AIBU to ask you to explain glasses prescription to me

[YouthGoneMild]

I’m just back from the opticians and my son has been given a score of +6 and +5 and I have no idea what that means.

No one else in my family wears glasses and I’m just baffled. I’ve googled +6 and it says 6/6 is perfect vision? So is the issue the +5? So is he 1 away from perfect?

The optician didn’t really explain anything and I was in shock as I had no idea he’d need glasses as none of us do so I didn’t ask the right questions.

Please can someone explain what this means? Is 20 good and 6 awful?

Thanks and sorry for my very tenuous AIBU.

(And yes, I’ve tried google, but got confused by the search results)

My optician always gives a copy of the prescription for my records. I can see how our vision has changed over time. Dd is +3.5 and +5.5 and has had glasses since she was 18 months old (now age 16)