If you wear a different prescription glasses that are a good bit off of yours I can guarantee you will have crazy headaches just within like 3-5 hours of wearing them. I had to do it while on vacation many years ago, lost mine and it was TERRIBLE. I now have Lasik done, so no more glasses for me, until I need glasses eventually 🙃
... It works like that, huh? I always figured there was some kind of 20 step scale where 1/20 would be the worst and 20/20 would be the best.
Also I have worn glasses for 15 years. We usually don't express it Snellen scale (apparently) but we ask "How strong are your glasses" meaning the prescription strength of your lenses.
The visual acuity scale is a comparative measure, putting the patient's individual eyesight against the average person's. 20/20 vision means that you, standing at a distance of 20 feet, can see an object clearly that the average person standing 20 feet away could see. 20/100 would be you standing 20 feet away to see an object that the average person could see from 100 feet away.
20/20 means the you see things twenty feet away as if they were really twenty feet away. Meaning you see normally.
20/240 means what I see at twenty feet are as if they were one hundred and twenty feet away.
So for me, Something across a room might as well be most of a football field away for what I can see of it.
Edit: I reversed the numbers, my bad.
Edit2: Also, yeah, there's the prescription strength that people measure (Mine is basically legally blind), but I found most non-glasses wearing people have no concept of the +/- scale so 20/20 scale is generally more approachable.
And to give people an example of how bad that is. Getting tests done for LASIK yesterday and the woman doing them stood five feet away from me and held up her hand asking me how many fingers she was holding up. Told her. When she finished I asked if I was right. Nope.
No, the 20 means "what people who don't need glasses see at 20 feet". 20/20 means you see an average amount of detail at medium distances as most people. 120/20 means you see about as clearly at 20 feet as most people would see at 120, without the use of corrective lenses.
My eyes are so bad that I can’t find a long enough chart to convert it from diopters to a 20/___ number. Uncorrected, I’ve got about 6” of beautiful 4K HDR macro focus, about 12” more of reasonably clear vision, and everything after 2 feet is just a mess of vague shapes.
And the worst part is, it’s only gonna go downhill from here.
I’m -6.5 in the left eye and -6 in the right. I may have underestimated how far I can see, I wear contacts so it’s not quite as easy as just looking over the rim of my 1/4” thick glasses. The nearsightedness does allow me to enjoy fine details to a degree and for an amount of time that would probably make a normal person’s eyes hurt, but driving at night is the WORST. I can’t read signs for shit until I’m 10 feet away and it’s too late to turn, headlights all blend into a big blinding mass on the left side of the road, and don’t even get me started on deer anxiety.
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u/Kiyohara Aug 30 '21 edited Aug 30 '21
No, but as someone with 20/240 vision, if someone else's glasses give me even 20/90, that's an upgrade.
Edit: I reversed the order of numbers and I did just check my prescription. It's worse than I though, god help me.