When the question arises about what different vision in the eyes is called, the answer will be the same: anisometropia. This pathological condition occurs when optical system loses the ability to refract rays. That is, the visual organs with this disease have different optical power. Anisometropia may be accompanied by the development of astigmatism. Of course, the disease is provoked by certain factors, and without proper treatment it causes complications.
When a person is impaired visual functions, are selected effective ways corrections. This refers to the use of glasses and lenses.
But if different vision is detected in the eyes, corrective optics are not always able to help. It's all about the reasons that cause anisometropia - a disease that is characterized by the presence of different vision in the eyes.
In order for a correct and unblurred image to be formed, it is necessary that the parallel rays emanating from the object intersect at the retinal focus. If this process is disrupted, a decrease in visual acuity is observed.
When the difference in refractive power between the eyes is one or two diopters, binocular vision will not be particularly affected. But if the indicators differ significantly more, then the development of refractive anisometropia should be expected. Moreover, the refraction in one eye may be normal, but in the other it will be abnormal. But, basically, the pathology affects both eyes.
It is advisable to eliminate anisometropia in time, otherwise the patient may experience dangerous consequences:
It is impossible to ignore the condition when the visual apparatus is subjected to various lesions.
You should know that different vision in the eyes can have various reasons:
Doctors usually diagnose pathology innate nature.
Acquired anisometropia occurs when:
If we talk about hereditary predisposition, then in babies under one year of age the disease is asymptomatic. With age, symptoms become more pronounced. Manifestations will depend on the extent of the disease.
It happens:
In addition, anisometropia occurs:
If the degree is weak, the disorders are almost not felt. When pathology of the highest degree develops, binocular vision is impaired. There is no clear image. At the same time, it is difficult for the patient to navigate in space. Often visual load cause excessive eye fatigue.
Whichever eye has the most severe damage, suffers more accordingly. In other words, its activity will be suppressed by the brain. The result is the development of amblyopia.
Another consequence is strabismus, which is caused by weakening of the rectus muscle of the affected eye and its deviation to the side.
Making a diagnosis requires:
The way in which the pathology will be eliminated is determined by the level and type refractive errors. Visual dysfunction is usually corrected with glasses or contact lenses. But this method is not suitable for every patient. It is necessary that the difference in refractive power should not be more than 3 diopters. 
The selection of lenses is carried out for each specific case separately. It is necessary to wear them correctly and periodically undergo examination by an ophthalmologist, receiving the necessary advice from him.
A patient who wears lenses may suffer from:
If conservative methods prove futile, the doctor decides to carry out laser surgery. It is also prescribed to patients whose degree of illness is high. After surgery, it should take a week or two for the improvement to become apparent.
There is no need to panic when anisometropia is diagnosed. If detected early, the problem can be completely eliminated, especially if there is a mild degree of the disease.
Eyes are given to man to contemplate the world around us, but can everyone answer how human vision works? After reading our article, you will find out what the difference is peripheral vision from the central one, how the lacrimal organs are arranged and eyeball. We will tell you everything about color reproduction and help you understand the difference between the normal vision of a young creature and an elderly person. Do you want to gain insight into the retina, optic nerve and blind spot? Then our article is for you.
In order for the eye to perceive its surroundings, it needs to tune in to the sun's rays. There is a direct relationship between the optical range and the rays hitting the cornea. Next, the light, in order to get to the retina, where incoming images are processed, has to pass through the lens and vitreous body.
Nourishes the lens intraocular fluid circulates through two ocular chambers. By using optic nerve ready information enters the brain. The dominant eye perceives the image more clearly - the responsibility for this lies with the macula located in the middle of the retina.
To good eyesight remained as such for as long as possible, constant “cleansing” is required. Eyelashes act as cleaners that act as tear filters.
The eyelids have the responsible function of protecting the senses from damage. The conjunctiva is located on the inner surface of the eyelids and sclera. This scientific name is given to the mucous membrane, which prevents foreign bodies from entering the eye. As a result defensive reaction tear fluid is released.
Psychology has established the fact that at birth a person does not have very good vision. The final formation of this sensory organ in infants occurs when they reach the age of nine months.
In accordance with the characteristics of human visual perception, they observe not the object as such, but the light that is reflected from its surface. Refraction is the refraction of light.
The arrival of the projection on the retina provokes the following actions:
Our sense organ is extremely high rate sensitivity to light. The main parameters characterizing healthy vision are elasticity and strength. There are significant differences in the color vision (and acuity) of infants, young adults, and the elderly.
And we are talking not only about the structure, but also about the stages of development that any person has to overcome throughout his life. The composition of an apple is as follows:
The location of the apple itself is a bone funnel, which also performs protective function. The funnel is usually called the orbit. Around the sensory organ there is a layer of fat, muscle and fibrous tissue. The environment for the apple is:
The characteristics of visual perception and healthy vision itself depend on the state of any of the listed organs.
Central vision plays a leading role in both preschool children and adults. Thanks to the fovea, which is responsible for shapes, a person is able to discern even the smallest details and contours of objects. Color in this case does not play any role, since main characteristic is the acuity that directly depends on the angle of perception. This relationship looks like this: as the angle expands, the sharpness decreases.
In psychology, spatial points are of great importance. If we consider the types of vision from the position of ranges and angles, then various types of pathologies are identified. Accessible to a person's dominant eye good review, however, only binocular perception of the environment can be considered ideal.
There is a connection between peripheral color vision and spatial orientation. A person determines his location based on his field of vision. The arrangement of things occurs without violating the limits of the coordinate system that the human brain is capable of building.
The peculiarities of visual perception explain the fact that even a person with healthy vision is not capable of clearly seeing all the objects around him in space. However, their position is fixed to them. When peripheral perception deteriorates, it leads to a sharp narrowing of the optical range.
The result of this is a person’s loss of the ability to freely navigate in the environment. Such cases are not observed often, but they do occur. Therefore, doctors have developed a number of tests to test the peripheral perception of the surrounding world and identify possible pathologies.
The perfection of human color vision is so great that his healthy vision allows him to distinguish about one hundred and fifty shades and tones. To determine color, the eye has so-called cones. This name was given to special light-sensitive cells that are localized in the brain of each individual. Thanks to rods, a person can see at night.
Each of the three types of cones is allocated its own part of the spectrum, for this reason heterogeneity of color vision occurs. Blue parts of the spectrum are perceived by the first type of cones, while for green shades the second analogue is used. And for the third type, red shades are “native”. Psychologists attach great importance to adequate perception of colors. This is especially true at the preschool level.
Normal vision is not the same for men and women. Thus, girls tend to distinguish a greater number of colors and shades, and young people are better able to concentrate on the details of individual objects. If for men it is considered normal for the development of visual perception to gravitate towards the central type, then for women a bias towards the peripheral is visible.
An explanation for such differences should be sought in the historical development of human society. Among our ancient ancestors, the man was exclusively engaged in obtaining food, while the woman was responsible for caring for the home.
For this reason, the man's eye was adapted to tracking and striking prey, sometimes over considerable distances. The woman monitored any changes that occurred in her environment and quickly took actions to eliminate them. This, for example, may concern the penetration of a snake into a home, which had to be killed as quickly as possible.
Women's color vision in the dark is more effective than men's. Thanks to the larger viewing width, girls have real opportunity fix more minor parts. But the vision of men allows them to quickly track objects that are in motion. Close distances are also more comfortable for women than for men.
A person’s age clearly affects his visual acuity. In order for vision to return to normal, a person needs about fifteen years of life. The acuity index in an infant who is four months old does not exceed 0.06 of the norm. By the year it rises to 0.3. To achieve one hundred percent worldview, some people need five years, while for others everything returns to normal only by the age of fifteen.
As a person grows older and crosses the “equator” of life, visual acuity begins to deteriorate. Muscles weaken and pupil size decreases. This leads to poor perception of light output. Older people need more light than those who are still in their youth. Elderly people experience painful changes in brightness. Color recognition and image contrast deteriorate.
By the age of sixty-five it happens sharp deterioration peripheral vision. The side view is blurred and the perception of images is narrowed. And nothing can be done about it, since all human organs tend to age.
The study of the functional abilities of human vision allows us to state that the left and right eyes do not see the environment in the same way. The leading eye has a more realistic perception of reality than the leading eye. This is especially noticeable in contact lens wearers.
When the visual axis is motionless, the dominant eye focuses on the image better, which is explained by a phenomenon called accommodation. Only after the object has been reliably “fixed” is the slave eye connected to the process.
Identifying the dominant eyeball is possible with a simple experiment. To carry it out, you need to acquire scissors, a piece of ordinary paper and any object that will become the object of observation.
You should proceed in the following order:
According to medical statistics, about thirty percent of the world's population has a left eye as their dominant eye. This is evidence of poor psychosocial health. Such people have a high level of emotionality; they are unable to win in the struggle for responsible administrative positions. With the help of special training and proper nutrition the process of weakening of the eyes can be weakened, but it is impossible to completely stop the process - such is life.
From the first day a child is born, vision helps him understand the world around him. With the help of the eyes, a person sees a wonderful world of colors and sun, and visually perceives a colossal flow of information. Eyes give a person the opportunity to read and write, and get acquainted with works of art and literature. Any professional work requires us to have good, full vision.
A person is constantly exposed to a continuous flow of external stimuli and a variety of information about processes inside the body. A person’s senses allow him to understand this information and correctly respond to a large number of events occurring around him. Among the irritants external environment For humans, visual ones are especially important. Most of our information about the outside world is related to vision. The visual analyzer (visual sensory system) is the most important of all analyzers, because it provides 90% of the information that goes to the brain from all receptors. With the help of our eyes, we not only perceive light and recognize the color of objects in the surrounding world, but also get an idea of the shape of objects, their distance, size, height, width, depth, in other words, about their spatial location. And all this is thanks to the subtle and complex structure of the eyes and their connections with the cerebral cortex.
Eye- located in the orbital cavity of the skull - in the orbit, surrounded from behind and on the sides by the muscles that move it. It consists of the eyeball with the optic nerve and auxiliary devices.
Eye- the most mobile of all organs human body. He makes constant movements, even in a state of apparent rest. Fine eye movements (micromovements) play a significant role in visual perception. Without them it would be impossible to distinguish objects. In addition, the eyes make noticeable movements (macro movements) - turns, shifting the gaze from one object to another, tracking moving objects. Various eye movements, sideways, up, down movements are provided by the extraocular muscles located in the orbit. There are six of them in total. Four rectus muscles are attached to the front of the sclera - and each of them turns the eye in its own direction. And two oblique muscles, superior and inferior, are attached to the back of the sclera. The coordinated action of the oculomotor muscles ensures the simultaneous rotation of the eyes in one direction or another.
The organ of vision needs protection from damage to normal development and work. The protective devices of the eyes are the eyebrows, eyelids and tear fluid.
Eyebrow- a paired arched fold of thick skin, covered with hair, into which the underlying muscles are woven. Eyebrows wick sweat away from the forehead and serve as protection from very bright light. Eyelids close reflexively. At the same time, they isolate the retina from the action of light, and the cornea and sclera from any harmful effects. When blinking, tear fluid is evenly distributed over the entire surface of the eye, thereby preventing the eye from drying out. The upper eyelid is larger than the lower eyelid and is raised by a muscle. The eyelids close due to contraction of the orbicularis oculi muscle, which has a circular orientation of muscle fibers. Along the free edge of the eyelids are located eyelashes, which protect the eyes from dust and too bright light.
Lacrimal apparatus. Tear fluid produced by special glands. It contains 97.8% water, 1.4% organic matter and 0.8% salts. Tears moisturize the cornea and help maintain its transparency. In addition, they wash away from the surface of the eye, and sometimes even the eyelids, any substances that have got there. foreign bodies, specks, dust, etc. The tear fluid contains substances that kill microbes through the lacrimal canaliculi, the openings of which are located in the inner corners of the eyes, enters the so-called lacrimal sac, and from here into the nasal cavity.
The eyeball has an irregular spherical shape. The diameter of the eyeball is approximately 2.5 cm. Six muscles are involved in the movement of the eyeball. Of these, four are straight and two are oblique. The muscles lie inside the orbit, start from its bony walls and are attached to the tunica albuginea of the eyeball behind the cornea. The walls of the eyeball are formed by three membranes.
On the outside it is covered with a tunica albuginea ( sclera). It is the thickest, strongest and provides the eyeball with a certain shape. The sclera makes up approximately 5/6 of the outer shell, it is opaque, white and partly visible within the palpebral fissure. The tunica albuginea is a very strong connective tissue membrane that covers the entire eye and protects it from mechanical and chemical damage.
The front part of this shell is transparent. It's called - cornea. The cornea has impeccable cleanliness and transparency due to the fact that it is constantly rubbed by the blinking eyelid and washed with tears. The cornea is the only place in the protein membrane through which light rays penetrate into the eyeball. The sclera and cornea are rather dense formations that ensure the eye maintains its shape and protects its internal part from various external harmful influences. Behind the cornea there is a crystal clear liquid.
The second shell of the eye is adjacent to the sclera from the inside - vascular. She is abundantly supplied blood vessels(performs a nutritional function) and a pigment containing a coloring matter. The anterior part of the choroid is called rainbow. The pigment in it determines the color of the eyes. The color of the iris depends on the amount of melanin pigment. When there is a lot of it, the eyes are dark or light brown, and when there is little, they are gray, greenish or blue. People who lack melanin are called albinos. There is a small hole in the center of the iris - pupil, which, narrowing or expanding, transmits either more or less light. The iris is separated from the choroid proper by the ciliary body. In its thickness is the ciliary muscle, on the thin elastic threads of which is suspended - lens- a transparent body, similar to a magnifying glass, a tiny biconvex lens with a diameter of 10 mm. It refracts light rays and brings them into focus on the retina. When contracting or relaxing ciliary muscle the lens changes its shape - the curvature of the surfaces. This property of the lens allows you to clearly see objects both at close and far distances.
The third, inner layer of the eye - mesh. The retina has a complex structure. It consists of light-sensitive cells - photoreceptors and perceives light entering the eye. It is located only on back wall eyes. There are ten layers of cells in the retina. Particularly important are the cells called cones and rods. In the retina, rods and cones are located unevenly. Rods (about 130 million) are responsible for the perception of light, and cones (about 7 million) are responsible for color perception.
Rods and cones have different purposes in the visual act. The first ones work on a minimum amount of light and constitute the twilight vision apparatus; Cones, on the other hand, operate in large amounts of light and serve for the daytime activities of the visual apparatus. Various function rods and cones provide high sensitivity of the eye to very high and low light levels. The ability of the eye to adapt to different brightness of light is called adaptation.
The human eye is capable of distinguishing an infinite variety of color shades. The perception of a variety of colors is provided by the cones of the retina. Cones are sensitive to colors only in bright light. In low light, color perception deteriorates sharply, and all objects appear gray in the twilight. Cones and rods work together. Nerve fibers depart from them, which then form the optic nerve, which leaves the eyeball and goes to the brain. The optic nerve consists of approximately 1 million fibers. Vessels pass through the central part of the optic nerve. At the exit site of the optic nerve, there are no rods and cones, as a result of which light is not perceived by this part of the retina.
The retina of the eye is the primary nerve center processing of visual information. The location where the optic nerve exits the retina is called the optic disc ( blind spot). At the center of the disc, the central retinal artery enters the retina. The optic nerves pass into the cranial cavity through the optic nerve canals.
The optic chiasm forms on the lower surface of the brain - chiasma, but only the fibers coming from the medial parts of the retinas intersect. These crossing visual pathways are called visual tracts. Most of the fibers of the optic tract rush into lateral geniculate body, brain. The lateral geniculate body has a layered structure and is so named because its layers bend like a knee. The neurons of this structure send their axons through the internal capsule, then as part of the visual radiation to the cells of the occipital lobe of the cortex cerebral hemispheres near the calcarine groove. This path carries information only about visual stimuli.
| Systems | Appendages and parts of the eye | Functions |
| Auxiliary | Brows | Removes sweat from the forehead |
| Eyelids | Protects eyes from light rays, dust, drying out | |
| Lacrimal apparatus | Tears moisten, cleanse, disinfect | |
| Eyeball membranes | Protein |
|
| Vascular | Nutrition of the eye | |
| Retina | Light perception, light receptors | |
| Optical | Cornea | Refracts light rays |
| Aqueous moisture | Transmits rays of light | |
| Iris (iris) | Contains pigment that gives color to the eye, regulates the opening of the pupil | |
| Pupil | Adjusts the amount of light by expanding and contracting | |
| Lens | Refracts and focuses light rays, has accommodation | |
| Vitreous body | Fills the eyeball. transmits rays of light | |
| Light-perceiving (visual receptor) | Photoreceptors (neurons) |
|
| Optic nerve | Perceives the excitation of receptor cells and transmits it to the visual zone of the cerebral cortex, where the analysis of excitation and the formation of visual images occurs |
In a parallel flow, light radiation hits the iris (acts as a diaphragm), with a hole through which light enters the eye; the elastic lens is a kind of biconvex lens that focuses the image; an elastic cavity (vitreous humor) that gives the eye a spherical shape and holds its elements in place. The lens and vitreous body have the properties of transmitting the structure of the visible image with the least distortion. Regulators govern involuntary movements eyes and adapt its functional elements to specific conditions of perception. They change the throughput of the aperture, the focal length of the lens, the pressure inside the elastic cavity and other characteristics. These processes are controlled by centers in the midbrain with the help of many sensitive and executive elements distributed throughout the eyeball. Light signals are measured during inner layer retina, consisting of many photoreceptors capable of converting light radiation into nerve impulses. Photoreceptors in the retina are distributed unevenly, forming three areas of perception.
First - field of view- located in the central part of the retina. It has the highest density of photoreceptors, so it provides a clear color image of the object. All photoreceptors in this area are basically the same in structure; they differ only in their selective sensitivity to wavelengths light radiation. Some of them are most sensitive to radiation (middle parts), others are in the upper part, and others are in the lower part. Humans have three types of photoreceptors that respond to blue, green and red colors. Here, in the retina, the output signals of these photoreceptors are jointly processed, as a result of which the contrast of the image is enhanced, the contours of objects are highlighted and their color is determined.
The volumetric image is reproduced in the cerebral cortex, where video signals from the right and left eyes are sent. A person's field of view covers only 5°, and only within its limits can he carry out visual and comparative measurements (orient himself in space, recognize objects, follow them, determine their relative location and direction of movement). Second area perception performs the function of target acquisition. It is located around the viewing area and does not provide a clear image of the visible picture. Its task is to quickly detect contrasting targets and changes occurring in the external environment. Therefore, in this area of the retina the density of conventional photoreceptors is low (almost 100 times less than in the viewing area), but there are many (150 times more) other, adaptive photoreceptors that respond only to changes in the signal. Joint processing of signals from both photoreceptors ensures high performance of visual perception in this area. In addition, a person is able to quickly detect the slightest movements with peripheral vision. Grasping functions are controlled by parts of the midbrain. Here, the object of interest is not examined or recognized, but its relative location, speed and direction of movement are determined and a command is given to the oculomotor muscles to quickly rotate the optical axes of the eyes so that the object falls into the viewing area for detailed examination.
The third area is formed marginal areas of the retina, which do not include the image of the object. The density of photoreceptors in it is the smallest - 4000 times less than in the field of view. Its task is to measure the average brightness of light, which is used by vision as a reference point to determine the intensity of light streams entering the eye. This is why visual perception changes under different lighting conditions.
Human vision(visual perception) - a person’s ability to perceive information by converting the energy of electromagnetic radiation in the light range, carried out by the visual system.
Processing of the light signal begins on the retina of the eye, then excitation of photoreceptors occurs, transmission and transformation of visual information in neural layers with the formation of a visual image in the occipital lobe of the cerebral cortex.
According to various sources, a person receives from 80% to more than 90% of information through vision. [ ]
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Due to the large number of stages in the process of visual perception, it individual characteristics are considered from the point of view of different sciences - optics (including biophysics), psychology, physiology, chemistry (biochemistry). At each stage of perception, distortions, errors, and failures occur, but the human brain processes the information received and makes the necessary adjustments. These processes are unconscious in nature and are implemented in multi-level autonomous correction of distortions. This way, spherical and chromatic aberrations, blind spot effects are eliminated, color correction is carried out, a stereoscopic image is formed, etc. In cases where subconscious information processing is insufficient or excessive, optical illusions arise.
In the process of evolution photosensitive receptors have adapted to solar radiation that reaches the surface of the Earth and spreads well in the water of the seas and oceans. The Earth's atmosphere has a significant transparency window only in the wavelength range 300-1500 nm. In the ultraviolet region, transparency is limited by the absorption of ultraviolet by the ozone layer and water, in the infrared region - by absorption by water. Therefore, the relatively narrow visible region of the spectrum accounts for more than 40% of the solar radiation energy at the surface.
The human eye is sensitive to electromagnetic radiation in the wavelength range 400-750 nm ( visible radiation) . The retina of the eye is also sensitive to shorter wavelength radiation, but the sensitivity of the eye in this region of the spectrum is limited by the low transparency of the lens, which protects the retina from the destructive effects of ultraviolet radiation.
The human eye contains two types of light-sensitive cells (photoreceptors): highly sensitive rods and less sensitive cones. Rods function in relatively low light conditions and are responsible for the night vision mechanism, but they provide only a color-neutral perception of reality, limited to the participation of white, gray and black colors. Cones operate at more high levels illumination than sticks. They are responsible for the mechanism of daytime vision, the distinctive feature of which is the ability to provide color vision.
Light of different wavelengths stimulates different types of cones differently. For example, yellow-green light stimulates L and M cones equally, but less stimulates S cones. Red light stimulates L-type cones much more than M-type cones, and does not stimulate S-type cones at all; green-blue light stimulates M-type receptors more than L-type, and S-type receptors a little more; light with this wavelength also stimulates rods most strongly. Violet light stimulates almost exclusively S-type cones. The brain perceives combined information from different receptors, which provides different perceptions of light with different wavelengths.
Genes encoding light-sensitive opsin proteins are responsible for color vision in humans and monkeys. According to proponents of the three-component theory, the presence of three different proteins that respond to different wavelengths is sufficient for color perception. Most mammals have only two of these genes, which is why they have two-color vision. If a person has two proteins encoded by different genes that are too similar or one of the proteins is not synthesized, color blindness develops. N. N. Miklouho-Maclay found that the Papuans of New Guinea, living in the thick of the green jungle, lack the ability to distinguish green.
The red light-sensitive opsin is encoded in humans by the OPN1LW gene.
Other human opsins are encoded by the genes OPN1MW, OPN1MW2 and OPN1SW, the first two of which encode proteins that are sensitive to light at medium wavelengths, and the third is responsible for an opsin that is sensitive to the short-wavelength part of the spectrum.
The necessity of three types of opsins for color vision was recently proven in experiments on the squirrel monkey (Saimiri), the males of which were cured of congenital color blindness by introducing the human opsin gene OPN1LW into their retina. This work (along with similar experiments in mice) showed that the mature brain is able to adapt to the new sensory capabilities of the eye.
The OPN1LW gene, which encodes the pigment responsible for the perception of red color, is highly polymorphic (recent work by Virrelli and Tishkov found 85 alleles in a sample of 256 people), and about 10% of women who have two different alleles of this gene actually have an additional type color receptors and some degree of four-component color vision. Variations in the OPN1MW gene, which encodes the “yellow-green” pigment, are rare and do not affect the spectral sensitivity of the receptors.
The OPN1LW gene and genes responsible for light perception medium length waves are located tandemly on the X chromosome, and non-homologous recombination or gene conversion often occurs between them. In this case, gene fusion may occur or the number of their copies in the chromosome may increase. Defects in the OPN1LW gene are the cause of partial color blindness, protanopia.
The three-component theory of color vision was first expressed in 1756 by M. V. Lomonosov, when he wrote “about the three matters of the bottom of the eye.” A hundred years later, it was developed by the German scientist G. Helmholtz, who does not mention Lomonosov’s famous work “On the Origin of Light,” although it was published and summarized in German.
In parallel, there was an opposing color theory by Ewald Hering. It was developed by David Hubel and Thorsten Wiesel. They received the 1981 Nobel Prize for their discovery.
They suggested that the information that enters the brain is not about red (R), green (G) and blue (B) colors (Jung-Helmholtz color theory). The brain receives information about the difference in brightness - about the difference in brightness of white (Y max) and black (Y min), about the difference between green and red colors (G - R), about the difference between blue and yellow flowers(B - yellow), and yellow color (yellow = R + G) is the sum of red and green flowers, where R, G and B are the brightness of the color components - red, R, green, G, and blue, B.
We have a system of equations - K b-w = Y max - Y min; K gr = G - R; K brg = B - R - G, where K b&w, K gr, K brg are functions of white balance coefficients for any lighting. In practice, this is expressed in the fact that people perceive the color of objects the same when different sources lighting (color adaptation). The opposing theory generally better explains the fact that people perceive the color of objects the same under extremely different lighting sources, including different colored light sources in the same scene.
These two theories are not entirely consistent with each other. But despite this, it is still assumed that the three-stimulus theory operates at the retinal level, but the information is processed and data that is already consistent with the opponent theory is received in the brain.
The maximum changes in the pupil for a healthy person are from 1.8 mm to 7.5 mm, which corresponds to a change in pupil area by 17 times. However, the actual range of changes in retinal illumination is limited to a ratio of 10:1, and not 17:1, as would be expected based on changes in pupil area. In fact, retinal illumination is proportional to the product of the area of the pupil, the brightness of the object and the transmittance of the ocular media.
The contribution of the pupil to the regulation of eye sensitivity is extremely insignificant. The entire range of brightness that our visual mechanism is capable of perceiving is enormous: from 10 −6 cd m −2 for an eye completely adapted to darkness to 10 6 cd m −2 for an eye completely adapted to light. The mechanism for such a wide range of sensitivity lies in the decomposition and restoration of photosensitive pigments in the retinal photoreceptors - cones and rods.
The sensitivity of the eye depends on the completeness of adaptation, on the intensity of the light source, the wavelength and angular dimensions of the source, as well as on the duration of action of the stimulus. The sensitivity of the eye decreases with age due to the deterioration of the optical properties of the sclera and pupil, as well as the receptor component of perception.
Maximum sensitivity in daylight ( daytime vision) lies at 555-556 nm, and at weak evening/night ( twilight vision/night vision) shifts towards the violet edge of the visible spectrum and is located at 510 nm (during the day it fluctuates between 500-560 nm). This is explained (the dependence of a person’s vision on lighting conditions when he perceives multi-colored objects, the ratio of their apparent brightness - the Purkinje effect) by two types of light-sensitive elements of the eye - in bright light, vision is carried out mainly by cones, and in weak light, preferably only rods are used.
The ability of different people to see larger or smaller details of an object from the same distance with the same shape of the eyeball and the same refractive power of the dioptric eye system is determined by the difference in the distance between the sensitive elements of the retina and is called visual acuity.
Visual acuity is the eye's ability to perceive separately two points located at some distance from each other ( detail, fine grain, resolution). The measure of visual acuity is the visual angle, that is, the angle formed by the rays emanating from the edges of the object in question (or from two points A And B) to the nodal point ( K) eyes. Visual acuity is inversely proportional to the angle of vision, that is, the smaller it is, the higher the visual acuity. Normally, the human eye is capable of separately perceive objects with an angular distance of at least 1′ (1 minute).
Visual acuity is one of the most important functions of vision. A person's visual acuity is limited by his structure. The human eye, unlike the eyes of cephalopods, for example, is an inverted organ, that is, light-sensitive cells are located under a layer of nerves and blood vessels.
Visual acuity depends on the size of the cones located in the area of the macula, retina, as well as on a number of factors: refraction of the eye, pupil width, transparency of the cornea, lens (and its elasticity), vitreous(which make up the light-refracting apparatus), the condition of the retina and optic nerve, age.
The inversely proportional value to visual acuity and/or light sensitivity is called the resolving power of the simple (naked) eye ( resolving power).
Peripheral vision (field of view) - determine the boundaries of the field of view when projecting them onto a spherical surface (using a perimeter). Field of view is the space perceived by the eye with a fixed gaze. The visual field is a function peripheral parts retina; its condition largely determines a person’s ability to freely navigate in space.
Changes in the visual field are caused by organic and/or functional diseases visual analyzer: retina, optic nerve, visual pathway, CNS. Violations of the visual field are manifested either by a narrowing of its boundaries (expressed in degrees or linear values), or loss of individual sections of it (Hemianopsia), or the appearance of a scotoma.
Looking at an object with both eyes, we see it only when the axes of vision of the eyes form such an angle of convergence (convergence), at which symmetrical, clear images on the retinas are obtained in certain corresponding places of the sensitive macula (fovea centralis). Thanks to this binocular vision, we not only judge the relative position and distance of objects, but also perceive relief and volume.
The main characteristics of binocular vision are the presence of elementary binocular, depth and stereoscopic vision, stereo visual acuity and fusional reserves.
The presence of elementary binocular vision is checked by dividing a certain image into fragments, some of which are presented to the left eye, and some to the right eye. An observer has elementary binocular vision if he is able to compose a single original image from fragments.
The presence of depth vision is checked by presenting silhouette vision, and stereoscopic vision - random dot stereograms, which should evoke in the observer a specific experience of depth, different from the impression of spatiality based on monocular features.
Stereo visual acuity is the reciprocal of the stereoscopic perception threshold. The stereoscopic threshold is the minimum detectable disparity (angular displacement) between parts of the stereogram. To measure it, the following principle is used. Three pairs of figures are presented separately to the observer's left and right eyes. In one of the pairs the position of the figures coincides, in the other two one of the figures is displaced horizontally by a certain distance. The subject is asked to indicate figures arranged in increasing order of relative distance. If the figures are indicated in the correct sequence, then the test level increases (disparity decreases); if not, the disparity increases.
Fusion reserves are conditions under which motor fusion of the stereogram is possible. Fusion reserves are determined by the maximum disparity between parts of the stereogram, at which it is still perceived as a three-dimensional image. To measure fusion reserves, the principle opposite to that used in the study of stereo visual acuity is used. For example, a subject is asked to combine two vertical stripes into one image, one of which is visible to the left eye and the other to the right eye. At the same time, the experimenter begins to slowly separate the stripes, first with convergent and then with divergent disparity. The image begins to bifurcate at the disparity value, which characterizes the fusion reserve of the observer.
Binocularity may be impaired with strabismus and some other eye diseases. If you are very tired, you may experience temporary strabismus caused by the non-dominant eye switching off.
Contrast sensitivity is a person’s ability to see objects that differ slightly in brightness from the background. Contrast sensitivity is assessed using sinusoidal gratings. An increase in the contrast sensitivity threshold may be a sign of a number of eye diseases, and therefore its study can be used in diagnostics.
The above properties of vision are closely related to the ability of the eye to adapt. Eye adaptation is the adaptation of vision to different lighting conditions. Adaptation occurs to changes in illumination (adaptation to light and darkness is distinguished), color characteristics of lighting (the ability to perceive white objects as white even with a significant change in the spectrum of incident light).
Adaptation to light occurs quickly and ends within 5 minutes, adaptation of the eye to darkness is a slower process. The minimum brightness that causes the sensation of light determines the light sensitivity of the eye. The latter increases rapidly in the first 30 minutes. staying in the dark, its increase practically ends after 50-60 minutes. Adaptation of the eye to darkness is studied using special devices - adaptometers.
Decreased adaptation of the eye to darkness is observed in some eye (retinal pigmentary degeneration, glaucoma) and general (A-vitaminosis) diseases.
Adaptation is also manifested in the ability of vision to partially compensate for defects in the visual apparatus itself (optical defects of the lens, retinal defects, scotomas, etc.)
The phenomenon of visual sensations that are not accompanied by the processing of visual information is called the phenomenon of pseudo-blindness.
The most common drawback is the discrepancy between the optical power of the eye and its length, leading to a deterioration in the visibility of close or distant objects.
Farsightedness is a refractive error in which rays of light entering the eye are focused not on the retina, but behind it. In mild forms of the eye with a good reserve of accommodation, it compensates for the visual deficiency by increasing the curvature of the lens with the ciliary muscle.
With more severe farsightedness (3 diopters and above), vision is poor not only near, but also at distance, and the eye is not able to compensate for the defect on its own. Farsightedness is usually congenital and does not progress (usually decreases by school age).
For farsightedness, reading glasses are prescribed or constant wearing. For glasses, converging lenses are selected (they move the focus forward to the retina), with the use of which the patient's vision becomes best.
Somewhat different from farsightedness, presbyopia, or age-related farsightedness. Presbyopia develops due to the loss of elasticity of the lens (which is normal result its development). This process begins at school age, but a person usually notices weakening of near vision after 40 years. (Although at 10 years old, emmetropic children can read at a distance of 7 cm, at 20 years old - already at least 10 cm, and at 30 - 14 cm, and so on.) Senile farsightedness develops gradually, and by the age of 65-70 a person has completely lost ability to accommodate, development of presbyopia is completed.
Myopia is a refractive error of the eye, in which the focus moves forward, and an already out-of-focus image falls on the retina. For myopia further point clear vision lies within 5 meters (normally it lies at infinity). Myopia can be false (when, due to overstrain of the ciliary muscle, its spasm occurs, as a result of which the curvature of the lens remains too large during distance vision) and true (when the eyeball increases in the anterior-posterior axis). In mild cases, distant objects are blurred while near objects remain clear (the furthest point of clear vision lies quite far from the eyes). In cases of high myopia, a significant decrease in vision occurs. Starting at approximately −4 diopters, a person needs glasses for both distance and near distance, otherwise the object in question must be brought very close to the eyes. However, precisely because for good image sharpness, a myopic person brings an object close to his eyes, he is able to distinguish finer details of this object than a person with normal vision.
IN adolescence myopia often progresses (the eyes constantly strain to work near, which is why the eye compensatory grows in length). The progression of myopia sometimes takes a malignant form, in which vision falls by 2-3 diopters per year, stretching of the sclera is observed, and dystrophic changes retina. In severe cases, there is a danger of detachment of the overstretched retina due to physical exertion or a sudden blow. Stopping the progression of myopia usually occurs by the age of 25-30, when the body stops growing. With rapid progression, vision by that time drops to −25 diopters and below, severely crippling the eyes and sharply impairing the quality of vision in the distance and near (all that a person sees are cloudy outlines without any detailed vision), and such deviations are very are difficult to fully correct with optics: thick glasses create strong distortions and make objects visually smaller, which is why a person does not see well enough even with glasses. In such cases better effect can be achieved using contact correction.
Despite the fact that hundreds of scientific and medical works have been devoted to the issue of stopping the progression of myopia, there is still no evidence of the effectiveness of any method of treating progressive myopia, including surgery (scleroplasty). There is evidence of a small but statistically significant reduction in the rate of growth of myopia in children with the use of atropine eye drops and (unavailable in Russia) pirenzipine eye gel [ ] .
For myopia, laser vision correction is often used (impact on the cornea using laser beam in order to reduce its curvature). This correction method is not completely safe, but in most cases it is possible to achieve a significant improvement in vision after surgery.
Defects of myopia and farsightedness can be overcome with the help of glasses, contact lenses or rehabilitative gymnastics courses.
Astigmatism is a defect in the optics of the eye caused by the irregular shape of the cornea and (or) lens. All people have different shapes of the cornea and lens. perfect body rotation (that is, all people have astigmatism of varying degrees). In severe cases, the stretching along one of the axes can be very strong, in addition, the cornea may have curvature defects caused by other reasons (injuries suffered infectious diseases etc.). With astigmatism, light rays are refracted with different strengths in different meridians, as a result of which the image is curved and unclear in places. In severe cases, the distortion is so severe that it significantly reduces the quality of vision.
Astigmatism can be easily diagnosed by looking with one eye at a sheet of paper with dark parallel lines - by rotating such a sheet, the astigmatist will notice that the dark lines either blur or become clearer. Most people experience congenital astigmatism up to 0.5 diopters, which does not cause discomfort.
This defect is compensated by glasses with cylindrical lenses having different curvature horizontally and vertically and contact lenses (hard or soft toric), as well as spectacle lenses having different optical powers in different meridians.
If the perception of one of the three primary colors in the retina is lost or weakened, then a person does not perceive a certain color. There are “color-blind” ones for red, green and blue-violet. It is rare to find a steam room, or even a full one color blindness. More often there are people who cannot distinguish red from green. This lack of vision was called color blindness - after the English scientist D. Dalton, who himself suffered from such a color vision disorder and first described it.
Color blindness is incurable and is inherited (linked to the X chromosome). Sometimes it occurs after certain eye and nervous diseases.
Colorblind people are not allowed to work related to driving vehicles on public roads. Good color vision is very important for sailors, pilots, chemists, geologists-mineralogists, artists, therefore, for some professions, color vision is checked using special tables.
Scotoma (Greek) skotos- darkness) is a spot-like defect in the visual field of the eye, caused by a disease in the retina, diseases of the optic nerve, glaucoma. These are areas (within the field of view) in which vision is significantly weakened or absent. Sometimes a blind spot is called a scotoma - an area on the retina corresponding to the optic nerve head (the so-called physiological scotoma).
Absolute scotoma (eng. absolute scotomata) - an area in which vision is absent. Relative scotoma is an area in which vision is significantly reduced.
You can assume the presence of a scotoma yourself by conducting a study using the Amsler test.
The desire to improve vision is associated with an attempt to overcome both visual defects and its natural limitations.
Anisometropia is a concept that characterizes different vision in the eyes. When the disease occurs, the body's optical system cannot refract rays correctly, and each eye has a different optical power. With such a pathology, the task of selecting corrective optics becomes more complicated, so you need to look for a special approach to patients. If the problem is not corrected in time, a complication such as astigmatism may develop.
The causes of the disease are divided into two groups:
More common are congenital forms of anisometropia, which are hereditary in nature. In infants, the disease does not manifest itself externally and is initially asymptomatic. But with age, the manifestations become brighter, and the disease progresses. The degree of development depends on the timeliness of diagnosis and correct correction.
The causes of the acquired form of the disease are divided into 3 groups:
The disease can be stopped if you choose the right treatment in a timely manner and do corrective exercises. Acquired forms develop faster than congenital ones, which contributes to early diagnosis, staging correct diagnosis and taking corrective measures. In most cases, the congenital form is genetic in nature, so they talk about the hereditary nature of the pathology. If you start on time proper care behind the eyes and choose corrective gymnastics, then the development of the disease can be slowed down or even stopped.
Separately, there is an idiopathic form of different vision in the eyes, in which it is impossible to identify the causes of the pathology. The diagnosis can only be made after full examination an ophthalmologist and geneticist who will help rule out other causes. According to statistics, the idiopathic form is very rare.
The experience of a person who has different vision depends on the degree of difference in the clarity of vision between the eyes. The classification of the difference in optical power is shown in the table:
With a low degree of difference, there are no symptoms.
Over time, the patient begins to see poorly and the image becomes blurred. Since the eyes of a patient diagnosed with anisometropia see differently, the organ of vision that has a higher optical power takes on the function of vision. The other eye, in turn, ceases to function and eventually ceases to see. Patients are poorly oriented environment and are unable to clearly distinguish objects. Patients also see poorly, the image is blurred, which forces them to squint and strain their vision, so their eyes get tired and their sharpness decreases.
A doctor is consulted only when the loss of vision noticeably affects the patient’s well-being. A person may not remember when and under what circumstances the discomfort began. It is important for the doctor to clarify whether close relatives have similar problems. The prognosis between the congenital and acquired forms is different and, accordingly, correction methods may differ.
The ophthalmologist will prescribe examination methods, such as:
