What is the lens? The lens is the structure in the eye that focuses light onto the retina, which senses and converts light into electrical signals sent to the brain to create an image. The lens is comprised of three main structures: the lens capsule (membrane that encases the lens), cortex (outer area of the lens), and nucleus (central area of the lens). The lens continues to change and produce new layers throughout an animal’s life. The older, inner layers of the lens in the