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The overlays were then placed over a plain sheet of paper and the
Vision, Reading Difficulties and Visual Stress
312
children were asked which colour they preferred. The overlays selected
for clarity increased reading speed in the autism group but not the
control group, as in the earlier study, but overlays chosen on the basis
of colour preference had no beneficial effect on reading speed in either
group. The beneficial effect of the overlays was not confined to reading.
The task of matching objects to samples of similar objects, see Figure
11.3, was also improved with an overlay chosen to improve the clarity
of text.
Figure 11.3. Examples of stimuli in a matching to sample task. Reproduced
under STM Permissions Guidelines
from Ludlow et al.
6
The Mind in the Eye task7 has been widely used to measure ‘theory
of mind’ in individuals with autism. It presents pictures of just the eyes
of a face (Figure 11.4) and requires the observer to make a judgement
as to which of four adjectives best describes the emotion the face is
expressing.
Figure 11.4. A face from the Mind in the Eye task. Reproduced with
permission from Simon Baren-Cohen.
Ludlow et al.8 administered this task to 15 children with autism
Chapter 11 Other potential clinical uses of precision tinted lenses
313
spectrum disorders aged 8-17 years and a control group matched
individually for age and sex. The test was given with and without
overlays with a colour selected as improving the clarity of text. The
children with autism performed more poorly than the typically
developing children, but their performance was improved with the
overlay. The extent of improvement in recognizing the emotion
correlated with the increase in reading speed that the overlay afforded.
Whitaker et al.9 corroborated and extended these findings using a
task that required holistic judgement of facial expression. Sixteen
children with autism spectrum disorder were asked to judge which of
two faces expressed the stronger emotion, a task that requires
observation of both the eyes and the mouth. The images were
presented side by side in shades of grey on a computer screen. The
screen was either white or tinted a shade of colour chosen previously
as improving the clarity of text. The discrimination was better when the
screen was coloured. There were no such effects for a control group of
typically developing children matched for age and intelligence.
The above findings were examined in a more realistic setting by
Ludlow et al.10 using the Emotion Evaluation Test, in which professional
actors enact ambiguous scripts recorded in video and representing
seven basic emotions: happy, surprised, sad, angry, anxious, revolted
(and neutral, not used in this study). The video sequences are in colour,
and they portray naturalistic complex expressions with appropriate
intonation and gestural cues. A series of statements is offered and the
viewer has to endorse or reject each. Fourteen children with autism
and fourteen typically developing children matched for intelligence
took part. Initially the participants were examined with the Intuitive
Colorimeter11 and a combination of tinted trial lenses was selected
matching the chosen settings (active tint). A computer was used to
select a combination of trial lenses having a difference in chromaticity
of 0.07 (control tint), see Figure 11.5. This difference has repeatedly
been shown to eliminate beneficial effects of a selected colour.12
Figure 11.5 Chromaticities of lenses chosen for clarity are represented by
open squares and connected by lines to the chromaticities of lenses with
control colour. The left hand chart shows data for children with autism
(ASD) and the right those with typical development (TD). Redrawn from
Ludlow et al.10
One month later the children watched two versions of the Emotion
Evaluation Test, one when wearing the active tint and the other when
wearing the control tint, in random order. The mean number of
emotions correctly identified is shown in Figure 11.6. The tint improved
performance of the children with ASD to the level of the typically
developing children.
Vision, Reading Difficulties and Visual Stress
314
Figure 11.6. Mean number of emotions identified in the Emotion Evaluation
Test using placebo and chosen (active) tint for ASD and typically developing
(TD) children. Bars show standard deviations. *p < .05; ***p < .001.
Reproduced under STM Permissions Guidelines from Ludlow et al.10
Ludlow et al.10 also administered the Social Inference-Minimal test
(SI-M) in which actors make sincere or sarcastic statements. It requires
the viewer to detect the sarcasm based on the demeanour of the
actors, such as their tone of voice, facial expression or gestures. For
comparison the test includes sincere verbal exchanges (five vignettes)
in which the targeted speakers mean what they are saying; i.e., the
words spoken, and the paralinguistic cues are consistent.
In the simple sarcasm exchanges (five vignettes), the literal meaning
is contrary to the spoken message, but this can only be determined by
reading the paralinguistic cues, such as facial expression, voice
prosody (rhythm) and hand and body posture. The content of the
verbal script for both the sincere exchange and simple sarcasm
exchange could be similar: “I’d be happy to do it. I’ve got plenty of time”
might be an example script for either. Paradoxical sarcasm is also
included in which the behaviours were not consistent with the verbal
Chapter 11 Other potential clinical uses of precision tinted lenses
315
expression. Participants were asked to endorse or reject statements
about what a specific actor was doing, saying, thinking, and feeling. The
results mirrored those of the Emotion Evaluation Test as shown in
Figure 11.7.
Figure 11.7. Mean number of sarcasm exchanges identified in the SI-M
using placebo and chosen tint for children with ASD and those that were
typically developing (TD). Bars show standard deviations. **p<.01.
Reproduced under STM Permissions Guidelines from Ludlow et al.10
Although the above series of studies involved small samples, the
studies tell a consistent story suggesting that coloured filters improve
the visual performance of children with autism spectrum disorders, in
particular the recognition of facial expressions. This can have clinical
significance. Ludlow and Wilkins13 reported the case of a 13 year-old
boy who was diagnosed at the age of four with autism spectrum
disorder and attention deficit and hyperactivity disorder. The boy
reported “hot eyes” in response to bright colours leading to headache
and nausea. He had a strong obsession for blue and purple. A good
response from a purple overlay was followed by colorimetry and blue
Vision, Reading Difficulties and Visual Stress
316
lenses. When the blue glasses were provided the periods of hot eyes,
vomiting and “burn out” abruptly stopped, and he was able to
participate in social activities. After about a year the glasses were
broken and until they were repaired the periods of “burn out” returned.
In all of the above studies of autism, the optimal colour has been
selected on the basis that it improved the perception of text, just as in
earlier studies of reading difficulty. Nevertheless, the chosen colour
has been effective in improving complex perceptual tasks, including
those involving the perception of faces and facial expression, which are
known to be subserved by specific cortical structures. It is possible that
both text and facial expression contribute to the well-recognised
sensory overload experienced by individuals with autism, which may
result from a cortical hyperexcitability, given the co-morbidity of autism
and epilepsy. One of the largest studies aimed at identifying the
prevalence of epilepsy in children with autism found that among
children aged 13 years and older, 26% were diagnosed with epilepsy.14
It was noted towards the end of Chapter 8 that visual stress affects
fewer than 20% of children with dyslexia. Therefore, it is not
appropriate for research on visual stress (or coloured filters for visual
stress) to study a group of dyslexic children. Rather a group of children
with visual stress should be selected using the diagnostic criteria in
Chapter 10. It is noteworthy that the research reviewed here indicates
that this principle does not apply to autism. The studies described
above have simply selected children with autism; not children with
autism who have visual stress. The positive results that have been
obtained would seem to indicate that visual stress has a much higher
prevalence in autism than in dyslexia, and/or the benefit from coloured
filters is more marked in autism. The finding that 11 out of 19 (58%)
children with autism read more than 15% faster at the WRRT with an
overlay4 supports the argument for a higher prevalence of visual stress
Chapter 11 Other potential clinical uses of precision tinted lenses
317
in autism than in dyslexia.
Migraine
A large survey indicates that photophobia is one of the most
bothersome symptoms in migraine.15 Aversion to bright light may
depend upon its colour. The aversion to narrow-band blue, green,
amber and red light has been explored in studies during the headache
phase of migraine and between headaches.
16
The patients were dark-
adapted for 3 minutes, and the light intensity was increased in steps
from mesopic (1 cd/m2; light levels similar to dusk) to photopic (100
cd/m2; daytime light levels). Although the results have been widely
interpreted as demonstrating that green light is less aversive, such an
interpretation is complicated by the fact that the light energy was
equated in terms of its photopic luminance, which was not appropriate
for equating the brightness at the mesopic levels used initially. Green
light (530 nm) is captured with similar relative efficiency at scotopic and
photopic light levels, whereas red and amber lights require more
energy at mesopic levels, and blue light requires less. This difference in
the initial apparent brightness of the lights may have affected the
associated ratings of aversion and, therefore, complicates any
inference as to colour preference. Nevertheless, treatment with green
LEDs has been evaluated17 and green lamps have been sold for
treatment of migraine pain.18
The use of tinted glasses for migraine is widely advertised on the
web, and such tints are often called FL41 or FL-41. The original FL41 tint
has a dark orange appearance and was designed over 30 years ago by
Wilkins and Wilkinson to reduce flicker from fluorescent lighting.19
Fluorescent lamps were then controlled by a magnetic ballast that
provided two gas discharges with every cycle of the alternating current
(AC) electricity supply, 100 or 120 times per second. The gas discharges
Vision, Reading Difficulties and Visual Stress
318
provided a mixture of blue light and ultraviolet light and at that time a
halophosphate coating on the inner surface of the tube converted the
ultraviolet light to long wavelength (orange) light. The mixture of light
from the discharge and from the phosphor resulted in white light. The
phosphor continued to glow between gas discharges, so the lamp
varied continually from bright white to dim orange. This flicker was
usually too rapid to be consciously perceived, but in 1989 it was shown
to cause headache,20 explaining the aversion to fluorescent lighting
hitherto expressed by people with migraine. The flicker could be
reduced by about one third when the FL41 tint was worn because the
tint attenuated the short wavelength light from the gas discharge.19
Good and Mortimer used the FL41 tint with school children and
compared it with a blue tint, which was less effective at reducing
headaches.21 The reason for the reduction in headaches with the FL41
was most probably the school lighting, which used halophosphate
fluorescent lamps operated from magnetic circuitry that flickered at
100Hz.22
Halophosphate lamps have been replaced by those with more
efficient phosphors (developed for television) that have relatively little
persistent afterglow. More importantly the lamps are now usually
controlled by electronic ballast and no longer flicker at low frequencies.
It therefore may appear curious that tints called FL-41 are widely
available on the internet and claimed to provide protection and relief
from migraine. The original tint has been re-designed by Dr Bradley
Katz (University of Utah, Salt Lake City, UT, USA) and there are now two
types of coloured lenses available on the internet, described as FL41
(the original, an orange tint), and the more recent one (FL-41), a
moderate pink. Both attenuate short-wavelength light.
The rationale that Katz and Digre23 give for the benefit from the
modern FL-41 illustrated in the right panel of Figure 11.8 is that this
Chapter 11 Other potential clinical uses of precision tinted lenses
319
reduces excitation of the intrinsically photosensitive retinal ganglion
cells. These photoreceptors were linked to photophobia in 2010 by
Noseda and colleagues.24 However, subsequent work by these authors
has shown that photophobia is not the result of the stimulation of any
one class of photoreceptors.
24 25
Figure 11.8. Transmission curves of original FL41 (left) and one of the
modern FL-41 (right) tints. The left graph is reproduced under STM
Permissions Guidelines from Wilkins and Wilkinson19 and the right graph
is reproduced under STM Permissions Guidelines from Katz and Digre.23
More recently, Katz and colleagues26 described a new “notch filter”
(Figure 11.9) that more specifically blocks the action spectrum of
melanopsin (see the black curve in Figure 6.2), the photopigment in the
ipRGCs. A notch filter is designed to attenuate light within a specific
wavelength range while transmitting most wavelengths with little
intensity loss. These researchers compared the melanopsin-blocking
notch filter (designed to be therapeutic) with a long wavelength notch
filter (designed to be a control). The effect of the lenses on migraine
symptoms was evaluated in a crossover randomized controlled trial of
37 migraine patients. Both tints were associated with reduced
symptoms, but there was no significant difference between the
performance of the two tints, perhaps because of a placebo effect or
Vision, Reading Difficulties and Visual Stress
320
because both tints simply reduced the light level. However, there is
another potential explanation. The authors report: “some subjects
preferred the 480 nm lenses, some preferred the 620 lenses, and some
perceived benefit from wearing both lenses”. It is therefore possible
that the participants simply needed individually prescribed tints.
A disadvantage of notch filters, compared with the more broad-
band filters that are more generally used for tinted lenses, is that the
performance of notch filters would be expected to differ under
different types of artificial lighting, depending on the position of any
spectral peaks in the lighting relative to the steep margins of the filters.
Figure 11.9. A notch filter designed to block the action potential spectrum
of melanopsin (blue line) and control notch filter (brown line), reproduced
under STM Permissions Guidelines from Hoggan et al.26 The black line
shows the luminous efficiency of the eye and indicates that both notch
filters will appear to have a similar depth of tint.
As described in earlier chapters, the Intuitive Colorimeter has also
been used to prescribe individual precision tints for people with
migraine, both in research and as part of clinical practice. Figure 7.6
shows the chromaticites of light that individuals with and without
migraine choose as comfortable for observing text taken from two
reports.
27 28
As can be seen, most individuals without migraine choose
Chapter 11 Other potential clinical uses of precision tinted lenses
321