Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: Hannah on 19/01/2003 18:45:03
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Hi,
For my physics coursework i have to do a presentation on Contact lenses, and as i dont have the need to wear contact lenses i really dont know anything about them. So i was wondering if anyone could tell me the physical properties of contact lenses, the advantages and disadvantages of wearing them and whether they have revolutionised technology for people who are long sighted or short sighted. Please help as i am desbrate to get a good mark in physics and it is not going to well so far. Thanks
Hannah -x-
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Hello Hannah
thanks for your question.
Here's a bit of history behind contact lenses and glasses, which ought to make a nice introduction to your talk...
The first artificial means to improve vision was conceived (inventor unknown) in about 1000AD. Called a reading stone, the device consisted of a glass sphere that was laid on top of the material to be read to magnify the letters. Glasses as we know them cropped up 2 centuries later in Italy around 1284, thanks to the genius of inventor Salvino D'Armate.
In 1508 Italian Leonardo Da Vinci (whose 'man of perfect proportions' is the logo for this site - look in the top left corner of the navbar) sketched out designs for contact lenses, and in 1632 in France, Rene Descartes came up with the idea of 'corneal contact lenses'. In 1801, Thomas Young used Descartes' idea, comprising a quarter-inch-long, water-filled glass tube, the outer end of which contained a microscopic lens, to correct his own vision, proving that the theory worked.
English Astronomer John Herschel suggested in 1827 that a lens could be specially ground to fit onto the eye surface, but it was 60 years before German glassblower F.E. Muller produced the first eye covering that could be seen through and tolerated by the wearer. Almost at the same time, 2 researchers, A. Eugen Fick, a Swiss physician, and Paris optician Edouard Kalt, published their results on the use of contact lenses to correct optical defects, and are hailed as the inventors of concept of contact lenses.
In 1960 Otto Wichterle and Drahoslav Lim began to experiment with contact lenses made of a soft, water-absorbing plastic they had developed, and in 1971 the first commerically-available plastic contact lenses went on sale.
In 1978 toric lenses, which are weighted and can correct astigmatism, were announced and in 1980 the first 'soft' contact lens, the most popular type in use today owing to the comfort they offer, became available. These have subsequently been improved to offer eye-tinting, increased water content (which increases the oxygen delivery to the eye), long-wear (30 days at a stretch) and also in disposable forms.
How do contact lenses work ?
Most (80%) of the focusing of light entering the eye is achieved by the cornea. The lens makes a more modest contribution to clear vision. Individuals with sight problems are unable to focus light onto the retina. If the lens is too strong and light falls in front of the retina, as in short sight, the individual can only see nearby objects clearly. Distant objects are blurred. Another way in which this may happen is if the eyeball is elongated and becomes like a rugby ball rather than a football. This is known as astigmatism. Contact lenses rectify the situation by refracting the light entering the eye so that it ends up being correctly focused on the retina by the cornea and lens. They work in an identical manner to glasses, but are a cosmetically more desirable, and often more practical option, compared with glasses.
TNS