A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the cornea of the eye. Modern soft contact lenses were invented bythe Czech chemist Otto Wichterle and his assistant Drahoslav Lím, who also invented the first gel used for their production. Some cosmetic lenses are deliberately colored to alter the appearance of theeye. It has been estimated that 2% people use contact lenses worldwide.
Leonardo da Vinci is frequently credited with introducing the idea of contact lenses in his 1508 Codex of the eye,Manual D, where he described a method of directly altering corneal power by submerging the eye in a bowl of water. Leonardo, however, did not suggest his idea be used for correcting vision—he was moreinterested in learning about the mechanisms of accommodation of the eye.
Types of contact lenses
Corrective contact lenses
A corrective contact lens is designed to improve vision. In manypeople, there is a mismatch between the refractive power of the eye and the length of the eye, leading to a refraction error. A contact lens neutralizes this mismatch and allows for correct focusing oflight onto the retina.
Cosmetic contact lenses
A cosmetic contact lens is designed to change the appearance of the eye. These lenses may also correct the vision, but some blurring or obstructionof vision may occur as a result of the color or design. These types of lenses tend to cause mild irritation on insertion, but after the eyes become accustomed, tend to cause no long term damage.Manufacturing of contact lenses
Most contact lenses are mass produced.
Spin-cast lenses - manufactured by whirling liquid silicone in a revolving mold at high speed.
Molded - Rotating moulds areused and the molten material is added and shaped by centrifugal forces. Injection moulding and computer control are also used to create nearly perfect lenses.
Multipurpose solution - The...