Is the lens grinding process more complicated or is there just too much variation in eyesight to make them feasible on a mass scale?
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there’s a reason you don’t need a prescription for them. they aren’t really corrective lenses. they don’t really “work” exactly. They’re just cheap and easy and if you just need text a foot from your face to be a little bigger they at least do that.
Reading glasses are nothing special. They’re just magnifying glasses in a fancy housing. They don’t correct vision like prescription lenses, they just make things look bigger.
Cheap reading glasses are just simple magnifying glasses in a frame
The strength only needs to be “about right” because you can make fine adjustments by holding the book/newspaper a bit closer or moving it away. They are “good enough” for their intended purpose.
You can’t make those adjustments with distance glasses, like when driving etc
So they need to be a far more accurate match for your individual eyes, and your prescription is tailored to you. And sometimes slightly different for each eye.
As you age, your eyes tend to be less flexible and less able to focus on things closer to you. Reading glasses are typically used by middle aged people whos eyes are showing this degradation.
Short-sightedness, or the ability to focus on close items but not far, is not related to aging and is likely to need correction at a younger age.
Older people need to tweak their vision to help them read. Younger people with vision issues are more likely to need a more accurate correction and they are far better off getting their eyes properly tested and ensuring that not only is the spherical correction correct for each eye, but the cylindrical (astigmatism) correction is also appropriate.
I suspect that is dollar stores wanted to sell glasses for distance vision, they would be considered medical devices and would require a lot more regulation than for reading glasses.
The difference is your prescription lenses are made so you can see perfectly at “infinity” (very far distance). You don’t want to be near or far sighted with your glasses on, so the lenses need the exact power to correct your eyes. For example if you were near sighted and got too strong glasses prescription you would be far sighted instead.
Reading glasses make you near sighted. You can no-longer see things far away, but you can focus on things closer to you now (this is actually true of people who are near sighted as well). That’s why you don’t wear them all the time you put them on just to read then take them off.
Because they’re already making you near sighted and stuff far away is blurry with them on you don’t need them to match your eyes, they just need to be strong enough that you can hold a book at whatever their focus distance is and read it. So you can sell just a few powers and people can pick the one that gives them their ideal reading distance.
reading glasses don’t correct farsightedness. They are the equivalent of changing the zoom level on your browser so that you can read reddit easier.
You can’t do that with a book or newspaper, so reading glasses magnify it for you. Even then, it still might be too blurry for you to read in which case you need corrective lenses…….and no two people really need the same lenses. Even person to person, your prescription changes. The glasses I used to wear 2 years ago don’t work as well as the ones I wear now.
but yes, there is too much variation. if you and I had an identical eye issue, my glasses might not correct your issue because the distance from my eyes to the lenses is different than yours.
Before I got lasik surgery, I bought swim goggles from Speedo called “Vanquishers” that were super close to my strong prescription. This was back in 2015 and the specific ones I got are now discontinued, but it looks like the current ones are still effective, based on reviews. I don’t remember what my exact prescription was anymore, but the -8.0 diopter was pretty damn close. So if someone doesn’t mind looking like a bit of a dork, there are always swim goggles.
Optometry is a powerful lobby in the U.S. There are other countries that sell glasses exactly as you describe.
It’s a historical artifact. Both positive lenses (correcting farsightedness/”reading glasses” correcting presbyopia) and negative lenses (correcting nearsightedness) are best prescribed after measurement, but for a long time only positive lenses were allowed to be sold OTC, ostensibly to correct presbyopia. However, nothing ever stopped a patient with farsighedness from buying positive lenses to correct their condition.
Right now, you can buy negative lenses OTC from Temu and similar sites, up to about -4 and even -6 diopters.
Generalling OTC lenses have the same strength in each eye and don’t correct astigmatism (cylindrical lens), but if you buy two glasses with different strengths, you can mix & match them by removing the lens from the frame.
If you want fully optimized lenses, you can buy them OTC through many websites without a formal prescription and have them custom made. I found Zenni.com a great source for cheap glasses. When you get an eye exam, always ask for PD (pupillary distance) measurements to be taken and get a written copy of the prescription. A few asshole opticians may hassle you over giving it to you, but in most states, laws require them to provide it upon request.
You can very easily buy disposable contact lenses for far sight, so there’s nothing too special about them.
The market for short sightedness is bigger (almost everyone over 45 yo) and since it appears with age, both eyes have the same graduation or very close.
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