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Sci Tech
Eyeglasses with adjustable power
MY FRIEND and former colleague, Dr. Sushil Chandani, sent me a report that appeared in the December 10, 2002 issue of The New York Times. This was about self-adjusting spectacles which will allow wearers to correct their own vision, without the need or help of an optometrist. They can also be used over a period of time, with no need to change the lenses as the power needed to focus on the eye keeps varying. An eminently useful and usable device! Dr. Joshua Silver of Oxford University had been working on it for some time. He says that he now has a easy to use model, self-adjustable by the user, and priced at 10 dollars a pair — glasses, frames and all. He has named these Adaptive Glasses and has started making them in the company `Adaptive Eyecare' that he has formed. The World Health Organization (WHO) is reported to be interested in this development, and has asked Dr. Silver to try these adaptive glasses on needy people in Ghana.
Magnitude of the problem
Why WHO and why Ghana? The answer is simple. There are a lot of people in Ghana who are blind, or nearly blind, because they do not have access to corrective eyeglasses that will help them see. The problem is not with Ghana alone; it is true of just about every developing country, and even some advanced countries like U.S.A.
The numbers are staggering. Take the case of India. About 9.5 million in our country are cataract-blind and 3 million more are blind because the refractive errors in their eyes (that is, the focusing `power' or the dioptre value of their eyes is abnormal) have not been corrected.
Staying blind is inexcusable when a simple pair of eyeglasses (or contact lenses) with the right power is all one needs to see. Dr. Bjorn Thylefors of WHO had once estimated that there might be almost a billion people (that is one in every six alive) in the world who could benefit from vision correction with spectacles, but are as yet uncorrected. How useful it would be if they could be provided inexpensive adaptive spectacles which would enable them to correct their own vision with a minimum of instruction!
History of glasses and contact lenses
Correcting for refractive errors using lenses has a long history. The Roman writer Seneca (4 B. C. to 65 A. D.) used a glass globe of water to peer through and read books. A millennium later, monks are reported to have used segments of glasses spheres to help magnify letters — basically a magnifying glass called a `reading stone'. Though the Chinese claim to have invented the frame to mount two such glass lenses, the earliest documented picture in Europe is a painting by di Modena in 1352 which shows two lenses with rims joined centrally. The inconvenience of holding such glasses in position was soon won over first by securing the glasses by a tape tucked under the hat (the earlier Chinese way). But it was only in 1718 that a London optician, Edward Scarlett, seems to have put arms on eyeglasses to hold them on the ears. Nosepieces were soon added to lessen the discomfort. These were the ancestors of the present day frames, made variously of gold, silver, steel, fish bone, horn, wood, leather and now plastics. It appears that bifocals were invented by the American statesman-scientist Benjamin Franklin, who had both myopia and presbyopia. Tired of having to change glasses, he cut the lenses in half and put them together in one frame, thus making the first bifocal eyeglasses.
(Over the last a few decades, contact lenses have become popular, and have been replacing spectacles. Nobody knows who the original inventor is. In 1801 the English scientist Thomas Young removed small lenses from his microscope, coated their edges with soft wax and placed them onto his own eyes. This of course made him highly shortsighted as long as he had them on; he then calculated the power of missing refraction. The Swiss ophthalmologist Fick tried to make spectacles with their glasses directly in contact with the ocular surface using a liquid layer. He called these visual aid contact spectacles. It was only around World War II that the American W. Feinboom described the manufacture of the first polymer contact lenses).
Using liquid lenses of adjustable power
As time progresses, the refractive power of the eye usually keeps changing and new glasses become necessary. People who are poor and/or illiterate often cannot afford these, or are even unaware of the need (or do not take the trouble) to go to the optometrist shop to get the lenses changed. How nice it would be if spectacles were available where the focusing power of the lenses are independently and continuously variable to suit the eye! This issue of single element lenses of variable power has been attempted earlier, with no satisfactory solution. It is here that an invention such as Dr. Joshua Silver's is notable. Since the focal length of the lens should be continuously tuneable to varying focal lengths, solid materials are not the best. He thus chose to use fluid- filled lenses so that each lens could be simply and independently adjusted over the range 6 to -6 dioptres. A pair of these covered liquid lenses is mounted on the frame, and each lens is independently adjustable to suit the vision need of the eye.
The optical quality of the lenses was checked and found to be comparable to that of the typical human eye. It also compared well with conventional glass lenses. Once ready with these results, Dr. Silver established collaboration with colleagues in Ghana (Drs. George Afenyo, Maria Hagan, Lynne Ager and Mrs. Agnes Addo-Mensah) and set up field trials both at the Korle-Bu Hospital at Accra and in rural areas. "Although applied to a very small number of subjects, it was quite successful, and suggests that good correction can be provided in the field in this way for those subjects who only have refractive errors, and who need spherical correction for near vision", write Drs. Afenyo and Silver.
Where do we go from here?
Some doctors in Ghana are enthusiastic about these glasses, as also educators. But there are others who worry about how durable the glasses will be, how long they will retain their power, and whether the oil or the shape may deteriorate over time. Also, it does not help in cases of astigmatism. In response to my query on the matter, Dr. Brien Holden (one of the world's leading optometrists, and Director of the Cooperative Research Centre for Eye Research and Technology at the University of New South Wales, Sydney, Australia) said: "The availability of low cost spectacles is a considerable logistical challenge but one that in this day and age is eminently solvable. The key is to have a source of good quality, that is, ISO standard compatible ready-mades, and a system of delivery to people in need... ...
The Silver Adaptive Spectacles are an innovative idea but in the stage I saw them, relatively expensive and not self-prescribable in children in particular, due to accommodation.
Perhaps future generations will overcome these problems, and hit the U.S. dollar 1 price target needed...In the meantime, we should be both stockpiling ready-mades, looking for more innovative prescription spectacle production systems and most importantly training the eye care personnel that will give local, low cost, readily available vision care to all those in need. (The action plan of the global initiative called) Vision 2020: The Right to Sight has made this a key priority and by year's end the Refractive Error Working Group should have its strategy in place for this revolution in vision care".
D. Balasubramanian
dbala@lvpeye.stph.net
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