There are very robust versions of these being made available in the Third World. (Several adjustable systems out there; a friend of mine has been involved in the distribution of one of them.) It's hard to imagine how transforming the ability to see clearly -- or at all -- is for people who are otherwise dysfunctional, and therefore destitute.

(And here I am grumping over the need to occasionally use 1.00 dollar-store readers when perusing the fine text. Sheesh.)