The lens is a transparent, avascular structure that, in concert with the cornea, focuses incident light onto the sensory elements of the retina. To do so, the lens must be transparent and must have an index of refraction higher than that of the surrounding fluids. The high refractive index is due to the high concentration of proteins—especially of soluble proteins called crystallins—in the lens cells. Furthermore, because there is little if any turnover of protein in the central region of the lens (where the oldest, denucleated cells are found), the proteins of the human lens must be extremely stable to remain functionally viable for a lifetime. Considering the lens’s mode of growth and the stresses to which the lens is chronically exposed, it is remarkable that in most people, lenses retain good transparency until later in life; visually significant opacities typically develop by the sixth or seventh decade of life.
This chapter discusses the structure and chemical composition of the lens, as well as aspects of membrane function, metabolism, and regulatory processes within the lens. BCSC Section 11, Lens and Cataract, provides additional information about the lens, cataractogenesis, and cataract surgery.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.