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.
) D0 e0 Q& G; S' a( b5 m8 kvisual aids (glasses or contact lenses) must have vision of 20:20 (6:6) with both eyes open.
: l+ `9 J) G: Y) c5 G. r0 _& }2 l
* x) }1 G& d/ y* h, S7 V: y- s2 r- A请问上面的意思是什么？相当于国内什么等级的视力？谢谢！