A transparent structure behind the iris of the eye that focuses light entering the eye on the retina.
A piece of glass or plastic shaped so as to focus or spread light rays that pass through it, often for the purpose of forming an image.
A combination of two or more such lenses, as in a camera or telescope. Also called compound lens.
A device that causes radiation to converge or diverge by an action analogous to that of an optical lens. The system of electric fields used to focus electron beams in electron microscopes is an example of a lens.