'No evidence' for vision-based dyslexia

The findings could raise questions around the effectiveness of ophthalmic interventions for dyslexic children, such as coloured filters to help with reading.

Researchers from Bristol and Newcastle universities reviewed data from almost 6,000 children aged 7–9, taken from a large cohort study run since the 1990s. Children underwent a number of tests, including comprehensive eye examinations. 

Of the 5,822 children, 3% had severe dyslexia and 8% had moderate dyslexia – as measured by the level of reading impairment. The researchers found visual eye symptoms in 20% of the children, with a slight increase in the prevalence of stereoacuity and fusion issues in those with dyslexia. However, they write that the increase seen in the dyslexic group could be as a result of their reading impairment or other factors.

Dr Cathy Williams, a paediatric ophthalmologist at Bristol Eye Hospital and lead author of the study, said the results show that “vision problems are rare in dyslexic children,” with a similar occurrence in their non-dyslexic classmates.

Dr Williams added: “Some practitioners feel that vision impairments may be associated with dyslexia and should be treated. However, our study results show that the majority of dyslexic children have entirely normal vision on the tests we used.”

However, some experts have highlighted limitations of the study, including the coarse nature of the ophthalmic tests used and the way in which the group analysed the data – reducing test results to normal and abnormal, omitting much of the variance.

Disputing the findings, director of research for the Institute of Optometry, Professor Bruce Evans, told OT that the visual correlates of dyslexia are subtle, “but can in some cases cause an extra burden when the child reads.”

“Unfortunately, the authors’ tendency to reduce their test results to pass/fail seems to extend to their conclusions, where they only seem to consider two options: visual problems cause dyslexia or visual problems are irrelevant to dyslexia,” said Professor Evans.

He added: “The situation is more complex than that and two children with [reading difficulties] are likely to have a very different pattern of abilities and disabilities. In a few cases, visual factors add to the disability and then a visual treatment, for example, glasses, eye exercises or coloured filters, will give the child better access to the extra teaching that they no doubt will also need.

“I fear that the authors will do work in this field a great disservice by taking us back to a time when there were entrenched views about whether vision is everything or nothing to do with [reading difficulties].”

The research is published in the US journal Pediatrics. 

Image credit: NORRIE3699