BIOCHEMISTRY OF THE HUMAN LENS

The main function of the crystalline lens is to transmit and focus light onto the retina by accommodation, just like the lens in a camera. At the beginning of embryonic life, the lens is opaque, but it becomes transparent over time as a result of nutrition. The main reasons for its transparency are the hexagonal structure of the fibrils, which are the main structural elements of the lens, and very little intercellular space. Lens transparency is maintained at both the cellular and molecular levels. The transparency of the lens is largely due to the very regular arrangement of the macromolecular components of the lens cells and the very small refractive index differences in the light-scattering components. The loss of the transparency of the lens is known as a cataract. Maintaining cellular homeostasis between protein and carbohydrate metabolism, cell division, cell differentiation, oxidative damage and protective mechanisms supports the maintenance of lens transparency. Regulation of water and electrolyte balance plays a critical role in maintaining normal lens water content and transparency. As a result of the regression of the tunica vasculosa lentis, which nourishes the lens during intrauterine life, the lens obtains its metabolic requirements from the aqueous humour and vitreous humour.