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Visual factors and reading difficulty.

This article provides an overview of the visual factors associated with reading difficulties in school-aged children.

Optometrists ***

Dispensing opticians **



Learning to read is a complex and demanding skill, which is vital in order to be able to access a broad curriculum of learning within the school environment. If a child does not learn to read adequately they may struggle to access other areas of the curriculum, which may have an impact on employment prospects and future success as adults.

Visual problems can be present in both 'good' and 'poor' readers; it is generally accepted that they are not the cause of reading difficulties but have been found to be correlates of reading difficulty. (1,2) However, visual problems may result in a child finding reading uncomfortable resulting in a reluctance to read or difficulty reading for long periods. Thus, visual problems may present an additional barrier to successful reading and subsequently accessing other areas of the curriculum. Children who have difficulties with reading may present with multiple deficits across many different skills associated with reading, (3) and vision may be only part of the problem.

The purpose of this article is to provide an overview of the visual factors associated with reading difficulties in school-aged children. The aim is to provide eye care practitioners with the ability to recognise which visual problems may contribute to reading difficulties, what to look for, and where to refer if necessary.

A child experiencing reading difficulties

Children struggling with reading may consult an optometrist if visual signs or symptoms are present; these may be noticed by the child or may have been observed by a parent or teacher. However, children may be unaware that what they experience is abnormal and, therefore, not report any symptoms. It is important for careful questioning to take place to determine whether any visual signs and symptoms are present which may need further assessment or onward referral to another professional.

It is important to ask how the child is doing at school. Are they meeting the expected standards for reading? Do they enjoy reading? Do they find reading comfortable? A child may be achieving the expected standards in reading but may still experience visual difficulties.

If a child is deemed to have good visual function (good acuity and no significant refractive error) during a sight test but has not had a sufficiently thorough examination to look for other reasons for the visual difficulties, problems may go undetected and children may suffer with unnecessary visual discomfort. It is the author's experience through working both in the University of Bradford Eye Clinic and during research that some children who have had a sight test and been told that their vision is fine continue to suffer from undetected visual problems giving rise to visual symptoms while reading. This may be due to undetected latent hyperopia and/or undetected binocular vision anomalies, such as convergence insufficiency, decompensated heterophoria, or accommodative insufficiency/infacility. Ideally, optometrists should be detecting these visual anomalies during a routine sight test.

Ocular health and refractive error

A routine sight test should establish whether any visual difficulties might be in part due to refractive error or pathology. Uncorrected refractive error, particularly uncorrected hyperopia, may cause blurred text, eyestrain, headaches and accommodation difficulties. Cycloplegic refraction should be considered when symptoms of near visual difficulties are present. Other indicators for cycloplegic refraction are low amplitude

of accommodation and increased accommodative lag which may suggest that the child is already compensating for a degree of hyperopia.

Binocular vision and accommodation

The resolution of text requires a well-functioning visual system, which includes adequate coordination of the eyes in addition to satisfactory visual acuity. Many studies have examined visual factors involved in reading, comparing groups of children with reading difficulties versus controls. Groups of 'poor' readers have been found to show reduced amplitudes of accommodation, (1,4,5) reduced accommodative facility, (4,5) reduced vergence amplitudes (1,5) and reduced near point of convergence, (4) and have poorer saccadic eye movements, (6,7) compared to control groups.

It is important to eliminate any binocular vision difficulties or accommodative dysfunction as potential contributing factors to visual symptoms while reading. Signs and symptoms of binocular vision disorders may include: blur, diplopia, headaches, eyestrain, difficulty changing focus, or movement of text. A thorough examination should be completed to include measurement of heterophoria/heterotopia (ocular alignment), vergence amplitudes and /or fixation disparity, near point of convergence, amplitudes of accommodation, accommodative facility, and assessment of saccadic function. Recent articles provide detailed explanations of examining ocular alignment, (8) and accommodative function, (9) in everyday practice. It is worthwhile including a measure of accommodative accuracy in those patients presenting with visual complaints at near; this can easily be done with a retinoscope using the MEM or Nott methods, details of which can be found elsewhere. (10) Most accommodation and / or vergence disorders can be easily corrected with eye exercises and /or refractive correction by optometrists or orthoptists. Table 1 provides an overview of the diagnostic criteria for binocular vision disorders relevant to near visual function.

Case report

Here is an example of a case, which is typical of many that the author has encountered in practice. A child was referred to participate in the author's research project at the University of Bradford Eye Clinic, as they were experiencing visual symptoms while reading. The child's teacher had expressed concern, as the child's difficulties with reading were not consistent with her overall academic performance. Screening for specific learning difficulties such as dyslexia within school had not indicated any below average performance. The child had previously had a routine sight test and was told that their vision was fine. On careful questioning it was clear that the child was getting diplopia while reading. After a thorough examination of their binocular vision it was noted that they could not converge any closer than 46cm (convergence insufficiency). Exercises and prismatic correction were required to manage the difficulties. Had the convergence problem been discovered earlier as part of a routine eye examination, prompt management could have taken place, resulting in less distress to the child.

What binocular vision tests should be included in a routine eye examination?

Optometrists are qualified eye care practitioners who have been trained to assess binocular vision. It is important that children have access to a thorough examination of binocular vision and accommodative function, particularly if they are experiencing near visual symptoms and/or difficulties with reading. It is feasible to include the following basic tests during a routine sight test: measurement of heterophoria, fixation disparity, near point of convergence, and amplitudes of accommodation. If the results of these tests indicate a problem, or visual symptoms are present that are suggestive of visual difficulties, onward referral to an orthoptist/specialist optometrist should be made for a more in-depth assessment. These children should not be discharged and told that their vision is fine; if they are presenting with visual difficulties it is important to find the origin of the symptoms, otherwise the child will continue to struggle with demanding near visual tasks such as reading.

Visual stress (VS)

Visual stress refers to a condition often termed Meares-Irlen syndrome, Irlen syndrome, or scotopic sensitivity syndrome. The terms all refer to a collection of signs and symptoms of visual distortions and discomfort, which an individual may experience when viewing text, particularly with closely spaced black text upon a white background. (11-13) Symptoms may include: blurring and/ or movement of text; patterns within text; disappearance of text; discomfort when viewing text; the appearance of rivers within text; and sensitivity to artificial lighting and bright light in some individuals. These symptoms appear to be alleviated with the use of coloured overlays or tinted lenses. (14) The practice has attracted criticism mainly due to the nature of the testing and the difficulty of collecting robust evidence. (15) However, it is a simple and effective treatment for some individuals and protocols have been developed to ensure consistency of assessment methods, with a recent Delphi study being published with suggested guidelines for practice. (16) Assessment should include careful questioning about symptoms, pattern glare assessment, (17) coloured overlay screening, (18) and measurement of reading speed using the Wilkins Rate of Reading Test (WRRT). (19) The Delphi study recommendations for diagnostic criteria are given in Table 2. These were also reported in a recent CET article by Professor Bruce Evans, which provided case studies discussing the assessment of visual factors in children who are underachieving. (20)

Assessments for visual stress are often done by optometrists, orthoptists, those within educational settings, and by Irlen diagnosticians. There are no regulations regarding who can do these assessments. The difficulty with this is that many of the signs and symptoms of visual stress are the same as those for uncorrected refractive error, binocular vision anomalies and accommodative disorders. Often children have a routine eye test, which does not discover any refractive error and then may be provided with coloured overlays in a school setting. If a child does not have access to a thorough assessment of binocular and accommodative function it can result in visual problems going undetected and therefore, untreated.

Visual perception

Visual perception refers to the ability to extract visual information from the environment via the eyes. This information is then related to stored information in the memory regarding past experiences to form the current perception at that time. Visual perception is how the brain interprets the visual information that is processed. Aspects of visual perception include: visual attention; visual closure; visual form constancy; visual discrimination; visual figure-ground discrimination; and visual memory. (21) Difficulties with visual perception may make it difficult for an individual to make sense of the information that is processed. Table 3 outlines a description of visual perceptual skills often assessed and the signs that may be noticed if a difficulty is present.

During reading, the process of extracting information from the text being read requires attending to the letters and words (visual attention, figure-ground), the processing of features of the letters and words such as size, shape and contrast (position in space, form constancy, visual closure) and the holding of visual information in memory (visual short-term/ working memory).

Early studies found a relationship between visual perception and reading ability, (22-24) but other researchers have disputed the relationship. (25,26) To attempt to clarify the relationship, a meta-analysis was conducted to include the results of 161 studies, which concluded that visual perception accounted for between 11% and 17% of the variance in reading skills and that visual perceptual skills were important correlates of reading achievement and that testing of visual perception should be included in a complete assessment of factors associated with reading difficulty. (27) To add further to the importance of visual perception, a longitudinal study found that visual spatial attention in pre-school children predicted future acquisitions of reading skills and that selective visual spatial attention was impaired prior to learning to read. (28)

How are visual perception skills assessed?

Characteristics of visual perception may be assessed by: educational psychologists as part of a wider cognitive assessment; occupational therapists; optometrists with a special interest in children with learning difficulties; and in NHS-funded orthoptist-led specific learning difficulties clinics. Visual perceptual skills are often assessed using standardised assessment tests such as the Developmental Test of Visual Perception (DTVP-2), (29) and the Test of Visual Perceptual Skills (TVPS). (30) These assessments often take the form of picture matching tests where a child is presented with an image and must choose the matching image from a number of other images, which have been altered slightly. However, it is useful for eye care practitioners to be aware of the possibility of visual perceptual problems if visual symptoms persist despite correction of any refractive or oculomotor difficulties or VS. If a child has normal visual acuity, normal binocular vision and no evidence of VS but still presents with visual difficulties such as losing their place while reading, confusing words, skipping words and/or reversing letters then they could have visual perceptual problems.

Can visual perception problems be treated?

Investigation and training of visual perceptual skills is now principally offered by orthoptists within specialist specific learning difficulties clinics. The protocol for the clinics is first to assess and treat any binocular vision or accommodation problems, then look at saccadic eye movements, then VS. If symptoms suggest that there may be other visual difficulties present then visual perceptual skills are assessed and treatment given if deemed necessary. Exercises can be done at home using apps and games to improve visual perceptual skills. A good source of information regarding the orthoptic clinics can be found here: http:/ /www.whh. Optometrists with a special interest in children with learning difficulties also provide assessments for visual perceptual difficulties, which are charged privately. Help can also be sought from occupational therapists if a significant impact on daily living can be established and referral is usually via the patient's general practitioner.

Evidence for the effectiveness of visual perception training alone is difficult to obtain as more than one intervention will be given to a child, thus making it difficult to know the relative benefits of each intervention. A recent study examined the effects of training visual perception skills in 10 participants with dyslexia versus 10 controls, reporting improvements in visual perception skills in both groups but to a greater extent in the dyslexic group. (31) However, no assessment was made regarding any gains in reading ability. Another study found that audio-visual training in Finnish children (aged seven years, n=48) with dyslexia resulted in neural changes, but more importantly the changes transferred to improvement in reading skills. (32)

Communication of findings

If a child is struggling with near visual difficulties and has been assessed by an optometrist and / or orthoptist, it would be useful if a report could be provided to parents/teachers detailing what, if any, difficulties have been found, how these difficulties may affect learning in the classroom and what treatment has been given. This enables parents and teachers to make adjustments where necessary to help the child reach their potential. Without this information, teachers may be unaware of how any visual problems may be affecting the child or whether the child should be complying with any spectacle wear or eye exercises during the school day.


Reading is a complex task and when difficulties arise they may be due to one or more of the factors involved in the reading process. It is important for eye care professionals to have an awareness of what visual problems may contribute to any reading difficulty, what to look for and where to send the patient for further assessment if necessary. Often visual symptoms while reading can require more than one intervention. Specialist eye care practitioners are best placed to examine the visual system in its entirety to establish whether visual difficulties may be contributing to any reading problems. Children may benefit from more than one visual intervention; thus, it is important to get a picture of the whole of the visual function of the child, which may require assessments across many different aspects of vision.

Exam questions and references

Under the enhanced CET rules of the GOC, MCQs for this exam appear online at Please complete online by midnight on 21 June 2019. You will be unable to submit exams after this date. Please note that when taking an exam, the MCQs may require practitioners to apply additional knowledge that has not been covered in the related CET article.

CET points will be uploaded to the GOC within 10 working days. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website ( to confirm your points.

Visit, and click on the 'Related CET article' title to view the article and accompanying 'references' in full.

Course code: C-70386 Deadline: 21 June 2019

Learning objectives

* Be able to elicit relevant detail from children presenting with reading difficulties (Group 1.1.2)

* Be able to understand the range of assessments required to assess children presenting with reading difficulties (Group 7.1.3)

* Be able to undertake a careful binocular vision assessment on children presenting with reading difficulties (Group 8.1.1)

* Be able to elicit relevant detail from children presenting with reading difficulties (Group 1.1.2)

* Be able to understand the range of assessments required to assess children presenting with reading difficulties (Group 7.1.3)

Dr Caroline Chambers PhD, MCOptom

Dr Caroline Chambers is an optometrist and researcher who has a PhD in the area of reading difficulties, at the School of Optometry and Vision Science, University of Bradford. Dr Chambers works part-time in independent practice and supervises on the undergraduate optometry programme at the University of Bradford.
Table 1 Criteria for diagnosis of binocular vision/accommodative
anomalies at near

Anomaly          Definition            Criteria for diagnosis

Accommodative    Low accommodation     Low AA, fails--AF, low
insufficiency    causing               PRA, high AL
                 difficulties with
                 near focus

Accommodative    Initially             As above but initially
fatigue          accommodation is      AA is normal but
                 fine but easily       decreases on repeated
                 fatigues on           testing
                 repeated use/
                 testing causing
                 difficulties with
                 sustained near

Accommodative    Spasm of              Fails + AF. Low NRA,
excess/ spasm    accommodative         esophoria at near
                 function causing
                 asthenopia at near,
                 variable near and
                 distance vision

Accommodative    Slow accommodation    LowAF, low PRA and NRA
infacility       response when
                 switching from near
                 to far focus and
                 back, commonly
                 presents as
                 distance blur when
                 looking up from

Convergence      Difficulty            EXOP at near, reduced
insufficiency    converging the eyes   PRV at near, receded
                 for near focus        NPC, low BO VF. Fails +
                 causing diplopia      AF, low NRA, low MEM,
                 and blur              fails FD

Convergence      Too much              ESOP greater at near
excess           convergence of the    than distance, high AC/
                 eyes at near          A ratio, low NRV at
                 causing asthenopia    near, fails FD
                 and blur

Note: AA=amplitude of accommodation, AF=accommodative facility,
PRA=positive relative accommodation, NRA=negative relative
accommodation, AL=accommodative lag, EXOP=exophoria,
ESOP=esophoria, FD=fixation disparity, VF=vergence facility. Signs
in bold italic are classed as fundamental signs of a binocular
dysfunction. (33) Other signs are complementary.

Table 2 Diagnostic symptoms and signs of visual stress from Delphi
Study by Evans and colleagues (16)

Symptoms (at least three should    Signs (two out of three required)
be present)

Words move                         Voluntary unprompted use of an
                                   overlay for three months or more

Words merge                        Improvement in performance on the
                                   WRRT of [greater than or equal to]
                                   15% using an overlay

Patterns or shapes in text         Pattern glare test result >3 with
                                   the mid-spatial frequency grating

Text appears to stand out in 3D
above the page
Words or letters fade or darken
Discomfort with certain
artificial lights and flicker

Table 3 Visual perception characteristics and explanations
of dysfunction

Perceptual       Explanation of skill        Practical difficulties
skill                                        faced if skill is

Position in      The ability to perceive     Letter reversals,
space            the correct position of     spacing of letters,
                 an object, important in     losing place, problems
                 recognising the             differentiating
                 orientation of letters/      'b.d.p.q ', poor sight
                 words                       vocabulary

Figure-ground    The ability to              Finding a shape in a
                 distinguish foreground      collection of shapes/
                 from background. Often      items, attending to
                 examined by using visual    words on page difficult
                 search tasks                as problems blocking the
                                             surrounding words

Form             The ability to identify     Letter confusions
constancy        letters despite changes      'p,q,g ' which may
                 in font size and style -    result in reversing
                 important for reading       letters. Difficulty
                 different fonts             understanding words
                                             written in different
                                             handwriting styles

Visual           The ability to recognise    May have difficulties
closure          a stimulus, which is        recognising whole words
                 incompletely drawn by       and have to study each
                 mentally completing the     word individually; this
                 images                      can result in slower
                                             reading speed

Visual           The ability to detect       Difficulties with
discrimination   difference and              confusion of similar
                 similarities between        letters and words
                 symbols and forms

Visual memory    The ability to remember     May have difficulty
                 information for further     remembering new words
                 processing                  resulting in poor sight
                                             word vocabulary.
                                             Difficulty remembering
                                             what has just been read
                                             which may affect overall

Visual           The ability to focus on     May show difficulties
attention        important information for   maintaining attention/
                 processing while blocking   fixation to a word or
                 out other potentially       set of words within a
                 distracting information     large passage of text
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Author:Chambers, Caroline
Publication:Optometry Today
Date:May 1, 2019
Next Article:Seeing double: assessing patients presenting with diplopia.

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