A clear disk that focuses light, as in a camera or microscope. In the eye, the lens is a clear, curved structure at the front of the eye behind the pupil. It focuses light rays that enter the eye through the pupil, making an image on the retina (light-sensitive layers of nerve tissue at the back of the eye).
Last updated: 2017-02-01
Source: The National Cancer Institute's Dictionary of Cancer Terms (http://www.cancer.gov/dictionary)