prepared by the Community Health Systems Resource Group
Hospital for Sick Children
Introduction
The present report
examines the case of Irlen precision tints as an intervention for
reading disabilities. As with any proposed learning disability (LD)
treatment, consumers are advised to investigate before accepting
claims of efficacy. Irlen's treatment represents a particular
challenge given the degree of contradiction and misrepresentation in
the field. Even though 20 years have passed since the inception of
this approach, controversy and uncertainty prevail. A summary of the
most relevant issues and findings provides some clarity as to the
actual status of precision tints. In general, it is argued that the
case for Irlen's treatment is weak and largely unsubstantiated. The
unscientific basis of Irlen's claims will become apparent following a
critique of the literature and a brief overview detailing the origin
of Irlen's "Method".
The origin of
"Scotopic Sensitivity Syndrome" and Irlen filters
In her book "Reading
by the Colors", Helen Irlen describes the birth of precision
filters and overlays (Irlen, 1991). From 1981 to 1983, while working
as an educational psychologist, Irlen interviewed 1500 adults with
reading disabilities. She identified a subgroup of readers who,
despite having adequate reading skills, described reading as
extremely difficult and unpleasant. These individuals complained of
perceptual distortions, visual stress, headaches, glare, and sore,
tired eyes. This led Irlen to propose a unique syndrome which she
named "scotopic sensitivity syndrome" (SSS).
Six months later,
quite by chance, Irlen noticed a student with SSS reading through a
coloured overlay. This observation led to the development of Irlen
overlays and filters. In 1983 Irlen presented a paper entitled
"Successful Treatment of Learning Disabilities" at the
Annual Convention of the American Psychological Association (APA).
In 1985 an Australian journalist, searching for a treatment for his
daughter's dyslexia read about SSS in a local newspaper. Several
exchanges with Irlen culminated in the airing of the 60 minutes
Australia program "Rose Coloured Glasses" in April of 1985.
Three years later, in May of 1988, the American version of 60
minutes aired "Reading by the Colors". Not surprisingly,
the APA presentation and two television broadcasts generated a surge
of interest in Irlen filters and the "Irlen Method".
Scotopic
sensitivity syndrome
Irlen describes SSS
as a visual-perceptual dysfunction involving excess sensitivity of
the retina to particular frequencies of light. According to Irlen, a
small part of the colour spectrum causes the brain to distort
information. Precision tints exert their effects by selectively
filtering out this part of the spectrum.
In some respects,
the legitimacy of coloured filters and overlays as an LD treatment
depends on the legitimacy of SSS. Although Irlen and proponents of
her method routinely refer to SSS as though it were an accepted
medical syndrome, many experts question its validity. Some insist
that the concept be rejected altogether on the grounds that it lacks
scientific credibility. The derivation, definition, diagnosis, and
even the name of SSS have all been subject to criticism.
The semantic basis
for "scotopic sensitivity syndrome" is questionable in many
respects. "Scotopic vision" and "scotopic sensitivity"
refer to processes of the visual system involving highly light
sensitive retinal receptors called "rods". However,
symptoms of SSS occur during reading which occurs under normal
illumination and involves detail sensitive "cone"
receptors. While Irlen insists that SSS is a coined term with a
different meaning she does not explain why she chose this seemingly
unsuitable label.
For many, the
problem goes far beyond that of semantics. Hoyt (1990) and others
maintain that "scotopic sensitivity syndrome" is not a
recognized medical syndrome and consists merely of a group of vague
and nonspecific symptoms derived from anecdotal accounts. To this
day, there are no clearly established criteria for SSS. The only
defining characteristic is a reported benefit of coloured filters
while reading.
The Research
Reviews of the
literature on Irlen lenses express little support for this approach
as a treatment for LD. For example, Parker (1990) reviewed several
Irlen filter studies and concluded that all were seriously flawed and
could not be considered scientifically valid. In a more extensive
review, Evans and Drasdo (1991) criticize the literature for having
no sound theoretical basis for SSS and for the unscientific testing
of precision tints.
Among the numerous
criticisms of Irlen's treatment, is the argument that precision tints
are highly susceptible to placebo effects. A placebo effect is said
to occur when a person responds favorably to a "treatment"
which is scientifically of no value. Expectations and desire can and
often do have a profound influence on treatment efficacy. Simply
believing or hoping that an intervention is effective is often enough
for it to be so.
To suggest that
placebo effects account for all positive responses to Irlen tints is
not unreasonable given that the main source of support for coloured
filters is anecdotal. Indeed the very conception of SSS and the
development of Irlen lenses were both entirely based on anecdotal
accounts and unscientific methods of data collection and "analysis".
By relying on anecdotal accounts or experiments that lack adequate
placebo controls, interpretations of findings are speculative at
best. Controlling for placebo effects requires, among other things,
the inclusion of placebo filters of similar colour to precision tints
but outside the effective range of chromaticity. Such filters have
been successfully produced, but have rarely been implemented in Irlen
lens research.
Wilkins et al.,
(1994) conducted the first double-blind placebo-controlled study
testing the effect of coloured filters on symptoms of SSS and reading
performance. While children in both the precision tint and placebo
control groups showed a reduction in symptoms of SSS, a more
pronounced effect occurred in the group using prescribed coloured
filters. Reading rate, accuracy and comprehension were not effected
by either the prescribed or placebo filters. This study suggests
that some effects of coloured lenses are not entirely due to placebo
effects. However, it is important to note that placebo filters also
had the effect of reducing symptoms of SSS.
The Wilkins et al.,
(1994) study is repeatedly cited as proof that the efficacy of
coloured filters is not due solely to placebo effects. However, the
contribution of placebo effects was not entirely ruled out. Further,
a positive finding in one study does not exempt others from following
proper control procedures. Despite the Wilkins et al., finding,
results are still inconclusive when placebo filters are not
implemented. Many studies include control groups but these are
typically composed of children who use no filters during testing and
who report no symptoms of SSS. Although this is one form of control
it does not adequately control for the possibility of placebo
effects.
The need for proper
control procedures was highlighted in a study by Robinson &
Foreman (1999). This study measured the effect of Irlen filters on
reading performance as well as students' perception of their academic
ability. The study included a control group (no SSS and no filter)
and 3 experimental groups (placebo, blue and precision filters).
Increased accuracy and reading comprehension occurred in all groups
with the 3 experimental groups demonstrating significantly more
improvement than the controls. Also the majority of subjects in all
3 experimental groups reported benefit from the filters which they
consistently wore throughout the 4 month period of the study. This
means that subjects perceived and demonstrated an advantage of
wearing filters regardless of whether they were diagnosed lenses,
blue tints or placebo tints. This study reveals a likely placebo
effect not only on perceived benefit but on actual reading
performance.
Robinson &
Foreman's study (1999) can also be used to illustrate the ambiguity
and unreliability of second hand accounts of research findings. The
Irlen web site "Synopsis of Research" page reports that
"This study found three year gains in comprehension and two year
gains in accuracy over the 20 months study period for three
experimental groups, compared to a one year gain for the control
group". The intended interpretation is likely that precision
filters were more effective than placebo filters. In fact, as
described above, the "three experimental groups" included
the group using prescribed filters as well as the blue filter and
placebo filter groups. This means that improvements occurred
regardless of filter type and that precision tints were no more
effective than placebo tints.
Irlen promotions
cite a number of studies claiming improvements in reading or symptoms
of SSS due to precision tints. The LD treatment consumer should use
caution in interpreting these apparent successes. Many of the
studies cited as proof of reading improvements actually measure
performance on visual processing tasks, or reading "sub-skills"
rather than reading per se. For example, several use the "Rate
of Reading Test" which involves reading a series of randomly
ordered common words. Others involve discriminating shapes from
background textures. Improvements in these skills do not necessarily
translate into improvements in reading.
Not only are some
findings less meaningful than they first appear, many are
questionable on methodological grounds. There continue to be serious
methodological concerns with most of the studies claiming support for
Irlen lenses. Biased sample selection, small sample size, and lack
of proper control procedures are just a few of the more common
limitations. Finally, consumers should be aware that many unreported
studies show no effects of coloured filters on measures of either
reading performance or SSS symptoms.
Discussion
Only a few of the
problems associated with the Irlen lens literature have been
addressed. A more extensive review goes beyond the scope of this
paper. In general, the present survey concludes that although
studies are routinely cited as proof of Irlen lens efficacy, closer
examination reveals methodological concerns and inconclusive results.
Irlen's theory of
SSS and the mechanism of precision tints is vague and purely
speculative. Twenty years after Irlen's initial proposal, SSS is no
more clearly defined and many maintain that it is not a legitimate
syndrome at all. Although perceptual distortions appear to occur in
some children with reading disabilities vision experts have not yet
determined the physiological basis for these effects. Further, there
is still no accepted theory as to why coloured filters should help
alleviate perceptual symptoms.
It is not surprising
that there is little support for improved reading performance with
the use of coloured filters. Even proponents of precision tints
maintain that while an improvement in print clarity may facilitate
the process of learning to read it is not enough to lead to
spontaneous improvements in word recognition skills and other complex
elements of reading. Evans (1999) explains that treating visual
problems or perceptual symptoms will likely alleviate only the
"visual component" of reading problems and will not impact
the phonological deficits underlying most cases of reading
disabilities.
Conclusion
The initial claims
of Irlen were based solely on observations, students' anecdotal
accounts and no formal experimentation. Nevertheless, her ideas were
highly popularized by an APA presentation, a book, and two television
broadcasts. Twenty years later despite the unscientific basis of the
"Irlen Method" the promotion of precision tints continues.
Contrary to the broad claims of many Irlen treatment promotions, the
efficacy of this approach appears to be limited to a subgroup of
children with reading problems. Coloured overlays and filters appear
to reduce the perceptual distortions and visual stress experienced by
some children during reading. However, evidence for the effects of
overlays and filters on reading performance per se is very limited.
Experts agree that even when lenses appear to be effective at
reducing perceptual distortions remediation for underlying reading
problems will still be required.
References
Cardinal,
D.N., Griffin, J.R., & Christenson, G.N. (1993). Do tinted
lenses really help students with reading difficulties? Intervention
in School and Clinic, 28(5), 275-279.
Evans, B.J.W.
(1999). Do visual problems cause dyslexia? Ophthalmic
Physiological Optics, 19(4), 277-278.
Evans,
B.J.W., & Drasdo, N. (1991). Tinted lenses and related therapies
for learning disabilities: a review. Ophthalmic Physiological
Optics, 11, 206-217.
Hoyt,
C.S. (1990). Irlen lenses and reading disabilities. Journal of
Learning Disabilities, 23(10), 624-626.
Irlen, H. (1991).
Reading by the Colors. Avery Publishing Group Inc. New York
Parker,
R.M. (1990). Power, control, and validity in research. Journal
of Learning Disabilities, 23, 613-620.
Robinson, G.L., &
Foreman, P.J. (1999). Scotopic sensitivity/Irlen syndrome and the
use of coloured filters: A long-term placebo controlled and masked
study of reading achievement and perception of ability. Perceptual
and Motor Skills, 89, 83-113.
Wilkins, A.J.,
Evans, B.J.W., Brown, J., Busby, A., Wingfield, A.E., Jeanes, R., &
Bald., J. (1994). Double-masked placebo-controlled trial of precision
spectral filters in children who use coloured overlays. Ophthalmic
Physiological Optics, 14, 365-370.
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