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.
+ h2 M* `% A( c+ p, F9 tvisual aids (glasses or contact lenses) must have vision of 20:20 (6:6) with both eyes open.
- Z, c' h6 `5 `. U! H6 S
" \- Z. `! _% w3 r) \# \  l6 f请问上面的意思是什么？相当于国内什么等级的视力？谢谢！