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.
$ ^1 u, C5 V. M8 Z1 w6 uvisual aids (glasses or contact lenses) must have vision of 20:20 (6:6) with both eyes open.
0 O5 n5 _/ d2 p7 ~  V
1 M! E8 q! f& S7 G% k5 R请问上面的意思是什么？相当于国内什么等级的视力？谢谢！