ABSTRACT
The lens of the eye is a deceptively simple tissue. It is a completely transparent, avascular body stationed behind the cornea and held in correct position by the zonular fibers (1,2). The function of the lens is to focus light onto the retina, changing shape to allow clear delineation of objects at varying distances from the eye. The lens is enclosed by an extracellular matrix, the capsule. It contains only a single layer of epithelial cells on the anterior side of the tissue which, in the equatorial region, terminally differentiate into fiber cells. These long hexagonal cells, extending both to the anterior and posterior of the tissue, gradually lose their nuclei and other intracellular organelles and finally become relatively inert bags of protein incapable of repairing damage. The newly formed fibers displace the previously formed fibers inward toward the center of the tissue. This process continues throughout life. Thus, the youngest and metabolically most active section of the lens is in the periphery and the oldest and least active section is in the center of the lens, the nucleus. The metabolically active periphery, consisting of the epithelium and the newly formed fibers, is primarily responsible for maintaining the homeostasis of the tissue and protecting the relative inert inner region from stress.
