A new comprehensive study of eyesight around the world has found that 80 to 90 percent of secondary school graduates in East Asia suffer from nearsightedness, or myopia. The new study, published in the Lancet medical journal recently, found that neither genes nor increased time reading and writing were to blame for the worsening rate of poor eyesight. The real cause was more basic — lack of sunlight.

The worst eyesight was found in major East Asian cities in China, Taiwan, Hong Kong, Japan, Singapore and South Korea. The rates of myopia there were consistently 80 to 90 percent throughout East Asia, with 10 to 20 percent of those affected suffering from high myopia, a condition that can ultimately lead to severely impaired vision and blindness.

The study concluded that lack of exposure to bright light outdoors was the major cause of the problem. This large comparative study found that the rate of myopia in Britain was 30 to 40 percent and in Africa only 2 to 3 percent.

Around the world, the average rate of myopia was only 10 to 20 percent. In the past, genetic factors were believed to be the primary reason Asians had weak eyesight. In those other areas of the world, exposure to sunlight was a more common part of the day, especially for children.

In East Asia, however, students tend to go to school and then go home and study or watch TV, computer or game screens. Excessive reading itself was not considered to be the primary cause, as had been assumed in previous studies.

Instead, it is now clear that exposure to bright natural light stimulates the release of dopamine, which helps the eyeball grow naturally without becoming elongated, a condition that distorts focus. Exposure to two or three hours of sunlight a day was found to counterbalance increased hours studying indoors.

It will be no surprise to learn that young children need a balance of activities to develop, but this study shows how activities deeply affect young people’s physical development. More time in sunlight should become a regular part of daily activities for all children so that their eyes can develop — not to mention other benefits such as learning about nature, enjoying play and reducing stress.

All those who supervise children should be sure sufficient time is spent outdoors. The current practice of letting children grow up inside is severely shortsighted.

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