Acute vision and good vision are not necessarily synonymous. What is visual acuity? Keen vision meaning

Canadian ophthalmologist Garth Webb made a sensational announcement about his invention of a device that can permanently solve the problem of poor vision. We are talking about Ocumetics Bionic Lens, which are implanted into the eyes and can provide visual acuity 3 times greater than the vision of a person with normal (healthy) eyes. Moreover, as the inventor assures, such vision will remain unchanged until the end of the life of the operated person.

Dr. Garth Webb is the founder and CEO of Ocumetics Technology Corp, a company created to eliminate glasses and contact lenses from everyday life. Dr. Webb and his collaborators spent 3 million US dollars and 8 years of research to develop the Ocumetics Bionic Lens.

The bionic lens may look like a small, clear button, but Dr. Webb says it could revolutionize eye care and treatment. “Excellent vision should become an inalienable human right,” the oculist-inventor is convinced.

The bionic lenses are expected to be implanted into the eyes during a painless 8-minute operation. This operation is very similar to cataract surgery, during which the clouded lens is replaced with an artificial intraocular lens. This microsurgical procedure does not even require pain relief or bed rest for the patient.

If you are interested, you can watch a short 4-minute video about cataract surgery:

A bionic lens, twisted into a tube, is inserted into the eye in exactly the same way using a syringe filled with saline. Then, within about 10 seconds, the Ocumetics Bionic Lens unfurls on its own, acquiring the desired shape, and, lo and behold! – a person’s vision becomes sharp and clear again!

According to Dr. Webb, if a person could clearly see a wall clock from a distance of 3 meters, then after installing bionic lenses, he will be able to clearly see the same clock from a distance of 9 meters.

From the above it follows that Ocumetics Bionic Lens, installed on a person with good (100%) vision, gives him the opportunity to see 3 times better!

While Garth Webb has not yet revealed all the secrets of his invention, he already has a whole list of patents on his hands to improve the characteristics of intraocular lenses.

How Ocumetics Bionic Lenses are made and work we can only guess at this point, but Webb assures that these lenses are extremely safe and cannot cause any biophysical changes in the eye.

Moreover, in addition to extremely sharp vision, Ocumetics Bionic Lens provide another important advantage to the person in whom they are implanted. With such lenses, a person is no longer at risk of cataracts, since natural lenses, which are prone to clouding in old age, are replaced by artificial bionic lenses.

Ocumetics Bionic Lens surgery is much safer than laser vision correction (LASIK), which burns away some healthy corneal tissue and often comes with negative side effects (such as photophobia and vision problems while driving at night) and significant limitations in lifting. heavy weights and during sports. Dr. Webb is confident that his invention does not have these problems, and a person’s vision with bionic lenses will always remain sharp and will not deteriorate over time.

Garth Webb has already demonstrated his bionic lenses to 14 top eye surgeons during the annual global cataract and refractive surgery conference in San Diego. Webb's colleagues were impressed by this invention and some of them even agreed to help further clinical trials of bionic lenses.

In the first stages of testing, Ocumetics Bionic Lens will be implanted in animals, then in blind people, and only after that regular studies will begin in specialized eye clinics in Canada and other countries.

It is planned that the first Ocumetics Bionic Lens will become available for vision correction in 2017, but only for people over 25 years old, since it is at this age that a person’s eyes are considered to be fully formed.

Here is a short interview with Dr. Garth Webb, where he, among other things, demonstrates the bionic lenses he invented:

Well, let’s hope that in just a few years the technology for producing and implanting Ocumetics Bionic Lens into a person’s eyes will be perfected and it will become available to everyone who wants to have good vision for life.

We continue ours. For example, the name of a student from Germany, Veronica Seider, is listed in the Guinness Book of Records; the girl has the sharpest eyesight on the planet. Veronica recognizes a person's face at a distance of 1 kilometer 600 meters, this figure is approximately 20 times higher than the norm. Also, people see well in the dark, but nocturnal animals such as cats will give us a hundred points ahead.

Who has the most sensitive eyes?

The human eye is one of the most amazing achievements of evolution. He is able to see small specks of dust and huge mountains, near and far, in full color. Working in tandem with a powerful processor in the form of the brain, the eyes allow a person to distinguish movement and recognize people by their faces.

One of the most impressive features of our eyes is so well developed that we don't even notice it. When we enter a dimly lit room from bright light, the level of illumination in the surrounding environment drops sharply, but the eyes adapt to this almost instantly. As a result of evolution, we have adapted to see in poor light.

But on our planet there are living beings who see in the dark much better than humans. Try reading a newspaper in the deep twilight: the black letters merge with the white background into a blurry gray spot in which you can’t understand anything. But a cat in a similar situation would not experience any problems - of course, if she could read.

But even cats, despite their habit of hunting at night, see in the dark no better than anyone else. Creatures with the sharpest night vision have evolved unique visual organs that allow them to capture literally grains of light. Some of these creatures are able to see in conditions where, from the point of view of our understanding of physics, nothing can be seen in principle.

To compare night vision acuity, we will use lux, a unit that measures the amount of light per square meter. The human eye works well in bright sunlight, where illumination can exceed 10 thousand lux. But we can see at just one lux—that’s about how much light there is on a dark night.

Domestic cat (Felis catus): 0.125 lux

To see, cats need eight times less light than humans. Their eyes are generally similar to ours, but they have several features that allow them to work well in the dark.

Cat eyes, like human eyes, are made up of three main components: the pupil, the hole through which light enters; lens - focusing lens; and the retina, the sensitive screen onto which the image is projected.

In humans, the pupils are round, but in cats they have the shape of an elongated vertical ellipse. During the day they narrow into slits, and at night they open to their maximum width. The human pupil can also change size, but not within such a wide range.

Cats' lenses are larger than those of humans and are able to collect more light. And behind the retina they have a reflective layer called the tapetum lucidum, also known simply as the “mirror.” Thanks to it, cats' eyes glow in the dark: light passes through the retina and is reflected back. This way, light hits the retina twice, giving the receptors an extra chance to absorb it.

The composition of the retina itself in cats is also different from ours. There are two types of light-sensitive cells: cones, which detect colors but only work in good light; and rods - which do not perceive color, but work in the dark. Humans have many cones, which give us rich, full-color vision, but cats have many more rods: 25 per cone (in humans, this ratio is one to four).

Cats have 350 thousand rods per square millimeter of retina, while humans have only 80-150 thousand. In addition, each neuron leaving the cat's retina transmits signals from about one and a half thousand rods. The weak signal is thus amplified and transformed into a detailed image.

There is a downside to such acute night vision: during the daytime, cats see about the same as people with red-green color blindness. They can distinguish blue from other colors, but cannot tell the difference between red, brown and green.

Tarsiidae: 0.001 lux

Tarsiers are tree-dwelling primates found in Southeast Asia. Relative to the rest of their body proportions, they appear to have the largest eyes of any mammal. The body of the tarsier, excluding the tail, usually reaches a length of 9-16 centimeters. The eyes have a diameter of 1.5-1.8 centimeters and occupy almost the entire intracranial space.

Tarsiers feed mainly on insects. They hunt early in the morning and late in the evening, under illumination of 0.001-0.01 lux. Moving along the treetops, they must look out for small, well-camouflaged prey in almost complete darkness and at the same time not fall, jumping from branch to branch.

They are helped in this by their eyes, which are generally similar to human eyes. The giant tarsier's eye lets in a lot of light, and the amount of light is regulated by the strong muscles surrounding the pupil. The large lens focuses the image on the retina, strewn with rods: the tarsier has more than 300 thousand of them per square millimeter, like a cat.

These large eyes have a disadvantage: tarsiers are unable to move them. As compensation, nature endowed them with necks that rotate 180 degrees.

Dung beetle (Onitis sp.): 0.001-0.0001 lux

Where there is dung, there are usually dung beetles. They choose the freshest pile of manure and begin to live in it, rolling balls of manure as a reserve or digging tunnels under the pile to make a storage room for themselves. Dung beetles of the genus Onitis fly out in search of dung at different times of the day.

Their eyes are very different from human eyes. The eyes of insects are faceted, they consist of many structural elements - ommatidia.

In beetles that fly during the day, ommatidia are enclosed in pigment shells that absorb excess light so that the sun does not blind the insect. The same membrane separates each ommatidium from its neighbors. However, in the eyes of beetles that are nocturnal, these pigment membranes are absent. Therefore, light collected by many ommatidia can be transmitted to just one receptor, which significantly increases its photosensitivity.

The genus Onitis includes several different species of dung beetles. In the eyes of diurnal species there are insulating pigment membranes, the eyes of evening beetles sum up signals from ommatidia, and in nocturnal species they sum up signals from a number of receptors twice as large as those of evening beetles. The eyes of the nocturnal species Onitis aygulus, for example, are 85 times more sensitive than the eyes of the diurnal Onitis belial.

Halictid bees Megalopta genalis: 0.00063 lux

But the rule described above does not always apply. Some insects can see in very low light, despite the fact that their visual organs are clearly adapted for daylight.

Eric Warrent and Elmut Kelber from Lund University in Sweden found that some bees have pigment membranes in their eyes that isolate the ommatidia from each other, but they are nevertheless perfectly able to fly and search for food in the dark at night. For example, in 2004, two scientists demonstrated that the halictid bees Megalopta genalis are able to navigate under illumination 20 times less intense than starlight.

But the eyes of Megalopta genalis bees are designed to see well in daylight, and during the course of evolution, bees had to adapt their visual organs somewhat. After the retina has absorbed light, this information is transmitted to the brain through nerves. At this stage, the signals can be summed to increase the brightness of the image.

Megalopta genalis has special neurons that connect ommatidia into groups. In this way, signals coming from all the ommatidia in the group are fused together before being sent to the brain. The image is less sharp, but significantly brighter.

Carpenter bee (Xylocopa tranquebarica): 0.000063 lux

Carpenter bees, found in the mountains called the Western Ghats in southern India, see even better in the dark. They can fly even on moonless nights. “They can fly in starlight, cloudy nights and strong winds,” says Hema Somanathan from the Indian Institute of Science Education and Research in Thiruvananthapuram.

Somanathan discovered that carpenter bee ommatidia have unusually large lenses, and the eyes themselves are quite large in proportion to other parts of the body. All this helps to capture more light.

However, this is not enough to explain such excellent night vision. It is possible that in carpenter bees, ommatidia are also grouped together, just like in their cousins Megalopta genalis.

Carpenter bees don't just fly at night. “I have seen them fly around during the day when their nests are being destroyed by predators,” says Somanathan. “If you blind them with a flash of light, they simply fall, their vision is not able to process a large amount of light. But then they come to their senses and take off again.”

Of all fauna, carpenter bees seem to have the most acute night vision. But in 2014, another contender for the championship title appeared.

American cockroach (Periplaneta americana): less than one photon per second

It is not possible to directly compare cockroaches with other living creatures, because their visual acuity is measured differently. However, their eyes are known to be unusually sensitive.

In a series of experiments reported in 2014, Matti Väckström of the University of Oulu in Finland and his colleagues examined how individual light-sensitive cells in cockroach ommatidia responded to very low light levels. They inserted the thinnest electrodes made of glass into these cells.

Light consists of photons—massless elementary particles. The human eye needs at least 100 photons to hit it to sense anything. However, the receptors in the cockroach's eyes responded to movement even if each cell received only one photon of light every 10 seconds.

A cockroach has 16-28 thousand green-sensitive receptors in each eye. According to Weckström, in dark conditions, signals from hundreds or even thousands of these cells are summed up (recall that in a cat up to 1500 optic rods can work together). The effect of this summation, according to Weckström, is “enormous,” and it seems that it has no analogues in living nature.

“Cockroaches are impressive. Less photon per second! says Kelber. “This is the sharpest night vision.”

But bees can outdo them in at least one respect: American cockroaches don't fly in the dark. “Control of flight is much more difficult - the insect moves quickly, and collision with obstacles is dangerous,” comments Kelber. “In this sense, carpenter bees are the most amazing. They are able to fly and forage on moonless nights and still see colors.”

And a little more interesting information about acute vision.

Eyes, nose, ears - in the wild, all organs serve the survival of the animal. Eyes play a vital role in the life of any living creature, but not all animals see the same. Visual acuity does not depend on the size or number of eyes.

Thus, even the most vigilant among many-eyed spiders, the jumping spider, sees the victim only at a distance of 8 centimeters, but in color. It should be noted that all insects have poor eyesight.

Animals that live underground, such as moles, have no vision at all. Mammals that live in water, such as beavers and otters, have poor vision.

Animals hunted by predators have panoramic vision. It is extremely difficult for a nightjar to sneak up on a bird unnoticed. Her bulging, large eyes have a wide slit that curves toward the back of her head. As a result, the viewing angle reaches three hundred and sixty degrees!
It is interesting, for example, that eagles have two eyelids, while insects do not have eyelids at all and sleep with their eyes open. The eagle's second eyelid is completely transparent; it protects the bird of prey's eye from the wind during a swift attack.

Birds of prey have the sharpest vision in the animal world. In addition, these birds can instantly shift the focus of vision from long distances to near objects.
Birds of prey, eagles, can see their prey at a distance of 3 kilometers. Like all predators, they have binocular vision, when both eyes look at the same object, this makes it easier to calculate the distance to prey.
But the absolute champions of vigilance in the animal world are representatives of the falcon family. The world's most famous falcon, the peregrine falcon or, as it is also called, the pilgrim, can spot game from a distance of 8 kilometers.

The peregrine falcon is not only the most vigilant, but also the fastest bird, and in general a living creature, in the world. According to experts, in a rapid diving flight it is capable of reaching speeds of over 322 km/h, or 90 m/s.

For comparison: the cheetah, the fastest-footed land mammal, runs at a speed of 110 km/h; The spiny-tailed swift, living in the Far East, is capable of flying at a speed of 170 km/h. But, it should be noted that in horizontal flight the peregrine falcon is still inferior to the swift.

The peregrine falcon (lat. Falco peregrinus) is a bird of prey from the falcon family, common on all continents except Antarctica. During a hunt, the peregrine falcon plans in the sky, having discovered prey, it rises above the victim and rapidly dives down almost at a right angle, inflicting fatal blows to the victim with its paw claws.

Such different eyes.

A series of works by Armenian photographer Suren Manvelyan ( Suren Manvelyan) “Your Beautiful Eyes” shows the pupils of the eyes of animals, birds and fish captured in macro mode. Suren was born in 1976, started taking photographs when he was sixteen years old, and became a professional photographer in 2006. His photographic interests range from macro to portraits. Now he is the chief photographer for Yerevan magazine.

When talking about certain visual impairments, we most often mean myopia or farsightedness. Less often we talk about astigmatism, even less often – about color blindness. Meanwhile, no less important role in the visual perception of reality is played by the so-called contrast vision. A person can have extremely acute vision and still have difficulty distinguishing objects that blend into the background.

Until recently, a routine visit to the ophthalmologist did not include a contrast vision test, since this procedure was associated with significant difficulties and required a lot of time.

Anya Muller's technique

And now the Technische Hochschule Jena has developed a technique that allows such control to be carried out quickly and reliably. Its author, optical engineer Anja Müller, says:

“When determining visual acuity, we do this with maximum contrast. Meanwhile, in practice, the main thing is not always to see the smallest details. It is much more important to see and recognize the object in general. And this is where it often turns out that acute vision and good vision are not necessarily synonyms."

Research... at the buffet

Anya Müller provided rich material for observations from the buffet at her native Higher Technical School: here the white dishes almost merge with the white surface of the tables. Anyone who accidentally knocks over a cup, even though they can easily read small print in a newspaper without glasses, almost certainly suffers from a contrast vision disorder. As a rule, such a disorder is caused by cataracts or clouding of the vitreous body of the eye, which, in turn, can be a consequence of injury, diabetes, or even simply the natural aging process. Anja Müller explains:

“At opacities, the light is scattered, superimposed on the image of the object on the retina, and as a result it becomes fuzzy, blurry.”

Visual acuity is determined by Landolt rings

However, retinal lesions caused by so-called macular degeneration also lead to the same effect. This feeling is familiar to anyone who wears glasses: it occurs when the lenses are dirty or severely scratched. However, this effect is also not new to those who do not use glasses: it is observed when direct sunlight hits the computer monitor screen. At the same time, the image contrast drops from 80 to 40 percent, as a result of which it becomes almost impossible to make out anything on the screen. This is exactly how people who suffer from severe contrast vision impairment perceive all surrounding objects. However, the diagnosis of these disorders, and especially the quantitative assessment of the degree of anomaly, until recently was a complex and expensive examination. The method proposed by Anya Muller is based on a number of graphic elements of the same table that flaunts in the office of any ophthalmologist. We are talking about the so-called Landolt rings - thin circles with a small slot at the bottom, top, left or right. Just like letters and numbers, rings serve to determine visual acuity, and they are more objective because they are more difficult to guess or confuse. Anja Müller says:

"The measurement begins with the smallest ring, the slot in which the patient correctly identified at maximum image contrast. Then the contrast gradually, step by step, decreases until the number of errors in determining the location of the slots reaches three. Thus, we set the first contrast threshold distinctive light sensitivity. After this, the same procedure is repeated with the next largest Landolt ring, which allows us to find the second threshold of contrast sensitivity. Upon completion of the measurements, we obtain a table from which it follows what visual acuity was necessary for the correct recognition of rings at one degree or another. contrast".

Preventative contrast vision tests can help diagnose serious conditions

The larger the ring must be for the patient to be able to see the slot in it with low contrast, the worse his contrast vision. After conducting an extensive series of experiments, Anja Müller compiled a standard chart that is entered into a computer, allowing doctors to obtain comparable, standardized data. But that's not all:

“It is also important that determining the individual characteristics of contrast vision can also reveal serious pathology: this diagnosis is quite sensitive.”

In other words, cataracts, diabetes or macular degeneration not only impair contrast vision, but also seem to give themselves away. That is, preventive contrast vision tests can help diagnose serious diseases at the earliest stages.

Vladimir Fradkin, GERMAN WAVE

Visual acuity is one of the most important characteristics of the human visual analyzer. This characteristic reflects the sensitivity of the eye, as well as its ability to determine details in visible objects.

Visual acuity 1.0

In this article, we tried to take a more detailed look at how to determine visual acuity and looked at how it is measured.

Visual acuity indicators

The optimal indicator is 100% visual acuity. This is the ability to distinguish between two points distant from each other, the angular resolution of which is equal to one minute, which corresponds to 1/60 of a degree. In simple terms, visual acuity is a qualitative indicator of the vigilance of human eyes, allowing one to measure in numbers how clearly a person sees the world around him.

Normal vision in Russia is considered equal to 1.0. Visual acuity is determined using special tables that depict optotypes, letters or special icons that the person undergoing the test must see. Many people do not understand where the number 1.0 comes from. This figure is determined using a specially designed scheme, which looks like this: V=d/D. Experts use the letter V to denote visual acuity. The letter d is the distance at which the test is carried out. The letter D is the distance from which an eye with normal vision sees a certain row on the measurement table.

Methods for studying visual acuity

Many experts argue that you need to regularly undergo studies to determine visual acuity (visometry). Timely detected indicators of a decrease in this function of the human eye make it possible to timely select certain corrective measures. The traditional method for determining eye vigilance is the use of special tables. In the check table, the signs (optotypes) are arranged in a certain order. These can be letters, symbols, shapes, numbers, lines, and drawings.

Each optotide occupies a visual angle of 5 minutes. Individual details of the sign are covered by a viewing angle of 1 minute. There are also universal tables with optotypes, which depict open circles of various diameters. These tables were named “Landolt rings” after the inventor.

If a person undergoes research on this table, then he is asked to determine in which direction the gap on the ring is directed. In our country, Sivtsev or Golovin tables are most often used to check visual acuity. They use the standard 7 letters: Sh, B, M, N, K, Y, I. In the research process, the distance to the table is also an important factor. It is about 5 meters. Before each line, the distance from which a healthy eye sees a certain symbol is indicated.

Standard vision test chart

Dividing the distance from which a person sees a certain symbol by the table value of a healthy eye, we obtain the level of visual acuity. A healthy eye sees the first line in the table at a distance of 50 meters. The visual acuity of the eye (Visus) that sees only the first line will be equal to 0.1. With each row of the table, one tenth must be added to this value. Thus, the tenth line will correspond to visual acuity, which is equal to 1.0. The exception is the eleventh (1.5) and twelfth line (2.0).

When determining visual acuity, you also need to know about the following features:

Maintain lighting level (700 lux).
The right eye is examined first, and then the left.
The eye must be covered using a special shutter. In this case, physical impact must be avoided.
In lines 1-3, errors in determining the sign are not allowed. From lines 4 to 6, one error is allowed. From lines 7 to 10, two errors are made.
The duration of viewing each sign should not exceed 3 seconds.

A more high-tech and modern method of verification can be considered the use of an optotype projector. Projectors provide a clear image of symbols and make it possible to move away from the mandatory distance of 5 meters.

Types of pathologies

Here is a list of the main pathological changes that lead to deterioration in the quality of vision:

(hypermetropia) – with an accelerated ocular axis, the image is formed behind the retina;
(myopia) – the image is formed in front of the retina;
– violation of the sphericity of the cornea;
changes in visual acuity in adults.

Age-related changes in the eye include::

presbyopia - the lens partially loses its elasticity, is not able to change the sphericity of its surface, since the ligaments lose their flexibility, and the lens itself becomes significantly denser;
– disturbances in the nutrition of the lens, a decrease in its transparency;
– increased intraocular pressure with damage to the optic nerve.

If you have presbyopia, you will have to increase the dioptres in your glasses as you age. With cataracts, restoration of normal eye functions will only be possible with surgical intervention. In the presence of glaucoma, intraocular pressure is normalized using medication, laser or surgery.

In fact, you can talk for a long time about visual acuity in numbers and medical terms. However, it is much clearer to explain this category using real-life examples. This will help you navigate your visual acuity indicators much faster.

Features of visual acuity

If the vision index is 1.0, a person can easily see the numbers and letters of a license plate from 40 meters if there is enough light. If visual acuity is less, then the distance from which a person will see clear, non-blurring symbols will be less. If visual acuity is 0.4, then the number will be clearly readable only from 16 meters, and as the distance increases, the characters will become fuzzy and gradually merge into an indistinguishable spot.

When visual acuity is 1.0, a person sees the upper letters of the test table from a distance of 50 meters. With visual acuity of 0.1, a person needs to move only 5 meters away from the table.

Improved vision

To maintain visual acuity at the proper level, you should take all measures that will help maintain eye vigilance:

Provide the body with sufficient amounts of vitamin A.
Organize comfortable and convenient lighting in the workplace.
Choose the right color scheme for the environment in places of long stay.
Give up bad habits that significantly impair vision.
Carry out timely correction of visual acuity.

Now you know exactly what visual acuity is and how it is determined. To maintain visual acuity for a long time, follow a proper diet and exercise regularly. We hope this information was useful and interesting.

Visual acuity becomes worse over time. And this happens for various reasons. There are natural reasons for decreased vigilance - aging of the body. Today, this indicator is getting worse in people even at a young age. The reasons for this are mass computerization and multiple diseases, which provoke the fact that a person begins to see poorly.

Visual acuity may be normal and decrease under the influence of certain factors. The norm of vigilance at 100% is the ability to distinguish between two objects distant from each other. In simple terms, visual acuity is an indicator of vigilance that can be measured in numbers.

In the Russian Federation, the norm is equal to one (1.0). You can determine how clearly a person sees using special tables. These tables are familiar not only to adults, but also to children. They undergo preventive examinations while still in preschool educational institutions. Tables may contain letters or symbols. Tables depicting symbols were developed specifically for children who cannot yet read and do not know letters. The norm is when a person sees the 10th line out of 12. At the same time, be at a distance of five meters from the table.

If the clarity of vision is impaired, this means that ophthalmic diseases are developing or are already present. The sooner a decrease in visual acuity is detected, the faster the situation can be corrected.

Interesting! You don't have to see an ophthalmologist to check for clarity. You can find the well-known constellation Ursa Major in the starry sky. Even in ancient times, traditional healers claimed that a person has excellent and acute vision if he is able to see the small Mizar star near the second star from the edge of the handle of the ladle.

Deviations from 1.0 are not always a pathology. For some people the ratio may be higher. In this case, visual acuity is called aquiline.

Interesting! The most acute vision in the animal world is that of the eagle. If we take a bird’s vigilance to be 100%, then a human’s vigilance is only 51%! At the same time, octopuses see clearly compared to eagles by only 32%, jumping spiders by 8%, cats by 7%, and goldfish by 5%.

Indicators above 1.0 are not a pathological deviation. The same cannot be said about numbers below 1.0. This indicates the presence of developing ophthalmological diseases. Indicators that are too low indicate diseases that are already present.

What do indicators below 1.0 indicate?

If a visual acuity of less than 1.0 was recorded during an eye examination, this may indicate the presence of:

Cataracts.
Retinal detachment and rupture.
Glaucoma.

Neuritis, toxic neuropathy, optic nerve atrophy.
Disorders of the functions of the corneal endothelium.
Detachments of the choroid.
Lens luxation.
Corneal injuries.
Lack of lens.
Vitreous prolapse.
Purulent endophthalmitis.
Myopia.
Hyperopia.
Corneal burn.
Astigmatism.
Iridocyclitis.
Chorioretinal inflammation.
Neoplasms in the area of the craniopharyngeal duct.
Acute increase in intraocular pressure.
Scars of the cornea of the conjunctiva.
Multiple sclerosis.
Keratitis.
Chorioretinal scars.

Tumors of the central nervous system.
Foreign body on the cornea.
Pituitary adenomas.
Parasagittal meningioma.
Late neurosyphilis.
Lagophthalmos.
Malignant or benign neoplasm of the eye.
Scarring of the conjunctiva.
Rossolimo-Melkersson syndrome.

How to check eye clarity - basic rules

The procedure for determining how sharp a person’s vision is is carried out in an ophthalmologist’s office or in stores that sell glasses, contact lenses, and when selecting them.

But it’s better, of course, to choose a clinic.

Basic Rules:

a person sits at a distance of five meters from the table;
the location of the tables is strictly from the window on the opposite side;
The 10th line of the table should be located strictly opposite the eyes;
the table must be illuminated by special lamps (there are certain requirements for the supply of light);
visual acuity should be measured for each eye separately (during examination, the second eye is covered with a special opaque instrument);
It is unacceptable to close the other eye (this will not give an informative result!), both eyes must be open;
You should not squint during the examination, this can also cause an unreliable result;
a sign or letter in the table is recognized within 2-3 seconds, longer time indicates a deviation.

During verification, the norm is to make 2 errors in the 7th line.

How to test your eyesight at home

Today, thanks to the World Wide Web, you can check clarity at home. There are online tests with detailed instructions on how to take them. But, of course, it is better to consult an ophthalmologist for more reliable results.

In addition to online tests, it is possible to print out the tables offered on the website. Arrange them according to the rules described above. The main thing is that table lighting, even in daylight, must be present.

To do this, you can take a regular fluorescent lamp and place it above the table. Or use two 40-watt lamps and place them on the sides of the table.

It is not necessary to print the table in a large format. It is enough to use white matte paper in landscape orientation in A4 format. Hang it on the wall so that the 10th line is approximately at eye level. If a person sees the entire 10th line, this indicates an indicator of 1.0. This is the norm. In all other cases, you should visit an ophthalmologist, and do not delay the examination.

Dangerous symptoms

Many people do not notice that visual acuity has begun to decline. Especially in the first stages of development of pathologies. There are some symptoms to be aware of.

If you have these signs, you should immediately visit an ophthalmologist:

There is a black curtain before my eyes. Causes: progressive retinal detachment. A distinctive symptom is decreased visual acuity. This disease requires immediate hospitalization and radical treatment.
Sharp pain in the eye, redness of the mucous membrane, fog before the eyes, attacks of nausea and vomiting, decreased visual acuity. Symptoms of angle-closure glaucoma. With a sharp increase in intraocular pressure, the optic nerve is damaged. The pathology requires urgent treatment. Otherwise, you cannot do without surgery.

An intense or gradual narrowing of visibility occurs (in medicine it is also called tubular vision). Causes: damage to the optic nerve. In this case, a sharp decrease in visual acuity occurs. Untimely treatment will lead to glaucoma and subsequently to removal of the eye.
Deteriorated, blurry, distorted vision. There is a decrease in visual acuity. A straight line may appear curved. Causes: dystrophic lesion of the central region of the retina. The pathology is typical for older people. In this case, visual acuity will be below 1.0. If the treatment is not up-to-date, this condition will lead to complete loss of vision without the possibility of recovery.
Hazyness before the eyes, lack of brightness and contrast. These are signs of cataracts, in which clouding of the lens develops. Treatment is carried out surgically - a lens implant is implanted. If not treated in a timely manner, complete loss of vision occurs without the possibility of recovery.
Appearance of dark spots, cloudiness, fog before the eyes. In diabetes mellitus, such signs indicate retinal damage. Complications include hemorrhage in the retina and vitreous body. This leads to loss of vision.
Burning sensation, sensation of foreign bodies, lacrimation, dryness. This is a symptom of dry eye. At risk are people who spend most of their lives at computers and work with documentation. The condition can cause poor vision and many eye diseases.

Visual acuity is a characteristic that helps identify vision problems in the early stages. The examination must be completed at least twice a year.

Especially for those people who have a genetic predisposition (the person in the family had relatives suffering from ophthalmological diseases); if there were injuries to the upper cervical vertebrae (pinching of blood vessels occurs, which affects clarity); Diabetes mellitus and cervical osteochondrosis are present. A decrease in visual acuity occurs in old age and during difficult childbirth. Some sexually transmitted diseases also cause a decrease in clarity.