Don't Be Myopic with Myopia
Undercorrection makes it worse, study finds; go for full correction, says British researcher
PARIS
Conventional way of fixing shortsightedness by "undercorrecting" the prescription for glasses can dramatically worsen one's sight and may even lead to blindness, a study says.
The research, conducted among 94 children in Malaysia, may help explain why myopia has become rampant, said a report in New Scientist.
For more than half a century, optometrists have been routinely undercorrecting myopia when prescribing glasses or contact lenses.
However, they have good intentions for doing this. Among shortsighted people, the eye muscles cannot flatten the lens in the front of the eye so that it focuses light directly onto the retina, the wall of light sensitive cells on the back of the eyeball. Instead, the point of focus is in front of the retina, which creates a bluffed image.
Glasses or contact lenses can fully correct this by shifting the focal point back to the retina. The problem is that when people wearing this prescription look at close objects such as books, the focus point is usually behind the retina.
The assumption is that this refocusing effort causes the eyeball to elongate-a movement that not only makes distance vision worse but also boosts the risk of sight threatening eye ailments such as glaucoma and retinal detachment.
Undercorrection, according to the theory, should help to stop elongation. Optometrists routinely do this by prescribing a lens that focuses light from distant objects just in front of the retina, rather than exactly on it.
The team led by Daniel O'Leary of Anglia Polytechnic University in eastern England carried out their study with the initial idea of confirming the undercorrection theory. He and colleagues at the National University of Malaysia in Kuala Lumpur undercorrected the sight of half of 47 child volunteers, and fully corrected the sight of 47 others.
They were astonished to find that among the 47 undercorrected children, the eyeball elongated faster-their sight got worse.
"The study was meant to run for three years but after two years, when we found out we were making the children's eyes worse, we had to stop it prematurely," O'Leary said. "Shortsighted people need to know [undercorrection is] not the thing to do."
Eye experts have puzzled over why myopia has become so common, especially among children who spend a lot of time reading or doing close work. Various factors, including diet, have been mooted as the cause, but O'Leary points the finger at the fashion for undercorrection, which has been explored in scientific research just twice.
The first was a study of 33 Japanese schoolchildren back in 1965 while the other was on chicks in the 1990s-and both have been dismissed as lacking rigor or relevance.
O'Leary speculates that undercorrection is dangerous because the eye cannot 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. That means any blurred vision will make the myopia worse.
"No glasses is the worst option of all," he said. "But don't undercorrect. Go for full correction."
Shortsightedness has reached epidemic proportions in Asia, where in Hong Kong, Singapore, and Taiwan, as many as 90 percent of young people are myopic, three times more than in Europe and the United States. AFP
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