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colours of light that they would normally experience from daylight or
electric lighting. The chosen chromaticities lie near the Planckian locus
(solid line), see Chapter 6. Individuals who experience migraine with
aura, however, choose very different colours as comfortable. They
choose chromaticities well away from the Planckian locus. Note that
the colours vary considerably, and few are orange or pink, the colours
of modern FL-41 tints.
The individuals who experienced migraine with aura shown in
Figure 7.6 b undertook a task in which they searched for a word in a
matrix of letters.28 Their performance was 30% faster with the
individual precision tint than without it. There was no effect for
individuals who experienced migraine without aura. This work
suggests that it is mainly migraine sufferers who experience aura who
will find tints useful, and that the tints may need to be individually
prescribed.
If precision tints improve visual performance, can they reduce
headache? Although there are many anecdotal reports of such success,
there is little scientific evidence. An early study of the effects of tints on
headache incidence29 evaluated a mixed group of migraine patients
with and without aura. In this small-scale study with double-masked
cross-over design 17 patients were given a tint that either matched the
colour selected in the Intuitive Colorimeter11 (‘optimal’ tint) or another
colour (‘control’ tint) that differed in chromaticity by 0.06, selected by
computer algorithm. The chromaticities of the optimal tints are shown
as points in Figure 11.10, connected by a line to the chromaticities of
the control tints.
Vision, Reading Difficulties and Visual Stress
322
Figure 11.10. The chromaticities of the optimal tints are shown as points,
connected by a line to the chromaticities of the control tints. Note the
preponderance of green and blue tints. Redrawn from Wilkins et al.29
The tints were given in random order and were each available for 6
weeks separated by a period of two weeks without tints. The study was
double-masked: neither participants nor researchers knew whether
the tint they were wearing matched the optimal colour they had
chosen some weeks before in the Intuitive Colorimeter.
Overall, there was a marginal reduction (p=0.02) in days with
symptoms when the optimal lenses were worn relative to those when
the control lenses were worn, see Figure 11.11. Most points in this
figure lie close to the diagonal, indicating little difference between the
optimal and control tints. The triangles represent the patients with
aura and the squares patients without aura. The four filled points are
patients for whom the difference was statistically significant for that
individual. These four all experienced migraine with aura, although one
did better with the control tint. Evidently it may be a minority of
patients with aura whose headaches are reduced with precision tints.
This study did not include a grey lens control group or a no-intervention
Chapter 11 Other potential clinical uses of precision tinted lenses
323
group, and no pre-intervention baseline was available for the patients
who participated. As will be seen from the next section, patients may
need to be selected on the basis of the photophobia they experience.
Figure 11.11. Results of the small-scale double-masked trial of the effect of
precision tints in migraine sufferers. Each symbol represents a patient, and
the position of a symbol is determined by the proportion of days with
symptoms when the ‘optimal’ tinted lens was worn (abscissa), and the
proportion when the ‘control’ tinted lens was worn (ordinate), neglecting
days when no lenses were worn. The symbols above the diagonal therefore
represent patients for whom wearing the ‘optimal’ tint was associated with
fewer symptoms than the ‘control’ tint. The solid symbols represent patients
for whom the difference between the tints was statistically significant for
that individual. The triangles represent patients who had migraine with
aura and the squares patients who had migraine without aura.
Reproduced under STM Permissions Guidelines from Wilkins et al.
29
Vision, Reading Difficulties and Visual Stress
324
Cluster headache
Cluster headaches are excruciatingly painful and occur in bouts of
frequent attacks, known as cluster periods. The pain is usually
unilateral and behind or around one eye. The headaches are often
preceded by a prodrome with symptoms warning of an imminent
headache. Wilkins and Cooper30 reported a case of a patient with
cluster headache who was examined with the Intuitive Colorimeter11
and given precision tints on a trial basis. He wore the tints only during
his prodrome and discovered that the prodrome no longer progressed
to headache. He has been free of cluster headaches for six years, and
has aborted innumerable prodromes by wearing his tints. Most cluster
patients are photophobic, and this case suggests that by treating the
photophobia it may be possible to prevent a cluster period. Although
this study describes just one patient, a second patient has now
reported prodromes that remit with tints and avoidance of an
expected cluster. Evidently a systematic trial is warranted.
Visual snow
Visual snow is a recently-named clinical syndrome31 that was earlier
described in two separate literatures, one concerning recreational drug
use and the other “persistent” migraine aura. Since 2014 more than
180 papers have been published with “visual snow” in the title, most in
the last five years. Patients report continuous ‘grainy’, ‘dotty’ or
‘pixelated’ vision affecting the entire visual field of both eyes equally.
The condition is often associated with mild traumatic brain injury and
light sensitivity.31 Persistent after images and comet tails on objects
may also be described, together with more conventional entoptic
phenomena (visual images that originate inside the eye). The pixelated
Chapter 11 Other potential clinical uses of precision tinted lenses
325
vision may be unremitting or may be modulated by the visual scene,
for example, its brightness. The patients also often describe an
instability of text when reading, and one of the explanations for the
phenomena is a cortical hyperexcitability.32
Pharmacological treatment is generally ineffective33. Sometimes
precision tints reduce the symptoms,31 and in the authors’ experience
tints are particularly effective when the symptoms are modulated by
the visual scene upon which they appear.
Stroke
After a stroke, visual dysfunction is the norm rather than the
exception,34 occurring in more than half of survivors.35 Four papers
have investigated possible effects of precision tints in stroke patients.
The first showed that stroke patients are particularly susceptible to
pattern glare (perceptual distortions and discomfort from patterns).36
The second study compared 17 stroke survivors with 17 age-matched
controls. The study showed that precision tints can significantly
increase reading speed and accuracy on the Wilkins Rate of Reading
Test, both in the short and long term.37 The third study is a case report
of a woman whose symptoms remitted with precision tints, only to
recur following a second stroke. A revision of the tint was then
successful in treating her symptoms.38
Multiple sclerosis
In a patient with multiple sclerosis and symptoms of dizziness Yadav
and Quan39 compared brown, grey and yellow lenses. With the yellow
lenses the symptoms remitted and visual evoked potentials were of
greater amplitude. No studies of precision tints in patients with
multiple sclerosis have yet been undertaken, although Newman Wright
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326
et al.40 investigated the effects of coloured overlays on reading and
visual search. With an overlay of a colour chosen for textual clarity,
25/26 patients reported fewer symptoms of visual stress, 50% read at
least 20% more quickly and 50% omitted at least 57% fewer targets
during visual search. Subsequently, 13 randomly selected patients
were given grey overlays, while the remaining 13 gender- and age-
matched patients were each given an overlay of their individually
selected colour. Patients were permitted to use their overlays as and
when they wished during the next two weeks. The reading and visual
search performance of those patients who had received a grey overlay
did not change, whereas the performance of those who received an
overlay of their selected colour improved, both when using the
overlays and also when not. The 13 patients who initially received a
grey overlay were then each given an overlay of their selected colour
and their performance subsequently improved.
Head injury
Headache and photophobia are very common following
concussion,41 and many patients attempt to control their photophobia
with dark glasses. Jackowski et al.42 reported improved letter contrast
sensitivity and reading rate with Corning photochromic lenses. In 39
patients with concussion and visual disturbances Clark et al.43 used a
large range of lenses of different colours. Most patients reported a
coloured lens provided relief (most commonly blue or green), and none
chose yellow. Three patients were photophobic but did not report
benefit. Fimreite et al.44 used the Intuitive Colorimeter11 and compared
the tints it provided with red, blue and grey lenses in a sample of 12
patients with concussion. Patients reported symptom relief but there
was little consistency in their choice of colour and no effect of the filters
on VEP amplitude or on the duration and number of fixations or
Chapter 11 Other potential clinical uses of precision tinted lenses
327
regressions during reading.
In a larger study of patients with concussion Monet and co-workers
(personal communication) examined 112 males and 253 females, aged
7-82. They were seen an average of 2 years after injury (range 13 days
to 26 years); 94% complained of headache and photophobia and 74%
of reading difficulty. They were assessed with the Intuitive
Colorimeter11 and the chromaticities of the tints are shown in Figure
11.13. In agreement with the findings of Clark et al., most tints were
green or blue, and most lay away from the chromaticities of
conventional lighting, whether daylight or artificial. Half the patients
needed a dark coloured lens to control their photophobia, achieved by
adding a grey dye to the two-colour dyes that usually comprise a
precision tint.
On the Wilkins Rate of Reading Test, the reading rate increased by
an average of 29% with the tint, and in 170 clients (57%) the increase
was more than 15%. Eighty-eight clients were seen on two occasions
with an interval of 53 days to 3 years 10 months between assessments.
The average difference in chromaticity between the two assessments
was 0.043. This difference is similar to that obtained by Aldrich et al.
when two colorimetry assessments of people with visual stress were
undertaken in immediate succession.12 The average transmission of
the tint increased from 38% at the first examination to 42% in the
second, due to a reduction in the grey dye needed. Evidently the
chromaticity of the tint changes little over the course of recovery even
when the transmission increases.
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328
Figure 11.12. Chromaticities of tinted lenses chosen in the Intuitive
Colorimeter by patients with a history of concussion. The Planckian locus is
shown (by the thin black line) from a colour temperature of 2000 degrees
Kelvin to 6500 Kelvin, and most conventional sources of lighting, natural
and artificial, lie close to this locus. Data from Karen Monet (personal
communication).
The greater frequency of tints on the left-hand side of the
chromaticity diagram in Figure 11.12 is obvious. There are more than
4 times the number of patients with a u’ chromaticity less than 0.21
than with a chromaticity greater than 0.21. (When the energy is equal
throughout the visible spectrum the light appears white and its
chromaticity is u’=0.21, v’=0.47). In the patients with migraine in the
three studies by Aldrich et al.,27 Veira et al.28 and Wilkins et al.
29
the ratio
of individuals with u’ chromaticity less than 0.21 is an average of 1.27
times larger than those with a u’ chromaticity greater than 0.21. In the
patients with ASD in the study by Ludlow et al. (Figure 11.5) the ratio is
1.75. The samples are small and the ratios cannot be estimated with
Chapter 11 Other potential clinical uses of precision tinted lenses
329
precision. Nevertheless, in the aggregated control groups, the ratio is
close to 1. By way of contrast, in the patients with photosensitive
epilepsy the ratio is slightly less than 1. Eventually with larger groups
some consistent trends in colour choice may emerge, dependent on
the diagnosis.
Low vision: a condition not helped by precision
tinted lenses
Low vision describes patients with impaired visual acuity, and
sometimes with visual field loss, resulting from ocular pathology.
Tinted lenses have been used for many decades by some people with
low vision and their use was reviewed by Eperjesi and colleagues in
2002.45 This review noted that, whereas luminance contrast can
enhance reading and object recognition for some low vision patients,
chromatic contrast does not aid reading but may be useful in object
recognition. These conclusions were tentative because of a paucity of
research and further investigations were recommended, noting the
Intuitive Colorimeter would be a useful tool for research. A later review
also noted the lack of objective data, meaning that eye care
practitioners had to rely on marketing literature and anecdotal reports
when considering prescribing tinted lenses or filters for low vision.46
In 2004, this research team investigated the effect of light filters on
reading speed in low vision due to age-related macular degeneration.46
A commercially available fixed yellow tint (Corning CPF 450) helped
some participants, but lenses prescribed with the Intuitive Colorimeter
were not found to be helpful. Colour was also found to be unhelpful
for age-related macular degeneration in a study of lamps of varying
spectral radiance.47
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330
Further reflections on why tints help in some
conditions
Reduction of colour differences
A recent study by Penacchio et al.48 (described in Chapter 8)
provides a possible mechanism as to why some people find tints
useful. Students were asked to rate the visual discomfort they
experienced from images of contemporary art. The images that were
particularly colourful were rated as more uncomfortable. A simple
metric (difference in chromaticity between neighbouring pixels
averaged over the entire image) explained 28% of the variance in
judgements of discomfort. When works of art were more colourful
than images from nature, they were rated as uncomfortable. These
findings suggest that vision becomes uncomfortable when there are
large and unnatural differences in colour in a visual scene. Tinted
lenses bias the chromaticities in a scene, but they also reduce the
differences in chromaticity. Perhaps this is one mechanism for the
reduction in discomfort that various tints can provide.
Reduction in rapid variation in chromaticity
Reduction in local chromaticity differences cannot be the entire
explanation, however, because different individuals choose different
colours of lighting and tints as comfortable and their individual choices
are reliable. Also, these choices are made when observing text, and text
varies in luminance rather than chromaticity. As we saw in Chapter 8,
fluorescent lighting can vary continually and rapidly in chromaticity at
100 or 120 Hz, well within the temporal resolution of retinal cells.
Individuals who wear coloured glasses have been shown to adapt to
the colour – the colour changes the wavelength at which they report
the neutral appearance of a yellow monochromatic light as neither
Chapter 11 Other potential clinical uses of precision tinted lenses
331