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In young patients, however, symptoms may return after a period of
time even with continued use of the spectacles, and a revised tint is
usually successful in giving a further period of remission. The
necessary change in tint can be substantial, but more frequently it is
relatively slight.9 A change in tint is more common in the young; adults
usually do not require a change in tint and typically only return for
repeat colorimetry if their symptoms return. In an open trial, 80% of
patients were still wearing their tints when followed up one year after
first provision.11 In a clinical audit, over 70% of people prescribed with
precision tinted lenses were still using them over a year later.9
Clinical experience of children with visual stress and reading
difficulties is that often the saturation that is required gradually
lightens over the years. There are exceptions to this, and sometimes
the gradual trend in a given individual is to lighter tints, but there can
be a temporary need for a period with increased tint saturation. The
overall trend toward lighter tints is not surprising in view of the
reducing hyperexcitability of the visual cortex that probably underlies
visual stress, as noted above (Chapter 8).10 For some cases, the
improvement in symptoms over the years means that a time comes
when the patient no longer requires precision tinted lenses.
In assessments of head-injured patients at Opticalm in Ottawa,
Karen Monet (personal communication) has undertaken repeated
colorimetry assessments separated by a year on average. The tint
chromaticity remained remarkably stable, although the lens
transmission increased from one assessment to the next because the
grey dye (necessary to darken the lens during periods of extreme
photophobia) could be reduced.
It is possible that the improvement in symptoms outlasts the use of
the filters. Newman Wright et al.7 in a study of patients with multiple
Vision, Reading Difficulties and Visual Stress
260
sclerosis, divided patients into two groups at random, giving one group
overlays of the selected colours, and the other group grey overlays.
After two weeks’ experience of overlay use, the group that had received
coloured overlays had improved their reading speed not only with the
overlay but also without. No such improvement was seen in the group
that received grey overlays. This group was then given their coloured
overlay, and after experience of its use, they too showed an
improvement in reading speed, both with the overlay and (to a lesser
extent) without. Although these findings suggest that the benefit of
overlays can outlast their use, in this particular group, few patients
continued using their overlays long-term because they preferred to
avoid reading.
Coloured paper
Some individuals with visual stress find coloured paper helpful.
Often fluorescent dyes are added to white paper. The dyes absorb
ultraviolet radiation and emit visible light, making the paper “whiter
than white” in the same way as washing powder. These dyes are not
used in recycled paper, coloured paper or in cream or buff
paper. Coloured paper (with a colour that suits the individual reader)
presumably has an effect similar to that of coloured overlays, but can
be used for writing tasks. There have been no studies of the use of
coloured paper. Just occasionally both coloured lenses and coloured
overlays or coloured paper can be used together, but this is rarely
necessary.
Designing electronic text to minimise visual stress
So far, we have considered the use of coloured filters to change the
apparent colour of paper on which text is printed. However, text often
Chapter 9 Management of visual stress
261
appears on electronic displays and most electronic displays have the
capability of displaying colours within a large gamut. There are many
websites that allow viewers to choose one of several different coloured
backgrounds. There are few that help the user choose the most
appropriate colour, one exception being iPad and iPhone. Users can
choose Settings>Accessibility>Display & Text Size>Colour
Filters>Colour Tint. They can then vary the hue and “intensity” (roughly
saturation) separately, using sliders, without changing brightness.
Similar settings are available for Android, although they differ between
phone manufacturers.
These electronic adaptations are favoured by some children who
would rather avoid coloured filters for cosmetic reasons. The main
limitation of the adaptations is that they can only be used on the device
for which they were developed and would not, for example, assist the
child using a different digital device or when reading a book.
Reading speed depends partly upon the similarity in size and
spacing between one letter stroke and another. In some fonts the word
“minimum” consists of regular strokes. Compare minimum printed in
Times with minimum printed in Open Sans and you can see that Times
has regularly spaced letter strokes whereas Open Sans does not. The
regularity reduces reading speed: it takes longer for the eyes to re-align
after each rapid eye movement (saccade) because the alignment then
has to be more precise, presumably the images of the stripes in the
two eyes can be mismatched.12 With electronic text the user has the
option to choose more readable fonts, and Google Open Sans is an
example of such a font.13
There is also the option to increase line spacing. Generally speaking
it is important to decrease the ratio of x-height to line spacing as much
as practical.13 (x-height is the height of the central body of letters,
ignoring ascenders and descenders). This can mean that small fonts
Vision, Reading Difficulties and Visual Stress
262
are acceptable provided the line spacing is sufficient. As a rule of
thumb, the line separation (baseline to baseline) should be about 3
times the x-height.
Coloured lighting
It is now possible to purchase LED lamps that can be controlled over
WiFi so as to provide light with any colour within a large gamut of
colours. These may provide an alternative to tinted spectacles in
individuals with autism who may find spectacles uncomfortable to
wear. However, it is important to ensure that the electronic circuitry
controlling the LEDs does not result in flicker, and that the gamut of
the lamps is sufficiently large and easily controlled.
Other approaches to reducing symptoms from
visual stress
For some people, coloured filters almost completely eliminate the
symptoms of visual stress but for others they are only partially helpful.
Other strategies that can be used to reduce the symptoms of visual
stress include the following:
• increasing the font size and line spacing so as to maintain or
increase the line spacing relative to x-height;
• avoiding high contrasts by printing work on grey or recycled paper
and using a grey background on interactive white boards;
• where possible, adjusting light levels;
• some people with visual stress experience symptoms from flicker.
These people will find it helpful to avoid fluorescent lights with
magnetic control circuitry and LED lighting that is poorly stabilized.
The slow-motion video (slo-mo) facility on a smart phone can be
Chapter 9 Management of visual stress
263
used to determine whether the lights are flickering. The flicker
may be imperceptible until the movie is played back.
• many modern LED computer screens also flicker as this is an
inexpensive way for manufacturers to dim the screen. The
proportion of the flicker cycle that is the screen is lit is varied to
control the light level, a technique known as pulse-width
modulation (PWM). For some people with visual stress this can
cause discomfort. An internet search for “PWM computer
monitors” is likely to reveal up-to-date information on flicker rates
with different computer screens.
Other tools used in the assessment of visual stress
The Wilkins Rate of Reading test is commonly used in the
assessment of visual stress and was described in Chapter 6. The role
of this test in the assessment of people with suspected visual stress is
described in Chapter 10.
The Pattern Glare Test is also a useful tool in the assessment of
visual stress and it does not require any assessment of colour
preference. This test is described in Chapter 10.
Summary
Contemporary use of coloured filters for treating visual stress has
its basis in the research and protocols reviewed here. The method of
use of coloured filters is described in greater detail in the various test
instructions and instrument manuals and is integrated with other
clinical tests involved in the examination of people with reading
difficulties in Chapter 10.
Vision, Reading Difficulties and Visual Stress
264
References
1. Wilkins AJ, Aldrich A, Lovell-patel R, Allen P, Wilkins A. The repeatability of
colorimetry is precise(ly) as expected. Neuro-Ophthalmology & Visual
Neuroscience. 2018;3:1–6.
2. Evans BJW, Allen PM, Wilkins AJ. A Delphi study to develop practical
diagnostic guidelines for visual stress (pattern-related visual stress). J
Optom. 2017;10(3):161-168. doi: 10.1016/j.optom.2016.08.002..
3. Wilkins AJ, Sihra N, Myers A. Increasing reading speed by using colours:
Issues concerning reliability and specificity, and their theoretical and
practical implications. Perception. 2005;34(1):109-20. doi: 10.1068/p5045.
4. Wilkins A, Sihra N, Smith IN. How precise do precision tints have to be and
how many are necessary? Ophthalmic Physiol Opt. 2005;25:269–76.
5. Waldie M, Wilkins A. How big does a coloured overlay have to be?
Ophthalmic Physiol Opt. 2004;24:57–60.
6. Smith L, Wilkins A. How many colours are necessary to increase the reading
speed of children with visual stress? A comparison of two systems. J Res
Read. 2007;30(3):332-343.
7. Lightstone A, Lightstone T, Wilkins A. Both coloured overlays and coloured
lenses can improve reading fluency, but their optimal chromaticities differ.
Ophthalmic Physiol Opt. 1999;19(4):279-85.
8. Wilkins AJ, Patel R, Adjamian P, Evans BJW. Tinted spectacles and visually
sensitive migraine. Cephalalgia. 2002;22:711–9.
9. Evans BJW, Patel R, Wilkins AJ, Lightstone A, Eperjesi F, Speedwell L, et al. A
review of the management of 323 consecutive patients seen in a specific
learning difficulties clinic. Ophthalmic Physiol Opt. 1999;19(6):454-66.
10. Evans BJW, Stevenson SJ. The Pattern Glare Test: A review and
determination of normative values. Ophthalmic Physiol Opt. 2008;28:295–
309.
11. Maclachlan A, Yale S, Wilkins A. Open trial of subjective precision tinting: a
follow‐up of 55 patients. Ophthalmic Physiol Opt. 1993;13(2):175-8.
12. Jainta S, Jaschinski W, Wilkins AJ. Periodic letter strokes within a word affect
fixation disparity during reading. J Vis. 2010;10(13):2. doi: 10.1167/10.13.2.
13. Wilkins A, Smith K, Penacchio O. The influence of typography on algorithms
that predict the speed and comfort of reading. Vision (Basel). 2020;
12;4(1):18. doi: 10.3390/vision4010018.
Chapter 9 Management of visual stress
265
Chapter 10
Clinical protocol
Chapter abstract
This chapter starts with an introduction outlining the evidence-
based approach, and a flow-chart summarising the typical procedure
for investigating visual factors that may be relevant to reading
difficulties. The limitations of a diagnosis of exclusion, as applied to
visual stress, are discussed. Symptoms are considered in detail, noting
that many symptoms can be caused by a variety of conditions. The
main components of the eye examination are summarised, together
with the diagnosis of binocular and accommodative anomalies and of
visual stress. The key diagnostic tests and criteria for visual stress are
described. This chapter is largely aimed at eye care practitioners but
may also be of interest to education professionals and parents who are
involved in the investigations that eye care practitioners are likely to
undertake. The last two sections of the chapter, which relate to funding
and finding an appropriate practitioner, are also likely to be of interest
to non-eye care practitioners.
Introduction
The role of the eye care practitioner when assessing people who
struggle with reading is to detect and treat any visual problems that
may be contributing to reading difficulties,1 or causing additional
barriers that might deter a child from accessing education. A person
does not need to have been diagnosed as having a condition such as
dyslexia before seeking help from an eye care practitioner. Indeed, it
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024
A. J. Wilkins and B. J. W. Evans, Vision, Reading Difficulties and Visual Stress,
https://doi.org/10.1007/978-3-031-65568-5_10
267
would seem sensible for any children whose teachers or parents
Vision, Reading Difficulties and Visual Stress
268
suspect underachievement at school to have a detailed investigation
with a practitioner who has specialised in vision and learning.
Optometrists and registered dispensing opticians have a statutory duty to
assist patients in making informed decisions about their care
2
the choices they make.
professions
, has many interventions for which the evidence base is not
Optometry, in common with other healthcare
and to respect
strong.3 The evidence-based model of healthcare has clear guidance
for this commonplace scenario, where strong evidence is lacking.
Sackett and colleagues define evidence-based practice as ‘integrating
individual clinical expertise and the best external evidence’, with a
consideration of patient preferences as part of good clinical expertise.4
Satterfield and colleagues modified Sackett et al.’s early model by
putting clinical expertise in the middle of the three considerations of
evidence-based practice, as this skill allows the integration of all three
(Figure 1).5
Chapter 10 Clinical protocol
269
Figure 10.1. Satterfield’s remodelling of the initial three-circle model of
evidence-based practice. (Reproduced with permission from Satterfield et
al., 2009, The Millbank Quarterly, Wiley).5
It is clear from Figure 10.1 that, in the evidence-based model,
research evidence does not replace, but rather complements, both the
clinician’s clinical expertise and patient preferences. Eye care
practitioners also have a duty to assist patients in making informed
decisions about their care, so controversial topics should be
acknowledged as such.
This chapter is aimed at the busy eye care practitioner who wants
to know how they can integrate the information in this book into a
clinical protocol for their patients with reading difficulties. Figure 10.2
gives an overview of this protocol used to investigate children
presenting with reading difficulties.
6 7
Figure 10.2. A clinical protocol for the investigation and management of
children with reading difficulties and/or symptoms with text, as might be
undertaken by a community optometrist or in the hospital eye service. VS,
visual stress.
The notion that conventional visual problems should be excluded
before coloured filters are tried is not new and was originally stressed
by Irlen.8 In 1991, Evans and Drasdo went further and argued that a
particularly thorough eye examination is required to rule out
conventional visual problems, and they argued that this “special
investigation” should concentrate on the optometric correlates of
dyslexia.9 These correlates are detailed in Chapters 2-4.
Vision, Reading Difficulties and Visual Stress
270