MILLIONS of people worldwide may have worse eyesight and even be more likely to go blind because of a long-held but misguided idea about how to correct short-sightedness. A study intended to confirm the theory has instead been stopped because the children鈥檚 eyesight was getting worse, New 杏吧原创 has learned.
For decades, many optometrists have been routinely 鈥渦ndercorrecting鈥� short-sightedness, or myopia, when prescribing glasses or contact lenses. 鈥淲hat was done was done with the best of intentions,鈥� says optometrist Daniel O鈥橪eary of Anglia Polytechnic University in Cambridge, England. Indeed, his study of 94 children in Malaysia sought to prove the value of undercorrection. Instead, it showed the opposite.
While the number of children involved was small, amazingly it is the largest and most rigorous study to date. 鈥淭he study was meant to run for three years but after two years, when we found out we were making the children鈥檚 eyes worse, we had to stop it prematurely,鈥� O鈥橪eary says. 鈥淪hort-sighted people need to know it鈥檚 not the thing to do.鈥�
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The results have been hailed by some optometrists as key evidence that could change the way children are treated. 鈥淚t鈥檚 the strongest evidence I鈥檝e seen in this field,鈥� says Paul Adler, a spokesman for Britain鈥檚 College of Optometrists. 鈥淚t could change prescribing practice worldwide.鈥�
There鈥檚 still much debate about the causes of myopia, but it is certainly common in children who spend a lot of time reading or doing close work. It has reached epidemic proportions in Far Eastern countries such as Taiwan, Singapore and Hong Kong, where 90 per cent of young people are short-sighted, compared with 15 to 30 per cent in Europe and the US.
In short-sighted people, the muscles in the eye can鈥檛 flatten the lens enough to focus light from distant objects directly on the retina. Instead, the point of focus is in front of the retina, creating a blurred image (see Graphic). Glasses can fully correct this problem, moving the focal point back onto the retina.
But when people wearing normal glasses look at close objects, the focus point is usually behind the retina. The theory is that to try to 鈥渞efind鈥� this focal point for near objects, their eyeballs actually elongate. Not only does this make distance vision even worse, it also increases the risk of serious eye diseases such as retinal detachment, glaucoma and retinopathy, all of which can lead to blindness.
According to this theory, undercorrection should help stop the eyeball elongating. When they undercorrect, optometrists prescribe a lens that focuses light from distant objects just in front of the retina, rather than exactly on the retina.
Yet the only proof that it works comes from a study of just 33 Japanese children in 1965, and from studies on chicks in the 1990s. And these studies have since been attacked as lacking rigour or relevance.
In their trial, O鈥橪eary and his colleagues at the National University of Malaysia in Kuala Lumpur, undercorrected the sight of half the children and fully corrected the rest. Then they measured the length of the eyeball with ultrasound every six months. To their surprise, they found that the eyeball elongates faster when vision is undercorrected.
As a result, the team reports in a paper that will appear in Vision Research, on average the vision of the 47 children with undercorrected myopia deteriorated more rapidly than those given full correction (see Graph). Yet full correction has long been out of fashion. 鈥淚 had to go back to 1938 to find someone in the literature saying a full correction should be made,鈥� O鈥橪eary says.
The explanation for his results, O鈥橪eary speculates, is that the eye can鈥檛 tell whether the focal point is in front of the retina or behind it. It just grows backwards if the image is out of focus 鈥� which means that not wearing glasses might be even worse than undercorrection. 鈥淎ny blurred vision will make myopia worse,鈥� he says.
Adler thinks this is a key conclusion that demolishes previous assumptions and could help optometrists develop better treatments in the future. Other researchers, however, think further studies are needed to prove that any kind of blurred vision makes myopia worse.
Undercorrection could be bad for adults as well, O鈥橪eary thinks, although any decline is likely to be slower than in children. His findings suggest that generations of people worldwide could have somewhat worse eyesight because of the popularity of undercorrection. The reason is that vision research isn鈥檛 a priority in Europe and the US, O鈥橪eary says. 鈥淪tudies have been few and far between. It鈥檚 hard to get funding for myopia research in the West.鈥�
O鈥橪eary鈥檚 message to doctors, patients and parents is unequivocal. 鈥淣o glasses is the worst option of all,鈥� he says. 鈥淏ut don鈥檛 undercorrect. Go for full correction.鈥�