Dyslexia-eyesight link 'unlikely'
Correcting vision problems in children with dyslexia is unlikely to have any effect on the condition, new research has shown.
In the first study of its kind, scientists found no evidence that visual deficiencies are linked to severe cases of "word blindness".
The results call into question the value of common private treatments that can cost parents thousands of pounds.
Many experts had already cast doubt on the effectiveness of the therapies, which typically involve the use of coloured lenses and overlays and eye exercises.
The new research, published in the journal Pediatrics, tested whether the supposed connection between dyslexia and eyesight problems was based on fact or just a myth.
Lead author Dr Cathy Williams, from the University of Bristol, said: "We want to spread the word that if you look at a whole population of children with dyslexia, very few of them have vision problems.
"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.
"Families now might want to ask: what visual impairment is actually being treated, how is it measured, and what is the evidence that treating it will help a child with dyslexia?"
Dyslexia affects around 375,000 children in the UK, impairing their ability to read and understand written words. It can have lifelong impacts on education, relationships, and employment prospects.
The scientists analysed the results of eye tests conducted on 5,822 seven and eight-year-olds taking part in the Children of the 90s study, a large investigation charting the health of children in south-west England.
Each child was given a reading assessment at age nine which revealed that 3% had severe and 8% moderate dyslexia.
The results were compared with those from 5,650 other children of the same age whose reading ability was normal.
More than 80% of the dyslexic children showed no evidence of a vision problem, the researchers found. Tests were carried out for squint, 3D imaging, long and short sightedness, contrast recognition, and "fusion" - the ability to compose a single picture from two slightly different images from each eye.
Only the fusion test showed any correlation with dyslexia - one in six dyslexic children had this problem. However, so did one in 10 children with no sign of dyslexia.
Co-author Dr Alexandra Creavin, from the University of Bristol's School of Social and Community Medicine, said: "Our findings may reassure families that their child's sight is very unlikely to be affecting their reading ability, assuming the need for glasses has been ruled out, and so they can pursue other options for supporting their child.
"Fortunately there are treatments and training programmes to help children with dyslexia that do have a good evidence base, including training in phonics (speech sounds)."
She added: "It would be really great to have some clear guidance for clinicians and parents about what is appropriate treatment."
Alternative therapists who focus on eyesight to treat dyslexia typically charge £100 to £200 for an initial consultation. Thereafter the package of treatment can cost hundreds or even thousands of pounds.