Is the lens grinding process more complicated or is there just too much variation in eyesight to make them feasible on a mass scale?
In: Other
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.
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