Lens

The lens is a transparent, biconvex, elastic, and avascular structure. It consists of three components:

• The lens capsule is a thick and transparent basement membrane-like structure enclosing the lens (Collagen IV). Beneath the anterior portion of the capsule is a single layer of cuboidal epithelial cells that extend posteriorly up to the equatorial region. There is no epithelial cell layer under the posterior surface of the capsule.
• The lens epithelium. In the cortical region of the lens, elongated and concentrically arranged cells (called cortical lens fibers) arise from the anterior epithelium at the equator region. Cortical lens fibers contain a nucleus and organelles. The nucleus and organelles eventually disappear when the cortical lens fibers approach the center of the lens.
• The lens substance, consisting of cortical and nuclear lens cell fibers. Lens cell differentiation consists of the appearance of unique cytoskeletal proteins, which include filensin, an intermediate filament that contains attachment sites for crystallins (lens-specific proteins). Filensin and crystallins maintain the conformation and transparency of the lens fiber cell.