The lens crystallina) is one of the main svetoprelomlyayuschimi transparent media eye.
The lens is a lenticular, splyusnutoy in front to the rear, transparent lens contained in elastic capsule. Is the lens inside the eyeball, in front of his Department, directly behind the iris. In the lens distinguish between the front and the back and front and rear respectively pole and the equator. Equatorial diameter of the lens adult 9-10 m; thickness of the lens axis (from the front to the rear pole) on average of 3.6 mm Front, less convex surface of the lens is the curvature radius of 10 mm, rear surface : 6 mm Total refractive power of the lens in the eye average of 20-38 diopters (see refraction of the eye). Afakii after removing the lens appoint glass 10-12 diopters (aphakia - eye condition in the absence in it of the lens observed after cataract removal operations). In the area of the pupil, the front surface of the lens is directly bordered with the front camera eyes; on the periphery, where the lens is covered with iris,with the rear camera. The back surface of the lens borders with vitreous body, forming at this place a small saucer-like depression, respectively curvature of the back surface of the lens (see Eyes, anatomy).
The main substance of the lens are long transparent hexagonal fibrils ectodermal origin. They develop from epithelial cells located in the embryonic stage of the development of the eye along the periphery of embryonic lens. Later, these cells are pushed closer to the front surface, are more spread out and become arch-like form, bending over the equator on the back surface of the lens. Transparent fibrils are collected in more massive compact groups, forming separate sectors of the lens. At a young age fiber these flexible and elastic, and the shape of the lens is determined mainly by the tension of his capsule. Itself capsule fixed around the equator of the lens strong thin fibers Zinn ligaments that hold it in the center of the ring formed by the ciliary body. Tension Zinn ligaments and gives H. tapered, lenticular shape. In response to an additional reduction of muscles, laid down in the thickness of the ciliary body, changed the degree of tension lens capsule, and hence the curvature of the front and rear surfaces. This leads to changes in the refractive power of the entire optical system of the eye; his eyes are set on getting the focal image that is close, far away objects (see accommodation of the eye).
Over time, some fiber lens begin to sklerozirovanie lose its elasticity, without losing in normal conditions of its transparency. Over the old Oplotnica fiber layers are superimposed younger elastic fibers, and old, concentrated in the center of the lens, increasingly harden, forming dense core H. the Process of gradual sclerosis fibers begins at a very early embryonic stages of fetal development. However, dense core Agricultural newborns (embryonic core) is very small. A gradual process seal fiber Kh. is continuous, and the elderly kernel (senile nucleus of the lens) occupies almost the entire Agricultural Eyes in these conditions loses the ability of accommodation, develop phenomena presbyopia (see).
cataractin Addition to the physiological senile involution of the lens, causing the development of presbyopia, there are a number of pathological processes, which lead to changing the position or shape of the lens, develop dimness of its fibers. The emergence of lens opacities (see Cataract) can be called any violations exchange between him and the surrounding fluids (moisture anterior and posterior chambers of the eye), vitamin deficiency, General illness (diabetes, and others), intoxication, local effects of radiant energy (x-ray, radium cataract). Violations intact capsule X. when perforated eye injuries lead to rapid swelling and further clouding fibers X. as a result of chemical processes occurring in direct contact fibers Z intraocular fluid can occur not only cataract, but severe inflammatory process toxico-allergic nature in the choroid. Such pakowanie uveitis often not amenable to any therapeutic drug influences, but are rapidly after removal by surgery of the eyes of all residues swollen and hazy lens.
Sometimes harmful effects, leading to increased turbidity of Agricultural fibers, are still in embryonic stage of development, that is why children can be born with already developed cataracts. Effects of various pathogenic factors on the lens is still in embryonic stage of development explains the origin and the number of congenital anomalies position and shape of the lens. This origin is the overall reduction of the sizes of Agricultural newborns (microface, often combined with high myopia and various other abnormalities of the eyes), anomalies provisions of Agriculture (twisted it into the vitreous body, congenital ectopia of the lens), change its form,is a partial rupture of the Central section of the front or rear surface of Agriculture (front and rear lenticonus), or the formation of a small defect in the lower part of the lens in the zone of the equator - coloboma H., often associated with colobomas choroid. All of these congenital anomalies is incurable. Radical method of treatment haze H. - operation cataract extraction.