The lens is located in the eye. By changing its shape, the lens changes the focal distance of the eye. In other words, it focuses the light rays that pass through it (and onto the retina) in order to create clear images of objects that are positioned at various distances. It also works together with the cornea to refract, or bend, light.

The lens is of ellipsoid, biconvex shape. An ellipsoid is similar to a sphere but stretched out, like an olive, and biconvex means it’s rounded outward on both sides. The lens is about 10 mm across and 4 mm from front to back in adults, although its shape and size varies as it changes its focus.

The lens consists of the lens capsule, the lens epithelium, and the lens fibers. The lens capsule is the smooth, transparent outermost layer of the lens, while the lens fibers are long, thin, transparent cells that form the bulk of the lens. The lens epithelium lies between these two and is responsible for the stable functioning of the lens. It also creates lens fibers for the lifelong growth of the lens.

Common diseases of the lens include cataracts, which cause opacity, or cloudiness, in the lens. Other common ailments are presbyopia, ectopia lentis, aphakia, and nuclear sclerosis.

Written and medically reviewed by the Healthline Editorial Team
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In Depth: Lens

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