1. in vision, a transparent, biconvex structure in the anterior portion of the eyeball (just behind the iris) that provides the fine, adjustable focus of the optical system. It is composed of tiny hexagonal prism-shaped cells, called lens fibers, fitted together in concentric layers.

2. an artificial enhancer to the eyes’ natural structure, made of glass or plastic, that serves to focus vision (e.g., eyeglasses or contact lenses).See accommodation.