contact process: see sulfuric acid.

contact lens, thin plastic lens worn between the eye and eyelid that may be used instead of eyeglasses. Actors, models, and others wear them for appearance, and athletes use them for safety and convenience. Contact lenses may also be used to correct certain abnormalities of the eye that cannot be corrected by regular glasses. A. E. Fick, a Swiss physician, made the first contact lens in 1887. His heavy glass lenses exerted an uncomfortable pressure on the eyeball, covered the entire eye surface, and were difficult to fit. In 1938, the first plastic contact lens was made by Theodore E. Obrig, using a newly discovered methylmethacrylate plastic, known as Plexiglas or Lucite, that could be molded into the proper shape. The major drawback was that a solution placed between the lens and eye had to be changed every few hours, because the wearer's tears could not circulate beneath the lens. In 1950, the corneal contact lens was introduced. It covered only the cornea of the eye, floated on the tears of the wearer, and could be worn all day without difficulty. Recent improvements include flexible lenses that shorten the initial period of adjustment for the wearer and porous lenses that do not have to be removed each day. Today, contact lenses that "breathe" have become popular. They allow oxygen to get to the cornea, preventing blurred vision due to the corneal exhaustion syndrome.

Contact between peoples with different cultures, usually leading to change in one or both systems. Forms of culture contact traditionally include acculturation, assimilation, and amalgamation. Acculturation is the process of change in material culture, traditional practices, and beliefs that occurs when one group interferes in the cultural system of another, directly or indirectly challenging the latter to adapt to the ways of the former. Such change has characterized most political conquests and expansions over the centuries. Assimilation is the process whereby individuals or groups of differing ethnicity are absorbed into the dominant culture of a society—though not always completely. In the U.S. millions of European immigrants became assimilated within two or three generations; factors included the upheaval of overseas relocation, the influences of the public school system, and other forces in American life. Amalgamation (or hybridization) occurs when a society becomes ethnically mixed in a way that represents a synthesis rather than the elimination or absorption of one group by another. In Mexico, for example, Spanish and Indian cultures became increasingly amalgamated over centuries of contact.

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Thin artificial lens worn on the surface of the eye to correct refractive defects of vision. Early glass contact lenses, invented in 1887, were uncomfortable and could not be worn long. Plastic-based lenses, made to measurements of corneal curvature taken by optical instruments, were first developed in the mid 20th century. Gas-permeable lenses allow more oxygen to reach the eye, thus increasing comfort and wear time. Contact lenses have advantages over eyeglasses for certain visual defects and may be preferred for the sake of appearance and other reasons.

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