A Florentine monk by the name of Nicholas Bullet is credited with the invention of spectacles, although it is believed that the idea of placing an article in front of the eye to aid vision was known as long ago as the days of Emperor Nero.
Common defects of the eye which are corrected by the use of spectacles are shortsight (or myopia) which is corrected by the use of concave lenses, and longsight (hypermetropia) which is corrected by the use of convex lenses. A less common complaint is astigmatism, for which special cylindrical lenses are used.
Glass had been used for optical purposes since the Chinese began to make magnifying glasses in the 10th century. However, Ravenscroft developed a lead glass which he discovered had particular optical properties, patenting it in 1673. Even though the invention of the microscope and telescope increased the demand for good quality optical glass, lenses of a satisfactory quality were not widely available until the early 1800's.
In 1887, E.A. Frick made the first refracting contact lenses. By 1912, Carl Zeiss began producing glass corneal lenses. In 1938 Obrig and Muller were successful in moulding scleral lenses, made from polymethyl methacrylate plastic (the trade name is Perspex in Britain). While glass is optically more superior, plastic is more hard wearing, lighter in weight, and fits to the eye better. Until about 1950, the majority of lenses were of the scleral form. For this an impression of the eyeball had to be taken in order to mould the lenses correctly.
After the development of the keratometer (or ophthalmometer) the need to acquire impressions of the eye was eliminated. As the cornea has an extremely shiny surface, the keratometer utilises this to create an image from a light source which can then be measured.
Contact lenses can now be made in a wide variety of colours and shapes. They can be produced either for medical or cosmetic reasons. They have the flexibility to be tinted to act as sunglasses, or with high magnifying powers for people who have problems reading small print. Contact lenses have to be very precisely produced as any small error can be extremely damaging to the eyes. With today's advanced technology contact lenses are machined and fitted for each patient's particular needs.
