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is shaped a little more like a rugby ball. This causes another type of
refractive error, astigmatism.
The lens inside the eye can vary its focus. This allows a normal eye
to change focus (accommodate) from the relaxed state, when it is
focussed for distance vision, to an accommodated state, for near
vision. The lens loses its ability to focus with age, which is why most
people in their mid-forties start to need reading glasses.
When a young person views objects close to, such as a book, the
eyes not only accommodate, but also turn inwards (converge) to align
on the object (Chapter 3). The accommodation and convergence are
linked, so that for a given amount of accommodation the eyes usually
converge to a predictable degree. This can be a problem for children
with long-sightedness who may use accommodation to compensate
for long-sightedness, causing them to over-converge. This is a common
cause of an eye turning inwards (convergent strabismus). In other
words, refractive errors can cause problems with eye alignment,
resulting in binocular vision anomalies.24 Binocular vision anomalies,
and their relationship with reading difficulties, are discussed further in
Chapter 3.
Are refractive errors associated with reading difficulty?
Experiments with lenses that induce blur find a reduced accuracy
and rate of reading.25 Myopia, astigmatism and anisometropia do not
seem to have an atypical prevalence in patients with reading
difficulties,
4 18
and the rest of this section will concentrate on
hypermetropia. In recent years, the prevalence of myopia has
increased markedly. In East Asia, nearly all university students are
myopic. In the UK, just over half of university students are myopic, and
the prevalence is increasing.26 Significant myopia will cause blurred
Chapter 2 Refractive errors & ocular health
27
distance vision, impairing a child’s ability to read the white board in
class. Myopia is relatively uncommon in the early school years, when
vision screening takes place. Also, children may not report blurred
distance vision, because it develops gradually. This is one reason why
all children should have regular eye examinations.
In children, there is a weak association between hypermetropia and
impaired visual perceptual skills27 and reading difficulties.28 The
relationship with reading persists after adjustment for differences in
intelligence, sex, and socioeconomic group.28 A large multi-centre
study of pre-school children found that uncorrected hypermetropia is
associated with lower levels of literacy, although this study did not
control for IQ.29 A similar finding in a study of secondary school
children,30 is also difficult to interpret because the study did not control
for IQ.28 It is important to control for IQ when researching refractive
error, because there is a slight but statistically significant tendency for
myopia to be associated with higher IQ.
28 31 32
Since these studies of the general population show a weak
association between hypermetropia and reading difficulties, it is
perhaps surprising that hypermetropia does not seem to be more
likely to occur in dyslexia than in normal readers.
3 4
In any event,
hypermetropia is so common that it is often found in any cross-section
of children, including those with dyslexia.
Do refractive errors contribute (causally) to reading difficulty?
In general terms, there is evidence that the correction of clinically
significant refractive errors can improve children’s cognitive and
educational well-being, psychological well-being, mental health, and
quality of life.33
Even if there is an association between hypermetropia and reading
difficulty the association is not necessarily causal. However,
Vision, Reading Difficulties and Visual Stress
28
hypermetropia is also associated with poorer visual perceptual skills
than are myopia or emmetropia,34 and this can be improved with early
correction of the hypermetropia.
35 36
This supports the view that, at
least in some cases, hypermetropia can be a cause of reading difficulty.
In young adults, the routine correction of low degrees of
hypermetropia does not have a significant effect on reading speed37,
but may have an effect when symptoms are present.38 In older adults
(over the age of 35 years), when the eyes are losing the ability to
accommodate, reading glasses significantly improve the speed of
reading.37 This is not linked to dyslexia, but a part of the ageing process
that will affect everyone, unless they are short-sighted.
How are refractive errors detected?
Visual acuity tests are useful to detect myopia, but are not reliable
for detecting hypermetropia in children.
30 39
Typically, vision screening
includes only tests of visual acuity and this is another reason why
children should have regular eye examinations.30
Although refractive errors are not strongly correlated with reading
difficulties, eye care practitioners will occasionally encounter cases of
suspected reading difficulties or dyslexia who turn out simply to have
uncorrected refractive errors.
Chapter 2 Refractive errors & ocular health
29
For example, astigmatism is an optical error of the eye which
requires correction by spectacles or contact lenses. High uncorrected
astigmatism is not strongly correlated with reading difficulty. This
statement means that research studies that have compared a group of
dyslexic children with a group of good readers do not find more
astigmatism in the dyslexic group. However, anyone can have
astigmatism and if this is present and not corrected it can make reading
more difficult for any child, whether dyslexic or not. A child presenting
with uncorrected astigmatism could be misdiagnosed as having
dyslexia, when in fact their difficulty is attributable to the astigmatism
Case study 2.1
A 29 years-old lady consulted an optometrist for her
first eye examination. She had underachieved at
school and was now engaging in adult education,
leading to referral to an educational psychologist. The
psychologist had diagnosed dyslexia and, noting visual
symptoms, the psychologist suspected visual stress.
Symptoms included text blurring and eyestrain.
Examination at presentation revealed reduced visual
acuities and a significant degree (three dioptres in the
right eye; four dioptres in the left eye) of myopic
astigmatism. All other optometric test results were
normal.
Spectacles were prescribed and with these, the
symptoms fully resolved. On questioning, the lady had
never undergone an eye examination or vision
screening, and thought her vision had been the same
all her life.
Vision, Reading Difficulties and Visual Stress
30
alone.40 Case study 2.1 illustrates a case who may have been mis-
diagnosed as having a learning difficulty when the underachievement
was attributable, at least in part, to uncorrected astigmatism.
Case study 2.1 is an example of a missed refractive error. When the
astigmatism was corrected, the reading skills rapidly improved.
Therefore, it seems possible the person was mis-diagnosed with
dyslexia.
Eye care practitioners who specialise in vision and learning will also
encounter another type of case, perhaps more commonly, where
visual stress is misdiagnosed as refractive error. Case study 2.2 is a
person who had visual stress misdiagnosed as uncorrected refractive
error.
Case study 2.2
Background
▪ 10 year-old boy referred to one of the authors
because of specific learning difficulties.
Symptoms
▪ With books and the white-board: text initially
clear, then blurs, moves, and doubles and causes
sore & tired eyes. Tends to skip words when
reading
History
▪ Reported these symptoms to an optometrist
about a year ago who prescribed spectacles with
a low/insignificant correction for longsightedness (R=L=+0.50DS)
▪ Patient and parents report the glasses were no
help and were soon discarded
Presenting
vision
▪ R6/6+ L6/6 (normal in each eye)
Refractive
error
▪ Retinoscopy: R+0.25DS L plano
▪ Subjective: R=L= plano (normal)
Chapter 2 Refractive errors & ocular health
31
Ocular
health
▪ Ophthalmoscopy, visual fields, pupil reactions,
colour vision (Ishihara) all normal
Ocular
motor
balance
▪ The tests described in this section indicate that
eye alignment and focussing was normal
▪ Cover test: D orthophoria N 2 XOP
▪ Convergence, accommodation, fusional reserves,
AC/A, stereopsis all normal, no fixation disparity
at D or N
▪ Accommodative accuracy (MEM): R=L=+0.50DS
Visual stress
▪ Pattern glare test: positive response to Pattern 2
▪ When viewing text patient reports that it blurs,
moves, & eyes hurt. +0.50DS R&L has no effect
on these symptoms.
▪ Consistent response to testing with Intuitive
Overlays, reporting that mint-green overlay
eliminates the above symptoms
▪ Issued with mint-green overlay to try
▪ Returns after 1 month reporting that parents,
teacher, and child have noticed improvement
▪ Consistent response to testing with Intuitive
Colorimeter & Precision Tinted Lenses
(as explained later in this book, these results
indicate visual stress was present)
Management
▪ Prescribed Precision Tinted lenses to use for
class, homework, reading
Follow-up
▪ Parents & teachers report improvement
▪ Child reports precision tints alleviate symptoms
AC/A, accommodative convergence to accommodation ratio; D, distance;
DS, dioptres spherical; L, left; MEM, monocular estimate method of testing
accommodative lag; N, near; R, right.
Vision, Reading Difficulties and Visual Stress
32
Cases like that in Case study 2.2 are perhaps not surprising. When
eye care practitioners who are not familiar with visual stress encounter
a patient reporting blurred vision during reading it is understandable
that the practitioner suspects refractive error. If the practitioner
encounters a normal degree of hypermetropia, they may be tempted
to try a refractive correction in the hope of alleviating blurring, even
though the low level of hypermetropia would not normally cause blur.
The normal result for tests of accommodation and binocular vision
(Chapter 3) in this case indicates that such a correction is unlikely to be
helpful and this was the patient’s experience. Testing with coloured
overlays revealed a colour that eliminated the symptoms, and
subsequent tests and feedback indicate that visual stress is the most
likely cause of the blurring in this case. Visual stress is explained further
in Chapters 6-11.
How are refractive errors corrected?
There is considerable debate as to when hypermetropia in children
should be corrected with spectacles.
27 41-45
It is important to take
account of symptoms and, in view of the relationship between eye
alignment and refractive error, practitioners should consider tests of
eye alignment (binocular coordination) and accommodation (Chapter
3) when deciding whether to prescribe.24
Some optometrists argue that children with SpLD routinely should
be prescribed low power convex (low plus) lenses (e.g., R=L=+0.50DS),
sometimes euphemistically called ‘reading lenses’. A review found no
convincing experimental evidence of a benefit from such
prescriptions.46 The College of Optometrists in the UK have cautioned
against prescribing low prescriptions, unless there is recorded
evidence of a clinical need.47 Examples of a clinical need are some eye
Chapter 2 Refractive errors & ocular health
33
alignment problems or a weakness of the muscles that focus the eyes
close to (accommodative insufficiency; discussed in Chapter 3).
24
One study that compared a group of dyslexic children with controls
found three times as many dyslexic participants (42%) had been
prescribed spectacles compared with the control group (14%).
48
However, the proportion of both groups who were using spectacles
was similar48 and the distribution of refractive error in the two groups
also was similar.18 There are several likely explanations for this finding:
parents of dyslexic children are more likely to seek optometric care,4
optometrists may be predisposed to correct low refractive errors
because they want to try to help children with reading difficulties, and
the increased prevalence of symptoms from other conditions such as
visual stress and binocular instability may be misinterpreted by
practitioners as a need for refractive correction (see Case study 2.2).
The scientific evidence justifies a conservative approach to prescribing
refractive corrections in these cases: a refractive error that would not
normally be corrected should not be corrected just because a child is
dyslexic.
Summary
Ocular pathology and refractive error do not seem to be commonly
associated with dyslexia, but hypermetropia can contribute to reading
difficulties. Refractive errors are common in the population, and it is
sensible for children with reading difficulties to have an eye
examination so that uncorrected refractive errors can be dealt with
appropriately. There is no good evidence that a low refractive error is
any more likely to require correction in people with reading difficulties
than in the general population. In Chapter 10, the clinical protocol for
testing people with reading difficulties is discussed in more detail.
Vision, Reading Difficulties and Visual Stress
34
References
1. Legge GE, Rubin GS, Pelli DG, Schleske MM. Psychophysics of reading--II.
Low vision. Vision Res. 1985;25(2):253-65. doi: 10.1016/00426989(85)90118-x.
2. Al-Bakri M, Skovgaard AM, Bach-Holm D, Larsen DA, Siersma V, Kessel L.
School performances in children with cataract: results from a
population-based cohort study. BMJ Open. 2023;13(8):e072984. doi:
10.1136/bmjopen-2023-072984.
3. Evans BJW, Drasdo N. Review of ophthalmic factors in dyslexia. Ophthal
Physiol Opt. 1990;10:123-32.
4. Evans BJW. Dyslexia and Vision. Chichester: Wiley; 2001.
5. Rima S, Kerbyson G, Jones E, Schmid MC. Advantage of detecting visual
events in the right hemifield is affected by reading skill. Vision Res.
2020;169:41-8. doi: 10.1016/j.visres.2020.03.001.
6. Kermani M, Verghese A, Vidyasagar TR. Attentional asymmetry between
visual hemifields is related to habitual direction of reading and its
implications for debate on cause and effects of dyslexia. Dyslexia.
2018;24(1):33-43. doi: 10.1002/dys.1574.
7. Facoetti A, Turatto M. Asymmetrical visual fields distribution of attention
in dyslexic children: a neuropsychological study. Neuroscience Letters.
2000;290:216-8.
8. Asberg Johnels J, Galazka MA, Sundqvist M, Hadjikhani N. Left visual field
bias during face perception aligns with individual differences in reading
skills and is absent in dyslexia. Br J Educ Psychol. 2022. doi:
10.1111/bjep.12559.
9. Hari R, Renvall H, Tanskanen T. Left minineglect in dyslexic adults. Brain.
2001;124(Pt 7):1373-80. doi: 10.1093/brain/124.7.1373.
10. Rutkowski JS, Crewther DP, Crewther SG. Change detection is impaired in
children with dyslexia. J Vis. 2003;3(1):95-105. doi: 10.1167/3.1.10.
11. Polikoff BR, Evans BJW, Legg CR. Is there a visual deficit in dyslexia
resulting from a lesion of the right posterior parietal lobe? Ophthal
Physiol Opt. 1995;15(5):513-7.
12. Pammer K, Wheatley C. Isolating the M(y)-cell response in dyslexia using
the spatial frequency doubling illusion. Vision Research.
2001;41(16):2139-47.
13. Edwards JD, DeLeon J, Bearden WH, Rumble ME, Girkin CA. Is reading
disability likely to interfere with glaucoma screening of adults using
frequency-doubling technology perimetry? Am J Ophthalmol.
2003;135:816-20.
14. Evans BJW, Busby A, Jeanes R, Wilkins AJ. Optometric correlates of
Meares-Irlen Syndrome: a matched group study. Ophthal Physiol Opt.
1995;15(5):481-7.
15. Scott JC, McWhinnie H, Taylor L, Stevenson N, Irons P, Lewis E, et al.
Coloured overlays in schools: orthoptic and optometric findings. Ophthal
Chapter 2 Refractive errors & ocular health
35
Physiol Opt. 2002;22:156-65.
16. Norn MS, Rindziunski E, Skydsgaard M. Ophthalmologic and orthoptic
Vision, Reading Difficulties and Visual Stress
36
examination of dyslexia. Acta Ophthalmol. 1969;47:147-60.
17. Pinckers A. Color vision and age. Ophthalmologica. 1980;181(1):23-30.
doi: 10.1159/000309021.
18. Evans BJW, Drasdo N, Richards IL. Refractive and sensory visual
correlates of dyslexia. Vision Research. 1994;34(14):1913-26.
19. Solebo AL. Identification of visual impairments. In: Emond A, editor.
Health For All Children. Fifth ed. Oxford: Oxford University Press; 2019.
20. Thomson WD, Evans BJW. A new approach to vision screening in schools.
Ophthal Physiol Opt. 1999;19(3):196-209.
21. Bailey IL, Lovie JE. New design principles for visual acuity letter charts.
Am J Optom Physiol Opt. 1976;53(11):740-5.
22. Barnard NA. Visual conversion reaction in children. Ophthalmic Physiol
Opt. 1989;9(4):372-8.
23. Veszeli J, Shepherd AJ. A comparison of the effects of the colour and size
of coloured overlays on young children's reading. Vision Res.
2019;156:73-83. doi: 10.1016/j.visres.2019.01.006.
24. Evans BJW. Pickwell's Binocular Vision Anomalies. Sixth ed. Philadelphia:
Elsevier; 2021.
25. Dickinson PMA, and Rabbitt CM. Simulated visual impairment - effects
on text comprehension and reading speed. Clin Vis Sci. 1991;6(4):301-8.
26. Logan NS, Davies LN, Mallen EA, Gilmartin B. Ametropia and ocular
biometry in a U.K. university student population. Optom Vis Sci.
2005;82(4):261-6.
27. Roch-Levecq AC, Brody BL, Thomas RG, Brown SI. Ametropia,
preschoolers' cognitive abilities, and effects of spectacle correction. Arch
Ophthalmol. 2008;126(2):252-8.
28. Stewart-Brown S, Haslum MN, Butler N. Educational attainment of 10year-old children with treated and untreated visual defects. Dev Med
Child Neurol. 1985;27(4):504-13.
29. Kulp MT, Ciner E, Maguire M, Moore B, Pentimonti J, Pistilli M, et al.
Uncorrected hyperopia and preschool early literacy. Ophthalmology.
2016;123(4):681-9. doi: 10.1016/j.ophtha.2015.11.023.
30. Quaid P, Simpson T. Association between reading speed, cycloplegic
refractive error, and oculomotor function in reading disabled children
versus controls. Graefes Arch Clin Exp Ophthalmol. 2013;251(1):169-87.
doi: 10.1007/s00417-012-2135-0 [doi].
31. Williams SM, Sanderson GF, Share DL, Silva PA. Refractive error, IQ and
reading ability: a longitudinal study from age seven to 11. Dev Med Child
Neurol. 1988;30(6):735-42. doi: 10.1111/j.1469-8749.1988.tb14635.x.
32. Saw SM, Tan SB, Fung D, Chia KS, Koh D, Tan DT, et al. IQ and the
association with myopia in children. Invest Ophthalmol Vis Sci.
2004;45(9):2943-8.
33. Govender-Poonsamy P, Yong AC, Mashige K, Naidoo K, Chan V. The
impact of spectacle correction on the well-being of children with vision