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.
6 t% @# E: u, o6 ^5 uvisual aids (glasses or contact lenses) must have vision of 20:20 (6:6) with both eyes open.
' y6 [% e+ u* ], k& H2 j* E1 k
2 }  ^4 x! A2 |3 j请问上面的意思是什么？相当于国内什么等级的视力？谢谢！