It was a chance conversation on March 23 1985 ("in the afternoon, as I recall") that first started Josh Silver on his quest to make the world's poor see. A professor of physics at Oxford University, Silver was idly discussing optical lenses with a colleague, wondering whether they might be adjusted without the need for expensive specialist equipment, when the lightbulb of inspiration first flickered above his head.
What if it were possible, he thought, to make a pair of glasses which, instead of requiring an optician, could be "tuned" by the wearer to correct his or her own vision? Might it be possible to bring affordable spectacles to millions who would never otherwise have them?
More than two decades after posing that question, Silver now feels he has the answer. The British inventor has embarked on a quest that is breathtakingly ambitious, but which he insists is achievable - to offer glasses to a billion of the world's poorest people by 2020.
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.