crystalline lens /kris″təlin, -līn/ [Gk, krystallos + L, lentil] , a transparent structure of the eye that is enclosed in a capsule between the iris and the vitreous humor and is slightly overlapped at its margin by the ciliary processes. It refracts light to focus images on the retina. The capsule of the lens is a transparent elastic membrane that touches the free border of the iris anteriorly and is secured by the suspensory ligament of the lens. The circumference of the capsule recedes from the iris to form the posterior chamber of the eye. The lens is biconvex in structure, with the posterior surface more convex than the anterior, derived from surface ectoderm. It is composed of a soft cortical material, a firm nucleus, and concentric laminae and is covered anteriorly by transparent epithelium. In the fetus the lens is very soft and has a slightly reddish tint; in the adult it is colorless and firm; in old age it becomes flattened, more dense, slightly opaque, and amber-tinted. See also eye.
