CRYSTALLINE LENS

From Big Medical Encyclopedia

CRYSTALLINE LENS [lens (PNA), lens crystallina (1NA, BNA)] — a part optiche-

sky system of an eye, participating in the act of accommodation. The crystalline lens has an appearance of a biconvex transparent lens of non-constant curvature, is located in an eyeglobe. Its refracting force equal on average apprx. 20 dptr, can increase in a condition of accommodation to 33 dptr.

The first laying of a crystalline lens in the form of a thickening of an ectoderm occurs approximately on the 4th week of embryonic development. In we otshnuro-vavshtsya a lenticular bubble epithelial cells of the tail are extended, creating primary lenticular fibers. From an epithelium of the forefront the capsular epithelium of a crystalline lens forms. On the 7th week hrustalikovyypuzyrek it is carried out by secondary lenticular fibers. In the course of embryonic development the crystalline lens receives food from a lenticular vascular bag, blood supply a cut, in turn, is carried out by an artery of a vitreous — a. hyaloidea (see an Eye, embryology). By the time of the birth these vessels, as a rule, undergo involution. On site remains to an artery of a vitreous the channel (klo-Kets the channel) filled with intraocular liquid (see the Vitreous); the remains of vascular network of a front surface of a crystalline lens come to light at biomicroscopy (approximately at x / 4 inspected) in the form of threads or star-shaped pigmental educations on the front capsule of a crystalline lens in the field of a pupil.

Throughout life the size, a form, a consistence and transparency of a crystalline lens changes. The newborn has it transparent and colourless, almost spherical shape, a soft consistence. At the adult the crystalline lens has the form of a biconvex lens with more plane front surface; despite transparency, it gets a yellowish shade, intensity to-rogo with age increases therefore at elderly people perception of blue and violet color is weakened, the xanthopsia is observed (see). After removal of such crystalline lens there is temporary blue vision (subjective perception of objects in blue color). At the age of 40 — 45 years the kernel of a crystalline lens becomes dense, loses elasticity. By this time there is a weakening of accommodation (see Accommodation of an eye) and the presbyopy develops (see). By 60 years ability to accommodation is quite often lost completely that is connected with the expressed sclerosis of a kernel of a crystalline lens.

The crystalline lens is located in an eyeglobe between an iris (see) and a vitreous in the frontal plane, several knutra and down, displaced (detsentrovan) rather optical axis of an eye (fig). The insignificant aberration (see the Aberration of an eye) arising in connection with this topographical feature is leveled by the sizes and the provision of a pupil (see the Iris). Together with an iris the crystalline lens makes iridokhrustalikovy di -

the afragma dividing an eyeglobe into front and back departments.

Distinguish front and back surfaces of a crystalline lens; the line of transition of a front surface to the back -



Fig. Diagrammatic representation of an eyeglobe (sagittal section): / - — cornea; 2 — a sclera; 3 — outside muscles of an eye; 4 — an anterior chamber; 5 — an iris; 6 — a ciliary body; 7 — the back camera; 8 — a crystalline lens; 9 — a tsinnova a sheaf; 10 — a vitreous; 11 — a retina; 12 — an idiovascular cover; 13 — an optic nerve; 14 — a conjunctiva.

To Nü call the equator, the center of a front surface — a front pole, back — a back pole, the line connecting both poles — an axis of a crystalline lens. Radius of curvature of a front surface at rest of accommodation makes 10 mm, back — 6 mm \length of an axis of a crystalline lens of 3,6 mm. The narrow crack separating a back surface of a crystalline lens from a vitreous forms for - lenticular (retrolentikulyarny) space.

The crystalline lens keeps in an eye by means of a tsinnovy sheaf (a ciliary corbel, T.), consisting of fine fibers (fibers of a corbel, T.), among to-rykh allocate front and back. Front fibers originate from a flat part of a ciliary (ciliary) body, go between tsiliarny (ciliary) shoots and are attached to the capsule of a crystalline lens in 2,5 mm of a kpereda from the equator. Back fibers begin in a flat part of a ciliary body in 1,5 mm from the gear line and are attached to the capsule on 1 mm of a kzada from the equator. Nek-rye proceed from them from front departments of a retina and from the basis of a vitreous. Other part of fibers is attached in the field of the equator. A part of the fibers of a tsinnovy sheaf which are attached to the front capsule of a crystalline lens ahead of the equator forms a homogeneous plate (a zonular plate). The equator of a crystalline lens has a circular space, • limited by front and back


fibers of a tsinnovy sheaf — gan-nover the channel (space of a corbel, T.), earlier being called the petito-vy channel.

At gistol. a research reveal the capsule of a crystalline lens — a transparent elastic cover, edges consists of an epithelial layer and substance of a crystalline lens. The part of the capsule covering a front surface of a crystalline lens call the front capsule, and the part covering a back surface — back. Thickness of the front capsule 11 — 15 microns, back — 4 — 5 microns. The single-layer cubic epithelium is located in the field of an inner surface of the front capsule, stretches to the equator where its cells get the extended form and pass into fibers of a crystalline lens; the back capsule of an epithelium has no. The equatorial zone of the front capsule is region of growth: during all life fibers of a crystalline lens are formed of its epithelial cells.

Fibers of a crystalline lens represent flat tape-like cells; in process of aging they move to the center of a crystalline lens and lose kernels, and their place is taken by again formed cells. The fibers located in one plane are connected among themselves by agglutinant and create radial plates. The soldered ends of fibers of the next plates form on a front and back surface of a crystalline lens seams — a so-called lenticular star.

The periblasts of substance of a crystalline lens adjoining the capsule create its bark, deeper layers — a kernel. In a crystalline lens there are no nerves, circulatory and absorbent vessels.

Is a part of a crystalline lens apprx. 65% of water and apprx. 35% of proteins. Besides, in it mucoprotein, nucleoprotein, compounds of sulfur, phosphorus, chlorine, potassium, sodium, calcium and magnesium in small amounts, traces of iron, copper, manganese, zinc and boron are found (the majority of these elements is a part of enzymes or is their activators). Take part in the oxidation-reduction processes which are taking place in a crystalline lens tripeptide glutathione and ascorbic to - that. In a crystalline lens there are also lipids, vitamins A, Vkh, B2, PP and other substances.

The metabolism in a crystalline lens is slowed extremely down and is carried out by diffusion and osmosis via the capsule playing a role of a semipermeable biological membrane. Nutrients come to a crystalline lens from intraocular liquid.

Clinical methods of a research of a crystalline lens include survey


at side lighting using a binocular magnifying glass, a research in a transmitted light — oftalmoskopichesky raying (see Inspection of the patient, ophthalmologic inspection). Modern method of a research of a crystalline lens is the biomicroscopy of an eye (see) allowing to establish situation and a form of a crystalline lens, to reveal opacifications and their localization. At a research by means of a figured light source (e.g., candles) three of its reflections observe: from a cornea, a front and back surface of a crystalline lens. These three images of a light source carry the name of figures of Purkinye — Sansón. At reflection from a cornea receive the bright, valid, but reduced image, from a front surface of a crystalline lens — less bright, valid, reduced image, but it is more, than from a cornea, from a back surface — the return reduced image. In the absence of a crystalline lens in the field of a pupil observe only one image — reflection from a cornea.

In pathology of a crystalline lens the main place is taken by its opacifications; any cataract is called a cataract (see). Inflammatory diseases in a crystalline lens do not happen as it is deprived of vessels.

Anomalies of development of a crystalline lens are characterized by change of its sizes, forms, localizations. Inborn lack of a crystalline lens — an aphakia — meets very seldom and is usually combined with other malformations of an eye (see an Eye, malformations).

Mikrofakiya — a small crystalline lens, as a rule, is followed by a spherophakia (a crystalline lens of spherical shape), high short-sightedness (see) and an iridodonesis (see the Aphakia). Process bilateral; has family hereditary character. Meets as an independent disease, as a symptom of a disease of Marfan or a symptom of a disease of Markezani (see Marfan a syndrome, Markezani a syndrome). Mikrofakiya can be combined with increase in intraocular pressure, buftalmy (see idroftaljm), etc.

A lenticonus — cone-shaped protrusion of a front or back surface of a crystalline lens. A lentiglobus — spherical protrusion any of these surfaces. Each of these anomalies of development of a crystalline lens is usually observed on one eye, combined with the expressed phacoscotasmus and its capsules and is followed by decrease in visual acuity, short-sightedness.


CARTILAGINOUS TISSUE 143

the Coloboma of a crystalline lens is localized in the bottom of the equator, has an appearance of dredging or flattening and is combined with an inborn coloboma of an iris and other anomalies of development of an eye (see the Coloboma).

Ectopia of a crystalline lens — its inborn shift as a result of local weakening of a tsinnovy sheaf. At an ectopia the uneven depth of an anterior chamber of an eyeglobe, an iridodonesis and fako-donez is observed; the edge of a crystalline lens sometimes becomes visible with a usual width of a pupil. This anomaly of development is followed by short-sightedness and disturbance of accommodation.

The anomalies of development of a crystalline lens which are not followed by various complications (e.g., secondary glaucoma, a cataract), do not demand special treatment.

See also Eye.

Bibliography: The multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 1, book 1, page 173, M., 1962, t. 2, book 2, page 305, 1960; Shmelyova V. V. Cataract, M., 1981; HoganM. J.,

Alvarado J. A. a. Weddell J.E. Histology of the human eye, Philadelphia, 1971; Lehrbuch und Atlas der Augenheil-kunde, hrsg. v. H. Serr, Jena, 1958; N about r DM a n n J. Biologie du cristallin, P., 1954.

B. H. Alekseev.

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