It is hoped the glasses will help millions of people
A retired Oxford University physics professor has designed adjustable glasses that can be used by people in the developing world.
Professor Silver's spectacles are altered by injecting tiny quantities of fluid into the lenses.
The spectacles mean people can have glasses that suit their eyes without the need for a prescription.
The invention should enable millions of people in poorer parts of the world to get glasses for the first time.
One billion target
Professor Joshua Silver decided to develop an adjustable spectacle after a chance conversation in 1985. It took him 20 years to come up with a design which could be made cheaply on a large scale.
The tough plastic lenses have thin sacs of liquid in the centre of each lens. The lenses come with small syringes attached to each arm and the wearer uses a dial to add or remove fluid from the lens.
Once the lenses have been adjusted, the syringes are removed and the spectacles are worn like a prescription pair.
Thousands of pairs of glasses have already been distributed in poorer countries during a trial project, supported by the Department for International Development.
Professor Silver is now preparing to launch an ambitious scheme in India to distribute one million pairs in a year. Eventually he wants to reach 100 million people a year, with a target of one billion in total by 2020.
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