为什么近视的人越来越多了?
<p><span word="Being">Being</span> <span word="nearsighted">nearsighted</span> <span word="is">is</span> <span word="far">far</span> <span word="more">more</span> <span word="common">common</span> <span word="than">than</span> <span word="it">it</span> <span word="once">once</span> <span word="was">was</span>. <span word="The">The</span> <span word="prevalence">prevalence</span> <span word="of">of</span> <span word="myopia">myopia</span>, <span word="the">the</span> <span word="condition">condition</span>'<span word="s">s</span> <span word="medical">medical</span> <span word="name">name</span>, <span word="in">in</span> <span word="Americans">Americans</span> <span word="has">has</span> <span word="soared">soared</span> <span word="by">by</span> 66 <span word="percent">percent</span> <span word="since">since</span> <span word="the">the</span> <span word="early">early</span> 1970<span word="s">s</span>, <span word="according">according</span> <span word="to">to</span> <span word="a">a</span> 2009 <span word="study">study</span> <span word="by">by</span> <span word="the">the</span> <span word="National">National</span> <span word="Eye">Eye</span> <span word="Institute">Institute</span>; <span word="in">in</span> <span word="China">China</span> <span word="and">and</span> <span word="other">other</span> <span word="East">East</span> <span word="Asian">Asian</span> <span word="countries">countries</span>, <span word="as">as</span> <span word="many">many</span> <span word="as">as</span> 90 <span word="percent">percent</span> <span word="of">of</span> <span word="recent">recent</span> <span word="high">high</span> <span word="school">school</span> <span word="graduates">graduates</span> <span word="are">are</span> <span word="thought">thought</span> <span word="to">to</span> <span word="be">be</span> <span word="nearsighted">nearsighted</span>.</p><p>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。</p><p><span word="Myopia">Myopia</span> <span word="results">results</span> <span word="when">when</span> <span word="eyeballs">eyeballs</span> <span word="are">are</span> <span word="longer">longer</span> <span word="than">than</span> <span word="normal">normal</span>, <span word="changing">changing</span> <span word="the">the</span> <span word="angle">angle</span> <span word="at">at</span> <span word="which">which</span> <span word="light">light</span> <span word="enters">enters</span> <span word="the">the</span> <span word="eye">eye</span> <span word="and">and</span> <span word="therefore">therefore</span> <span word="the">the</span> <span word="ability">ability</span> <span word="to">to</span> <span word="focus">focus</span> <span word="on">on</span> <span word="distant">distant</span> <span word="objects">objects</span>.</p><p>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。</p><p><span word="The">The</span> <span word="disorder">disorder</span> <span word="involves">involves</span> <span word="a">a</span> <span word="complex">complex</span> <span word="interplay">interplay</span> <span word="of">of</span> <span word="genetics">genetics</span> <span word="and">and</span> <span word="environment">environment</span> <span word="and">and</span> <span word="usually">usually</span> <span word="begins">begins</span> <span word="before">before</span> <span word="adolescence">adolescence</span>, <span word="when">when</span> <span word="the">the</span> <span word="eye">eye</span> <span word="is">is</span> <span word="growing">growing</span>, <span word="but">but</span> <span word="it">it</span> <span word="can">can</span> <span word="worsen">worsen</span> <span word="in">in</span> <span word="early">early</span> <span word="adulthood">adulthood</span>.</p><p>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。</p>
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