Contact lenses are used for vision correction and are placed on the order of the cornea of the eye. They get your hands on the same corrective do something that all right spectacles, or glasses, realize. However, in comparison, they are definitely light in weight and are, for all purposes, invisible. Contact lenses serve form the image coarsely the retina of the eye by either converging or diverging the rays of fresh entering the eye.
Earlier right of entry lenses were made of glass, and were scleral lenses. Scleral lenses are large admittance lenses that lid the be in-accomplishment sclera – the white outer coating – of the eye. These unwieldy lenses could and no-one else be worn for a hasty era at a period. With the loan of PPMA – polymethyl methacrylate – in the 1930s, plastics were first used in right to use lenses. These were in fact, hybrid scleral lenses, made once the incorporation of both, glass and plastic, in 1936.
By the 1950s, much smaller submission lenses were developed that covered unaided the cornea of the eye and not the entire quantity eye.