Dyslexia is a common learning difference that affects how individuals process language, particularly when it comes to reading. Despite its prevalence, there is widespread confusion regarding its origins, with many believing it stems from problems with the eyes. This article explores the scientific understanding of dyslexia, differentiating between its neurological basis and co-occurring vision issues, to clarify whether it is a problem of the eyes or the brain. We will delve into common misconceptions and examine the evidence behind various proposed interventions.
The Myth of Seeing Words Backwards
A common misconception about dyslexia is that individuals see letters or words jumbled or reversed. While some children with dyslexia may transpose letters like ‘b’ and ‘d’ or ‘was’ and ‘saw’ during reading or writing, this is not a visual perception issue. Such reversals are common in early literacy development. However, these difficulties tend to persist longer in children with dyslexia compared to their peers.
Studies consistently show that the eyes of individuals with dyslexia function normally, and they do not perceive text differently than those without dyslexia. For example, research involving dyslexic and non-dyslexic students asked to reproduce unfamiliar Hebrew letters found that both groups performed equally well in copying them. This demonstrates that the challenge lies not in how the eyes see the letters, but in how the brain processes and interprets those symbols in relation to sounds and language.
The Neurological Basis of Dyslexia
Dyslexia is a language-based learning difference originating in the brain, not a visual problem. It primarily involves difficulty with phonological processing, which is the brain’s ability to identify and manipulate individual sounds (phonemes) within spoken words and to map these sounds to written letters. The brain struggles to access its “sound library” to decode written words, making it challenging to sound out or recognize them quickly. This internal processing challenge distinguishes dyslexia from a vision problem.
Neuroimaging studies, such as functional magnetic resonance imaging (fMRI), consistently reveal distinct patterns of brain activity in individuals with dyslexia. These studies often show under-activation in specific left hemisphere brain regions involved in language processing and reading. These areas include the left temporoparietal cortex, involved in phonological processing, and the left occipitotemporal region, important for visual word form recognition. Alterations in white matter pathways connecting different brain regions have also been observed, further supporting its neurological basis.
Co-occurring Vision Issues and Visual Stress
While dyslexia is not caused by vision problems, certain visual difficulties can co-occur and make reading more challenging. Common co-occurring vision issues include refractive errors (nearsightedness or farsightedness), which affect clarity of vision. Binocular vision problems, like convergence insufficiency, are also observed, where eyes struggle to work together efficiently, causing eye strain or difficulty focusing on near tasks. Approximately 62% of children with dyslexia have also been found to have eye tracking disorders, which can result in skipping lines or losing one’s place while reading.
Another related phenomenon is “visual stress,” sometimes referred to as Meares-Irlen Syndrome. Symptoms include words appearing to blur, move, or shimmer, glare from bright lights, or headaches and eye strain during reading. Visual stress is a perceptual processing condition linked to over-excitability of neurons in the brain’s visual cortex when exposed to text patterns. While not dyslexia itself, visual stress is prevalent among individuals with dyslexia (affecting an estimated 37.5% to 50%), and can significantly impact reading comfort and fluency.
Evaluating Vision-Based Therapies
Given co-occurring visual symptoms, various vision-based therapies have been proposed for reading difficulties. These often include colored lenses or overlays and eye-tracking exercises (vision therapy). While these approaches aim to alleviate visual discomfort or improve eye coordination, their scientific standing regarding dyslexia is important to understand. Treating a diagnosed vision problem, such as convergence insufficiency, can make reading more comfortable and allow for longer reading periods.
However, major scientific and medical organizations (including the American Academy of Pediatrics, American Academy of Ophthalmology, and International Dyslexia Association) consistently state there is no scientific evidence supporting these therapies as treatments for dyslexia’s core language-processing deficits. They emphasize these interventions do not address dyslexia’s neurological foundation, which is related to phonological processing. Claims of “curing” dyslexia with vision-based methods are not supported by rigorous research; studies advocating for them often have methodological limitations.