From his talk:

Joshua Silver reckons that around half the world’s population needs corrective eyewear, yet has no access to it. His ultra-utilitarian spectacle design relies on the principle that the fatter the lens, the more powerful it becomes. The lenses are filled with liquid, and can be adjusted to different strengths by adding or removing fluid from tiny syringes on each arm, then locked to the right strength.

More than 30,000 of his lenses have been distributed in 15 countries, and a new model will scale that number up to millions.