Glasses

Optical devices that use lenses to correct focusing errors in the eyes to achieve clear vision. Lenses are made of glass or plastic, and the shape and thickness are chosen during a vision test. Convex lenses are needed for hypermetropia (longsightedness), and concave lenses for myopia (shortsightedness). Tinted lenses protect the eyes from sunlight. (See also bifocal; contact lenses)