![]() ![]() Pattern of lens fibers (anterior and lateral aspect) It constantly lays down fibers in the embryo, fetus, infant, and adult, and continues to lay down fibers for lifelong growth. The cells of the lens epithelium also serve as the progenitors for new lens fibers. The activity of the Na +/K +-ATPases keeps water and current flowing through the lens from the poles and exiting through the equatorial regions. As ions, nutrients, and liquid enter the lens from the aqueous humor, Na +/K +-ATPase pumps in the lens epithelial cells pump ions out of the lens to maintain appropriate lens osmotic concentration and volume, with equatorially positioned lens epithelium cells contributing most to this current. The cells of the lens epithelium regulate most of the homeostatic functions of the lens. The lens epithelium, located in the anterior portion of the lens between the lens capsule and the lens fibers, is a simple cuboidal epithelium. The capsule varies from 2 to 28 micrometres in thickness, being thickest near the equator and thinnest near the posterior pole. ![]() The capsule is very elastic and so allows the lens to assume a more spherical shape when not under the tension of the zonular fibers (also called suspensory ligaments), which connect the lens capsule to the ciliary body. It is synthesized by the lens epithelium and its main components are type IV collagen and sulfated glycosaminoglycans (GAGs). The capsule is elastic and is composed of collagen. The lens capsule is a smooth, transparent basement membrane that completely surrounds the lens. The lens itself lacks nerves, blood vessels, or connective tissue. The cells of the lens epithelium, located between the lens capsule and the outermost layer of lens fibers, are found only on the anterior side of the lens. The lens capsule forms the outermost layer of the lens and the lens fibers form the bulk of the interior of the lens. The lens has three main parts: the lens capsule, the lens epithelium, and the lens fibers. In the adult, the lens is typically circa 10 mm in diameter and has an axial length of about 4 mm, though it is important to note that the size and shape can change due to accommodation and because the lens continues to grow throughout a person's lifetime. The anterior surface is less curved than the posterior. The lens has an ellipsoid, biconvex shape. Posterior to the lens is the vitreous body, which, along with the aqueous humor on the anterior surface, bathes the lens. The lens is suspended in place by the suspensory ligament of the lens, a ring of fibrous tissue that attaches to the lens at its equator and connects it to the ciliary body. In front of the lens is the iris, which regulates the amount of light entering into the eye. The lens is part of the anterior segment of the human eye.
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