What a cool idea! Adjustable spectacles for about 4 Euros -- a potential benefit to hundreds of millions of poor people around the world with vision problems. See this Times article for more.
One design is based on the Alvarez Lens, invented by Berkeley physicist Luis Alvarez (an amazingly creative guy!). See here for other adjustable lens mechanisms.
I need to stockpile some of these just in case society collapses...
I'm at an age when an increasing number of my former classmates and colleagues, after being trained in science and earning their fortunes in finance or technology startups, are starting to retire! If you're looking for a way to give back to society, why not work on or contribute to a project like this one?
U-spec: Whereas normal spectacles contain fixed, single lenses, the U-Spec lenses are formed from two complementary parts mounted together. The complexly curved surface of these parts resembles a saddle, with a hollow to one side and a little "hill" to the other. These two parts can fit together with the hill of one sitting in the hollow of the other, but they can also slide apart in opposite directions. The key thing is that in any configuration they together form a viable lens for assisting defective eyesight, with the power of the lens changing depending on their position.
It may sound complicated, but for the wearer of the U-Spec adjusting the lenses couldn't be easier. You simply close one eye at a time and find the correct focus for the other by sliding a small knob up and down in a vertical slot in the frame, next to the lens in question.
"People wearing these spectacles can look at a far away object and move the knob until they have it sharp," says Dr van der Heijde. "You don't need a specialist to get good spectacles, you can do it yourself — and that's a good opportunity to have in Third World countries."
U-specs.org: The principle of the universal spectacles is based on the discovery of Alvarez, an American who, in 1968, won the Nobel Prize in the field of high-energy Physics. The lens is composed of two moveable parts with a flat surface facing each other and “saddle form“ outer surfaces (see fig. 1). Alvarez mathematically demonstrated in 1964 that the refractive power of the combined lenses vary proportionally with the amount of relative movement of the lens parts.