RETINA [retina (PNA, JNA, BNA, LNH); synonym: mesh cover, retina] — internal cover of an eyeglobe. Page — the peripheral part of the visual analyzer providing vision due to transformation of light energy to the nervous impulse which is transmitted on a chain of neurons to bark of an occipital share of a brain.
S. belongs to derivatives of a brain, it develops from a wall of the eye bubble which is standing apart from expansion of a diencephalon. At the end of the 4th — the beginning of the 5th week of the embryonal period there is invagination of an eye bubble and formation of the eyecup consisting of two layers (outside and internal) neuroblastic cells. Apical surfaces these layers contact with each other, and their basal surfaces are turned to primary choroid and primary vitreous. Further the periblast of cells of an eyecup is differentiated in a pigmental epithelium of S., in Krom granules of melanin are formed, and from the inner layer other layers of Page develop. At this stage high mitotic activity of cells of the inner layer of an eyecup therefore the multinuclear outside zone (a primitive nuclear layer) and a denuclearized internal zone are formed is noted. On the 5th week of the embryonal period the primitive nuclear layer is subdivided into internal and outside nuclear (neuroblastic) layers; between them is defined a tranzitorny mesh layer (Shiyevich). From the inner nuclear layer consisting of 5 — 6 rows of cells ganglionic, amakrinovy and myullerovsky cells (ganglionic, amakrin-ny neurocytes and beam gliotsita), from outside — photoreceptors and horizontal cells (horizontal neurocytes) develop. The differentiation of cells goes unevenly from the center C. to its periphery. The nuclear layer in a macular zone develops before others, on the 3rd month of the embryonal period, shoots of ganglionic cells of this zone in the shortest way reach a nervous pedicle, creating an optic nerve. On 9 — the 10th week there are distinguishable kernels of sticks (rhabdoid visual cells) and flasks (kolbochkovidny visual cells). At the expense of shoots of myullerovsky cells the outer boundary membrane forms (an outside boundary layer, a membrane the Woman cinchona). By 4 months of the embryonal period completely disappears a tranzitorny mesh layer (Shiyevich), from the outer side from ganglionic cells at the expense of their dendrites the inner plexiform layer (an inner mesh layer) is formed. Within the 5th month the layer of photoreceptors is removed knaruzh at the expense of an outside plexiform layer (an outside mesh layer). Topographical features of area of a macula lutea begin to form by 6th month of the embryonal period, however they reach full development in several months after the birth (as a rule, by 6 months). Gear line (gear edge, T.) it is formed by 7th month of pre-natal development, by 8th month reaches a full maturity a layer of ganglionic cells and nerve fibrils. The circulatory system C. begins to develop on the 4th month. Endothelial cells extend along partitions of an optic nerve, by 6th month they form primitive vessels, in to-rykh the blood stream appears. They are located at distance with 1 — 2 mm from an optic nerve. To 7 — to the 8th month vessels reach the gear line. Pericytes of vessels of S. become distinguishable in 2 months of post-natal life, and all system mikr about circulation becomes similar to system of microcirculation of the adult approximately in 5 months after the birth.
The anatomy and histology
In S. distinguish three parts: raduzhkovy (pars iridica retinae), adjacent behind to a stroma irises (see), ciliary (pars ciliaris retinae), the covering inner surface ciliary body (see), and visual (pars optica retinae) — the main part C. The last is located between an optic disk and the gear line, and in these two zones it is attached most strongly. According to structure and function in visual part C. distinguish two departments: central and peripheral. The central department is presented by the macular zone, or a macula lutea (a spot, T., macula) which is located from the temporal party from a disk optic nerve (see). The name «macula lutea» is connected with oranzhevo - yellow color of this zone in a denucleated eye.
The macular zone has the form of an oval with a horizontal meridian apprx. 5,5 mm, in the center it deepening — the central pole (fovea centralis) is allocated.
S.'s thickness in the field of the central pole makes 0,2 — 0,25 mm. At the bottom of the central pole there is a deepening diameter apprx. 0,2 mm — a dimple (foveola); here S. has the smallest thickness — 0,08 — 0,1 mm. The greatest thickness of S. (0,5 mm) is noted in perifovealny area. Towards the gear line it decreases to 0,1 mm. Changes of thickness of S. are connected with the fact that the dimple contains only flasks, and the central pole is limited to kernels of the ganglionic cells lying in 5 — 6 rows.
The pigmental epithelium of S. is densely connected with a vitreous table, or Bruch's membrane (a basal plate, or a basal complex, T.), idiovascular cover. Ahead of the gear line the pigmental epithelium of S. passes into a pigmental epithelium of a ciliary (tsiliarny) body, and other layers of S. — into a pigment-free epithelium of a ciliary body.
The page has vertical and horizontal associative bonds. Vertical bonds are presented by a reflex arc, in a cut the first neuron are neuroepithelial cells — sticks and flasks, the second — bipolar cells, the third — ganglionic cells which axons form an optic nerve, a hiazma (visual decussation, T.), visual tracts (see. Visual centers, ways ) also terminate in an outside cranked body where there are bodies of the fourth neurons. Horizontal bonds are carried out at the expense of the amakrinovy and horizontal cells which are closely connected with bipolar cells and grouping them to associative fields.
Microscopically in S. distinguish 10 layers (fig.): 1) pigmental epithelium; 2) bacillary layer (neuroepithelial, or fotosei-weed layer); 3) outer boundary membrane (outside boundary layer, Babukhin's membrane); 4) outside nuclear layer; 5) outside plexiform layer (outside mesh layer); 6) inner nuclear layer; 7) internal plexiform (internal mesh) layer; 8) layer of ganglionic cells (ganglionic layer); 9) nerve fiber layer; 10) inner boundary membrane (inner boundary layer).
The pigmental epithelium performs function of absorption of light, phagocytosis, products of acid mucopolysaccharides, accumulation of vitamin A; together with a vitreous table of an idiovascular cover creates outside structures of a gema-toretinalny barrier. Gistol. structures of a pigmental epithelium are adapted to its functions. Intensively pigmented hexagon cells form a monolayer of the elements which are densely connected among themselves. Connection of their basal surfaces with a vitreous table is carried out at the expense of numerous folds of a cellular membrane, and side surfaces of cells of a pigmental epithelium are connected among themselves with the help formed by them the folds coming each other, desmosomes and dense membrane complexes. These intercellular contacts interfere with passing of krupnomolekulyarny proteins from an idiovascular cover in the Village. The apical surfaces of cells of a pigmental epithelium turned to sticks and flasks have numerous short (3 microns) and long (5 — 7 microns) cilia. The first are located between terminal departments of sticks and flasks, the second — between photoreceptors. The space between cilia of a pigmental epithelium and outside joints of photoreceptors is filled with glikozamiio-glycanes. Cytoplasm of cells of a pigmental epithelium is polarly oriented — basal parts of cells contain kernels with two kernels and diffusion chromatin, mitochondrions, the granular endoplasmic reticulum — a granular cytoplasmic reticulum is well-marked (see. Endoplasmic reticulum ), free ribosomes, Golgi's complex (see. Golgi complex ), structures of a smooth endoplasmic reticulum (not granular cytoplasmic reticulum) and lysosomes (see). In a middle and apical part of cells the pigmental granules consisting of melanin prevail; granules have the sigarovidny form, length to 1 micron, to dia. 2 — 3 microns. In a macular zone of a cell of a pigmental epithelium have the cylindrical form and contain a large number of pigmental granules. On the periphery of a cell are flattened. Cells of a pigmental epithelium contain also lipofuscin (see) which has an appearance of the residual little bodies developing from lysosomes. Besides, in cells there are membrane structures connected with function of phagocytosis of outside departments of sticks and flasks and also the microperoxisomas which are taking part in lipidic exchange.
The bacillary layer is presented by outside and internal joints (segments) of photoreceptor cells. Joints are connected among themselves by a thin crossing point (eyelash). Sticks are longer and thinner, flasks are wider and shorter. In outside joints of photoreceptors the disks having a membrane structure and containing a svetovosprinimayushchy rhodopsin are located (rhodopsin — in sticks, iodopsin — in flasks). The distance between disks in outside joints of flasks is wider, than in outside joints of sticks. Internal joints of photoreceptors shorter, have the form of an ellipsoid and contain a large number of mitochondrions (especially in flasks), ribosomes, granules of a glycogen, Golgi's complex and nervous tubules. The internal joint is separated from next by shoots of myullerovsky cells.
The outer boundary membrane represents the fenestrirovanny education created by shoots of myullerovsky cells. It is located at the level of border between an internal joint of photoreceptors and their basal part.
The outside nuclear layer is made by internal departments of photoreceptors. In relation to covers of an eye of a kernel of sticks knutr, kernels of flasks — knaruzh lie, the sizes of the last it is slightly more. Cytoplasm of cells contains ribosomes and a large number of nervous tubules, to-rye turn into synoptic expansion.
Outside plexiform layer — a transition synoptic zone between the first and second neurons. The venters of axons of photoreceptors containing synoptic bubbles contact to shoots of bipolar and horizontal cells. The Sinaptichesky zone creates a midline of S., edges is border of two pools of blood supply; layers, the lying knaruzh from it, eat at the expense of a choriocapillary layer (a choroidal and capillary plate), internal — at the expense of the central artery of Page.
In an inner nuclear layer kernels of horizontal amakrinovy, myullerovsky and bipolar cells are located, and the last make ground mass. Horizontal and amakrinovy cells have a set of shoots, to-rye contact to other neurons, carrying out the integrating associative bonds. The bipolar cells which are the second neurons have synoptic contacts with photoreceptors and ganglionic cells. Among bipolar cells distinguish poly-and monosinapti-chesky cells, dendrites to-rykh are located in an outside plexiform layer, axons — in internal. Cytoplasm of bipolar cells contains mitochondrions, ribosomes, structures of a smooth and granular endoplasmic reticulum. Myullerovsky cells belong to the glial elements which are carrying out in S. skeletal (supporting), and also trophic function. Cytoplasm of myullerovsky cells looks more dense at the expense of a large amount of microfibres.
An inner plexiform layer — a synoptic zone of the second and third neuron, and also amakrinovy cells. In this layer the capillary network of S. Amakrinovye is located, bipolar and ganglionic cells have synoptic bonds of various structure that comes to light at electronic microscopic examination.
The layer of the ganglionic cells which are the third neuron has uneven thickness, in a nasal half of S. of a body of cells are located in one row, in temporal — in two, density of cells decreases to the periphery of Page. Cells have poly-and mono-sinaptichesky bonds with bipolar and amakrinovy cells, axons to-rykh lie in an inner plexiform layer. Axons of ganglionic cells form a nerve fiber layer. The form of cells round, cytoplasm dense, fibrous, supports the aggregated structures of a granular endoplasmic reticulum (Nissl's substance), mitochondrions, free ribosomes and a large number of nervous tubules, especially in dendrites and axons. Granules of lipofuscin are found in elderly people.
The nerve fiber layer consists of axons of ganglionic cells, to-rye form an optic disk (see). From a macular zone nerve fibrils go straight to a temporal half of an optic disk, forming a so-called papillomakulyar-ny bunch.
The inner boundary membrane formed by myullerovsky fibers separates a retina from a boundary membrane of a vitreous.
Blood supply. Double blood supply belongs to ana-tomo-physiological features of S.: at the expense of vessels of an idiovascular cover of an eye and central artery of Page. Depending on the power supply C. divide on outside and internal speak rapidly; border between them is the synoptic zone of an outside plexiform layer. Outside part C., a cut is a part a bacillary layer (the first neuron), is supplied with blood at the expense of vessels of an idiovascular cover of an eye (a choriocapillary layer). Capillaries of this layer of a fenestrirovana that causes a free exit of krupnomolekulyarny protein in intercellular spaces of an idiovascular cover of an eyeglobe. The central artery of S. supplying with blood the interior of S. where the second and third neurons are located dichotomizing is divided into four main branches feeding four quadrants of Page. Parallel to arteries there are veins. About an optic disk the central artery has diameter of 0,1 mm, and wall thickness — of 18 microns. In the same area in a wall of an artery distinguish 5 — 7 layers of pericytes, in its equatorial branches — 2 — 3, on S.'s periphery — 1 — 2 layer. Endothelial cells of vessels of S. are oriented tsir-kulyarno or slantwise in relation to an axis of a vessel. 50 years are aged more senior reduction of quantity of pericytes and endothelial cells is noted. On the periphery S.'s vessels are surrounded with the perivascular glia consisting of astrocytes. The capillary network of S. is located between the feeding artery and the draining vein.
In S. occurs complex process of transformation of light energy to nervous impulse. Function of light absorption of a visible part of a solar range (from about 390 to 760 nanometers) and transfers of the energy received thus a photoreceptor carry out rhodopsins, to-rye contain both in sticks, and in flasks. Rhodopsins represent the complex painted proteins (chromoproteids). That their part, edges absorbs light, is called chromophore. In the chemical relation — it is aldehyde of vitamin A (retinal). Protein of rhodopsins, about the Crimea is connected a retinal, call opsin (see. Rhodopsins ).
Under the influence of light in a rhodopsin of sticks — rhodopsin, or rhodopsin, there is photochemical reaction which is externally shown its fading. At decomposition of rhodopsin (see) opsin and a trance-reti-nal are formed, to-ry under the influence of special enzyme turns into Retinolum (see). The last then migrates from a photoreceptor in a pigmental epithelium, with cilia to-rogo a photoreceptor is in close contact. In the dark there is a resynthesis of rhodopsin. Vitamin A passes back from a pigmental epithelium into a receptor and, being oxidized, the cisretinal turns into a special aldehydic form 11. Only this form is capable to form again at connection with opsin rodopsinony Obligatory participation of vitamin A in dark adaptation of an eye disorder of twilight sight at insufficiency of this polyneuramin speaks an organism (see Gemeralopiya).
It is known of photochemical process much less, to-ry proceeds under the influence of light in flasks. Instead of rhodopsin they contain other rhodopsin — yodopsinony Process of disintegration of the last demands considerably bigger intensity of light, than process of decomposition of rhodopsin. In the dark the broken-up pigment of flasks is recovered without any participation of a pigmental epithelium again, and with a much bigger speed, than rodopsinony connect existence in S. With inhomogeneity of iodopsin of three different elements (or components) flasks, each of to-rykh is intended for perception only of one of three primary colors — red, green and blue. At action approximately of color beams all three elements, but are excited in different degree, as allows to perceive all mnogooorazy color shades.
Fiziol. as substrate of excitement of photoreceptors under the influence of light serves electric potential, to-ry is generated by one of intermediate products of transformation of a rhodopsin. Distinguish two types of receptor potentials — early, almost not having stage of latency, and late with stage of latency more than 1 1/2 ms. From flasks and sticks nervous excitement is transferred to bipolar cells, and from them — ganglionic. A code of signal strength, sent to a brain on axons of ganglionic cells — to fibers of an optic nerve, the frequency of pulse categories serves.
A functional unit of S. is the receptive field. It is set of the sticks and flasks connected with one ganglionic cell. One receptive fields react only to inclusion of light, others only to its switching off, the third — both to inclusion, and to switching off of light. In S. of animals the ganglionic cells which are selectively reacting only to certain characteristics of an incentive, napr on the movement light (or dark) spots or strips only in one certain direction are found. Such neurons are called detectors. Receptive fields are changeable. Depending on the changing conditions and problems of vision there is their functional reorganization.
At the level C. at the expense of spatio-temporal summation of a light incentive, brake interaction between receptive fields and between zones in fields there is an underlining of contours of the image. In overlying departments of the visual analyzer (see) data of hl are transferred. obr. about those parts of the image where there is a difference, the gradation of brightness also contains the greatest novelty and informational content.
The minimum quantity of light energy causing a feeling of light characterizes absolute light sensitivity of an eye. Due to change its visual system adapts, adapts to various levels of brightness with the broad range — from 10 - 6 to 10 4 nt (cd/m2). Light sensitivity sharply increases in the dark (dark adaptation) and goes down upon transition from smaller illumination to bigger (light adaptation). In the presence of under review sites with an unequal brightness their distinction is estimated by means of contrast, or distinctive, allows to distinguish to sensitivity of an eye, edge spatial configuration of images (see. Photoperception ).
According to the standard theory of duality of sight distinguish two of its devices — central (or coneal) and peripheral (or bacillary). The first is the device of day vision providing perception of color and detailed distinction of objects of the world around, the second — the device of twilight sight, to-ry is sensitive to very weak light, but does not perceive color shades (see. Sight ).
Methods of a research
the Main methods of a research of functional capacity of S. are definition of visual acuity (see) and perimetry (see). The first method allows to judge a condition of the central sight, the second — peripheral sight, i.e. borders of a field of vision and existence of defects in it — scotomas (see. Scotoma ). More detailed characteristic of the last can be received with the help kampimetriya (see). For a research of function of color sight use special tables or the device — the anomalscope (see. Color sight ). Determination of size of light sensitivity and the course of its change in conditions of adaptation of an eye to darkness carry out by means of special devices — adaptometers (see. visual adaptation ). For objective assessment of a condition of S. use oftalmoskopiya (see). Normal S. at a research almost does not reflect beams in achromatic light and therefore remains transparent and invisible. A little bit more dark coloring of a macular zone and a light reflex on its edge is well caught. For more careful research C. resort to an oftalmoskopiya in redless light, at a cut preferential blue-green beams get into an eye, to-rye, being reflected from S., do it well visible (see. Eyeground ).
Diameter of vessels of a retina is determined by means of an oftalmokalibro-metriya, projecting on an eyeground during an oftalmoskopiya various measuring systems.
For assessment fiziol. S.'s conditions apply elektroretinografiya (see) and a research of electric sensitivity of an eye (see. Electrophysiology of an organ of sight ). The electroretinogram reflects a condition of periblasts of S., electric sensitivity — its inner layers.
A valuable method of a research of a hemodynamics of an eye is fluorescent. angiography (see) — photography of vessels of an idiovascular cover of an eye and S. after their contrasting flyuorstseiny.
Diffusion opacifications of the big or small sizes give to S. dim gray color and especially sharply act in the field of an optic disk. The limited centers of opacification of S. can have various form, size and color — white, light yellow or bluish-yellow. Being located in a nerve fiber layer, they take the shtrikhoobrazny form; in a macular zone form the figure reminding a star. The round form and pigmentation of the centers are observed at localization of process in periblasts of Page. Caused then atrophies of a choroid on these sites the sclera is bared and they take a form of the white centers which are often surrounded with the pigmented rim.
Fresh hemorrhages in S. have cerise color and different size. At localization in a nerve fiber layer they are presented in the form of the radial strokes or triangles turned by top to an optic disk. Pre-retinalnye hemorrhages of a round or cross and oval form.
The main forms of pathology of S. are defects of its development, damage, a disease of neurocirculatory character (retinopathy), inflammatory diseases S. (retinites), its dystrophic changes (or a degeneration) and new growths of Page. S.'s diseases are shown by decrease in the central and peripheral sight, disturbance of color sight, dark adaptation and losses under review. Their character and expressiveness depend on localization and prevalence patol. process.
Anomalies of development of a retina meet seldom. Carry an inborn fold of S., edges to them to treatment is not subject, and also a coloboma of a macula lutea (see the Coloboma) in the form of the light or yellowish pigmented center with sharp borders.
Injuries of a retina are most often shown in the form of contusional hypostasis (see. Retinopathies ) and amotio of a retina (see), hemorrhages in its layers, are possible S.'s ruptures and its separations from the gear line (see. Eye, damages ).
Disturbances of dirkulya-c and and blood in a retina figure prominently in its pathology. At impassability of the central artery of S. owing to a spasm, thrombosis and an embolism suddenly there occurs partial or total loss of sight. The eyeground gets milky-white coloring because of hypostasis of Page. On this background the macular zone is allocated in dark red color (a symptom of «a cherry stone»). Arteries are sharply narrowed.
At fibrinferment of the central vein of S. on an eyeground (see) the papilledema is noted (see. Congestive nipple ). Veins on a surface of a disk and around it are expanded, izvita, dark coloring, massive hemorrhages on the course of veins are noted.
At disturbances of passability of vessels of S. acute management in the conditions of a hospital is required. Apply to treatment vasodilating and antispasmodics, anticoagulants, fibrinolitic means, lipotropic substances, vitamins, carry out dehydrational therapy.
The forecast at a spasm of the central artery of S. favorable, at other types of its impassability visual acuity sharply decreases. At fibrinferment of the central vein of S. visual acuity decreases not so sharply, as at impassability of an artery of a retina.
The periphlebitis of a retina (Ilz's disease) is one of severe forms of defeat of Page. It usually develops against the background of tuberculosis, diseases of blood, viral infections, etc. Distinguish four stages of a periphlebitis. In the first stage expansion, crimpiness, intermittence of veins of Page is noted. In the second stage periphlebites are formed, retinal hemorrhages develop. In the third stage recurrent vitreous hemorrhages, in the fourth — a gliosis, amotio of Page are observed. Treatment is begun with therapy of the general contributing diseases. Apply also the corticosteroids hyposensibilizing means (see. Desensitization ), photocoagulation of the affected veins of Page. The forecast concerning sight adverse.
Dystrophic changes of a retina (retino-dystrophy). The most common and severe form of this pathology is the pigmental degeneration of a retina (see. Tapetoretinaljny dystrophies ).
The senile degeneration of S. arises usually at people 60 years are more senior. The etiology and its pathogeny are studied insufficiently. It is shown in the form of accumulations of a pigment in the field of a macula lutea; then there are dot merging ochazhka of yellow color and all this area gradually gains dark red or yellowish-brown color.
One of forms of a senile degeneration of S. is the disease of Kuna-that — Yuniusa, edges is shown by mottling of area of a macula lutea, and then emergence of the edematous center of a discal form with the subsequent new growth of connecting fabric here.
The cystic degeneration of S. is characterized by emergence in the field of a macula lutea of the small thinned sites in the form of cells.
Apply vasodilators, vitamins to treatment of dystrophy of S., fabric therapy (see), anabolic steroid drugs, ultrasonic therapy, method of neovascularization of Page.
The treatment begun in early stages of dystrophy of S. in some cases promotes stabilization of process.
Retinites arise in connection with a drift in S. of virulent microflora, under the influence of light or ionizing radiation, at injuries of a retina (see the Retinitis).
Retinopathies can be both independent diseases, and displays of other diseases which are followed by circulator and exchange disturbances in the area C. One of forms of retinopathies is the berlinovsky opacification of S. arising at contusions of an eyeglobe and which is shown in the form of opacification of whitish color usually on S.'s periphery (see. Retinopathies ).
Tumors — see. Retinoblastoma .
make Operative measures on S. generally concerning its amotio (see. Amotio of a retina ) and gaps. Methods of laser microsurgery apply at retinopathies, napr, diabetic, hypertensive (see. the Laser, lasers in ophthalmology ).
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