What kinds of sight are there? What features do they have? You will find answers to these and other questions in the article. The eye is a living optical apparatus, a wondrous organ of the human body. Thanks to him, we distinguish the volume and colors of the picture, we see it at night and during the day.
The eye is built like a camera. Its lens and cornea, like a lens, refract and focus light rays. The retina lining the fundus acts as a receptive film. It consists of specific, light-perceiving elements - rods and cones. Consider the views below.
Daytime vision
What is daytime vision? This is a mechanism for the perception of light by the human visual system, functioning in conditions of relatively high illumination. It is performed using cones with a background brightness exceeding 10 cd/m², which corresponds to daylight conditions. Sticks don't work in this environment. This vision is also called photopic or cone vision.
Day vision differs from night vision in the following ways:
- Lowphotosensitivity. Its format is almost a hundred times lower than with night vision. Cones are less sensitive to light than rods.
- High resolution (visual acuity). This is achieved due to the fact that the density of the placement of rods is much lower than the density of cones.
- The ability to perceive colors. It is implemented due to the fact that there are three types of cones on the retina. At the same time, the cones of each species capture color from only one zone of the spectrum, characteristic of this species.
Using day vision, a person receives a large share of visual data.
Vision in the evening
What is twilight vision? This is a mechanism of contemplation of light by the visual structure of a person, working in conditions of illumination that are buffer in relation to those in which day and night vision function. It is performed using cones and rods acting synchronously with background brightness values between 0, 01 and 10 cd/m². This vision is also called mesopic.
G. Wyszecki and D. Judd describe the illumination under which twilight vision operates as follows: “Twilight is the range of illumination, extending from the illumination that the sky produces with the sun more than two degrees below the horizon, to the illumination that the moon produces at half phase soaring high into the clear sky. Vision in a dimly lit (for example, candles) room also belongs to twilight vision.”
Since both rods and cones take part in the realization of evening vision, then in the moldingspectral dependence of the light sensitivity of the eye, receptors of both types contribute.
At the same time, along with the transformation of the background brightness, the contribution of cones and rods is rearranged. Accordingly, the spectral dependence of light susceptibility is also transformed.
Thus, when the illumination decreases, the sensitivity to red (long-wave) light decreases and increases to blue (short-wave). It follows that for twilight vision, in contrast to day and night vision, it is impossible to introduce any single typed function that would describe the dependence of the light sensitivity of the eye.
For the reasons presented, when the background brightness is transformed, the perception of light also changes. One of the manifestations of such changes is the Purkinje effect.
Vision at night
What other types of vision exist? Night vision is a mechanism for contemplating light by a human visual structure operating in relatively low light conditions. Performed with sticks at a background brightness of less than 0.01 cd/m², which coincides with night lighting conditions.
Cones do not work in this environment, as there is not enough light power to excite them. This vision is also called rod or scotopic vision. Photopic and scotopic vision are significantly different from each other, as discussed above.
Monocular vision
Many people wonder: "Monocular vision - what is it?" With this vision, moving objects and objects that are in the field of viewof the person looking, are caught mainly with only one eye.
In a normal environment, people with normal vision use binocular vision, that is, they evaluate visual information with both eyes. Monocular vision is usually measured in terms of angle.
It is known that birds have a very extensive circular vision. They not only see in front of them, but also on the sides, and even behind them. In birds, the eyes are placed on the sides. The quality of a bird's vision outweighs the acuity of human vision by four to five times.
The total field of view in birds reaches more than 300° (the field of vision of each bird's eye is 150-170°, which is 50° more than in humans). Basically, birds use lateral (lateral) and monocular vision (this is normal for them). Its total field is localized at about 70°. But in owls, the eyes do not move at all, which is compensated by the agility of the neck (about 270 °).
Binocular vision
Don't you know what binocular vision is? This is the ability to clearly see an image of an object simultaneously with both eyes. A person in this case sees one picture, which he looks at. That is, this is a vision with both eyes, with a subconscious combination in the cerebral cortex (visual analyzer) of the drawings received by each eye into an integral image.
In fact, binocular vision is a system that creates a three-dimensional image. It is also called stereoscopic. If it is not improved, the personcan only see with the left or right eye. This vision is called monocular.
There is also alternating vision: either with the left or with the right eye - alternating monocular. Sometimes there is simultaneous vision - vision with both eyes, but without merging into a whole visual image. If a person does not have binocular vision with two eyes open, then he will gradually develop strabismus.
Sharpness of vision
So we've covered all kinds of vision. We continue to study the human visual system further. Many people ask: "Vision 1 - what does it mean?" Each of us, starting from early childhood, is examined by an ophthalmologist. You can find yourself in the doctor's office in connection with the appearance of various complaints or for the purpose of clinical examination (preventive examination).
Those patients who went to the ophthalmologist must undergo a simple test, which will reveal visual acuity. Vision is evaluated on a special scale. They find various defects, deviations from the standard, as well as methods for their correction.
What does visual acuity mean, not everyone knows. To identify this indicator, doctors measure the smallest angle at which two different points are located that are distinguishable by the human eye. This indicator is normally equal to 1 °. To determine visual acuity, specific tables are used. They usually have letters, hooks, signs, and drawings painted on them. The most popular for diagnosing visual acuity in adults is the Sivtsev-Golovin table.
It contains 12 lines, on whichletters are drawn. The letters on the top lines have the largest parameters. They gradually decrease towards the bottom of the table. If the patient has 100% vision, that is, his acuity is 1.0, he can distinguish the upper line from a distance of 50 m. To see the lower letters, you already have to go to the table at 2.5 m.
Test conditions
Surely you will no longer ask the question: "Vision 1 - what does it mean?" We continue further. During the diagnosis, it is necessary that the patient and the doctor adhere to certain rules. If this is not done, the results may be distorted. It is important that the table is lit evenly. Outdoor lighting can be used for this, but it is better to place the poster in a Roth device, equipped with mirrored walls, which provide even lighting.
Sufficient lighting should also be an office. Each eye is tested individually. The eye that is not involved in the study is covered with a palm or a special white shield.
Revealing normal vision
How is visual acuity determined? First, the patient must sit in a chair placed five meters from the table. Diagnosis usually begins with the right eye, and then the doctor switches to the left. The doctor asks the subject to name the letters in the 10th line in order. If the answers are correct, the medic sets 100% vision, that is, 1, 0. This indicator is considered normal.
If the patient is unsure of reading letters or making mistakes, the testcontinue with reading the letters placed on the top line. As a result, the doctor identifies the line number on which the subject can distinguish letters from a distance of 5 m.
Card entry
After the test, the doctor makes the proper entries in the certificate or card. Usually they are presented like this: Vis OD and Vis OS. These symbols are deciphered very simply. The first indicator concerns the right eye, and the second - the left. If visual acuity is adequate on both sides, then next to these signs will be the number 1, 0.
However, very often the visual acuity of one eye is not the same as that of the other. In this case, the doctor will write different indicators near the icons. If the visual acuity of any eye is less than 1.0, then this indicates its decrease. As a result, the doctor will select an optical corrective device for the patient - contact lenses or glasses.
Sometimes people can tell the 11th line from the 12th line. This skill correlates with a visual acuity score of 1, 5, and 2.
Reduced visual acuity
What does vision minus 1 mean? Probably every person on Earth at least once in his life felt fatigue in his eyes, which is instantly reflected in vision. For some, this defect, caused by various factors, is only temporary. But in the worst case, it may not disappear after a warm-up or regular sleep.
Then you need to seek help from doctors who will make an accurate diagnosis and give recommendations on how to restore lost vision. And so, you passed all the tests in a reliable ophthalmological clinic, and the doctor told you that your vision is minus 1. Take your timeget upset or panic. Doctors believe that this is an initial stage myopia, ordinary people say that this is a mild degree of myopia. So what is it? Answer the question below.
What is the refraction of the eye?
What do the concepts "minus" and "plus" mean? These are the standards of diopters - units in which the refraction of the eye is measured. Refraction refers to the position of the eye relative to the retina. There are three types of refraction:
- Hypermetropia - placing the focus behind the retina, that is, farsightedness. Denoted by the word "plus".
- Emmetropia is vision without refractive error when the focus is on the retina. In this case, the refraction is 0.
- Myopia - the focus is in front of the retina, which causes distortion of distant vision, blurring of the image or contours. Diopters are marked with the word "minus".
Types of myopia
So, we have already found out that minus vision is one of the variations of myopia, which is divided into three types:
- Severe myopia - up to -15 diopters.
- Average myopia - up to -6 diopters.
- Mild myopia - up to -3 diopters.
It is known that when seeing -1 a person loses up to 10% of sight. This standard is not critical, but every person wants to be he althy. If you take care of your vision, you can reconstruct it to the state of emmetropia.
Twilight vision disorder
What is twilight vision impairment? This disease is known to medicine sinceancient times and received the name of hemeralopia. Doctors do not distinguish between its degrees (there is either a disease or it is not), but ophthalmologists are sure that the twilight vision disorder significantly reduces the quality of life, which sometimes has fatal consequences.
Hemeralopia is also called night blindness. This vision disorder is caused by damage to the optic nerve and retina. Its characteristic features are manifested by a drop in visual acuity in the dark. It has these symptoms:
- narrowing the fields of vision and the transformation of light adaptation;
- reduced vision with impaired areal orientation at night.
Sometimes problems with the contemplation of blue and yellow colors are attached to this symptomatology.
Hemeralopia affects both men and women equally. But when women enter menopause and endocrine adjustments occur in the body, they have a slightly higher risk of night blindness. Interestingly, the natives of Australia have a natural increased vigilance, especially at night. Scientists have found that these people have visual acuity of up to 400%.
The peoples of the North also see better in the dark. This skill has been formed over the centuries, because there are very few sunny days in the North. That is why their eyes have adapted to such an environment "historically". In winter, when daylight hours become too short, the problem of hemeralopia worsens.
Why does night blindness develop?
Scientists have conducted many tests, with the help of which they found out that a violation of twilight vision cancause hypovitaminosis. Lack of vitamin A provokes a decrease in the secretion of the lacrimal glands, dryness of the conjunctiva, its thickening and redness, clouding of the cornea, and so on.
It is known that vitamin A takes part in the mechanisms of photoreception. With its lack, the retinal rods are destroyed, and it is their dysfunction that is the first sign of hemeralopia. This pathology is detected using electroretinography, dark adaptometry and scotometry.
Among the probable causes, doctors name hidden ailments of the body: anemia, general exhaustion, pregnancy or glaucoma. Sometimes this disease appears if a person had chickenpox or measles in childhood, it can also be associated with hereditary moments. Often the cause of its occurrence are diseases of the retina, liver, optic nerve, sunburn of the eyes, chronic alcoholism, exposure to toxins in the body. Basically, hemeralopia develops when there is a lack of vitamins PP, A and B2 in the human body. Congenital night blindness, as a rule, manifests itself in early adolescence or childhood.
Checking binocular vision
What is a binocular vision test? A violation of this vision can be suspected when, pouring boiling water from a teapot into a cup, you pour it past the container. An easy experiment can also help test this function. Vertically at the top at a distance of 30-50 cm from the face at eye level, you need to place the index finger of your left hand. Next, you need to try with the same finger, but already with the right hand, quicklyhit the end of the left, moving from top to bottom.
If this trick worked the first time, we can assume that the binocular vision is in order. If the finger passes further or closer, then a disorder of this vision can be suspected. If a person has divergent or convergent strabismus, then, naturally, he does not have vision of this kind.
Double vision is also a criterion for a disorder of binocular vision, more precisely synchronous, although if it is absent, this does not mean that there is binocular vision. Double vision appears in such cases:
- In paralytic strabismus caused by disturbances in the nerve apparatus that controls the activity of the oculomotor muscles.
- If one eye is out of position. This happens with a deliberate (artificial) displacement of the eyeball with a finger through the eyelid, with the progression of a dystrophic process in the fatty pad of the orbit near the eye, or with neoplasms.
You can confirm the existence of the vision we are considering as follows:
- The subject must look at a point in the distance.
- One eye should be lightly pressed through the lower eyelid with a finger up. Next, they trace what happens to the picture.
- If a person has full binocular vision, vertical double vision will appear at this moment. A single visual image forks, and the picture goes up.
- When the pressure on the eye stops, a single visual image should be restored again.
- If during the experiment there is no doubling and the picture is not transformed, then the nature of the visionmonocular. In this case, the eye that was not displaced works.
- If there is no double vision, but at the moment of eye displacement a single image shifts, then the nature of the vision is also monocular, and the eye that was displaced acts.
One more experiment can be done. To do this, the subject must look at some point in the distance. Let him cover one eye with his hand. If after that the fixed point moves, the nature of vision is monocular, and with open eyes only the one that was covered functions. If this point disappears, then the nature of vision with the same eye is also monocular, and the eye that was not covered does not see at all.
In order to have a visual depth perception and actually contemplate a three-dimensional picture, our brain must apply the visual data received from both eyes. If the vision of the two eyes differs significantly, the brain is forced to choose between these pictures.
As a result, the brain begins to ignore visual information that it cannot use to build a single image, since such a picture worsens the overall picture and creates additional "noise".
Binocular vision is important not only for long distances, but also for activities at medium or near distances. It can be, for example, needlework, reading, working on a PC, writing. A binocular disorder can lead to headaches, increased fatigue, deterioration in general condition, and even vomiting and nausea.
