Visual pathways — the nerve fibrils which are carrying out visual irritations from the periphery (a retina of an eye) to subcrustal educations (primary visual centers) and further to bark of an occipital share (the cortical visual centers). The visual way is divided into two parts — peripheral and central. The optic nerve (n. opticus), visual decussation (chiasma opticum), a visual tract (tractus opticus), to central — a lateral cranked body belong to a peripheral part (corpus geniculatum lat.), pillow (pulvinar), upper hillocks (colliculi sup.) roofs of a mesencephalon, visual radiance (radiatio optica), or Grasiole's bunch, and a cerebral cortex in occipital area. Optic nerve (see) originates from visual and ganglionic neurocytes retinas (see) which are located in its deep layers and through bipolar neurocytes make contact with phototouch cells; protoplasmatic shoots of the last (a stick and a flask) receive visual irritation from the environment. Axial and cylindrical shoots of visual and ganglionic neurocytes, gathering, form an optic nerve which via the visual channel (canalis opticus) gets into a head cavity, goes on the basis of a brain to the centerline where forms incomplete visual decussation. All fibers which are a part of an optic nerve subdivide into four groups: 1) direct macular bunch; 2) the crossed macular bunch; 3) a direct peripheral bunch and 4) the crossed peripheral bunch. The macular bunch begins several knaruzha and from top to bottom from the center of a macula lutea of a retina (macula), consists of fibers which partially cross in visual decussation. The fibers originating from outside parts of a retina form the direct, or not crossed, peripheral bunch, fibers beginning from an internal half of a retina together with a part of fibers of a macular bunch come over to the opposite side, forming visual decussation, and then connect to not crossed fibers of the opposite side, forming a visual tract. Fibers of an optic nerve are various not only in the direction, but also on caliber (fine and thick fibers). Assume that thick fibers transfer photoirritation to the visual centers whereas thin are reflex and serve for transfer of photoirritation on an additional (parasympathetic) kernel of a third cranial nerve (nuci. accessorius). Except centripetal fibers, take place in an optic nerve also centrifugal, going to a retina; assume that they originate in a plate of a roof (lamina tecti) and come to an end in a granular layer of a retina; value of these fibers is insufficiently studied. According to some authors, the above described bunches both in an optic nerve, and in a visual tract are isolated; other authors assume that in visual decussation all fibers mix up so is not present neither isolated, nor crossed, nor direct fibers.
The visual tract after the education goes kzad and knaruzh, bends around a leg of a brain and at its outside departments is divided into three roots which terminate in a lateral cranked body, in a pillow of a thalamus and in an upper visual hillock. At the person and the highest mammals the main place of the termination of a visual tract is the lateral cranked body, and then a pillow of a thalamus; to upper hillocks there are not visual fibers, but reflex which terminate in their third layer, but give numerous branches up and from top to bottom. The ascending fibers come to contact with cells of a surface layer, descending go down in average and deep layers.
Primary visual centers are connected to bark of an occipital share centripetal and centrifugal fibers; these fibers are located in the white matter surrounding a back horn of a lateral cerebral cavity and in a so-called zachechevitseyaderny part of the internal capsule (pars retrolenticularis capsulae internae). The centripetal fibers going from a lateral cranked body and a pillow of a thalamus form at first Vernike's sex, a cut turns into visual radiance, and occupy an outside sagittal layer in white matter of an occipital share (stratum sagittale ext.); the centrifugal fibers going from bark of an occipital share to a roof of a mesencephalon and to a pillow of a thalamus occupy an inner sagittal layer (stratum sagittale int.). Fibers of visual radiance reach a limit in an occipital share, hl. obr. on its inner surface, in both lips of a shporny furrow (sulcus calcarinus); this area of bark has a special structure and is allocated under the name of the striped field (area striata) — the 17th field on Brodmanna (see. Very tectonics of a cerebral cortex ).
Concerning borders of the visual center in an occipital share of opinion disperse. S. Henshen (1930) and other authors consider that it is only on an inner surface, about a shporny furrow; at the same time they assume that there is a projection of a retina both on all visual way, and in bark of a shporny furrow, i.e. in an upper lip upper quadrants of retinas of the same name, and in lower — lower are projected; the macular bunch comes to an end at the bottom of the same furrow. K. Monakov (1914) and K. Brodmann (1909), without denying that the main visual center is apprx. a shporny furrow, consider that it extends also to adjacent crinkles of an inner surface and even to an outer surface; they deny existence of a projection of a retina and believe that else in primary visual centers all fibers mix up and in such look reach bark; they do not agree also with opinion that the macular bunch has strictly localized termination, same wide, as well as at fibers of peripheral sight.
Defeat of different departments of a visual way is clinically expressed variously. At a disease of a retina and optic nerve the blindness arises on one corresponding eye; it is observed at neuritis optic nerve (see), multiple sclerosis (see). At the centers in the interior of visual decussation bitemporal is observed hemianopsia (see), and in not crossed outside bunch — a binazalny hemianopsia. The bitemporal hemianopsia is characteristic of tumors hypophysis (see), the binazalny hemianopsia meets at basal arachnoidites (see), aneurisms of an internal carotid artery (see. Aneurisms of vessels of a brain ). Defeat of a visual tract, the subcrustal visual centers, visual radiance and the cortical center gives a contralateral hemianopsia, edges can be with gemianopichesky reaction of pupils with participation in process of a visual tract and primary centers and with normal reaction at a disease of one visual radiance and bark of a great brain. At final fracture of both visual centers the double hemianopsia, or a cortical blindness, sometimes with preservation of the central field of vision turns out that is quite often observed at damage of back brain arteries. The irritation of visual pathways or the visual centers can give photopsias (see), and also visual or light hallucinations (see) which can be combined with a hemianopsia. Defeat of an outer surface of an occipital share of the left hemisphere is followed by the phenomena of psychic blindness — visual agnosia (see), loss of ability to understand read — an alexia. These manifestations most often are found at vascular diseases of a brain, is more rare — at the getting wounds and tumors of the specified areas.
Treatment is directed to treatment of a basic disease. According to indications appoint the antiinflammatory, desensibilizing means, spasmolytic, dehydrating drugs. If necessary perform surgery — an oncotomy, cysts. At hron, diseases dispensary observation for the patient, carrying out courses of the therapy promoting the prevention of a recurrence of a disease is necessary.
Bibliography: Saradzhishvili P. M. and Gurgenidze R. V. Elements of topographical anatomy of peripheral neurone of a visual way in clinical practice of an oftalmonevrolog, Tbilisi, 1965, bibliogr.; Tronas E. Zh. Diseases of a visual way, L., 1968, bibliogr.; Physiology of touch systems, under the editorship of G. V. Gershuni, p.1, L., 1971; D e n n at-B rown D. Chambers R. A. Physiological aspects of visual perception, Arch. Neurol. (Chic.), v. 33, p. 219, 1976, bibliogr.; Denny-BrownD. Fischer E. G. Physiological aspects of visual perception, ibid., p. 228, bibliogr.
E. P. Kononova.