Retired AME here.
As an aside, and not really relevant to the OP's question.
"20/20" is an American description of " normal" distant visual acuity, not usually used in the UK. It means, basically, that an eye can see at 20 feet what a "normal" eye can see at 20 feet.
In the UK it is "6/6" which means the same really, that an eye can see at 6 metres what a "normal eye" can see at 6 metres.
There is a link to a CAA conversion table here https://www.caa.co.uk/WorkArea/DownloadAsset.aspx?id=4294973558
Many young people, with healthy eyes, and appropriate correction if necessary, can actually see rather better than 6/6. My eye chart went down to 6/4 and many youngsters could read that.
If anyone read the "Made in England" line at the bottom, I knew they had cheated and read it in advance.