State-of-the-art warplane cockpit systems that allow pilots to aim missiles with their eyes are being adapted by defence researchers and Oxford University scientists to help diagnose dyslexia by measuring whether children's eyes work properly when they read.

The diagnosis kit - designed to measure "eye wobble", one of the key components of dyslexia - uses two tiny video cameras fixed to a pair of spectacle frames. These contain reflective glass, like that used in one-way mirrors. When children put on the glasses and look towards a fixed point or a moving target, the cameras film their eye movements, which are measured with infrared light reflected by the glass.

A computer link then shows whether the child's eyes are fixing and tracking steadily, or whether they wobble.

Eye wobble can be catastrophic for young readers. Eight-year-old Alex Ing, for example, had "absolutely chaotic" eye movement when he visited Dr Sue Fowler at the Dyslexia Research Trust (DRT) clinic in Oxford.

Despite extra help at school and tests by an educational psychologist, nobody could discover why Alex, who scores above average on IQ tests, was failing to read.

Using existing techniques, Fowler found that, like many children, Alex could not fix his eyes for the fleeting second needed to read words, nor could he move his eyes steadily along a line of text. The words were a flickering jumble of letters to him, which was why he was frustrated, working hard, but still with a reading age 18 months behind where it should have been.

Six months later and Alex's reading age has caught up. His success is due to daily eye exercises prescribed by Fowler.

John Stein, professor of neurology at Oxford University, who with Fowler studies hundreds of children a year in the DRT clinic, believes that more than half of dyslexic children may have eye control problems. Some can be helped with exercises, others simply by putting a patch over one eye to stop their eyes competing to take the lead. Many improve with coloured glasses, which boost the contrast between the words and the page.

Should QinetiQ, the defence research agency, manage to bring the military's kit into commercial production in the next few years, it will make it much easier for opticians or specialist teachers to see at once whether a child is failing to read because of eye wobble and to prescribe exercises or glasses.

It will also show if a child has normal vision, in which case teachers and parents can then focus on the child's difficulties in understanding the relationship between the sounds and shapes of letters - the other key feature of dyslexia.

But whatever the cause, says Stein, the key factor in whether dyslexic children succeed at school is the age at which they are diagnosed and helped. It is vital they are caught young.For eye-training exercises, "ideally, you want to catch them by the age of eight".

For help with letter-sounds, research shows that "early intervention is roughly 10 times as effective as intervention later on", says Rod Nicolson, professor of psychology at Sheffield University.