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As the editorial writers from Erasmus University Medical Center in the Netherlands suggested, “young children may be more sensitive to myopic triggers from the environment.” An earlier eye study among children in Sydney, Australia, also found that only the younger ones who became myopic had spent more time on near work rather than being out in daylight.
Although many people have long believed that excessive reading fosters nearsightedness in children, current thinking is that too much time spent indoors has the greater effect and likely accounts for any apparent association between close work or screen time and myopia.
Dr. Neil M. Bressler, an ophthalmologist affiliated with Johns Hopkins Medical Institutions, said that the high intensity of outdoor light has an important influence on the shape of the eye, which in turn affects whether images are seen clearly.
To be in focus, light rays from an image have to converge on the retina. In myopic eyes, the convergence occurs in front of the retina, and a corrective lens is needed to redirect incoming rays so that distant objects are in focus.
Most children are born slightly farsighted. Their eyes are shaped like partly deflated balls, causing images to converge behind the retina. But as they get older, their eyes elongate to form a sphere, permitting images to converge directly on the retina. However, if elongation fails to stop at some point, the eyes become more oval and images then converge in front of the retina, the definition of myopia. Outdoor light stimulates the release of dopamine that may slow elongation of the eye, Dr. Bressler said.
Although the rise of myopia is happening worldwide, the epidemic is raging in east and Southeast Asia, where 80 percent to 90 percent of high school children are now myopic.
Concern over the increasing prevalence of myopia goes beyond a growing need for glasses, contact lenses or, for those so inclined and who can afford it, laser treatment to redirect images by changing the shape of the cornea. In general, people with myopia are more likely to develop sight-threatening complications later in life like cataracts, glaucoma and degeneration of the macula, the center of the retina.
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