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.
' A9 D+ h6 T# ]4 S( ~3 @# wvisual aids (glasses or contact lenses) must have vision of 20:20 (6:6) with both eyes open.
5 Z. {+ Q! V" Q& Q
2 V$ `  Y3 Z: B4 `, D请问上面的意思是什么？相当于国内什么等级的视力？谢谢！