Crystalline Lens

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crystalline lens

[′kris·tə·lən ′lenz]

Crystalline Lens


a lenticular transparent body (convex lens) of the eye located behind the iris and opposite the pupil; part of the light-refractive (dioptric) system of the eye in vertebrates, including humans. The crystalline lens is divided structurally into the anterior epithelium of the cornea and the body, which consists of fibers and intercellular cementing substances. Externally it is clad in a capsule—an elastic membranous envelope. The lens has anterior and posterior surfaces, with corresponding anterior and posterior poles through which the optical axis of the eye passes. The maximum circumference on the lateral surface in a plane perpendicular to the optical axis is called the equator of the lens.

The annular Zinn’s ligament is attached to the capsule at the equator; change in its tension changes the curvature of the lens surface, as a result of which accommodation is effected in higher vertebrates. In fishes and amphibians the lens is suspended by a ligament and during accommodation moves away from or toward the retina by means of a special muscle. In embryonic development the lens is formed from the covering epithelium under the inductive influence of the eye rudiment. Water constitutes about 65 percent of the lens, and proteins 35 percent. The crystalline lens of vertebrates grows throughout life. With age the lens scleroses, and there is a consequent weakening of accommodation (presbyopia). The most common pathological change in the lens is opacification, that is, the formation of cataracts.