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 by the Czech chemists Otto Wichterle and Drahoslav Lim, who also invented the first gel used for their production.

Contact lenses usually serve the same corrective purpose as conventional glasses, but are lightweight and virtually invisible—many commercial lenses are tinted a faint blue to make them more visible when immersed in cleaning and storage solutions. Some cosmetic lenses are deliberately colored to alter the appearance of the eye.

It has been estimated that 125 million people use contact lenses worldwide (2%),Barr, J. "2004 Annual Report". Contact Lens Spectrum. January, 2005. including 28 to 38 million in the United StatesDixie Farley. "Keeping an Eye on Contact Lenses: Safety, Options Shape Contact Lens Decisions." U.S. Food and Drug Administration: FDA Consumer. March-April 1998; revised August 1998. and 13 million in Japan. The types of lenses used and prescribed vary markedly between countries, with rigid lenses accounting for over 20% of currently-prescribed lenses in Japan, Netherlands and Germany but less than 5% in Scandinavia.

People choose to wear contact lenses for many reasons, often due to their appearance and practicality. Contact lenses are less affected by wet weather, do not steam up, and provide a wider field of vision. They are more suitable for a number of sporting activities. Additionally, ophthalmological conditions such as keratoconus and aniseikonia may not be accurately corrected with glasses.

History

René Descartes proposed another idea in 1636, in which a glass tube filled with liquid is placed in direct contact with the cornea. The protruding end was to be composed of clear glass, shaped to correct vision; however the idea was impracticable, since it would make blinking impossible.

In 1801, while conducting experiments concerning the mechanisms of accommodation, scientist Thomas Young constructed a liquid-filled "eyecup" which could be considered a predecessor to the contact lens. On the eyecup's base, Young fitted a microscope eyepiece. However, like Leonardo's, Young's device was not intended to correct refraction errors.