Roger Harrabin Today programme correspondent

Professor John Stein, who runs free clinics for children in Oxford and Reading, says his latest research suggests that more than 30% of dyslexics can improve their reading with yellow glasses.

He believes still more can be helped by blue glasses and eye exercises.

"The root cause of dyslexia is a change or a difference in the way certain nerve cells in the visual system work," he said.

"What the coloured spectacles can do is to redress the balance of input of visual information into the system and thus help dyslexics to read."

First resort

The coloured glasses are not available on the NHS, and parents of dyslexic pupils in other parts of the country have to pay privately to see if their children can be helped in this way.

Funding for Professor Stein's free clinics is now running out. He says this is madness while educational special needs budgets are soaring, and he urges the government to try cheap medical solutions for dyslexic children as a first resort.

One 14-year-old from Oxford, Charlie Freeston, recently saw her reading age jump by four years after being prescribed a pair of blue tinted spectacles.

Dyslexia is an umbrella term covering a range of difficulties and only some people have a visual difficulty Dr Lindsay Peer, BDA

"You do it with all different coloured glasses and I think I did best with blue-coloured ones so they gave me some to take home.

"I'm loads more confident with my reading and my work now.

Professor Stein believes there may be widespread under-diagnosis of dyslexia because education authorities fear that it will cost too much if more sufferers are discovered.

This might mean thousands of children are failing to reach their potential.

Professor Stein is seeking funding from medical charities to continue the free clinics.

But he says the government should pay for a network of free clinics, because it's much cheaper for the taxpayer to offer dyslexics cheap coloured glasses than to provide expensive special needs tuition.

He says he has problems getting funding because dyslexia is considered an educational problem not a medical problem, and because educational experts have been slow to acknowledge the potential of medical solutions to the disorder.

Complex condition

The British Dyslexia Association, which advises the Department for Education, says there is some suggestion that coloured glasses can be helpful but there are many different forms of dyslexia that cannot be helped by medical methods.

The organisation's Dr Lindsay Peer told the Today programme on BBC Radio Four that dyslexia was a wide term.

"What we need to understand is that dyslexia is an umbrella term covering a range of difficulties and only some people have a visual difficulty," she said.

There is also scepticism among the psychologists who dominate the world of dyslexia that science can provide cures for an extremely complex condition.

But Professor Stein urges that the cheapest options for tackling dyslexia should be tried first.

The Department for Education said that it was up to the Department of Health to decide if the coloured glass tests should be incorporated into a standard eye test.

Scientists are not yet certain why the coloured glasses help some dyslexics.

In a lecture at the Royal Institution on 2 July, Professor Stein suggests that the lenses filter out the wavelengths of light that disturb cells in the brain damaged by an auto-immune disorder in the womb.

He thinks the damage affects the relationship between the cells that perceive the words in a book and the different cells that perceive the background page.