While phonological processing is a key factor, it is not the complete picture, writes Alex Old.
Since dyslexia was first identified, researchers have debated the role of vision in the condition. Historically, dyslexia was even referred to as “word blindness” or “congenital word blindness”, highlighting its perceived link to vision. People with dyslexia often describe having visual symptoms such as headaches or eyestrain during reading. Text may appear double or blurry. The letters b and d may be confused with each other. Words and letters may appear to move on the page. A reader may tend to lose their place in a paragraph, or skip lines while reading. They may have difficulty reading small or unusual fonts, and they may experience discomfort from bright lights or high contrast between text and background. Other indications may include holding books unusually far away while reading, or covering one eye or tilting the head while reading.
A shift in how we define dyslexia
In the early 2000s, there was a shift in how dyslexia was defined. Today, it is primarily recognised as a language-based learning disorder, due to a phonological deficit rather than visual difficulties. Consequently, current teaching methods for students with dyslexia focus on phonics instruction and the development of phonological awareness. While this has helped improve teaching strategies, it has also led to less attention being paid to visual difficulties that often occur alongside Dyslexia.
Visual difficulties
In this context, visual difficulties do not refer to common vision problems, such as near-sightedness or far-sightedness, which can typically be corrected with glasses. Instead, the term refers to issues such as convergence insufficiency (difficulty keeping both eyes aligned when focusing on close objects), or accommodation insufficiency (difficulty maintaining clear focus on nearby objects, particularly over extended periods).
The research
Recent studies have shown that many children with dyslexia also experience these visual problems. A 2015 study from the University of Leeds found that 35% of children with dyslexia had accommodation insufficiency, compared to 0% in the control group. A 2018 study by Harvard Medical School and Boston ophthalmology hospitals found that 55% of children with developmental dyslexia had accommodation insufficiency, only 9% in the control group had this issue, and the level of difficulty was significantly higher in the dyslexic group. Other studies have also found a strong connection between convergence insufficiency and reading difficulties, including dyslexia.
Why this matters
Despite growing evidence, most support for children with dyslexia still focuses only on phonological skills. As a result, children with both dyslexia and visual difficulties may not receive the full support they need. This limited focus can mean that visual challenges go undiagnosed. Children may continue to struggle, despite phonics instruction or improved phonological awareness, and some students may be misidentified as having low motivation or poor attention, when visual strain is the underlying cause of their reading difficulties.
How to identify visual issues
There are simple tools available to help identify visual issues in children, such as the Convergence Insufficiency Symptom Survey (CISS). If a child shows signs of visual strain or discomfort, they may benefit from vision training – either online or in person -alongside phonics-based instruction.
Dyslexia is complex. While phonological processing is a key factor, it is not the complete picture. By also considering visual difficulties, we can gain a better understanding of, and provide more effective support for, the many children who struggle with reading.