SPECTACLES make no difference to long-sighted children with Down's syndrome and can make those with short sight worse off at near distances, recent research has shown.
About 96 per cent of children with Down's cannot focus accurately on close objects. While they have difficulty focusing from birth, their detailed vision tends to be normal until they are about two, when it starts to fall behind the norm.
The vast majority become long-sighted but those who develop short sight are usually severely short-sighted.
A six-year project at the University of Cardiff, which has monitored the sight of 76 of these children since birth, found they could not focus any better at near distances with glasses.
The only advantage of spectacles appeared to be that the children had to work slightly less hard at seeing objects, although their vision remained just as blurred.
But those with short sight - estimated at between 6 and 20 per cent of people with Down's syndrome - actually saw less.
J. Margaret Woodhouse, senior lecturer in the department of optometry and vision sciences, who is conducting the research, said in the six years of the study, some of the children had started to wear glasses and they had been able to monitor their ability to focus on near objects before and afterwards.
"They are remarkably consistent in still being out of focus at near," she said. "The next step is to find out why."
The researchers have a number of untested hypotheses about the reasons for the children's vision remaining blurred.
It may be that those with Down's syndrome do not recognise blurred images in the same way as other people. Or they may have problems with the binocular action of looking at something close to them. When people look at something close their focus converges and it is possible that people with Down's have difficulty making this link.
Solving these questions should help those with Down's syndrome to use spectacles more effectively and could eventually prevent the defect in the first place.
The research is part of a wider study into the link between vision and cognitive performance.