From Big Medical Encyclopedia

SIGHT (Latin visio, visus) — the function of an organ of sight and the visual analyzer consisting in perception and transformation of energy of the light radiated or reflected by various objects and obtaining information on the world around.

Ability to 3. in a rudimentary look it is inherent in the elementary unicells as the photoharmose is inherent to each living cell. During evolution the special photosensitive cells which are selectively reacting to a light irritant were allocated. Such cells are available in cover tissues of some lowest animals, napr, worms. An eye as body of perception of light appears at arthropods. As a result of further evolution of body 3. two of its look were allocated: difficult — a so-called facet eye at invertebrates and in the form of the optical camera at vertebrate animals. At the heart of process 3. at that and others light absorption in a layer of photosensitive cells and emergence thereof the nervous signal transmitted to a brain lies. This process carries the name of photoreception. Irregularity in space and time falling on a layer photoreceptors (see) light causes eventually reproduction in a brain of all difficult and changing picture of the world around.

The greatest perfection body 3. reaches at the person. It includes the optical apparatus of an eye creating the image of an object retina (see), in a cut it turns into a mosaic of the excited and slowed down sites, optic nerve (see) and a visual tract, transmitting a visual signal to a brain, the subcrustal and cortical visual centers in which this signal is processed into an image (see. Visual centers, ways ).


On modern representations 3. — complex functional system. It is accepted to distinguish several functions 3.: photoperception (see), color sensation (see. Color sight ), perception of a form of objects, a quantitative measure to-rogo is visual acuity (see), ability to see big space at a motionless look — field of vision (see), ability to connect images of two eyes and to localize the received image of a subject of the direction and on relative depth from the observer — solid vision (see).

All visual functions depend on previous experience and training of an individual, in a smaller measure such as photoperception and color sensation, to a large extent — visual acuity and solid vision.

Photoperception of body 3. the person it is characterized by extremely high sensitivity. Studying observation of quantum fluctuations of light, S. I. Vavilov (1936) established that in certain conditions hit of several photons (light quantums) in an eye can cause photoperception. However 3. perhaps only within rather narrow site of a range of electromagnetic radiations — with the wavelength from about 390 to 760 nanometers. At the same time spectral response of an eye matches a maximum of a curve of distribution of energy of the sun.

Sensitivity of an eye to light varies over a wide range and depends first of all on surrounding illumination: at stay of the person in the dark the threshold of photoperception decreases, at stay on light — increases. This property 3. is called visual adaptation (see. visual adaptation ). It is accepted to distinguish night, or scotopic, 3. (at the brightness of a surrounding background which is not exceeding 0,01 candelas), twilight, or mezopichesky, 3. (at background brightness from 0,01 to 10 candelas), day, or photopic, 3. (at background brightness of St. 10 candelas).

Fig. 1. The curves characterizing the maximum sensitivity of an eye on light (1) and in the dark (2). On ordinate axis — light sensitivity in relative units, on abscissa axis — wavelength in nanometer.

In addition to limit of sensibilitys to light, at change of illumination of a background also its spectral characteristics change: the maximum sensitivity of an eye on light to more long-wave beams, than in the dark (fig. 1).

These features 3. are caused first of all by existence in a retina of an eye of the person of two types of photoreceptors — flasks and sticks. The first are located with hl. obr. in the central area of a retina also provide photopic sight, the second — on the periphery of a retina and provide scotopic sight. Coneal 3. responsibly for perception of a form and color of the objects which are in a midfield of sight, bacillary 3. — for detection of weak light signals on the periphery of a field of vision.

Basic process of photoreception — absorption of a light quantum and emergence of excitement — happens in outside segments of sticks and flasks. The outside segment of both types of photoreceptors represents a pile thin (thickness of 20 — 25 nanometers) the disks containing a rhodopsin [F. S. Sjostrand, 1959]. Among rhodopsins of sticks (see. Rhodopsins ) it is fullestly studied rhodopsin (see). At absorption of a light quantum cisrhodopsin turns into other isomer — trans-rhodopsin that in turn leads to a number of the chemical and ionic transformations which are coming to an end with excitement of electric potential.

Similar process happens in flasks which rhodopsins iodopsin or cyanodogs react to light of various spectral structure. Functional insufficiency of rhodopsin leads to development of the disease which is shown in falloff of visual acuity in the conditions of the lowered lighting — to hemeralopias (see).

Photochemical mechanism of adaptation 3., formulated still by P. P. Lazarev (1925) and Gekht (S. Hecht, 1938), it is based on compliance between light sensitivity of an eye and concentration of a rhodopsin. Direct measurements of these sizes [Dowling, 1963] brought specification in these representations: light sensitivity of a photoreceptor is defined not by quantity of the pigment which is available at present, but quantity of the molecules which broke up at effect of light, i.e. is defined by some intermediate or end products of fading of a rhodopsin. In addition to the photochemical mechanism, adaptation 3. it is carried out by other mechanisms — pupillary reflex (see), and also reorganization of nervous bonds in visual system that decides or changes of receptive fields (or influences of so-called collateral irritants) in visual system, or interaction on other sense bodys.

The color sensation is connected with function of flasks. From numerous theories of color sight the ternary theory for the first time stated by M. V. Lomonosov (1756) and which gained further development in Jung's works is most recognized (H. T. Joung, 1802) and G. Helmholtz (1866). Its essence comes down to the fact that in an eye there are three receivers, each of which has the maximum sensitivity in a certain spectral range: one — in red, another — in green, the third — in blue. Light of any spectral structure can be spread out to these three components and, therefore, causes the answer of three light-sensitive receivers of an eye. Based on the ratio of their excitement there is an identification of color of the radiation which got into an eye. The ternary theory of color sensation receives increasing morfofiziol. confirmation. In a retina of vertebrata three types of flasks which rhodopsins have characteristic ranges with maxima in the field of primary colors are allocated. Remains not clear whether the specific light-sensitive pigment or mix of the same pigments contains each type of flasks in different proportions.

Photoperception and color sensation are that basis, on a cut other functions 3 are based. The most important of them — distinguishing and an identification of a form of objects. Not absolute sensitivity of an eye to light and color, and sensitivity to their changes in space and time — so-called contrast sensitivity of an eye is important for its implementation. Its properties express the numerous quantitative relations established by practical consideration — psychophysical laws 3.

In the middle of 19 century Weber's law — Fekhnera was established to one of the first: the minimum found difference of brightness of a spot (V) and background brightness, on Krom this spot is located (Vf), belongs to background brightness in a nek-swarm of a constant proportion. The difference In - Vf is designated usually ΔВ and is called a differential threshold of brightness; the relation ΔB/Bф — a differential threshold, or threshold contrast. Weber's law — Fekhnera can be written down in a look ΔB/Bф = by const.

Thresholds of visual feeling depend not only on brightness of a light incentive, but also on its area: in certain limits of intensivnost of an incentive the threshold brightness of an incentive In and its area S are inversely proportional: BS = const. This relation which received the name of the law of Rikko (1877) is fair at the small areas of photoirritation. It means that there is full summation of irritation. A zone, in limits the cut acts this law (6 — 10' in the center of a retina and to 1' on its periphery), received the name of a zone of full summation. Does not happen to increase in the area of an incentive of full summation any more. The relation of threshold brightness In and the areas of an incentive takes a form of BS^n = const., where the exponent of n varying from 0 to 1 reflects summatsionny ability of a retina in these conditions.

Are not less important for 3. temporary characteristics of a light incentive. At incentives of small duration Bloch's law which is an analog of the law of Rikko for temporary summation works: threshold intensity of light flash I and its times of t are inversely proportional: It = const. At increase in duration of flash summation becomes incomplete and expression takes a form of It n = const., where n — coefficient of temporary summation.

In addition to spatial and temporary summation of a light incentive a number psychophysical is described. the phenomena having significant effect on perception of a form of objects. So, at observation an eye of the surface having two and more than levels of brightness on limit of their section notes strengthening of contrast: the region of lighter field

adjoining border brightens, and the edge of more dark field darkens even more. Fields of different color subjectively change the coloring depending on a background, on Krom they are located (the phenomenon of a color contrast).

All types of interaction in visual system can provide more accurate vision of objects (in particular their borders, contours), but, on the other hand, can bring mistakes in assessment of the sizes of objects and their relative positioning (see. Visual illusions ).

From temporary phenomena of vision the greatest value has an ocular spectrum, or a postimage — time remaining on a nek-swarm visual impression after the termination of an incentive. The ocular spectrum at first seems in the same color, as the incentive (a positive ocular spectrum) which caused it, and then accepts coloring additional (at a color incentive) or opposite (at an achromatic incentive) colors (a negative ocular spectrum). Ocular spectrums reflect an inertance 3. This property is the cornerstone of merge of light flashings above a certain frequency in continuous feeling of a luminescence, it causes an opportunity to connect separate shots of cinema and the television image in a uniform moving picture.

All properties of interaction of visual feelings were studied on the basis of psychophysical phenomena earlier. With development of the theory of processing of information in visual system material bases of these patterns begin to appear. The visual system is multi-level structure with difficult pattern of signal transmission from the lowest levels on the highest. Set of the elements of the lowest level which are functionally connected with one element of the highest level following it is called the receptive field of this element. As the receptive field of a retina understand set of the photoreceptors tied through bipolyara with one ganglionic cell of a retina. X. Hartlayn (1940) showed that receptive fields of a retina happen three types: reacting to inclusion of light (on — the answer), switching off of light (off — the answer) and on inclusion and switching off of light (on — off — the answer). Further researches revealed that in the receptive field of the same ganglionic cell zones with different types of answers concentrically alternate. Elektrofiziol, Barlow's researches (N. V. of Barlow, 1953), allowed to establish V. D. Glezer (1966) on a retina of various animals that the receptive field is not strictly limited structure: size, and sometimes and its form change depending on lighting of the neighboring fields and all retina. As showed long-term researches A. JI. Byzova with sotr. (1966, 1977), this regulation is carried out as due to horizontal interactions in a retina at the level of bipolyar, horizontal and amakrinny cells, and due to the descending influence from upper parts of a retina on lower. Assume that in the mechanism of these interactions an essential role is played by distribution of electric potentials on interneural synapses. Changes of receptive fields provide local adaptation of a retina, i.e. disappearance of a signal from sites of constant illumination. The signal is sent only from those sites where the difference of osveshchennost appears — edge or their contour. If distribution of light on a retina a long time remains to constants i.e. if the image on a retina not movably, the signal also gradually stops. The phenomenon of «a fixating blindness» — disappearance of visibility of a subject, the image to-rogo not movably concerning a retina is connected with it. From here continuously to see a subject at which it is aimed zorny line (see), an eye shall make the small movements constantly. Such movements happen three types: 1) a tremor — high-frequency (30 — 150 Hz) fluctuations around a point of fixing with very small amplitude (to 17 angular seconds); 2) drift — slow (up to 6 angular minutes in 1 sec.) sliding of a look from the set direction (at a size from 3 to 30 angular minutes); 3) mikrosakkada (microjumps) — bystry movements of a look from 1 to 50 angular minutes. Consider that drift generally promotes recovery of visibility of the image on a retina, and mikrosakkada — to recovery of the set direction of a look.

From ganglionic cells of a retina on fibers of an optic nerve the signal comes to the lateral cranked body which is the subcrustal center 3. Here the cells having receptive fields of two types are concentrated: one are responsible for transfer of data on brightness, others — about contours (form) of the image on a retina.

The last neuron of a visual way begins in a lateral cranked body and comes to an end in visual bark. Receptive fields of cortical neurons react to various difficult long incentives.

Three types of cortical visual fields are described: 1) simple, having the extended form and reacting to the line, a strip or a contrast image edge passing across the field; 2) difficult, reacting to moving edge of different orientation; 3) superdifficult, answering figures like a corner, cambers, a piece of a straight line, a strip of a certain thickness.

By I. A. Shevelyov (1975, 1976) in an experiment it is shown, as cortical receptive fields are not stable textural features: their size, a form and character of the answer change depending on illumination and the level of wakefulness of an animal.

Thus, the visual system is presented in the form of multi-storey hierarchical network of the elements allocating (detecting) separate harder and harder elements of the image. A final stage of work of this system is synthesis of a visual object and an identification in its way of comparison to a stock of the images which are stored in memory. According to V. D. Glezer (1966, 1975), there are three types of a visual identification. On the first type by means of inborn mechanisms (standards detectors) simple space signs of the image are identified: orientation of lines and figures, their location under review, size. On the second type by the multistage analysis of signs and comparison of their combination to a feature set of the visual objects acquired during life subject drawings, geometrical figures are identified. On the third type the same difficult images after their repeated repetition are identified: in visual system standards of these images like inborn standards for simple figures form; letters, figures and other graphic symbols are identified by such way.

The research of visual acuity — ability to distinguishing of the smallest details of the image is closely connected with a visual identification. It is accepted to distinguish signs, on the Crimea it is learned: 1) smallest visible (minimum visibile); 2) smallest distinguishable (minimum separabile); 3) smallest recognizable (minimum cognoscibile). In the first case it is about detection of an object on a homogeneous background, in the second — about an identification of a simple sign (the first type of an identification), in the third — about an identification of a difficult figure (the second, and at sufficient fitness — the third type of an identification).

Development of ideas of detectors of signs of the image in visual system played an important role theories 3. However specialization of detectors cannot be boundless. It forced to look for the universal elements of images suitable for the analysis of any visual object. The general theory of transfer of images allowed to establish that such element is the lattice from the alternating black and white strips.

Any distribution of light to surfaces can be spread out to the sum of such lattices of various orientation, frequency and contrast. F. W. Campbell with sotr. (1966, 1970) showed that the visual system can be considered as a multi-storey set of the spatial-frequency filters. The optical apparatus of an eye limits a transmission of hl. obr. low-frequency lattices, whereas the visual and nervous channel — hl. obr. high-frequency. Researches on animals showed existence in visual system of the real detectors specifically sensitive to lattices of certain frequencies and the directions. Such multichannel spatial-frequency hypothesis 3. allows to explain a number of phenomena 3. the person, in particular a so-called meridional amblyopia — various visual acuity for lines of different orientation at a high nekorrigirovanny astigmatism.

The majority of the stated data on work of visual system are received on animals by assignment of biopotentials from cellular elements at the different levels of a visual way. Obtaining such data on the person is impossible, however the research of summary electric answers to a light incentive allows and to receive data on processing of visual information at the person. R. Granit (1930, 1947) for the first time gave interpretation of components of the electroretinogram — the summary answer of a retina of a human eye to a light incentive. A carp (Karpe, 1945) entered elektroretinografiya (see) in a wedge, practice of ophthalmology. Electric phosphene — visual feeling of flash in response to electric irritation of an optic nerve — allows to judge a condition of this link of a visual way, and the potentials of a brain caused by light (see. Bioelectric potential ) characterize a condition of all way in general.

A. I. Bogoslovsky with sotr. (1976) the uniform system of diagnosis of defeats of the visual and nervous device using the specified phenomena is created.

Fig. 2. Record of micromovements of eyes (on the right) at free examining within two minutes of a sculptural portrait (at the left).

The stated representations characterize 3. as the single act of processing of information which is contained in the image. Actually 3. represents continuous process, in Krom along with a touch link motor components, first of all the accommodation providing continuous focusing of the image on a retina constantly participate (see. Accommodation of an eye ). Continuous fluctuations of optical installation of an eye with an amplitude of 0,2 — 0,3 dptr, apparently, are also necessary for receiving a sharp image, as well as the micromovement of eyes for preservation of visibility of the fixed object. They allow to smooth the small aberrations of optical system which are present practically at each eye (see. Aberration of an eye ). In the course of 3. constantly the movements of eyes participate. On the nature of movements distinguish jumps — the bystry, almost instant turns of eyes transferring a look from one purpose on another, and the slow tracing movements allowing to watch a moving subject. On a sochetannost of movements of two eyes distinguish versionny at which both eyes turn in the same party on the same corner, and vergentny at which eyes make turn towards each other or, on the contrary, in different directions in the plane passing through their centers and a point of fixing. The Versionny movements aim to keep the general point of fixing of two eyes at invariable distance to the purpose, vergentny — at change of distance to it. The movements of eyes in these cases provide solid vision (see). As well as process of visual fixing of an object one eye, and process of joint fixing (bifiksation) is provided with the characteristic micromovements of eyes (fig. 2) having the nature of counter drift with the greatest density in an oval of 5 in size — 10 angular minutes across and 3 — 4 angular minutes down with the center of a point of joint fixing.

Solid vision has three parties: 1) merge of two images at the expense of what increase in reliability of information on an object is reached a nek-swarm; 2) localization of the direction regarding under review; 3) definition of relative remoteness of objects from the observer thanks to their unequal projection on retinas of both eyes; this property is called sometimes stereoscopic sight.

The listed properties 3. allow to get an impression about the considered subject. Time having received this impression, the person aims to keep it until the end of observation, irrespective of change of illumination, the movement of a subject concerning the observer or the head of the observer concerning a subject, and also distortion of its form various optical factors (a konstantnost of vision). Partly it is provided with motor systems of fixing, a bifiksation and keeping track of by an object, but generally due to invariant transformations of a visual object in a brain.

Thus, 3. represents not the instant act, but the complex multistage process including obtaining the image in an eye, allocation of the most important information from it, transfer of this information in a brain, interpretation of the image; allocation of important sites of an object, targeting of eyes by means of motor systems on these sites and obtaining their sharp image, connection of images of two eyes in a uniform visual object, an identification of an image by comparison to the stock which is available in memories, localization of an object and its details in space.

Methods of a research

Definition central 3. (see. Visual acuity ), peripheral 3. (see. Field of vision ), color sight (see), a research of an eyeground (see. Eyeground , Oftalmoskopiya ).


there are different types of pathology 3. — both inborn, and acquired (see. Eye , Optic nerve , Coloboma ). Patol, process can be localized in any department visual analyzer (see), it can be caused by changes in the eye and other bodies and systems of an organism. Disturbances 3. are shown in disorder of color sensation (see. Color sight ), photoperceptions (see), visual acuities (see), change fields of vision (see), napr, at to scotoma (see). They exert impact on ability of merge of the image two eyes in a uniform image (see. Solid vision ).

These disturbances are connected with various damages of body 3. and conduction paths (see. Eye , Congestive nipple , Visual centers of a way ), inflammatory processes of an eye and its covers, covers and substances of a brain (see. Iridocyclitis , Keratitis , Meningitis , Uveitis , Encephalitis etc.) and tumors (see. Melanoma , Meningioma , Retinoblastoma etc.). Various dystrophic processes in a cornea, an iris, a crystalline lens, a ciliate body, a vitreous, a retina, an optic nerve also quite often involve disorder of visual functions (see. Optic nerve , Iridocyclitis , Keratitis , Cataract etc.). Disturbances 3. are observed at the persons suffering idiopathic hypertensia (see), atherosclerosis (see) owing to circulator changes in various departments of the visual analyzer, especially on on an eyeground (see).

At diseases of a nervous system there are various frustration 3.: decrease in visual acuity, loss of a field of vision, disturbance of color sensation, oculomotor disturbances and changes on an eyeground. The reasons of visual frustration are various: injuries of a skull, disturbance of cerebral circulation, inflammatory processes of a brain and its covers, granulomas, parasitic cysts, intoxications, tumors.

At defeat of an intracranial part of an optic nerve (the central fibers) central is observed scotoma (see); defeat of its peripheral fibers is characterized by peripheral narrowing of the field 3., and central 3. does not suffer (see. Hemianopsia , Optic nerve ).

Defeat of visual decussation is clinically shown by primary atrophy of optic nerves in combination with a geteronimny hemianopsia. At influence patol, the center (most often tumors of a hypophysis) on a medial part of visual decussation where fibers cross, the bitemporal hemianopsia, and influence of two patol, the centers on lateral parts of visual decussation where there pass not crossed fibers develops, is followed by a binazalny hemianopsia. As pressure upon visual decussation patol, the center displaces it, extent of defeat of the nerve fibrils going to it from both eyes is not identical. Therefore the hemianopsia can be full or partial. The partial hemianopsia is followed by asymmetry of defects of a field of vision. Sometimes patol, process in visual decussation completely switches off the crossed and not crossed fibers going from one eye. Then the blindness of one eye is combined with a temporal hemianopsia of another, napr, at obstruction of an internal carotid artery, tumors of hiazmalno-sellyarny localization. Visual acuity owing to defeat of visual decussation can be not changed, further owing to an atrophy of an optic nerve in the beginning «3. sharply decreases. Oftalmoskopicheski in an early stage of development of visual frustration is marked out blanching of an optic disk from the temporal party, in late — primary atrophy with sharp narrowing of arterioles of a retina. At defeat of a visual way proksimalny visual decussation the gomonimny hemianopsia develops: traktusovy — at a disease of visual tracts, central — at a disease of a bunch of Grasiole or bark of an occipital share. Are characteristic of a traktusovy hemianopsia: gemianopichesky reaction of pupils to light, primary atrophy of optic nerves with considerable decrease in visual acuity, asymmetry of defects of a field of vision.

The hemianopsia as a result patol, process in the central part of a visual way can be full, partial, quadrant (upper, lower), in the form of scotomas. Idiosyncrasy of the central hemianopsia is clearly the expressed symmetry of defects of a field of vision on both eyes with preservation of high visual acuity. The eyeground does not change, gemianopichesky reaction of pupils is absent, on EEG disturbance of an alpha rhythm is noted. Development of a gomonimny hemianopsia is preceded photopsias (see), visual hallucinations. The most often gomonimny hemianopsia is caused by tumors of a brain and disturbance of cerebral circulation. The full hemianopsia is more often observed at tumors of a brain, oftalmoskopichesk are noted congestive nipples of optic nerves; the partial or quadrant hemianopsia develops seldom and even more rare — gemianopichesky scotomas. Disturbance of cerebral circulation usually is followed by a partial or quadrant hemianopsia with preservation of the central sight, there can be gemianopichesky scotomas, more considerable tendency to recovery of defects of a field of vision is noted; congestive nipples develop very seldom. Bilateral defeat of bark of an occipital share in area of a shporny furrow and the sites adjoining to it leads to cortical to a blindness (see).

Disturbances 3. at Kennedy's syndrome (see. Kennedy syndrome ), sometimes developing at tumors of a frontal lobe, arise owing to an atrophy of an optic nerve on one eye in combination with a congestive nipple on another. Various adverse production factors (infrared radiation, fields microwave ovens, trinitrotoluene, products of oil refining etc.) can have various influences on 3. (see. Eye, occupational diseases ).

In an experiment and in clinic data on negative influence on 3 are obtained. various toxic chemicals applied in agriculture and the industry and also ionizing radiation.

Extent of disturbances 3. at ionizing radiation depends on the size of an absorbed dose. The retina is most sensitive to beam influence. The changes in it revealed on the electroretinogram are possible at radiation in a dose to 1 is glad. However these changes are reversible even after influence of high doses.

At general irradiation or only the heads in doses 200 — 800 I am glad perhaps decrease in light sensitivity and lengthening of time of dark adaptation, change of a form and reaction of pupils to light, disturbance of accommodation and convergence owing to defeat of c. and. page. In the heat of a radial illness on an eyeground it is possible to observe vasodilatation, especially veins, hypostasis of a retina, hemorrhage and a plasmorrhagia in a retina which at an arrangement in macular area lower visual acuity. Changes smooth out during the recovery period of a disease a little. At radiation of area of an eye in doses of 3 — 5 thousand I am glad as a result of defeat of vessels of a retina and a choroid the degenerative chorioretinal centers and an atrophy of an optic nerve leading to sharp decrease in visual acuity and a blindness can develop.

At development of a beam cataract, depending on intensity of a phacoscotasmus, decrease in visual acuity is noted (see. Cataract ).

Defeat of a cornea at influence of various doses of ionizing radiation is shown by suppression of mitotic activity of an epithelium, its passing desquamation with decrease in sensitivity of a cornea, development of an erosion and ulcer which consequence the cicatricial opacifications of a cornea which sometimes are sharply lowering visual acuity (can be see. Keratitis ).

Hygiene of sight

Main objective of hygiene 3. — preservation full 3., allowing the person throughout all life it is successful to carry out the tasks connected with study, work and life. Hygiene 3. develops rules for creation of visual comfort in different conditions: 1) rational lighting; 2) optimum selection of color contrasts; 3) creation of a favorable emotional situation. These three major factors shall warn the visual exhaustion leading to frustration 3.

The main requirements imposed to natural and artificial lighting — intensity of light, its uniformity, spectral structure, etc. Need of adequate intensity of light is caused by the fact that at weak lighting it is difficult to perform delicate work, and at very intensive there is an osleplennost. Regulation of quality of artificial lighting consists in approach of its spectral structure to a visible radiation spectrum of the Sun as to the most usual for a human eye. In a gigabyte. the relation direct lighting is adverse as the light sources which are under review will stick together eyes. The semi-reflected lighting in most cases is most reasonable.

Fiziol. researches established the optimum size of illumination in a workplace — 200 — 3000 lx. Natural lighting often creates the big shining and reflective surfaces giving high diffusion illumination in a workplace that favorably affects working capacity. The questions connected with development of optimum natural and artificial lighting are in a complex developed by various specialists, and their standards find reflection in special rules (see. Lighting ).

Color contrasts are of great importance in ensuring visual comfort, make esthetic impact on the person, also influence his working capacity. By special researches it is established that optimum influence on 3. (yellow-green-blue) — so-called optimum colors render rather low-saturated colors of a middle part of a visible range. For the alarm system the most saturated (safety) colors are used. Use of various conditional flowers in the industry and transport facilitates storing of safe and dangerous situations. Negatively some influence normal color sensation professional harm, intensive smoking, an alcohol abuse, etc. (see. Color sight ).

A favorable emotional situation for 3. (lack of constant continuous changes of fields of vision, sharp color contrasts, strong illumination, the blinding surfaces etc.) promotes increase in safety in performance of productions, labor productivity, including at persons whose work demands intensive participation 3., napr, on the conveyor, transport, etc.

The visual exhaustion can lead to decline in production of work, promote development patol, conditions of an eye (see. Amblyopia , Asthenopia , Short-sightedness , Nystagmus etc.). Under the influence of long and adverse visual work the volume of accommodation of an eye decreases, the balance of outside muscles of an eye worsens a little (see. Convergence of eyes , Divergence of eyes ).

In system of actions for preservation and promotion of health at children hygiene 3. has special value. Among them the important place is taken by quality of printing of school textbooks (see. Book ), good lighting in educational classes and houses (especially during the performance of homeworks), regulation of duration and the nature of visual work, the correct landing during the occupations, observance of a day regimen, the prevention of overfatigue 3., a cut can cause its frustration, in particular short-sightedness.

Timely and correct correction 3 is necessary for children with anomalies of a refraction. (see. Astigmatism of an eye , Short-sightedness , Far-sightedness ).

Bibliography: Abdullaev of B. M. Patogistologicheskiye of change of eyes at radiation defeat, Baku, 1976, bibliogr.; Avetisov E. S. Concomitant strabismus, M., 1977; B yz about in A. L. Electrophysiologic researches of a retina, M., 1966; Vavilov. I. Glaz and the sun (About light, the sun and sight), M., 1976; V. V. Wolves, Gorban A. I. and Dzhaliashvili O. A. Klinicheskaya vizo-and refractometry, L., 1976; Glezer V. D. Mechanisms of an identification of visual objects, M. —, 1966; Guskovaa. To. G. D ibay-sogol. Radial illness of the person, M., 1971; The Visual identification and its neurophysiological mechanisms, under the editorship of V. D. Glezer, L., 1975, bibliogr.; Kravkov S. V. An eye and its work, M. — L., 1950; Lindy P. and Norman. Processing of information at the person, the lane with English, M., 1974, bibliogr.; The organization of dispensary observation behind the persons working with sources of ionizing radiation under the editorship of. A. K. Gusko-voy, M., 1975; Sokolova of O. N. Oftalmonevrologiya of defeats of a mesencephalon, M., 1971; Tronas E. Zh. Glaz and neurosurgical pathology, L., 1966; Physiology of touch systems, under the editorship of A.S. Batuyev, L., 1976; Shevelyov I. A. Dynamics of a visual touch signal, L., 1971; Campbell F. W. a. Robson J. G. Application of furier analysis to the visibility of graitings, J. Physiol. (Lond.), v. 197, p. 551, 1968; Neuroophthalmologie, hrsg. v. R. Sach-senweger, Lpz., 1975, Bibliogr.; Scho-b e r H. Das Sehen, Bd 1 — 2, Lpz., 1960 — 1964; System of ophthalmology, ed. by S. Duke-Elder, v. 4, L., 1968.

Hygiene 3. — Avetisov E. S. Protection of sight of children, M., 1975; The Multivolume guide to eye diseases, under the editorship of V. N. Arkhangelsky, t. 1, book 2, page 171, M., 1962; The Guide to rational color registration, under the editorship of V. N. Chernigovsky, M., 1964, bibliogr.; Baumgardt E. To L'hygi-yopa of de la vue, P., 1962.

A. I. Bogoslovsky, V. V. Volkov; Yu. G. Grigoriev (I am glad.), A. I. Kolotova (not BP.).