence they can give conflicting information as to the direction of the target, letter or word. This suggests that retinal information is preferentially and consistently associated with the position signals from the eye that is providing the retinal signals, (the reference eye) in order to know exactly where a letter is on the page. In order for this complex association, of what is seen and where it was in space, to take place, the eyes must be able to keep still during periods of fixation. The stability of the image is therefore dependent upon the control of either eye individually and both eyes together.

The movement of each eye is controlled by six muscles, which work together with the corresponding muscles of the other eye. The muscles are moved in response to signals from the brain stem, but many other brain areas (parietal and frontal lobes) are involved in the control of saccades, smooth pursuit and fixation, which move both the eyes together in the same direction. To move the eyes in opposite directions in relation to each other, as in convergence, involves additional areas in the brain stem. Thus the control of saccades, smooth pursuit, fixation and convergence all play their part in producing a stable image of the word on the page, and enable smooth tracking of the eyes along a line of print. (Robinson 1981).

The form of the letter word is analysed in the infero temporal cortex (temporal lobe) whereas the movement of the image together with the signals about the movement of the two eyes are processed in the posterior parietal cortex of both sides of the brain. However, the association of the visual patterns with language to gain meaning is specialised in the left side of the cortex, necessitating transfer of that information previously processed in the right hemisphere to the left side of the brain. It is possible that this crossing of information may be responsible for mirror imaging confusions. (Glickstein 1991)

In order for the constituent parts of the letter and the individual letters that form the word, to be recognised, a clear image must be formed on the retina. This clarity will depend on a healthy eye, normally working eye muscles, and correction of any refractive error. Light entering through the cornea at the front of the eye is bent, refracted and further refracted by the lens within the eye, brought to a focus on the retina. Anything that prevents such clear image formation may effect learning to read. It is important that all children who are having difficulty learning to read should be checked first by an Optician, Optometrist or Ophthalmologist, to assess the health of the eye and muscles and prescribe corrective glasses, if necessary, to bring acuity up to a normal level.

When Dr. Piers Cornellisen, (Cornellisen et al 1991) was researching the hypothesis that what a child sees effects the way he reads, he started by asking children if the words appeared to blur, move about, go double or seem too glarey on the page. The results of his findings led us to asking parents to complete a questionnaire before the child is given an appointment in our research clinic run by an Orthoptist. We have found if we restrict the children we see to those who have visual symptoms we find 80% of those seen are found to have some visual problem that we can identify and try to overcome. In clinics where such initial screening is not used the percent of children who benefit from Orthoptic, or Optomotric treatment is reduced to 30%. This matters when we are talking about free treatment funded by the N.H.S. So in our clinic we discriminate between those children who have visual symptoms, and those who don't.

It is therefore important for parents and teachers of children with difficulties learning to read, that they ask the child these questions before considering investigation or treatment for possible visual difficulties associated with reading. Not all children with slight abnormalities or vision or eye movement control find learning to read difficult. They do not all need treatment just because something is just outside so-called normal levels. Many children develop compensatory strategies, and not all children learn to read in the same way. (Seymour 1986). Sometimes interference can produce difficulties, which were not originally there. It is important to follow the guidelines of only treating to overcome symptoms, when considering intervention into possible visual problems in relation to children with learning difficulties.

We have shown that if a child with learning difficulties, identified as dyslexic by comparing reading age performance to IQ levels, has visual symptoms and defective eye movement control, reading age can be improved by treatment designed to bring about changes in visual processing, but can a child be identified as dyslexic by visual tests alone? No, what we can do is show that some dyslexic children, possibly 2/3 do have visual problems.

Symptoms in association with reading or looking at print.

  1. Do letters or words blur, go out of focus?
  2. Do letters move about, appear back to front, shimmer or shake?
  3. Does reading makes your eyes or head ache?
  4. Do words or letters break into two, appear double?
  5. Is it easier to read large, widely spaced print, than when small and crowded.
  6. Are you upset by glare on the page, oversensitive to bright lights?

If a child complains of a least one of these problems they should be referred to an Optician, Optometrist, or Orthoptist.

Why should letters appear blurred, or out of focus?

(A) Uncorrected refractive error.
If a child is long sighted (hypermetropic) he may only see close print clearly by making extra effort to over focus. If the long sight is outside the normal range the Optician may order glasses for close, or constant wear. Uncorrected long sight may also result in eye ache or strain from the constant need to over focus. In rare cases convergent squint in association to close work with double vision, can develop, and would require an Ophthalmologist.

If a child is short sighted or myopic the blur will be mainly for distant objects, such as when reading from the blackboard or TV, and glasses may again be necessary. Astigmatism is a condition where the refractive error is unequal in different directions, and is similarly corrected by glasses. Once glasses have been prescribed any symptoms resulting from these specific problems should be resolved, if they persist further investigation is necessary.

(B) Problems with accommodation, focusing. Although rare in young children difficulty in maintaining a clear image for near can result from defective function of the focusing mechanism which changes the shape of the lens within the eye, and is controlled by special muscles. The Optician, Orthoptist or Ophthalmologist will identify this condition. Special eye exercises or temporary glasses may be required.

(C) Problems of contrast sensitivity.
Difficulty in detecting the print from the background, both print on a page, chalk on a black board, or coloured pens on a white board, can all be difficult to see, when contrast is reduced. Sensitivity to contrast should be investigated if symptoms of blur fail to respond to correction of a refractive error or defective accommodation. The simple use of bright plastic overlay, or lenses, to increase the contrast sensitivity has a treatment effect and may resolve within six months. (Fowler, et al 1991).

(2) Letters that move about.

(A) Poor control of fixation, difficulty keeping the eyes still, is often closely linked to problems of attention, but can be an isolated problem of eye control. Poor control of fixation causes small eye movements of single letters, letters appear in the wrong order within a word.

Our research clinic has devised special exercises which teach the child to first recognise that their eyes are moving, by using small pictures which they see moving. They can learn to keep their eyes still by learning to keep the picture still. These exercises are carried out by an Orthoptist, using three-dimensional pictures called stereograms.

Improvement in the control of fixation results in improvement in reading age. Where the poor fixation is only due to visual inattention, the eyes make constant large movements away from the target, exercises are difficult and further investigation is required for help with attention. (Conners, 1990).

(B) Poor control of saccades and smooth pursuit.
Poor control results in jerky reading, difficulty following along the line, missing words out, loosing the place. Exercises to help to improve this kind of eye movement defect are difficult. It is usually better to advise the use of a finger to move across the line under each word, with the other finger marking the beginning of the line. Tracking exercises are of help, using small print, similar to print used for reading.

(C) Lack of a fixed reference eye.
Identification of this condition can only be done with a synoptophore by an Orthoptist. The Dunlop test indicates whether or not the child can consistently associate the information about what is seen, with where it is in space, always to the same eye. If the child uses first one eye and then the other, letters may appear to move in space and become mirror reversed. Mirror reversals are due to the way in which information is transferred from one side of the brain to the other. Only if a Dunlop test has been used to identify this problem can occlusion (covering) of the left eye be suggested for reading, writing and number work only using special glasses.

Reading age improves as the confusion is overcome and the child develops a fixed reference eye, after 3/6 months of treatment. (Stein & Fowler 1985, Stein et al 2000).

(D) Alternating squints
Most children who develop a squint before going to school have no difficulty learning to read, from any visual problems. However, if when starting to read they still squint with first one eye then the other, that is they alternate, not using their eyes together, then they may see words move as they fix first with the left then the right eye. In such a rare situation an Orthoptist can give advice.

(3) Eye and Headache
Any child with persistent headaches should be seen by their GP. However, rubbing of eyes and complaints of aching only associated with reading, may be due to any of the problems already mentioned, which give increased need for concentration, and is tiring for the child. There is always the fact that a bright child having difficulty learning to read suffers psychological problems associated with failure in school, and complaints of eye and headache may be a cry for help, or an attempt to avoid reading. Recognition of the condition and understanding by parents and teachers goes a long way to overcoming many such problems.

(4) Words that appear double.
Words appear double when the two eyes stop working together and move apart, no longer both fixing on the same target in space. This is usually due to failure of convergence, which is closely linked to accommodation. Thus words may go blurred and double. This is obviously confusing when trying to read, and the child should be referred to an Orthoptist, Optician of Ophthalmologist. Any associated refractive error will first be corrected, and then simple exercises can be given. The child has to learn to pull both eyes inward towards the nose, maintaining a single image. Practise over a few weeks usually improves the control of the eyes. Conditions like this should not be left untreated, as they tend to get worse. (Evans et al 1994).

(5) Larger print is easier to read than small print.
Most small children prefer to read large print not because they cannot see the smaller print clearly, but because the gaps between the words are also larger. Any difficulty that makes letters move about is less confusing when there is a gap for the letters to move to without interfering with the next word. However, this complaint may suggest the child is having confusion with print and should lead to further questioning as to what the child sees on the page. (Cornelissen 1991).

(6) Glare and sensitivity to light
Some children and adults with or without reading problems complain of glare of the black print against the white background. Light shining on white rather than blackboards. Basically the background appears to interfere with the print. They may see patterns in the gaps between lines and words, which can be distracting, can cause headache and migraines. (Wilkins & Nimmo-Smith 1984)

The use of tinted coloured glasses has been particularly successful in treating these conditions. Many High Street opticians now have a Colourimeter, which enables an individual choice as to the preferred colour to stop the individuals symptoms. Most choose the blue, mauve end of the spectrum to overcome these problems of glare. A fuller investigation by specially trained teachers or psychologists can also be carried out by The Irlen Institute, where an even wider range of colours is provided. Mixing of colour shades may be of some value, but can add to the difficulties of child to choose, and prevents scientific analysis of why such colours may be helpful and costs even more.

However, a much cheaper and often just as successful option is to first try blue, green, pink and yellow plastic coloured overlays.

Blue not only appears to reduce glare, but also the apparent motion of print. If the trial with overlays is successful, coloured glasses can often be found in trendy shops where they are sold more as a fashion accessory, rather than expensive individual glasses.

Children who complain that words seem to shimmer or shake, rather than actually move, may also be helped by blue glasses, or overlay. Some children find it easy to explain what they see on a page of print, but others may use the word "blur" to cover a multitude of visual confusions, so careful questioning is needed.

Please remember that the idea that subtle disturbance of eye movement control can cause great confusion when learning to read, while marked, much more serious abnormalities, fail to have such an effect. This fact is still causing reluctance by some practitioners to accept the visual problems associated with reading. If you are told that the child sees very clearly and uses his eyes together well, in the absence of more detailed investigation of eye movement control, please ask for referral to an Orthoptist or specialised Optometrist, if the child continues to complain of obvious visual symptoms.

The investigation of visual problems related to reading are carried out by some Opticians and Optometrists, but their services have to be paid for and special glasses can be expensive. If a child have visual symptoms associated with reading they can be referred to their GP, to an Orthoptist in the Eye Clinics of most NHS hospitals, free of charge to the patient.

The Dyslexia Research Trust runs a charity funded research clinic in the Royal Berkshire Hospital in Reading, Berks where children with visual symptoms can be referred free of charge to a patient or GP. (Contact Dyslexia Research Trust at Magdalen College, Oxford OX1 4AU. Telephone: 0118 934 0580 or email:

Because not all dyslexics have problems with visual processing it doesn't mean that no dyslexics have visual problems. It is important that those who do suffer from visual problems are identified so that the appropriate treatment can be given.

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Robinson, D.A (1981) Neurophysiology of eye movements. Annual review Neuroscience 4, 463-503.

Seymour, P (1986) Cognitive Analysis of Dyslexia. London: Rowledge & Kegan Paul.

Stein, J.F & Fowler, M.S (1985) Effect of Monocular Occlusion on visuomotor perception and reading in Dyslexic children. Lancet 11, 69-73.

Stein, J.F, Richardson, A.R, Fowler, M.S (2000) Monocular Occlusion improves binocular control and reading in dyslexics. Brain 123, 101-107.

Wilkins, A.J & Nimmo-Smith, I (1984) On the reduction of eyestrain when reading Ophthalmic & Physiological Optics (1) 53-59.

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