Simplest case is you are farsighted. So your lenses are magnifiers. You move them away from a printed page til the magnification is at maximum. The distance to the page is the focal length. Diopter is 1/FL in meters, so eg. 50cm FL is 2.0 diopter. Negative diopters, astigmatism corrections etc are more complicated.
It looks like you can also test your own vision with a phone app and simple device:
Seems neat I guess. I just wonder why the hell I can’t just go in with my old prescription, tell them straight up that this is perfectly fine, I just need new lenses that ain’t all scratched up…
That’s easiest I guess. Just find out your prescription when you get tested. Yes a lot of the industry is bogus, but then a lot of the world in general is bogus. Part of being an independent and flexible person is being able to find ways around bogosity.
They can’t legally measure my old old lenses. You know, the ones I tell them work the best?
Yeah, for ‘liability’ reasons, they can’t go by my 6 year old lenses, even though they’re the best I can see through, as a backup monocle…
You can do it yourself with a tape measure.
That’s gotta be the dumbest shit I’ve ever heard.
But sure, I’ll bite. How do you measure the exact curvature of a prescription lens with a tape measure?
Simplest case is you are farsighted. So your lenses are magnifiers. You move them away from a printed page til the magnification is at maximum. The distance to the page is the focal length. Diopter is 1/FL in meters, so eg. 50cm FL is 2.0 diopter. Negative diopters, astigmatism corrections etc are more complicated.
It looks like you can also test your own vision with a phone app and simple device:
https://www.cnet.com/tech/mobile/in-the-era-of-warby-parker-measure-your-own-eyeglass-prescription-at-home/
Idk anything about that though.
Seems neat I guess. I just wonder why the hell I can’t just go in with my old prescription, tell them straight up that this is perfectly fine, I just need new lenses that ain’t all scratched up…
That’s easiest I guess. Just find out your prescription when you get tested. Yes a lot of the industry is bogus, but then a lot of the world in general is bogus. Part of being an independent and flexible person is being able to find ways around bogosity.