Defined: Contact lens

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 contact lenses were invented by the Czech chemist Otto Wichterle, 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 for altering the appearance of the eye.

It has been estimated that about 125 million people use contact lenses worldwide (2%), including 28 to 38 million in the United States 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 various reasons. Many consider their appearance to be more attractive with contact lenses than with glasses. 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.

The prescribing of contact lenses is usually restricted to appropriately qualified eye care practitioners. In countries such as the United States (where all contact lenses are deemed to be medical devices by the Food and Drug Administration), the United Kingdom and Australia, optometrists are usually responsible. In France and eastern European countries, ophthalmologists play the major role. In other parts of the world, opticians usually prescribe contact lenses. Prescriptions for contact lenses and glasses may be similar, but are not interchangeable.

The practitioner or contact lens fitter typically determines an individual's suitability for contact lenses during an eye examination. Corneal health is verified; ocular allergies or dry eyes may affect a person's ability to successfully wear contact lenses. Especially above the age of 35 years dry eyes often makes wearing contact lenses too risky, especially soft lenses.