请教这里的视力标准如何换算成国内的数值？

nils_li

an uncorrected visual acuity of at least 20/40 (6/12) with both eyes open.
4 u- w+ W( Z: X  r6 w7 ~/ ]visual aids (glasses or contact lenses) must have vision of 20:20 (6:6) with both eyes open.
9 g# U2 S0 J# r' O* l# W4 ?
7 e$ b$ M! N2 b请问上面的意思是什么？相当于国内什么等级的视力？谢谢！