Which is the Snellen chart used for?

They should have explained what the numbers mean. 20/20 means that the patient can see at 20 ft what a normal person can see at 20 feet. That is, they have normal acuity. But if they have 20/40, they need to be at 20 ft what a normal person can see at 40 ft. They need corrective lenses.

Just had this question on a a re-run of “Who wants to be a Millionaire “ I think it’s worth £16000. Can I have my money please.

I'm not good at maths

I have an eye condition so I know all about this.

Timoteo, Thanks for that very interesting info!