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.
5 P/ q" V% K% _. l" _& `1 ^8 X9 qvisual aids (glasses or contact lenses) must have vision of 20:20 (6:6) with both eyes open.
+ S4 x# |6 O. K% o
* [/ q- ]7 R$ R* W* i4 _1 S请问上面的意思是什么？相当于国内什么等级的视力？谢谢！