Article for Category: ‘Behavioural Optometry’

Dyslexia and coloured glasses

January 07th, 2013

Recent media article on coloured glasses as a treatment for dyslexia. It is a little hard to read as we had difficulty scanning the broadsheet format.

dsylexia week0002 This link will go to another page. Click on the file name a second time and the PDF will download.

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Coloured overlays and glasses as a treatment for dyslexia

September 09th, 2012

I probably have a thing variously called Irlen-Meares syndrome, scotopic sensitivity syndrome, visual stress or visual discomfort. I use the term visual discomfort in deference to my old PhD supervisor Liz Conlon (my PhD is old not Liz) who is a leader in the field although she hardly ever gets cited. Here are some of her papers you bums! (Conlon et al, 1999; Conlon, Sanders, & Wright, 2009; Conlon & Humphreys, 2001; Conlon et al., 1998; Conlon & Sanders, 2011).

What is visual discomfort?

No one really knows what visual discomfort is. My own view, somewhat consistent with the literature, is that it is an abnormal sensory sensitivity to stimuli of high contrast, and/or low spatial and/or high temporal frequencies. Black text on a white page is an example of a high contrast stimulus. Single spaced text with small font size is an example of a stimulus of low spatial frequency. One of the reasons universities require assignments to be typed in 12-point font, double spaced is that double spaced text is more comfortable to read than single spaced. High temporal frequency stimuli are characterised by rapid flashing. Think of the rapid flicker emitted by strobe lights or a fluorescent bulb. These stimuli lead to excessive neuronal firing that can lead to perceptual distortions or, in my experience, simply make the stimuli uncomfortable to be around.

My own visual discomfort manifests as light sensitivity, too much time in harsh sunlight sans sunglasses results in eye strain and a headache (although this may be psychosomatic as I spent many years as a kid surfing and playing cricket sans sunglasses with no ill effects). I dislike fluorescent lights, which unfortunately light our clinic offices. One office has a bulb that runs directly along my left eye line as I sit in the therapy chair. After a heavy day of consulting I can actually feel a “buzzing” and some days a bad headache in the part of my head that seems to match where the light runs. Again, this may be neurotic but needless to say I attempt to avoid this room. I had trouble with the old CRT computer screens at university; LCD screens were still rare back then. Flashing lights drive me nuts. Laser shows, strobe lights at concerts, and my 3-year old son’s flashing Batman toothbrush (a light on the brush flashes, not Batman) all make me a little more grumpy than usual.

Visual discomfort, reading and dyslexia

There is a theory that visual discomfort causes print to become distorted, which affects word reading and comprehension in turn. Visual discomfort is also claimed to affect reading efficiency such that sufferers can only read for short periods and are prone to reading related headaches.

Visual discomfort has been reported to be more prevalent in dyslexic populations. However, the relationship between dyslexia and visual discomfort remains controversial. Visual complaints are made by many healthy people and visual discomfort also exists in skilled readers (I’m an example). That visual discomfort exists in skilled readers makes a nonsense of claims that it is a form of “visual dyslexia”. Dyslexia and visual discomfort are separate conditions.

Visual discomfort, dyslexia and coloured overlays/lenses

Coloured overlays or lenses are a common treatment for visual discomfort (Allen, Gilchrist and Hollis, 2008; Wilkins, 19952003; Wilkins, Huang and Cao, 2004). Coloured overlays are thin transparent coloured films that are placed over a page of text. They are designed to colour the page without affecting clarity of the text.

The evidence for whether coloured overlays improve reading is mixed. A lot of the existing data published in “scientific” journals are plagued by methodological concerns, including no controls on other therapies/intervention or poorly matched intervention groups. Of the better studies Singleton and Trotter (2005) used undergraduate students with (n =  10) and without (n =  10) dyslexia. Each group had 5 students with high visual discomfort (HVD) scores and 5 with low visual discomfort (LVD) scores. All participants read faster using their chosen overlay. The dyslexics with HVD scores made significant gains in reading speed with an overlay while the other groups made non-significant change (gains of 3-4%).  Singleton and Henderson (2007) showed children (6-14 yoa) made greater improvement in reading rate with coloured overlays relative to reading-age matched controls. In contrast, Ritchie, Della Sala and McIntosh (2011) reported on 61 children (7-12 yoa) with reading difficulties (77% were diagnosed by an Irlen diagnostician as having the visual discomfort). There was limited evidence that individually prescribed Irlen coloured overlays had any immediate benefit for reading rate.

A recent study from the lab of respected reading scientist, Maggie Snowling, investigated the effect of coloured overlays in a well-designed experiment. They took 26 controls and 16 people with dyslexia, all undergraduate students, matched for IQ. Both were tested on two reading tests. The Wilkins Rate of Reading Test (WRRT) measures the impact of overlays on reading. The WRRT requires speeded oral reading of a passage of text comprising 15 high-frequency words (familiar to children from 7 years) that are repeated in random order, ensuring that no word can be guessed from the context. The test was administered with and without the chosen overlay placed over the text to test for an immediate benefit in reading rate. Reading rate was calculated as the number of words read correctly per minute (wpm) not including errors, omitted words and omitted lines. They also used two passages adapted from passages in the secondary school edition of the York Assessment of Reading for Comprehension (YARC). Passage 1 consisted of 311 words, and Passage 2 consisted of 302 words. Five  comprehension questions followed each passage.

Both groups read more words per minute in the Overlay versus No Overlay condition. The group with dyslexia showed marginally greater gains relative to controls. However, these data need to interpreted with a healthy dose of salt because the dyslexics were slower readers to begin with and therefore had more room to improve.

When reading real text (YARC), there was an effect for Group on passage reading time. Unsurprisingly, the dyslexic group was slower than controls in both Overlay and No Overlay conditions. But there was no effect for Overlay (the overlay made no difference to reading rate for either group) or a Group by Overlay interaction (there was no relative advantage for the dyslexic group in the Overlay condition v No Overlay). Reading comprehension scores did not change in either group as a result of using an overlay. These data are consistent with those reported by Ritchie, Della Sala and McIntosh (2011) in children. They suggest that coloured overlays are not as effective as claimed for improving reading accuracy or fluency.



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Vision therapy and dyslexia: What’s the evidence?

March 25th, 2012

The title of the original version of this post may have implied that vision therapy is an inappropriate treatment in general. Whereas, I intended only to refer to it as inappropriate for treating dyslexia/reading problems. There is evidence that vision therapy is an appropriate treatment for some vision problems such as convergence insufficiency. I regret that any adverse inference may have been drawn from the title.

Vision and reading

Many people have attributed reading problems to one or more subtle ocular or visual abnormalities, including Samuel Orton, who wrote about the difficulty he thought children with dyslexia had with reversible letters and words (eg. b/d, god, dog). However, scientific research has shown that Orton’s view and other views that reading problems are the result of issues with visual processing, visual perception or visual memory are almost certainly incorrect.

In the 1970′s Frank Vellutino and colleagues performed a series of studies in which they compared poor and good readers on a variety of visual processing tasks (e.g., visual discrimination, spatial orientation, visual memory, and visual learning). Most importantly, the tasks carefully controlled for verbal coding ability.

For example, Vellutino et al. found that memory for visually presented words and letters that were visually similar (e.g., b/d, was/saw) was the same in good and poor readers when a written rather than a verbal response was required. In other words, the kids with dyslexia see the same thing and can replicate the symbol but have more difficulty producing the letter or word name verbally. Another experiment showed that good and poor readers performed equally on visual recognition and recall of symbols from the Hebrew script with which both groups were equally unfamiliar. Finally, poor readers do make more ‘visual’ errors when reading compared to good readers of the same age. However, they DO NOT make more ‘visual’ errors than younger children of the same reading age. These data tell us that ‘visual’ errors are the result of poor reading, not the cause.

Even when individuals make errors that seem “visual”, such as migration errors within words (e.g., reading trail as trial) or between adjoining words (e.g., reading fig tree as fig free) what seems to be a visual or attention problem is actually a specific problem with the word-reading process. We know this because people who make these errors do not make the same errors for digit stimuli.

Eye movements and dyslexia

The eye movements of individuals who have dyslexia do differ from those of skilled readers (Rayner, 1998). While reading, the people with dyslexia exhibit longer duration of eye fixation, shorter saccades and a higher proportion of regressions (backward) saccades than controls (Huxler et al., 2006). However, research has demonstrated that abnormalities in eye movements occur specifically in reading tasks. When people with dyslexia and controls are compared on non-reading visual tasks that require similar perceptual and ocular motor demands to reading, there are no differences between eye movements of the groups. Hence the divergent eye movement patterns of people with dyslexia during reading reflect difficulties in the reading process rather than a primary impairment of ocular motor control (Huxler et al., 2006). This conclusion is supported by studies that have demonstrated that the eye movements of people with dyslexia do not differ from younger, reading age matched controls (Hyona & Olson, 1995) and that when people with dyslexia are given reading-level texts, their eye movements are comparable to controls (Olson et al., 1983).

Vision therapy

Vision therapy involves eye exercises, eye-hand coordination tasks and other exercises designed to improve the individual’s motor memory activity. Although in widespread use, a number of reviews have concluded that vision therapy has limited evidence for efficacy (e.g., Barrett, 2009Bishop, 1989, Wright, 2007). In response to concerns regarding the use of visual therapies, a number of influential bodies have conducted reviews and released policy statements for their members. For example, the joint statement of the Committee on Children With Disabilities, American Academy of Pediatrics, American Association for Pediatric Ophthalmology and Strabismus, and the American Academy of Ophthalmology states the following in regard to visual therapy:

“No scientific evidence supports claims that the academic abilities of children with learning disabilities can be improved with treatments that are based on 1) visual training, including muscle exercises, ocular pursuit, tracking exercises, or ‘training’ glasses; 2) neurological organisational training (laterality training, crawling, balance board, perceptual training).”

They go on to say that: “diagnostic and treatment approaches for dyslexia that lack scientific evidence of efficacy such as behavioral vision therapy and eye muscle exercises are not endorsed or recommended.”

Other recent reviews (e.g., The American Academy of Ophthalmology; Wright, 2007) have concluded that there is no scientific evidence that supports behavioural vision therapy or orthoptic vision therapy as effective treatments for reading difficulties. Claims of improvement after visual therapy have typically been based on poorly controlled studies and testimonials and reported benefits can often be explained by the traditional educational strategies with which vision therapies are usually combined or by placebo effects. Eye movements and visual perception are not critical factors in the reading impairment found in dyslexia and the majority of people with known ocular motility and eye movement defects read normally and even people with severely misaligned eyes can excel in reading and academics.

What is the evidence?

Evidence for any form of therapy can come from two sources: (a) theoretical evidence linking a treatment to a problem in a logical manner (e.g., excessive caloric intake results in weight gain so reducing caloric intake will probably result in weight loss) and (b) direct evidence for the efficacy of the treatment in reducing symptom severity (e.g., reducing caloric intake leads to greater weight loss in people with obesity compared to a placebo treatment). Of the two, the latter is a far stronger form of evidence. Both of these forms of evidence are missing for vision therapy as a treatment for dyslexia/reading problems.

Theoretical evidence linking vision and vision therapy to reading

It is likely true that people with dyslexia and other reading difficulties experience vision problems. However, it is also likely that there are good readers who experience vision problems. To prove causality between low scores on vision/visual processing tests one would have to demonstrate: (a) the vision/visual processing problems are specific to individuals who have reading problems, (b) that individuals who have vision/visual processing problems have different behavioural sequelae to individuals who do not have vision/visual processing problems, (c) that therapy that targets the putative visual problem leads to improvements in reading skills in the therapy group but not in an equivalent control group who received a placebo therapy and, (d) vision therapy produces greater gains in reading ability than reading intervention alone. There is currently no evidence showing a-d to be true. Therefore, one has to conclude that there is limited theoretical evidence for using vision therapy to treat reading problems.

Evidence for efficacy

The importance of demonstrating that vision therapy is an effective and therefore appropriate treatment for reading problems has been highlighted in a recent review (p. 5). It was noted that: “Demonstrating treatment efficacy is especially important here because these children and their parents represent a vulnerable group” and  “the onus is clearly on treatment providers to produce the evidence in support of the treatment(s) that they are offering. Without such evidence, parents inevitably run the risk of wasting their time, effort and resources, and they and their children may become disillusioned if expectations are repeatedly raised and then dashed.

There is currently no evidence that vision therapy improves reading ability directly or that greater reading growth occurs following vision therapy (i.e., that it enables better learning). The one study of sufficient scientific merit showed that vision therapy did not improve reading and spelling scores in poor readers compared to a control group of poor readers who received a placebo treatment.

Given the widespread use of vision therapy in a range of learning difficulties and its considerable cost, in terms of money and time, it is astounding that the clinicians and professional bodies that represent those clinicians have not invested in better research. The onus must surely be on clinicians and their professional bodies to prove scientifically that their treatments work. Until they manage that the conclusions of previous reviews that vision therapy is not recommended remain valid.




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