What animals have poor eyesight? Which animals, fish and birds have the best eyesight. Falcon vision is the most vigilant in the world

We see the world around us and it seems to us that it is exactly like this. It’s hard to even imagine that someone sees it differently, in black and white, or without blue and red. It’s hard to believe that for some people our familiar world is completely different.

But that's exactly how it is.

Let's take a look at the world through the eyes of animals, let's figure out how animals see, in what colors they perceive the world.

So, first, let's look at what vision is and what functional abilities it includes.

What is vision?

Vision is the process of processing images of objects in the surrounding world.

• carried out by the visual system
• allows you to get an idea of ​​the size, shape and color of objects, their relative position and the distance between them

The visual process includes:

• penetration of light flux through the refractive media of the eye
• focusing light on the retina
• transformation of light energy into nerve impulse
• transmission of nerve impulses from the retina to the brain
• processing information with the formation of a seen image

Visual functions:

• light perception
• perception of moving objects
• field of view
• visual acuity
• color perception

Light perception is the ability of the eye to perceive light and determine varying degrees of its brightness.

The process of adapting the eye to different lighting conditions is called adaptation. There are two types of adaptation:

• to darkness - when the light level decreases
• and to light - with increasing light levels

Light perception is the basis of all forms of visual sensation and perception, especially in the dark. The light perception of the eye is also influenced by factors such as:

• distribution of rods and cones (in animals, the central region of the retina at 25° consists predominantly of rods, which improves night vision)
• concentration of light-sensitive visual substances in rods (in dogs, the sensitivity to light of rods is 500-510 nm, in humans 400 nm)
• the presence of tapetum (tapetum lucidum) - a special layer choroid eyes (the tapetum directs photons back to the retina, causing them to once again act on the receptor cells, increasing the light sensitivity of the eye, which in low light conditions turns out to be very valuable) in cats, the eye reflects 130 times more light than in humans (Paul E. Miller, DVM, and Christopher J. Murphy DVM, PhD)
• pupil shape - the shape, size and position of the pupil in various animals (the pupil can be round, slit-like, rectangular, vertical, horizontal)
• the shape of the pupil can tell whether an animal is a predator or a prey (in predators the pupil narrows into a vertical stripe, in preys into a horizontal stripe - scientists discovered this pattern by comparing the shapes of the pupils in 214 species of animals)

So, what are the different pupil shapes:

• Slit pupil - (in predatory animals such as domestic cats, crocodiles, gecko lizards, snakes, sharks) allows you to more accurately adjust the eye to the amount of light around, so that you can see in the dark and not go blind in the midday sun

• Round pupil - (in wolves, dogs, big cats- lions, tigers, cheetahs, leopards, jaguars; birds) because they are spared the need to see well in the dark

• The horizontal pupil (herbivores) allows the eye to clearly see what is happening near the ground and covers a fairly wide panorama of the eyes, protected from direct hits sun rays from above, which could blind the animal

How do animals perceive moving objects?

The perception of movement is vital because... moving objects are signals of either danger or potential food and require quick appropriate action, while stationary objects can be ignored.

For example, dogs can recognize moving objects (due to a large number of rods) at a distance of 810 to 900 m, but stationary objects only at a distance of 585 m.

How do animals react to flickering light (for example, on TV)?

The response to flickering light provides insight into the function of the rods and cones.

The human eye is capable of detecting vibrations at 55 hertz, while the dog's eye detects vibrations at a frequency of 75 hertz. Therefore, unlike us, dogs most likely see only flickering and most of them do not pay attention to the image on TV. Images of objects in both eyes are projected on the retina and transmitted to the cerebral cortex, where they are merged into one image.

What are the visual fields of animals?

Field of view is the space perceived by the eye with a fixed gaze. There are two main types of vision:

• binocular vision - perception of surrounding objects with both eyes
• monocular vision - perception of surrounding objects with one eye

Binocular vision is not present in all species of animals and depends on the structure and relative position of the eyes on the head. Binocular vision allows you to make fine coordinated movements of the forelimbs, jumping, and move easily.

For predators, binocular perception of hunting objects helps them correctly assess the distance to the intended victim and choose the optimal attack trajectory. In dogs, wolves, coyotes, foxes, jackals, the binocular field angle is 60-75°, in bears it is 80-85°. In cats, 140° (the visual axes of both eyes are almost parallel).

Monocular vision with a large field allows potential victims (marmots, gophers, hares, ungulates, etc.) to notice the danger in time. reaches 360° in rodents, 300-350° in ungulates, and more than 300° in birds. Chameleons and seahorses can look in two directions at once, because... their eyes move independently of each other.

Visual acuity

• the ability of the eye to perceive two points located at a minimum distance from each other as separate
• the minimum distance at which two points will be visible separately depends on the anatomical and physiological properties of the retina

What does visual acuity depend on?

• on the size of the cones, the refraction of the eye, the width of the pupil, the transparency of the cornea, lens and vitreous(make up the light refractive apparatus), states retina And optic nerve, age
• The diameter of the cones determines the value of maximum visual acuity (the smaller the diameter of the cones, the greater the visual acuity)

Visual angle is the universal basis for expressing visual acuity. The normal sensitivity limit of the eye of most people is 1. In humans, to determine visual acuity, the Golovin-Sivtsev table is used, containing letters, numbers or signs of various sizes. In animals, visual acuity is determined using (Ofri., 2012):

• behavioral test
• electroretinography

The visual acuity of dogs is estimated at 20-40% of the visual acuity of humans, i.e. a dog recognizes an object from 6 meters, while a person recognizes an object from 27 meters.

Why doesn't a dog have the visual acuity of a human?

Dogs, like all other mammals except monkeys and humans, lack the central fovea of ​​the retina (the area of ​​maximum visual acuity). Most dogs are slightly farsighted (hyperopia: +0.5 D), i.e. they can distinguish small objects or their parts at a distance of no closer than 50-33 cm; all objects located closer appear blurry, in circles of dispersion. Cats are nearsighted, meaning they cannot see distant objects as well. The ability to see well up close is more suitable for hunting prey. The horse has low visual acuity and is relatively myopic. Ferrets are myopic, which is, no doubt, a reaction to their adaptation to a burrowing lifestyle and searching for prey by smell. Ferrets' nearsighted vision is as sharp as ours and maybe even a little sharper.

Thus, the eagle has the sharpest vision, then in descending order: falcon, man, horse, dove, dog, cat, rabbit, cow, elephant, mouse.

Color vision

Color vision is the perception of the color diversity of the surrounding world. The entire light part electromagnetic waves creates a color spectrum with a gradual transition from red to violet (color spectrum). Color vision is carried out by cones. There are three types of cones in the human retina:

• the first perceives long-wavelength colors - red and orange
• the second type perceives mid-wave colors better - yellow and green
• the third type of cones is responsible for short-wavelength colors - blue and violet

Trichromasia - the perception of all three colors
Dichromasia - seeing only two colors
Monochromacy - seeing only one color

How do animals perceive color?

Color vision in dogs:

Color vision of cats:

Horse color vision:

Do animals see colors? This is an interesting question, but it is not easy to give an accurate and comprehensive answer. It is difficult for us, who have color vision, to imagine the universe without colors, and we naturally have the assumption that all living beings also perceive the world around us in the form of multicolored pictures. However, this idea does not correspond to reality.

Color is a rather arbitrary and difficult to define concept. Color perception is not easy to research and explain; This is why scientists have long had difficulty interpreting this ability objectively and accurately. In essence, no object has color; it just absorbs white daylight and reflects only one fraction of this light, one or another part of the solar spectrum. For example, green trees absorb all parts of the spectrum except green, which is reflected by them; this is what makes them green to our eyes.

Try to explain to a blind person, without resorting to comparisons, what the color red is. This will turn out to be completely impossible. Even among sighted people they are widespread various degrees color blindness. People often evaluate the same color differently; Additionally, our color appreciation continues to improve and change. After all, Homer constantly calls the sea wine-red, and some ancient Greek authors mention the green color of the human face.

Ultimately, everything here depends on the peculiarities of the perceiving optical apparatus - a small defect or deviation from the norm is enough, for example, the absence in a person of one of the three light-sensitive “wires” leading from the retina of the eye to the brain. Each of these pathways provides the perception of one of the primary colors: red, green or blue. Most colorblind people do not have a green "wire"; others lack the red “wire” and are blind to the color red. In the physical sense, the changes in the human body are extremely insignificant; they come down only to features nervous system. There is every reason to believe that a number of animals that have eyes similar to humans completely lack those small details that provide color perception.

WORLD OF WHITE AND BLACK

From what has been said, it is quite clear how difficult it is (considering also that we ourselves may suffer from color blindness to some small extent) to apply our limited and not entirely accurate knowledge in the field of color perception to other creatures. A lot of research has been devoted to this topic, but many of them are insufficiently evidence-based. It is extremely difficult to establish whether or not a particular animal distinguishes colors. After all, animals themselves are not able to answer this question. Moreover, it is almost always difficult to decide what the animal is reacting to - to the color or to the degree of brightness and whiteness of the object. Therefore, in order for the experiment to be valuable, it is necessary to use colors that are equivalent in brightness and degree of whiteness. Otherwise, the experimental animal, especially if it belongs to higher animals, can distinguish red from green by relative brightness, as is the case in people suffering from color blindness.

But despite the obvious limitations, we still know something in this area. Thus, we can say with confidence that almost all mammals, with the exception of all species, are completely color blind. They live in a world of black and white, with a significant range of gray shades in between. They often clearly perceive the difference in the intensity of black, in the light saturation of white and gray tones. The latter circumstance often leads people to the conclusion that certain animals (for example, dogs) distinguish between certain colors.

How often an admiring owner is ready to swear that his dog recognizes a dress by the color, even if it is worn by a stranger, that he distinguishes a bowl or a pillow solely by its color! It's hard to imagine that you can live in a world devoid of colors! Meanwhile, most mammals in their habits belong to the type of nocturnal or crepuscular animals; they emerge from their shelters only when the world begins to plunge into darkness and lose its colors, illuminated only by the weak and uncertain light of the moon.

However, all this is not so unusual for people. After all, we easily watch monochrome films; Many newspapers and magazines are still illustrated with monochromatic photographs, and we perceive them as a reflection of true life. A simple drawing made in black pencil often seems extremely natural and alive to us. Despite all of humanity’s predilection for colors, we feel their absence much less than we might sometimes think.

A TOREADOR DOESN'T NEED A RED CAPE

Along with others, the following simple experiment was carried out. Small squares of gray paper (various shades, but the same brightness) were arranged in a checkerboard pattern; There was a blue square in the center. A feeder was installed on each square, and syrup was poured into the feeder located on the blue square; the rest were empty. After some time, the bees were trained to fly only to the blue square, even if its position relative to the others changed.

When the blue paper was replaced with red (of the same brightness), the bees turned out to be disoriented - they could not distinguish the red square from the gray ones. Bees are not only blind to the color red; they live as if in a world of blue, purple and yellow shades; at the same time, they (like a number of other insects) are able to penetrate further than humans into the ultraviolet part of the spectrum. Of course, insects that carry pollen fly to flowers, guided not only by color, but also by smell; This is evidenced, in particular, by how easily bees find flowers of willow, ivy, and linden.

MOSQUITOES PREFER BLACK

As a rule, only insects with well-developed, compound eyes have color perception. Dragonflies have the best color perception among insects; second place appears to be occupied by wasp flies, as well as some species of moths. Common flies see the color blue; they probably don’t like it, since they avoid windows washed with blue, blue walls and curtains. Mosquitoes, which distinguish between yellow, white and black, apparently prefer the latter. In one of the areas abounding in these insects in Oregon (USA), an experiment was conducted in which seven people participated, dressed in dresses of different colors. It was found that greatest number mosquitoes were attracted by black clothing (1499 in half a minute); in second place, with a significant lag, was white (520 insects over the same period of time).

Eyes are a special organ that is endowed with all living beings on the planet. We know in what colors we see the world, but how do animals see it? What colors do cats see and what colors do they not? Do dogs have black and white vision? Knowledge about animal vision will help us take a broader look at the world around us and understand the behavior of our pets.

Features of vision

And yet, how do animals see? According to certain indicators, animals have more advanced vision than humans, but it is inferior in the ability to distinguish colors. Most animals see only in a palette specific to their species. For example, for a long time it was believed that dogs see only in black and white. And snakes are generally blind. But recent research has proven that animals see different lengths waves, unlike humans.

Thanks to vision, we receive more than 90% of the information about the world that surrounds us. The eyes are our predominant sensory organ. It is interesting that the sharpness of animal vision is significantly higher than that of humans. It's no secret that feathered predators see 10 times better. An eagle is able to detect prey in flight from a distance of several hundred meters, and a peregrine falcon tracks a pigeon from a height of a kilometer.

Another difference is that most animals have excellent vision in the dark. Photoreceptor cells in the retina of their eyes focus light, and this allows nocturnal animals to capture streams of light of several photons. And the fact that the eyes of many animals glow in the dark is explained by the fact that under the retina there is a unique reflective layer called tapetum. Now let's take a look individual species animals.

Horses

The gracefulness of the horse and its expressive eyes are unlikely to leave anyone indifferent. But often those who learn to ride are told that approaching a horse from behind is dangerous. But why? How do animals see what is happening behind them? No way - it’s behind the horse’s back and therefore it can easily get scared and buck.

The horse's eyes are positioned so that it can see from two angles. Her vision is, as it were, divided in two - each eye sees its own picture, due to the fact that the eyes are located on the sides of the head. But if the horse looks along the nose, then it sees one image. This animal also has peripheral vision and sees excellently at dusk.

Let's add a little anatomy. The retina of any living creature contains two types of receptors: cones and rods. Color vision depends on the number of cones, and rods are responsible for peripheral vision. In horses, the number of rods exceeds that in humans, but the cone receptors are comparable. This suggests that horses also have color vision.

Cats

Many people have animals at home, and the most common are, of course, cats. The vision of animals, and especially of the cat family, differs significantly from that of humans. A cat's pupil is not round, like most animals, but elongated. It reacts sharply to large amounts of bright light by narrowing to a small gap. This indicator says that in the retina of the animal’s eye there is a large number of rod receptors, due to which they see perfectly in the dark.

What about color vision? What colors do cats see? Until recently, it was believed that cats see in black and white. But studies have shown that it distinguishes between gray, green and blue colors. In addition, it sees many shades of gray - up to 25 tones.

Dogs

Dogs' vision is different from what we are used to. If we return to anatomy again, then in the human eye there are three types of cone receptors:

• The first perceives long-wave radiation, which distinguishes orange and red colors.
• The second is medium wave. It is on these waves that we see yellow and green.
• The third, accordingly, perceives short waves, in which blue and violet are distinguishable.

Animals' eyes are distinguished by the presence of two types of cones, so dogs do not see orange and red colors.

This difference is not the only one - dogs are farsighted and see moving objects best. The distance from which they see a stationary object is up to 600 meters, but dogs notice a moving object from 900 meters. It is for this reason that it is best not to run away from the four-legged guards.

Vision is practically not the main organ of a dog; for the most part, they follow smell and hearing.

Now let's summarize - what colors do dogs see? In this they are similar to colorblind people; they see blue and violet, yellow and green, but a mixture of colors may seem simply white to them. But dogs, like cats, are best at distinguishing gray colors, and up to 40 shades.

Cows

Many believe, and we are often told, that domestic artiodactyls react strongly to the color red. In reality, the eyes of these animals perceive the color palette in very blurry, fuzzy tones. That's why bulls and cows respond more to movement than to how your clothes are colored or what color is waved in front of their face. I wonder, who will like it if they start waving some kind of rag in front of their nose, sticking spears into the back of their neck?

And yet, how do animals see? Cows, judging by the structure of their eyes, are able to distinguish all colors: white and black, yellow and green, red and orange. But only weakly and blurry. Interestingly, cows have vision like a magnifying glass, and it is for this reason that they are often scared when they see people unexpectedly approaching them.

Nocturnal animals

Many nocturnal animals have, for example, tarsier. This is a small monkey that comes out to hunt at night. It is no larger than a squirrel, but it is the only primate in the world that feeds on insects and lizards.

The eyes of this animal are huge and do not rotate in their sockets. But at the same time, the tarsier has a very flexible neck, allowing it to rotate its head a full 180 degrees. He also has extraordinary peripheral vision, allowing him to see even ultraviolet light. But the tarsier distinguishes colors very poorly, like everyone else

I would also like to say about the most common inhabitants of cities at night - bats. For a long time it was assumed that they do not use vision, but fly only thanks to echolocation. But recent research has shown that they have excellent night vision, and what's more, bats are able to choose whether to fly towards a sound or turn on night vision.

Reptiles

While talking about how animals see, one cannot remain silent about how snakes see. The fairy tale about Mowgli, where a boa constrictor bewitches the monkeys with his gaze, leaves you in awe. But is this true? Let's figure it out.

Snakes have very poor vision, which is affected by the protective membrane covering the reptile's eye. This makes the named organs appear cloudy and take on that terrifying appearance about which legends are made. But vision is not the main thing for snakes; they mainly attack moving objects. That's why the fairy tale says that the monkeys sat in a daze - they instinctively knew how to escape.

Not all snakes have unique thermal sensors, but they still distinguish infrared radiation and colors. The snake has binocular vision, which means she sees two pictures. And the brain, quickly processing the information received, gives it an idea of ​​the size, distance and outline of the potential victim.

Birds

Birds are amazing in their diversity of species. It is interesting that the vision of this category of living beings also varies greatly. It all depends on what kind of life the bird leads.

So, everyone knows that predators have extremely acute vision. Some species of eagles can spot their prey from a height of more than a kilometer and drop like a stone to catch it. Did you know that certain species of birds of prey are able to see ultraviolet light, which allows them to find the nearest burrows in the dark?

And the budgie living in your home has excellent eyesight and is able to see everything in color. Studies have proven that these individuals distinguish each other using bright plumage.

Of course, this topic is very broad, but we hope that the facts presented will be useful to you in understanding how animals see.

Vision is one of the five human senses. With its help, a person receives information about the world around him, recognizes objects and their location in space. Importance high level vision cannot be overestimated, because with poor vision a person’s life becomes very difficult. It is especially important to have good vision for children, since a decrease in visual acuity can become a serious obstacle to the full development of the child.

Why is verification needed?

Starting from the newborn period, children need regular vision examinations by an ophthalmologist. This must be done for preventive purposes in order to prevent future vision impairment or deterioration in the child.

Eye diseases in many cases tend to progress. For example, myopia (or myopia), as a rule, can develop intensively in children in school years when the visual load on the eyes increases. Eye hypermetropia is also a common disease in children of preschool or primary school age. Therefore, parents need to take all measures to improve their child’s visual acuity as soon as possible and prevent the development of blindness. As a rule, progressive myopia leads to irreversible changes in the central parts of the retina, which significantly reduces visual acuity.

Vision testing for newborns occurs according to the following schedule:

• The baby's eyes are first examined by an ophthalmologist in the first hours after birth. WITH special attention premature babies and children with congenital pathologies or birth injuries, newborns after a difficult birth, since it is in this category of children that hemorrhages or retinal pathologies most often occur.
• The first examination by an ophthalmologist for this category of children is usually scheduled a month after birth, if there are indications.
• A healthy child should be examined for the first time in an ophthalmology office 3 months after birth.
• Next inspection healthy child carried out at 6 months and then at 12 months.

At 12 months, the child’s visual acuity is determined for the first time. Normally, it is 0.3–0.6 diopters.

A table for checking vision in children was developed by Orlova. This table is used for children preschool age who have not yet learned to count

Existing vision testing charts

IN modern times Many versions of tables have been created to test visual acuity in children.

The first table by which a child’s vision is checked, as a rule, is the Orlova table. This table is used to conduct vision tests for children from the age of 3, when they have not yet learned to read and write. In this table, instead of letters, pictures are used that are familiar to the child and which he can easily name.

To test visual acuity in older children, tables with printed letters are used. In the CIS countries, the Sivtsev or Golovin table is most often used. There is also a foreign analogue - the Snellen table.

In many tables, visual acuity is determined at a distance of at least 5 meters. This distance was chosen by ophthalmologists for the reason that in an eye with normal refraction (the so-called emmetropia), at this distance the point of clear vision is located, as it were, at infinity and on the retina, thus parallel rays are collected, forming a focused, clear image.

Sivtsev table

The Sivtsev table is the most common table in the former USSR, which is used to test visual acuity in children.

The table received its name in honor of the Soviet ophthalmologist D.A. Sivtseva. The Sivtsev table is actively used for examining vision in children and adult patients in modern times.

Sivtsev’s vision test table uses 12 lines with printed characters, which can be used to effectively examine the patient’s visual acuity.

7 letters are used as printed characters - Ш, Б, М, Н, К, У, И. The letters have different sizes, but the same width and height. In this case, the size of letters decreases in lines from top to bottom.

Sivtsev’s table also has two additional columns located to the left and right of the rows. The symbols on the left side indicate the distance from which the patient sees the letters of the line with a 100% level of vision. It is expressed in meters and is marked with the symbol “D=…”.

The left column shows the level of refractive error expressed in diopters. Refraction of the eye is the position of the focal point of the eye relative to the retina. With a normal focus position on the retina, refraction is usually zero. This position of the focal point is called emmetropia.

In case of visual impairment, the position of the focal point changes. For example, with myopia, the focal point is in front of the retina, and with farsightedness, the focal point moves behind the retina. Thus, the image is not fixed in the center of the retina and objects appear blurry and indistinct.

As a rule, refractive errors affect visual acuity and require correction. The more the refraction deviates from the norm, the more visual acuity decreases. However, there is no direct relationship between these values. If the refraction is normal, but the patient has poor vision, this may indicate a possible decrease in the transparency of the optical media of the eye. For example, the patient may exhibit symptoms of amblyopia, cataracts with clouding of the lens or cornea.

The right column indicates the patient’s visual acuity if he is located at a distance of 5 meters from the table. These values ​​are marked with “V=...”. Visual acuity in the professional terminology of ophthalmologists is the ability of the eye to see and distinguish two distant points with a minimum distance between them.

In ophthalmology, the accepted rule is that an eye with normal visual acuity can distinguish two distant points with an angular distance between them equal to 1 arc minute (1/60 degree).

Normal human visual acuity corresponds to V=1.0, that is, a person with 100% vision should be able to distinguish printed characters of the first 10 lines. However, some subjects may have visual acuity that is greater than normal, for example, 1.2, 1.5, or even 3.0 or more. With refractive errors (myopia, farsightedness), astigmatism, glaucoma, cataracts and other visual impairments, the visual acuity of the subject decreases below normal and acquires values ​​of 0.8, 0.5 and lower.

In Sivtsev’s table, the values ​​of visual acuity in the first ten lines differ in increments of 0.1, the last two lines - in 0.5. In some non-standard versions of the Sivtsev table, additional 3 lines are used with visual acuity values ​​from 3.0 to 5.0.

But these tables, as a rule, are not used in ophthalmology offices of modern clinics.

Visual acuity according to the Sivtsev table is checked according to the following instructions:

• The patient should be at a distance of 5 meters from the table. Studies are carried out for each eye separately.
• The right eye must be tightly covered with the palm of the hand so that it cannot see the letters in the table. Instead of your palm, you can use a piece of dense material (for example, cardboard or plastic). Thus, the visual acuity of the left eye is examined.
• The lines must be read in order, left to right, top to bottom. It takes no more than 2-3 seconds to recognize the sign.

Determining visual acuity using the Sivtsev table is quite simple. The patient, as a rule, has normal visual acuity if he was able to correctly read letters in rows with V = 0.3-0.6. Only one mistake is allowed. In rows below V=0.7, no more than two errors are allowed. The numerical value of visual acuity corresponds to the numerical value of V in the last row, in which no errors were made beyond the norm.

Using this table, only myopia is determined. Farsightedness is not determined according to the Sivtsev table. That is, if the subject sees all 12 lines at a distance of 5 meters, this does not mean that he suffers from farsightedness. This indicates visual acuity above the average.

If the test result is unsatisfactory and a deviation from the norm is detected, then possible reason decreased visual acuity, the child may have a refractive error. In this case, a subsequent determination of refraction is necessary.

Snellen chart

Snellen chart

The Snellen chart is one of the popular tables for testing visual acuity in children. In modern times, this table is especially common in the United States.

The Snellen chart was developed in 1862 by Dutch ophthalmologist Hermann Snellen. The Russian analogue of this table is the Sivtsev table.

The table includes a standard set of strings consisting of Latin letters, which are called optotypes (test types). The size of the letters, just like in Sivtsev’s table, decreases with each line in the downward direction.

The top row of the Snellen chart contains the largest characters that a person with normal visual acuity can read at a distance of 6 meters (or 20 feet). A person with 100% vision is able to distinguish the subsequent lower lines at distances of 36, 24, 18, 12, 9, 6 and 5 meters, respectively. A traditional Snellen chart typically has 11 lines printed. The first line consists of the most capital letters, which can be E, H, N, or A.

The subject's vision is checked using the Snellen chart as follows:

• The subject is located at a distance of 6 meters from the table.
• Cover one eye with the palm of your hand or some dense material, and read the letters in the table with the other.

The visual acuity of the subject is usually checked by the indicator of the smallest row, which was read without errors at a distance of 6 meters.

As a rule, if a person with normal visual acuity is able to distinguish one of the lower rows at a distance of 6 meters, then the visual acuity value is 6/6. If the subject is able to distinguish only lines located above the line that a person with normal visual acuity can read at a distance of 12 meters, then the visual acuity of such a patient is 6/12.

Orlova table

Orlova's vision test table is used to determine visual acuity in preschool children. This table contains rows with special pictures, the size of which becomes smaller with each row from top to bottom.

Orlova table

On the left side of the table, next to each line, the distance from which a child with normal visual acuity is able to distinguish symbols is indicated.

Variation of Orlova's table

The distance is marked with the symbol “D=...”. IN right side The table indicates visual acuity if the child recognizes them at a distance of 5 meters.

Vision is considered normal if a child is able to recognize pictures of the tenth line with each eye from a distance of 5 meters.

If the child’s visual acuity is reduced and he is not able to recognize the signs on the tenth line, then he is brought closer to the table at a distance of 0.5 meters and asked to name the characters in the top row. The child's visual acuity is determined by the line in which the child can correctly name all the symbols.

Before the examination, it is advisable to show the child pictures so that he understands what is required of him and ask him to say the names of the pictures out loud.

Golovin table

The Golovin table is also a fairly common table for checking visual acuity in children. Like Sivtsev’s table, it is used mainly in the CIS countries. The table got its name in honor of the famous ophthalmologist S.S. Golovin, who lived in the USSR.

Unlike Sivtsev's table, this table uses symbols - Landolt rings - instead of printed letters. There are also twelve rows in Golovin's table and the rings printed in these rows decrease in size with each row in the downward direction. These rings are of equal and equal width in each row.

Golovin's vision table

Visual acuity indicators are indicated on the right side of the table and are marked with the symbol “V=...”.

In the traditional Golovin table, it is possible to determine visual acuity in the range of 0.1-2.0. The first 10 lines, as in Sivtsev’s table, differ in increments of 0.1, the remaining two - in 0.5. In some versions of the tables, three extra rows are additionally used to determine visual acuity above the average. These lines differ in increments of 1.0.

The left side of the table indicates the distance in meters from which a person with normal visual acuity is able to recognize the symbol in a given line. It is marked with the symbol “D=...”.

Visual acuity is determined at a distance of 5 meters separately for each eye.

Causes and symptoms of retinal detachment, what kind of disease it is and what effective methods You will learn about the treatment in the article.

Treatment of eye blepharitis, its symptoms and common pathogens are described here.

Glasses to protect your eyes from the computer: http://eyesdocs.ru/ochki/kompyuternye/ochki-dlya-raboty-s-kompyuterom.html

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conclusions

IN childhood You should never ignore ophthalmological examinations, since it is at this age that serious eye diseases, which over time can lead to a noticeable deterioration in vision and even blindness, which can greatly impede the normal development of the child. Nowadays, various eye tables have been created for testing vision, which are used to determine the quality of peripheral vision, acuity, and other indicators. Especially considering that a disease such as farsightedness in children is now actively gaining momentum.

Most animals have visual organs. Some people have eyes that are close together, improving depth perception. Others have eyes far apart, creating a larger field of vision and receiving advance warning of a possible attack.

There are many types of eyes in the animal kingdom. The human eye is not anatomically similar to the eye of a fly, designed for a lightning-fast reaction to movement.

Only humans have the whites of their eyes, which show their mood and emotional background.

Peculiarities of eye function in animals and insects

The chameleon controls its eyes independently of each other. They can look in different directions at the same time.

Goats, mongooses, sheep and octopuses have eyes with rectangular pupils.

The volume of an ostrich's eyes is larger than the volume of this bird's brain!

The owl's eyeballs occupy the entire space of the skull; they rotate with difficulty. The owl compensates for this by turning its neck half a circle in any direction.

Some scorpions have up to six pairs of eyes. Many of the spiders have four pairs. The tuatara lizard has three eyes!

Jumping spiders have two main eyes and six auxiliary eyes.

Starfish have eyes at the end of each ray and receptors throughout their bodies. These marine animals can only distinguish between light and dark lighting.

A whale's eye weighs about a kilogram. But the whale can only see at a distance of 1 meter.

The eyes of the mantis shrimp are a complex system. She can see in polarized light, in the optical, IR and UV ranges.

A person will obtain such accuracy only by using equipment weighing a hundredweight.

Among marine animals, cuttlefish, squid and octopuses have the most perfect vision.

How animals and insects see colors

Cats cannot distinguish the color red. Their colors are dim. A person has only 4 rods for each cone, while a cat has 25. That's why cats see the world as gray.

Dogs clearly see blue and purple tones, but cannot recognize warm colors such as yellow, orange and red.

Bulls and cows do not emit red. The bullfighter irritates the animal not with the red color of his cloak, but with sudden movements.

The bee does not distinguish red; it confuses it with green, gray or black. The bee accurately sees yellow, blue, blue-green, indigo, violet and purple. Excellently highlights ultraviolet tones and the corresponding radiation.

How animals and insects see near, far and to the sides

Dogs see well in the distance, but poorly up close. A dog's visual acuity is approximately 60% weaker than a human's. But dogs can easily determine the distance by eye.

An eagle's visual acuity is twice as strong as a human's.

A falcon can see an object 10 cm in size from a height of 1500 m.

The vulture sees small rodents from a distance of up to 5 kilometers.

The dragonfly is one of the most vigilant insects. She sees a match head a meter away. The dragonfly's eye is made up of 30 thousand individual biological chambers. Each camera captures one point, then the array of images in the brain is combined into a single object. The dragonfly's eye captures up to 300 images per second.

Frogs see only moving objects, considering them as possible prey.

Thanks to horizontal and rectangular pupils, goats and bison see 240°. The horse's field of vision is 350%.

The viewing angle for cats is 190°, while for dogs it is only 40°.

Each person has a unique iris pattern. Along with fingerprints, the iris pattern is used to identify a specific person.

Ordinary human eye with all the richness of its functions, it weighs less than a bullet for the 7.62x54 cartridge. The bullet weighs 9 grams, the eyes are only 8.

Diameter eyeball for most adults it is approximately 24 mm.

The least common eye color in humans is green. Occurs in 2% of cases.

At birth, a person has an indeterminate eye color. The eyes acquire a permanent color after two to three years.

The human eye distinguishes up to 5 million different shades of color, having a huge number of light-sensitive cells (over 130 million).

Eye color is determined by melanin, the pigment in the iris. A low concentration of pigment contributes to the acquisition of light, cold tones - blue, gray, green. With a high concentration of melanin, the iris turns black or brown. The absence of melanin in the iris is only found in albinos.

The primary colors perceived by humans are red, blue and green. Their different saturations allow you to get all the color options visible to the eye.

For every hundredth person, the colors of the iris of the left and right eyes are different.

Color blindness is detected in 8% of men and only 1% of women.

Europe has the most light eyes among the Swedes, Finns, Poles and residents of the Baltic states. The most dark eyes- among the Yugoslavs, Turks and Portuguese.

About night vision

Of the birds, owls see best in the dark. Owls can accurately see mice or squirrels even without the Moon. During the day, owls see poorly, so they hide in secluded places.

Cats see in the dark better than people. At dusk and at night, the pupils of cats dilate to 14 mm. In humans, the diameter of the pupil, even at night, is no more than 8 mm. In bright light, cats instinctively close their eyes to avoid damaging the retina.

The human eye has 150 eyelashes on each eyelid.

Sneezing is always accompanied by closing the eyes, as this develops a speed of 170 km/h and pressure on the nasal sinuses.

The man blinks every 10 seconds, each blink taking from one to three seconds. During the day, men blink for about an hour.

Women blink approximately twice as often as men.

Women cry about 40 times a year, men about 6.

The eyes adapt to the dark in about an hour. During this time, the sensitivity of the eyes to light increases thousands of times. The sudden transition from darkness to bright light causes discomfort.

The human eye is a complex biological organ that receives visual information from the outside and transmits it further to the brain. High speed processing received information allows you to respond to sudden changes.

The inner surface of the eye is lined with retinal tissue. Its function is reminiscent of the film in a camera or the digital matrix of a mobile phone.

The cornea is an element of the eye that changes shape and focuses on objects at different distances. The cornea is transparent; it is covered by the iris, which is a colored film. In the center of the iris is the pupil, through which a stream of light passes to the retina. The pupil regulates the amount of incoming light.

In the human eye, where the optic nerve passes through the retina, there is a small blind spot. This feature is compensated by information from the other eye.

Eye transplantation is not possible. When the optic nerve is separated from the brain, the first one dies immediately. However, the cornea of ​​the eye is successfully transplanted.

Tears in a newborn appear in the second month of life.

Ordinary people recognize thousands of color shades, but artists recognize millions.

Circles under the eyes indicate dehydration, and bags indicate kidney problems.

In the first days, babies can see only 25 cm into the distance.

When reading quickly, your eyes get less tired than when reading slowly.

Illuminating the eyes with red light increases sensitivity to darkness for half an hour.