French scientists believe they have identified a physiological cause for dyslexia which could lead to a potential treatment.
They found that in people with the condition, tiny light receptor-cells were arranged in matching patterns in the centre of each eye.
In non-dyslexics, they did not match, allowing the brain to choose one eye to override the other and create a single image.
They now believe the matching cells do not allow for this and confuse the brain by producing “mirror” images in opposing hemispheres.
“Our observations lead us to believe that we indeed found a potential cause of dyslexia,” Professor Guy Ropars, the study's co-author told the Agence France Presse (AFP) news agency.
Prof Ropars, who is based at the University of Rennes, added that the discovery offers a potentially simple way to diagnose people with dyslexia - by looking into someone's eyes.
The scientists claims they were also able to develop a treatment for the condition after discovering a slight delay between the brain producing a primary image and the other hemisphere’s mirror image.
By flashing an LED lamp, which switches off and on so quickly it is invisible to the naked eye, Prof Ropars and his colleague Albert le Floch say they were able to “cancel” one of the images in the brains of participants who were reading.
The new study, published in the Proceedings of the Royal Society B journal, found a major difference between the arrangement of rods and cones – the eye’s light-receptor cells – in dyslexic and non-dyslexic people.
Cones, which are responsible for seeing colours, come in red, green and blue variants. But there is a tiny hole in the centre of the cornea where there are no blue cones.
In non-dyslexics they discovered one eye had a round hole, making it dominant over the other eye, which had an uneven shaped hole.
In people with dyslexia both holes were round, meaning neither eye was dominant and giving rise to potential “mirror errors” in reading, such as confusing “b” and “d”.
“The lack of asymmetry might be the biological and anatomical basis of reading and spelling disabilities,” the study’s authors said.
They added: “For dyslexic students their two eyes are equivalent and their brain has to successively rely on the two slightly different versions of a given visual scene.”
Around one in 10 people in Britain suffer from dyslexia, with as many as 700 million people with the condition globally.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies