[Animats]

How do they do cylindrical axis with a small inventory of lenses and non-round lenses? The three parameters for lenses are spherical radius, cylindrical radius, and axis of the cylinder. A complete set of a good range in all three is large, which is what leads to custom lenses.

There's a known way to cut costs with round lenses. With round lenses, you can have a small inventory of premade lenses with only two parameters. The axis is set with a little notcher that makes a notch which locks it to a bump in the frame, so it can't rotate. These have been used in India for decades. There's an optical store in an attache case.

If the One Dollar Glasses guys only use 25 different lenses, are they just blowing off the cylindrical correction entirely? Are these just "readers" like the ones available cheaply at most drugstores? Those you can get on Alibaba for $0.75 each in bulk.[1]

[1] https://www.alibaba.com/product-detail/Premade-Distance-Glas...

[codingdave]

That is the impression that I got - they are just like off-the-shelf reading glasses. But so what? They are giving cheap glasses to people in poverty who had nothing before. Sure, you can buy similar thing in bulk for similar prices, but can you then also deliver them to these people for the other quarter? Even if you can do so, are you actually doing so? These guys are. I'm not going to criticize them for it.