With solar lanterns or houses, you can just make prefab ones and sell the same one to everyone. If you can make them cheap enough, middle men will pop up to make a profit selling them to help with the distribution problem.
Eyeglass lenses on the other hand, need to be made for a person and often changed every couple years.
The problem is not making $2 glasses, but determining the prescription of 1 billion people with limited access to an optometrist.
Adaptive Eyecare[1] has done some interesting things with liquid lenses which solves both of the problems for people with spherical ametropia. Unfortunately, it won't work for people with astigmatism which is quite common (upwards of 30% in people over 30 according to some studies).
A portable device that allows someone with minimal training to determine a person's prescription, even if fairly expensive, would go a long way to solving the problem.
Do eyeglass prescriptions make a normal distribution? If you measured that you could produce a whole bunch of lenses following the distribution.
Then I wonder if you could loosen tolerances in your production process so that the lenses produced follow the prescription distribution in the population. If you can loosen tolerances like that you can potentially save $$$.
Now you have a bunch of lenses whose distribution matches the population. At this point, could the people who need these lenses not simply walk up and try on glasses until a matching pair is found?
Netra is an MIT Media Lab project ($2 attachment that attaches to a cameraphone) for measuring prescriptions. Huge market.
They're in the process of making it into a company and putting the team together. If you send them a friendly email, might even get you a job/consulting position.
Eyeglass lenses on the other hand, need to be made for a person and often changed every couple years.
The problem is not making $2 glasses, but determining the prescription of 1 billion people with limited access to an optometrist.
Adaptive Eyecare[1] has done some interesting things with liquid lenses which solves both of the problems for people with spherical ametropia. Unfortunately, it won't work for people with astigmatism which is quite common (upwards of 30% in people over 30 according to some studies).
A portable device that allows someone with minimal training to determine a person's prescription, even if fairly expensive, would go a long way to solving the problem.
[1] http://www.adaptive-eyecare.org/