While these aren’t going to work to replace my tri-focals, three pairs of them would.

These are water filled lenses that individuals can adjust to their own needs, then freeze the correction.

Silver has devised a pair of glasses which rely on the principle that the fatter a lens the more powerful it becomes. Inside the device’s tough plastic lenses are two clear circular sacs filled with fluid, each of which is connected to a small syringe attached to either arm of the spectacles.

The wearer adjusts a dial on the syringe to add or reduce amount of fluid in the membrane, thus changing the power of the lens. When the wearer is happy with the strength of each lens the membrane is sealed by twisting a small screw, and the syringes removed. The principle is so simple, the team has discovered, that with very little guidance people are perfectly capable of creating glasses to their own prescription.

– The Guardian

While there are definitely vision correction issues that aren’t solved by this (like astigmatism), in places like sub-Saharan Africa, the ratio of opticians to general population is approximately one to a million.  This would change the quality of life of millions of people.

link at Core77   Pointed to by Rebecca Watson Tweet.