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.