HEMIANOPSIA (hemianopsia; Greek hemi-to a floor + an-of otritsa. prefix + opsis sight; synonym gemianopiya) — loss of a half of a field of vision of each eye; at quadrant G. — a quarter of a field of vision. When visual function in the dropped-out half of a field of vision is reduced, speak about relative G., or a gemigipopsiya; if in fields of vision perception only for the colors at preservation of perception of white color drops out, speak about a gemikhromatopsiya.
Distinguish gomonimny, or of the same name, G. (the right or left half of sight on each eye drops out, and right-hand or left-side G.) and geteronimny, or heteronymic respectively develops, G. (a temporal or nasal half of a field of vision on each eye drops out, and bitemporal or binazalny G. respectively develops). Can be bilateral: defect of a field of vision on each eye takes temporal and nasal half. Top and bottom G. and the tubular field of vision representing right-hand and left-side gomonimny G.'s combination to preservation of macular sight belong to this type of G.
These or those defects of a field of vision come to light a research on perimeter and a kampimetra (see. Kampimetriya , Perimetry ). At defeat of a visual way defects of a field of vision on green and red colors, and then on white develop earlier.
the tumors located in the field of the Turkish saddle (a tumor of a hypophysis, a cranyopharyngioma, a meningioma of a hillock of the Turkish saddle and wings of a wedge-shaped bone, a glioma of visual decussation), aneurisms of vessels of an arterial (villiziyev) circle of a great brain, optokhiazmalny arachnoidites, a craniocereberal injury are the Most frequent reason of defeat of visual decussation.
Visual tracts are surprised at cranyopharyngiomas, tumors of a hypophysis, aneurisms of an arterial circle of a great brain, tumors of a temporal share. Defeats of the central neuron of a visual way and the cortical visual centers are observed at tumors by a temporal and occipital share of a brain, a cherepnomozgovy injury, arteriovenous aneurisms and disturbances of blood circulation in system of back and average brain arteries.
Arises at organic lesions of a visual way and is an important topografo-diagnostic character of defeat of a visual way in its various departments, including in a brain (fig. 1).
The visual way consists of two parts: peripheral and central.
A peripheral part begins in a bacillary layer of a retina and comes to an end in ganglionic cells of a lateral cranked body. These cells are the beginning of the central part of a visual way, fibers to-rogo later escaping of a lateral cranked body pass the internal capsule, a parietal lobe of a brain, a part of fibers comes into a temporal share of a brain and reaches a limit on a medial surface of an occipital share of a brain in the field of a shporny furrow.
In a peripheral part of a visual way anatomically distinguish three departments: optic nerves, visual decussation and visual tracts. Fibers of the central part form visual radiance (see. Visual centers, ways ). In a visual way of fiber, the retinas of both eyes going from a nasal half, cross and go to an opposite visual tract; the fibers going from a temporal half of a retina of both eyes do not cross and go to the visual tract of the same name.
Clinical and topiko-diagnostic value of a hemianopsia
Geteronimny bitemporal G. (fig. 2 and 3) develops at defeat of the crossed fibers of a visual way located in a middle part of visual decussation (hiazma). Its development most often begins with loss of a field of vision in verkhnevisochny quadrants, then — in nizhnevisochny.
Binazalny G. (fig. 4) develops in the presence of two centers located on lateral parts of visual decussation where there pass not crossed fibers of a visual way. As fibers from upper half of a retina of both eyes pass in an upper part of visual decussation, and fiber from the lower half — in a lower part, at defeat of visual decussation horizontal G. — upper or lower can develop.
Defeat of visual decussation is always followed by the subsequent development of the descending primary atrophy of optic nerves that is an important differentsialnodiagnostichesky sign at establishment of level of defeat of a visual way in the presence of horizontal G. as it can be as well result of defeat of bark of an occipital share of a brain.
Gomonimny G. (fig. 5) can arise in connection with defeat of a visual tract or visual radiance (Grasiole's bunch) or the medial surface of bark of an occipital share of a brain in the field of a shporny furrow. A ventral part of visual radiance comes into a temporal share of a brain (Maier's loop), bends around the front end of the lower horn of a side ventricle and goes along the lower wall of a side ventricle to an under lip of a shporny furrow. Defeat of a loop of Maier or an under lip of a shporny furrow causes verkhnekvadrantny gomonimny G. (fig. 6). A dorsal part of fibers of visual radiance goes to an upper lip of a shporny furrow through a parietal lobe; defeat of these fibers leads to nizhnekvadrantny gomonimny G.'s (fig. 7) development. At damage of an upper lip of a shporny furrow of both occipital shares of a brain there is lower horizontal G.; at defeat of an under lip of a shporny furrow of both occipital shares of a brain develops upper horizontal. As a result of extensive destruction of all bark of both occipital shares of a brain, except for a pole, in Krom the area of a macula lutea is projected, bilateral G. with preservation of the central sight, or a so-called tubular field of vision develops.
Gomonimny G. at defeat of a visual tract differs from gomonimny G. at defeat of visual radiance.
For determination of level of defeat of a visual way at gomonimny G. it is necessary to consider a row a wedge, symptoms. The combination of primary atrophy of optic nerves to gomonimny G. indicates defeat of a visual tract. At gomonimny G. as a result of defeat of the central part of a visual way disks of optic nerves remain normal since the developing atrophy of nerve fibrils of the central part does not go down below lateral cranked bodies. At G. arising owing to defeat of a visual tract asymmetry of defects of a field of vision is more often noted. Idiosyncrasy of gomonimny G. at defeat of the central part of a visual way is clearly the expressed symmetry of defects of a field of vision of both eyes that is explained by features of the course of nerve fibrils within the central part, to a cut of fiber from identical sites of a retina of an eye go nearby.
At full gomonimny G. the line of the section between the dropped-out and kept half of a field of vision in one cases passes through a point of fixing, in others dugoobrazno deviates towards the dropped-out half, keeping area of a macula lutea that is adaptation of functional character and does not matter for topical diagnosis of level of defeat of a visual way.
For determination of level of defeat of a visual way gemianopichesky reaction of pupils to light at use of strong and weak light is investigated.
Gemianopichesky reaction of pupils to light is expressed that the pupillary test on light (narrowing of a pupil) arises only at illumination of an able to see half of a retina, at illumination of a blind half of a retina it is absent. For identification of this reaction the special conditions of a research excluding a possibility of hit of light on an able to see half of a retina are required. Strictly local is applied to this purpose zasvt retinas of different intensity. Gemianopichesky reaction of pupils is caused in general at G., but it has diagnostic value for identification of level of defeat of a visual way only at gomonimny. Emergence of a gemianopichesky pupillary test on light is explained by anatomic features of the course of fibers of a visual way and features of the course of pupillary fibers.
At defeat of peripheral neuron of a visual way local illumination of any intensity of the seeing half of a retina causes normal reaction of pupils to light (an instinctive protective reflex) whereas at illumination of a blind half of a retina the pupillary test on light is absent. At defeat of the central neuron of a visual way gemianopichesky reaction of pupils is caused only on weak local illumination of the seeing half of a retina (an orientation response on novelty) while bright lighting causes normal reaction of a pupil both with blind, and from an able to see half of a retina (unconditional defense reaction).
Valuable differential diagnostic character of localization patol, process in an occipital share of a brain is development of optikognostichesky syndromes — disorders of the highest visual functions — optical agnosia (see), an alexia (see. Aphasia ), etc.
Treatment is carried out depending on character of the basic disease which caused G.
G. can be a temporary or constant symptom that depends on character and weight of a basic disease and defeat of a visual way.
Bibliography: Merkulov I. I. and Vasilenko Yu. V. Visual disturbances at defeat of occipital area and zones, boundary with it, in book: Vopr, neyrooftalm., under the editorship of I. I. Merkulov, t. 10, page 5, Kharkiv, 1962, bibliogr.; The multivolume guide to surgery, under the editorship of B. V. Petrovsky, t. 3, book 1, page 176, Zh., 1968; To Trona. Zh. Glaz and neurosurgical pathology, JI., 1966; about N e, Diseases of a visual way, L., 1968; Shakhnovich A. R. and Shakhnovich of V. R. Pu pi of l log raffia, Objective research of pupillary tests and movements of eyeglobes, page 208, M., 1964; Frontera A. T. Bilateral homonymous hemianopsia with preservation of central vision, Mt Sinai J. Med., v. 41, p. 480, 1974, bibliogr.; P e e 1 e T. L. The neuroanatomical basis for clinical neurology, L., 1954.
O. H. Sokolova.