Monday, August 03, 2009
More Vision Wars: Visual Training for Dyslexics
The role of visual challenges in dyslexia has a long and contentious history. Although the authors of the recent consensus statement on Vision and Dyslexia were trying to clarify the most effective approach to diagnosing and treating visual processing issues in dyslexia, their statement is more likely to misinform than inform.
While not all children or adults with dyslexia have visual processing problems, many--at least two-thirds in some studies--do. This makes sense from a neurological standpoint, because several of the structural neurological features associated with dyslexia appear to predispose to visual difficulties. For example, coordinated control of the movements of the two eyes requires sending signals over long distances in white matter tracts, as well as sharing information between the two hemispheres of the brain, and oversight, modulation, and coordination by the cerebellum. Deficiencies in white matter function, interhemispheric communication, and cerebellar function are each known to be more common in dyslexic than non-dyslexic individuals (especially in the pre-adult years). In addition, many dyslexic children are known to have difficulty with muscular coordination, especially for fine motor actions. Consequently, it should not be surprising that their visual movement functions, which are controlled by many of the same neural pathways, are also poorly coordinated.
Not surprisingly, several types of visual difficulties are more common in dyslexic than non-dyslexic children. In one study of dyslexic children, just one type of visual problem, near-point convergence insufficiency, was present in 30-40% of the dyslexic children, compared to just 20% of controls. (As can be seen from this control figure, visual processing problems are also quite common in non-dyslexic school-age children). For children with convergence insufficiency, peer-reviewed NIH sponsored research has shown that home therapy can work as can home exercises with computer training, but that in-office therapy shows the best efficacy.
Not all dyslexic individuals have visual processing problems, and correction of these visual problems will not "cure" dyslexia. However, for children who have both dyslexia and visual problems, interventions (whether visual exercises, vision therapy, or glasses) will often improve their ease and endurance for reading. Many of the children who have visual difficulties will experience visual symptoms both with reading and--importantly--with other kinds of near work, and they will often be able to describe their visual symptoms if asked. They may report that they can't read clearly because the letters are blurry, or that letters wiggle or seem to move in-and-out of the page. They may also report fatigue, eye strain or tearing, headaches, or other symptoms. Both in our clinical experience and in published research data, children with such symptoms will often show benefits from visual therapy.
Again, it would be a mistake to believe that vision training "cures" dyslexia or that dyslexia is entirely or even primarily a visual disorder. Dyslexia usually involves a range of issues, nearly always including important challenges in the phonological processing system. That's why training in phonics/phonological awareness is the cornerstone of therapy for dyslexic challenges in literacy. However, differences in the phonological processing module cannot account for many of the common findings associated with dyslexia. Instead, the preponderance of available research strongly suggests that the difficulties with phonological processing, along with the difficulties with visual processing, are in turn due to more fundamental differences in neurological structure and function. That's why it is important not to limit interventions to simply addressing phonological processing challenges when children show other important challenges. When visual problems are present in individuals with dyslexia, and they commonly are, these individuals can be greatly helped by interventions that directly address their visual challenges.
The video below is from Finland, but look at the eye movements a child needs to make in order to read a passage fluently.
But also check out this video showing eye tracking movements as a fluent reader scans a web page. Many dyslexics would have trouble with this: the reading is so fast and not word-by-word, and the eyes leap to different sections of the page.
Finally, if you'd like to learn more how convergence insufficiency presents with vision problems, check out this video from the NEI:
Eide Neurolearning Blog: Training the eyes to see
Convergence insufficiency from the Mayo Clinic
Visual Training in Basketball
Benefits of visual training at the US Airforce academy
Retraining the brain after visual stroke
Visual training improves stroke-induced hemianopic alexia