The eye lens is an important refractive one. It was a double-convex lens-shaped, the front radius of curvature of about 10mm, back about 6mm, elastic. Lens diameter of about 9mm, a thickness of 4 ~ 5mm, front and rear sides of the junction is called the equator, on both sides of the vertices are called the anterior pole, the posterior pole. As the camera lens in the lens, the light refractive effect, but also can filter out part of the ultraviolet light, protecting the retina, but its most important role is to change the ciliary muscle contraction or relaxation of refraction, so look away or look at when the condenser near the eye can focus accurately on the retina. Lens from the lens capsule and lens fibers. Lens capsule is a transparent film, completely surrounded by the lens out. Anterior subcapsular layer of epithelial cells, when epithelial cells reach the equator, it constantly stretch, bend, move the lens, a lens fibers. Lens fibers in the human life continue to grow, and the old center of the fiber pressed against the lens, and gradually become hardened lens nucleus, outside the core of the newer lens fibers called the lens cortex. Therefore, with age, the lens nucleus gradually condensed, expanded, and loss of elasticity, when the eye's ability to regulate would be worse, there presbyopia.

No blood vessels within the lens, it needs nutrition from the aqueous humor, if the metabolism of the aqueous humor is a problem, or damage to the lens capsule, the lens opacity occurs due to lack of nutrition, the original transparent lens becomes milky, and become opaque, and ultimately affect vision, this is the cataract. Now many ways to treat cataracts, there is a way that is simply to have become opaque lens removed and replaced by an artificial crystal, which is the artificial lens implantation.

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