By 2050 it's estimated that over 50% of the world's population will live in "chabolas" - i.e. in semi-urban shanty towns with no formal infrastructure, yet still very close to major city centers. So distribution is increasingly less of a problem than you would assume, simply because population centers are concentrating at a very quick rate.

It's an antique method of thinking about these things, but one way to conceptualize "third-world" countries is that they lack a middle class. However, these aren't entirely "urban poor" people either. The movement to these poor slums also has a large degree of private innovation and some leap-frogging that brings millions of these new urban dwellers into a "pseudo-middle-class". They have cell phones, they organize informal water and electricity for their dwellings, improve them, and basically begin to see an slowly improving standard of living.

So, there really is a billion people who aren't well off, but not too-badly off to not afford a $2 pair of eyeglasses. They're working, and moving up socially, and this new class of people need affordable products. There's an enormous, growing market for this stuff.

Anyhow, just my two cents.