twenty-twenty vision的词源

英文词源

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elf

elf: [OE] In Germanic legend, elves were potent supernatural beings, capable of exercising considerable magic powers to the benefit or harm of human beings. Their decline to their modern status as small mischievous sprites seems to have begun in the 16th century. The word comes from a prehistoric Germanic *albiz, a variant of which produced Old Norse álfr (source of English oaf [17]) and German alp ‘nightmare’.
=> oaf

中文词源

twenty-twenty vision：正常视力，极好的视力

来自视力测试公式 20/x vision,其中分子 20 即 20 英尺，约为 6 米，人与视力 E 图站立的距 离，分母为字体大小鉴别力，如分母为 20，则除数为 1，即正常视力，如分母为 10，则除 数为 2，视力好于正常视力的人一倍，如分母为 40，则除数为 0.5，较差视力。鉴于现代社 会近视眼越来越多，所以由正常视力引申词义极好的视力。

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