Oil-Filled Lenses

"AdSpecs" allow the corrective power of the glasses to be adjusted by means of a clear fluid injected into the lenses; they were developed in 1996 by Joshua Silver, a physics professor at Oxford University who directs a research institute there called the Center for Vision in the Developing World. The idea behind the adjustable glasses is to allow people to fit their glasses to their optic needs – the technology enables untrained wearers to set the right focus themselves in less than a minute. This will greatly reduce the need for trained optometrists, who are rarely available in Africa and many parts of Asia. Though these adjustable glasses cannot yet help with conditions like astigmatism, at least 80 percent of refractive errors can be fixed  link