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Figure 10.6. The Wilkins Rate of Reading Test.
The Pattern Glare Test
In Chapter 8 we discussed the mechanism for the benefit from
coloured lenses and noted that the most likely explanation relates to a
hyperexcitability of the visual cortex. As explained in Chapter 8,
hyperexcitability is likely to result in sensitivity to certain patterns.77
This pattern glare can be detected with the Pattern Glare Test. With this
very simple test, the patient describes their symptoms (in answer to a
list of questions) whilst viewing each of three patterns, and their
responses indicate their susceptibility to pattern glare. The test can be
useful for determining the cases most likely to benefit from coloured
filters.
78 79
Chapter 10 Clinical protocol
291
Figure 10.7. The Pattern Glare Test. The test comprises three patterns,
instructions, and a simple scoring system. Only one of the patterns (that
most likely to cause symptoms) is shown here. Note that the third pattern
is no longer thought to be clinically useful.
72
DO NOT STARE AT THIS
PATTERN IF IT CAUSES DISCOMFORT.
Vision, Reading Difficulties and Visual Stress
292
The Pattern Glare Test comprises three gratings of differing spatial
Chapter 10 Clinical protocol
293
frequencies (SFs): low (Pattern 1), medium (Pattern 2; Figure 10.7), and
high (Pattern 3). A normative study of the Pattern Glare Test showed
that people have an abnormal degree of pattern glare if they achieve a
score of >3 on the medium grating.80 Such people are likely to benefit
from coloured filters.78 In clinical practice, the high SF grating often is
not used (partly because the results are critically dependent on viewing
distance) and the cut-off for the medium SF grating is the most
commonly used criterion. The low SF control grating is useful because
it is unlikely that symptoms will occur with this grating. If patients
report more than one or two symptoms with this grating, it is likely that
they are suggestible and their response with the medium grating is less
trustworthy.
Computerised screening for visual stress
A comprehensive computerised system for screening for visual
stress was developed and evaluated by Singleton and Henderson.81
This Visual Stress Screener can be used in association with a visual
stress questionnaire.
Thomson Software Solutions supply a system for prescribing
coloured filters called ReadEZ Screening Software. However, this does
not seem to have been described or evaluated in the scientific
literature (PubMed search, February 2024).
The Intuitive Colorimeter
Figure 10.8. Coloured trial uses used in conjunction with the Intuitive
Colorimeter. Note that the small lenses on the spectacles shown would need
to be carefully fitted to ensure that the entire visual field is covered.
Generally, larger lenses are preferable for use in tinted spectacles.
The Intuitive Colorimeter, described in Chapter 9, is an instrument
that illuminates a page of text with coloured light, and it can be used to
prescribe individually specific tinted lenses. It enables independent
variation in hue (colour) and saturation (depth of colour) without an
associated change in luminance (brightness). One major advantage of
the Colorimeter compared with overlays is that the variation in colour
is continuous rather than in discrete steps. The entire visual field is
stimulated with coloured light, as when tinted spectacles are worn. The
design of the colorimeter system is described in Chapter 9 and detailed
instructions are provided in the instrument manual.
Vision, Reading Difficulties and Visual Stress
294
and refined using precision tinted lenses (Figure 10.8). At the end of
this testing, the patient looks at text with and without their chosen
precision tinted lens combination and is asked to report on the
difference that the tints make to their perception of text. It is
preferable to tint spectacles so that the patient sees no cast of colour
when looking through the lenses. Coloured surfaces can, and ideally
should, appear quite normal. The tint saturation is dependent on
choices made by the examiner and their patient and in severe cases
a strong (highly saturated) colour is necessary to remove symptoms.
This may affect the appearance of surface colours, and as symptoms
remit the tint should be lightened. Some individuals with severe
photophobia find the addition of a grey dye together with the
coloured dyes helpful, but this is exceptional.
Adults can decide whether they think that it is worthwhile to have a
pair of precision tinted spectacles made up. Adults with symptoms that
are typical of visual stress usually find the effect of precision tinted
lenses self-evident. This is why, a screening stage with overlays is often
unnecessary with adults.
Prescribing advice for precision tinted lenses
It is important that the chosen spectacle eye size is sufficiently large
to ensure that the wearer is always looking through the precision tinted
lenses. Children should be advised to wear their precision tinted lenses
for schoolwork, including homework, if they find them helpful. For
adults, they are likely to be helpful for office work and reading. Often
users find them valuable for computer use, sometimes for television,
and for environments where there are high levels of fluorescent
lighting, such as supermarkets. But patients should be advised not to
The results obtained with the Intuitive Colorimeter are checked
Chapter 10 Clinical protocol
295
wear them outdoors as sunglasses since they are not likely to protect
the eyes from sunlight.
Precision tinted lenses should usually not be worn when driving or
riding a bicycle, if they are likely to impair the perception of traffic
signals. The computer program that is provided with the colorimeter
allows practitioners to check this. This is useful for the rare cases where
a patient wishes to wear the lenses constantly (e.g., a migraine
sufferer). The wearing of any tint for driving at night is not
recommended. Even if the program indicates that perception of traffic
signals should be normal, patients should wear the glasses as a
passenger under a range of lighting conditions to check this
themselves. Some particularly symptomatic individuals such as those
with autism report greater comfort if they wear their lenses all the time.
If the lenses are not strongly saturated this is probably acceptable,
provided the individuals do not drive.
Follow-up colorimetry
Sometimes the need for precision tinted lenses reduces over the
years and this may relate to a finding of reduced pattern glare in older
people,80 which could result from the expected reduction in cortical
hyperexcitability with age.
Irlen claimed that 6% of people with visual stress cannot be helped
by coloured filters.8 This claim has not been systematically
investigated, but if the cortical hyperexcitability explanation for visual
stress (Chapter 8) is correct then it is feasible that patients will be
sometimes encountered for whom no colour is particularly helpful.
Similarly, there are likely to be many patients whose visual stress
symptoms are not completely alleviated by precision tinted lenses.
Other approaches that may be helpful for these cases were discussed
in Chapter 9.
Vision, Reading Difficulties and Visual Stress
296
When to treat or correct
Most cases of visual stress in children are detected when they are
faced with reading and fail to show the usual development. In many
children with visual stress the early acquisition of reading shows good
progress until they encounter paragraphs of closely spaced text.
Assessment with coloured overlays can be undertaken as soon as a
child starts to struggle with reading. The child is required simply to say
which of two pages of text covered with differently coloured overlays
is the clearer and more comfortable, and young children find this easy.
The youngest age for assessment with the Intuitive Colorimeter is
probably about seven. The child is required to compare two colours
presented successively, and this is difficult for younger children.
Binocular vision anomalies only require treatment if they are
causing symptoms, impairing performance, or are likely to worsen if
left untreated.14 In some cases, it can be difficult to determine whether
these criteria are met.
With refractive errors, the situation is simpler because the proposed
correction can be introduced in a trial frame and demonstrated to the
patient. This is appropriate for older children and adults and, as
already noted, this approach can be taken with adults after
colorimetry. The proposed correction can be demonstrated with trial
precision tinted lenses and the patient asked if they find it helpful
enough to warrant spectacles. With children, this approach could lead
to over-prescribing and so diagnostic criteria for visual stress are
generally applied before colorimetry is considered. These diagnostic
criteria will now be discussed. These involve the tools detailed above.
Chapter 10 Clinical protocol
297
Diagnostic criteria for visual stress
There are several possible reasons why a child might choose a
coloured filter, and these are summarised in Figure 10.9. Some of the
conditions in Figure 10.9 can be excluded following the detailed eye
examination outlined in this chapter. In addition to this, the clinician
should determine if there are positive signs of visual stress, as detailed
below.
Figure 10.9. Possible reasons why children might choose a coloured overlay
on first testing. LCA, longitudinal chromatic aberration. The white boxes
represent reasons for which there is a physiological explanation, and the
grey boxes have psychogenic mechanisms. Reproduced from Evans & Allen
(2016)69 under Creative Commons open access.
In 2017, Evans, Allen and Wilkins79 used a Delphi study82 to canvass the
opinion of a group of leading prescribers of precision tinted lenses in the
UK on the diagnostic criteria for visual stress. Some of the findings were
as the researchers anticipated, and indeed as they had taught on
courses. However, other findings represented an evolution of
diagnostic criteria, revealing convergent opinions amongst
independent practitioners in different regions of the UK. For example,
the researchers were interested to find that respondents favoured
Vision, Reading Difficulties and Visual Stress
298
stricter cut-off criteria for the Wilkins Rate of Reading Test than had
hitherto been used.79 This cut-off, a 15% improvement in the Rate of
Reading Test with an overlay, was also indicated in two independent
studies published after the Delphi study data were collected.
83 84
The
diagnostic criteria produced by the Delphi study are summarised in
Table 10.2.
Table 10.2. Putative diagnostic indicators* of visual stress from Evans et al.
(2017) under Creative Commons.79
*WRRT, Wilkins Rate of Reading Test; PGT, Pattern Glare Test.
The diagnostic criteria in Table 10.2 are labelled putative because,
ideally, they would be investigated in prospective clinical trials.
However, to date they represent the best attempt at defining criteria
for the diagnosis of visual stress. It should be noted, Evans et al.
stressed that before considering a diagnosis of visual stress, eye care
practitioners must seek to exclude other explanations for the
symptoms and signs in Table 10.2.
Chapter 10 Clinical protocol
299
Recently, Gilchrist and colleagues have carried out further analysis
of Wilkins Rate of Reading Test data to determine the minum criteria
for change.85 Their results are broadly in agreement with the 15%
criterion, although they preferred to use the absolute value of words
correctly read per minute (wcpm) rather than percentage
improvement. Their preferred criterion was 22 wcpm, which equates
to~13% for a typical adult and ~21% for a typical child.85 However, this
study did not include any people with reading difficulties.
Funding and finding an appropriate practitioner
The main contributor to the most common reading difficulty,
dyslexia, is poor phonological decoding.86 The most accepted
mainstream intervention for children with reading difficulties is
therefore specialist teaching, ideally in small groups or on a one-to-one
basis.87 Some children with reading difficulties or other specific
learning difficulties will also have visual problems. In exceptional cases,
children may be mis-diagnosed as having reading difficulties when in
fact all they need is a visual intervention.
In the authors’ opinion, the most common visual problem in people
with reading difficulties is visual stress, but before this can be
diagnosed practitioners need to rule out a variety of other visual
disorders (Figure 10.2). This requires a detailed eye examination which,
including the testing for coloured filters, typically takes about an hour.
For community optometrists in the UK, this detailed investigation will
not be covered by the NHS sight test fee. There are very few secondary
care NHS hospitals that currently fund precision tinted lens testing. It
is unfortunate that people who need this testing and precision tinted
lenses typically must fund this themselves, and many of the patients
who are in greatest need cannot afford to pay.
Guidance from the College of Optometrists concerning the
Vision, Reading Difficulties and Visual Stress
300
examination of patients with specific learning difficulties is to “ensure