I wear glasses. I like them. I like how they look, and I like that they stop me poking things in my eye. But I can afford to buy them. For many, especially in developing countries, spectacles are an out-of-reach luxury.
Why? They're just plastic, right? Some of that is the styling (or application of a designer label to a pair of commodity frames), but a lot os the actual shaping of the lenses. Enter a new breed of spec: adaptable, adjustable eyeglasses. Instead of solid, one-off lenses, these glasses have a hard lens at the front and a softer, flexible plastic sheet at the back. In between is a layer of viscous liquid with a high refractive index (light-bending ability). By pumping more of less of this liquid between the layers, you can custom fit your glasses to yourself, no expensive opticians or lens-grinding needed.
The main difference between manufacturers is the method of adjustment. Adlens' specs (pictured) have a knob on the side which you turn to adjust the amount of fluid in the lens. Those from TruFocals have a slider on the bridge of the frames to do the same thing.
Why would you need adjustable lenses? For the elderly, one pair of adjustable glasses could replace glasses for reading and regular use. For the young, whose prescription can change rapidly, one pair of glasses could last a lot longer (assuming they don't get smashed at school). And hopefully, should this technology become widespread, identical pairs of glasses (with basic, non-astigmatic corrections) could be made in bulk for the developing world and adjusted by the new owners themselves.
The biggest limitation right now is the shape. In order to work, the lenses need to be a perfect circle. Good news if you're John Lennon or a high-school poet, bad news for everyone else.
Adlens product page [Adlens]
Trufocals product page [Trufocals. Thanks, Jessica!]
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