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.
# |& e; J9 Y' O  Ovisual aids (glasses or contact lenses) must have vision of 20:20 (6:6) with both eyes open.
+ }$ m3 _/ C$ ?$ Q- H  [; b: i( y4 X
$ H5 |4 t9 @- m请问上面的意思是什么？相当于国内什么等级的视力？谢谢！