The lens is avascular, with its nutrients supplied by the aqueous humor and vitreous body. It primarily derives energy through the anaerobic glycolysis pathway. As a critical component of the eye's refractive system, the lens functions as a convex lens with a refractive power of approximately 19 diopters, offering unique transparency and refractive capabilities. It also filters out part of ultraviolet light, providing protection to the retina. The zonular fibers of the lens originate from the pars plicata and pars plana of the ciliary body and attach to the anterior and posterior capsule around the equatorial region of the lens. Through the contraction and relaxation of the ciliary muscle, these components collectively contribute to the accommodative function of the eye.
The transparency of the lens is maintained by the precise arrangement of lens cells and the highly ordered protein matrix of the lens fibers. This transparency persists even as the lens changes shape during accommodation. The high refractive power of the lens is attributed to the extremely high protein concentration in lens cells, particularly a class of soluble proteins known as crystallins. The proteins within the human lens remain remarkably stable throughout life to preserve its normal function. The lens capsule plays a crucial role in metabolic transport. Damage to the lens capsule or changes in the metabolism of aqueous humor can cause lens opacity, leading to cataract formation. Furthermore, lens opacity is closely associated with aging, which is influenced by the lens's growth pattern and the stress it experiences during chronic exposure over time.