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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ITT: Almost everyone is super incorrect.
In store reading glasses and prescription readers of the same correction values are basically the same thing. The differences are:
Prescription glasses may have higher quality materials for the frame or lens, or a wider set of style options. You typically have options for different lens thickness, coatings, and in some cases grinding methods, but those shouldn’t affect your actual vision.
Prescription glasses aren’t limited to 0.25 diopter increments, can include different values for the left and right eye, and can include more complex corrections for astigmatism. It would be too costly to stock every variant a patient could need, and people getting a prescription tend to get a much more exact (though typically still subjective) measurement of their vision.
With that said, if your prescription happens to be something your drug store offers, it would be effectively the same. Also, the idea that drug store readers “only magnify things” is kind of a silly thing to say, because prescription glasses for simple ~~nearsightedness~~ farsightedness or presbyopia do the exact same thing.
As a side note, if you don’t want to deal with the Luxottica racket, there are many online stores that will make you custom glasses for way less than your eye doctor or local store, including some options not much more than a pair of drug store readers. In the US, your eye doctor is required to provide you your prescription, unprompted, and you can have anyone make the lenses. Ask them for the “PD” (pupillary distance) as that is often not on the prescription, but easy for them to measure and give you.
Many of these comments are wrong, cheap off the shelf glasses for near sightedness do exist, as I’ve used them to great effect for some years before I got proper prescription glasses.
I got them at a book and interior tidbit type chain store, that had a shelf with normal reading glasses, from +4 to +0.25, and then the next shelf continued in the same direction with glasses from -0.5 up to -3 in 0.25 diopter increments.
Worked great for far less eye strain when driving, and while not as good as prescription glasses, just looking across the store and trying different glasses you’d easily find a pair that dramatically improved your nearsightedness. I found that getting within about a quarter diopter would be close enough to where the glasses help significantly, but obviously with some eye strain if you don’t get it perfect. I only got prescription glasses as my myopia got worse.
And yes, reading glasses are just magnifying glasses in a frame, but that doesn’t mean they’re any less complex to make, especially in cheap plastic lenses, than negative diopter glasses. The difference is literally just concave vs convex shape in the lense.
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The real question I’d why are my frames made in the same factory as every other brand for a few dollars and upcharged to be 150-300$ for something I need to get changed every 2 years(annually sometimes) plus the damn prescription?! (Add’l 150ish) and it’s all out of pocket because I don’t have insurance (usually).
IM JUST OUT HERE TRYNA SEE DAMMIT!
Not saying it would be a good idea, but you could make up pretty much any prescription you want and one of the overseas glasses companies would cheerfully fill it.
They absolutely exist.
Stores like Walgreens or CVS usually carry both “reading glasses”, diopter values from about +1.25 to about +3.5 for farsighted, or if you are nearsighted you can get “driving glasses” that go from about -1.25 to about -3.5 diopter. You can ask if they don’t have them in stock.
If you can’t find them at your corner drugstore, you can get them through Amazon for about $20.
Talk to your eye doctor and understand what strength you actually need. As long as both eyes need roughly the same power they can be far cheaper than prescription lenses.
To add to other answers. You can buy custom (per eye) prescription glasses from aliexpress for about 20 bucks.
I am 65 and have bifocals. Reading glasses for me are about 3.25. Distance vision is okay, but it needs help. Interestingly, if I were to lose my bifocals, I could get some 1.5 reading glasses and be able to use them as distance glasses.
Your eyeball muscles should only focus to infinity, not past it. It’s relaxing for both eyes to rest at that focus. Fixing nearsightedness should get you just exactly there, and one eye will likely take more than the other.
The diopter of your prescription lenses are a reciprocal of how far you can see. If I can focus to 50 cm but no further I need a negative 1/0.50 or a minus-two prescription.
But with farsightedness I could just get bifocals that let the top of my vision be in focus and my near vision “better”. Since my eyeball still has some focus abilities and I can move closer to or farther from my object of interest it all works.
In general, you can’t really hurt yourself with plus lenses for near, and it’s more straightforward because readers are meant for people who are already corrected for distance. Distance is more complicated, and it would be much easier to end up wearing a prescription that’s detrimental.
(I’m an optometrist. Yes, we’re real doctors who, in addition to generally being the best at prescribing glasses, also diagnose and treat a variety of ocular diseases and refer to ophthalmologists as needed when more invasive treatments are indicated).
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