Being nearsighted is far more common than it once was. The prevalence of myopia, the condition’s medical name, in Americans has soared by 66 percent since the early 1970s, according to a 2009 study by the National Eye Institute; in China and other East Asian countries, as many as 90 percent of recent high school graduates are thought to be nearsighted.

近视比以前普遍多了。据美国国家眼科研究所2009年的一项研究显示，自20世纪70年代初，美国人近视的比例飙升了66%;而在中国和其他东亚国家，高达90%的高中毕业生被视为近视。

 

Myopia results when eyeballs are longer than normal, changing the angle at which light enters the eye and therefore the ability to focus on distant objects.

当眼球比正常情况下长时，近视就会发生，改变光线进入眼睛的角度，从而改变眼睛聚焦远处物体的能力。

 

The disorder¹ involves a complex interplay of genetics and environment and usually begins before adolescence², when the eye is growing, but it can worsen in early adulthood³.

这种疾病涉及了遗传和环境的复杂相互作用，通常发生在青春期之前，那时候眼睛还在成长，但在成年初期可能会恶化。

 

Some experts connect the elevated rates of myopia to the many hours young people stare at computers and other screens. But a recent study published in JAMA Ophthalmology suggests that a greater factor may be a side effect of all that screen-watching — it’s keeping children inside.

一些专家认为近视率升高与年轻人长时间盯着电脑和其他屏幕有关。但最近发表在《美国医学会眼科杂志》上的一项研究表明，更重要的因素可能是使孩子长时间盯着屏幕看的副作用是让孩子呆在了室内。

 

This new study joins a growing body of research indicating that a lack of direct sunlight may reshape the human eye and impair⁴ vision.

越来越多的研究表明，缺少与阳光的接触可能会改变眼睛的形状，而损害视力。

 

Strong correlations⁵ were found between current eyesight and volunteers’ lifetime exposure to sunlight, above all UVB radiation (which is responsible for burning).

研究发现，志愿者目前的视力与其暴露在阳光下(尤其是导致灼伤的中波紫外线辐射)的时长有很强的相关性。

 

Those who had gotten the most sun, particularly between the ages of 14 and 19, were about 25 percent less likely to have developed myopia by middle age.

那些经常晒太阳的人，尤其是14岁到19岁之间的人，中年近视的可能性要低25%。

 

Exposure to sunlight up to the age of 30 also conferred a protective benefit.

30岁之前晒晒太阳也有保护作用。

 

This relationship held true even when the researchers controlled for education as a marker primarily of time spent reading and gazing at screens.

即使研究人员把教育作为阅读和盯着屏幕看的主要原因，这种关系仍然成立。

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