Adjustable spectacles

MILLIONS around the world would have their lives improved by a pair of glasses, but cannot afford one. The problem is particularly acute in East Asia where, according to a recent report in the Lancet, as many as 90% of school leavers suffer from myopia. This high prevalence of short-sightedness (the comparable figure in the West is about 10-20%) is probably a result of the long hours of close work that many such pupils put in over the years of their youth. A visit to an optician to get a pair of spectacles with custom-made lenses will correct the problem, of course. But at a price not all can afford.

How to help such people is a problem with which Joshua Silver has been grappling for many years, while continuing his day job as an atomic physicist at the University of Oxford. His answer is cheap, self-adjusting glasses designed so that users can alter the power of the lenses in order to correct their own eyesight.

This idea is not new. The first published example of a variable-focus eye glass that Dr Silver can find is the “dynamoptometre”. This was described by Dr Cusco, a Parisian physician, in a paper in La Nature in 1880. Cusco's tabletop contraption involved a fluid-filled lens that could be adjusted by pumping water in and out. Dr Silver's first lenses, developed in the 1980s, worked similarly. They consisted of two polyester membranes with a water-filled gap between. The more water in the gap, the greater the curvature of the lens and thus the greater the magnification.

Over the years Dr Silver has refined the design. Instead of water, he employs a transparent silicone fluid developed by Dow Corning for use in scientific instruments. And instead of the original, rather goggle-like design, the latest version has light, thin frames. He has also founded the Centre for Vision in the Developing World (CVDW), and produced more than 40,000 pairs of adjustable glasses. Some have been used in trials, including several in rural China and India, in which young people with poor vision in at least one eye were able to correct their own vision.

That is done with a pair of small syringes attached, one to each side of the frame (see picture). Each syringe is operated by turning a small dial. Using one eye at a time, while looking at an eyechart, the wearer alters the curvature of the lenses until he can see clearly. When he has finished, he seals the lenses with clips and detaches the syringes.

Dr Silver reckons it will be possible to make this version of the glasses for about $20 a pair, and perhaps much less than that. They would come as part of a kit that included instructions and the eye chart. Later this year, with the support of Dow Corning, the CVDW hopes to begin the production and distribution of 50,000 pairs to China, India and Indonesia.

User-adjusted glasses could also help with eye conditions besides myopia—for example presbyopia, a common age-related condition that diminishes the ability to focus on nearby objects, and thus to be able to read. Dr Silver suspects adjustable reading glasses may find a role in the rich world, too. And one pair, at least, has already done so. These are at Lézard Bleu, a restaurant near Dr Silver's home in Vieussan, in the south of France. They have had their syringes attached permanently, so that diners who forget their reading glasses can use them to focus clearly on the menu.