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视力标准表为什么用e

更新时间: 2020-10-28 00:00:00     

视力标准表用e是为了让不认识英文字母的人,也可以看懂E字三横线缺口的方向。常用的E字国际标准视力表是根据视角的原理设计的。所谓的视角就是由外界两点发出的光线,经眼内结点所形成的夹角。在5米距离,10行的E字上下两横在视网膜上的投影正好是1度角,计算公式为:视力=1/度角。

关键词: 视力 标准 为什么

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