What types of vision exist? 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 wonderful organ of the human body. Thanks to him, we distinguish between the volume and colors of the picture, see at night and day.
The eye is designed like a camera. Its lens and cornea, like a lens, refract and focus the rays of light. The retina lining the fundus acts as a receptive film. It consists of specific elements that perceive light - rods and cones. Consider the types of vision below.
Day vision
What is daytime vision? This is the mechanism of perception of light by the human visual system, functioning in conditions of relatively high illumination. Performed with cones with background brightness exceeding 10 cd / m², which corresponds to daylight conditions. Sticks do not work in this setting. This vision is also called photopic or cone-shaped.
Day vision from night vision differs in the following nuances:
- Low photosensitivity. Its format is almost a hundred times lower than with night vision. Cones in comparison with sticks have less light sensitivity.
- High resolution (visual acuity). This is achieved due to the fact that the density of the rods is much lower than the density of the cones.
- The ability to perceive colors. It is realized due to the fact that there are three types of cones on the retina. In this case, the cones of each species capture color from only one spectral region characteristic of this species.
Using day vision, a person receives a large share of visual data.
Evening vision
And what is twilight vision? This is a mechanism of contemplation of light by the human visual structure, working in conditions of illumination, buffer in relation to those in which day and night vision function. It is performed using synchronous cones and rods operating simultaneously with background brightness values ranging between 0.01 and 10 cd / m². This vision is also called mesopic.
G. Vyshecki and D. Judd, the illumination under which twilight vision works, is described as follows: “Twilight is a range of illumination extending from the illumination that the sky creates under the sun, which has decreased by more than two degrees per horizon, to the illumination that the moon produces in half phase, rising high into the clear sky. “Twilight vision also includes vision in a dimly lit room (for example, with candles).”
Since both rods and cones participate in the realization of evening vision, receptors of both types contribute to the formation of the spectral dependence of the light sensitivity of the eye.
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 sensitivity is also converted.
So, when the illumination is diminished, the sensitivity to red (long-wave) light decreases and increases to blue (short-wave). It follows that for twilight vision, in contrast to daytime and nighttime, 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 manifestation of such changes is the Purkinje effect.
Night vision
What other types of vision exist? Night vision is a mechanism of contemplation of light by the human visual structure, operating in relatively low light conditions. It is performed by means of sticks with a background brightness of less than 0.01 cd / m², which coincides with night lighting conditions.
The cones do not work in this situation, since there is not enough light power to excite them. This vision is also called wand or scotopic. Photopic and scotopic vision are significantly different from each other, as we discussed above.
Monocular vision
Many people ask themselves: “What is monocular vision?” With this vision, moving objects and objects that appear in the field of vision of a looking person are captured mainly with only one eye.
In normal situations, people with normal vision use binocular vision, that is, they evaluate visual information with two eyes. Monocular vision is usually measured in angular parameters.
It is known that birds have 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 bird's vision prevails over the visual acuity of four to five times.
The total field of view in birds reaches more than 300 ° (the field of view of each bird's eye is 150-170 °, which is 50 ° more than in humans). Mostly birds use lateral (lateral) and monocular vision (this is normal for them). Its general field is localized at about 70 °. But the eyes of the owls do not move at all, which is offset by the agility of the neck (approximately 270 °).
Binocular vision
You do not know what is binocular vision? This is the ability to clearly see a picture of an object simultaneously with two eyes. In this case, a person sees one picture that he is looking at. That is, this vision with both eyes, with a subconscious combination in the cerebral cortex (visual analyzer) of the drawings received by each eye into a single image.
In fact, binocular vision is a system that creates a three-dimensional image. It is also called stereoscopic. If it is not improved, a person can see only with his 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 strabismus will gradually develop.
Visual acuity
So, we have examined all types of vision. We continue to study the human visual system further. Many people ask, "Vision 1 - what does it mean?" Each of us, from early childhood, undergoes an examination by an optometrist. You can find yourself in the doctor’s office in connection with the appearance of various complaints or for the purpose of medical examination (preventive examination).
Those patients who contacted an optometrist should undergo a simple test, with which visual acuity will be detected. 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, distinguishable by the human eye. This indicator is normally 1 °. To identify visual acuity, specific tables are used. Usually they are painted with letters, hooks, signs and drawings. The most popular for the diagnosis of visual acuity in adults is the Sivtsev -Golovin table .
It consists of 12 lines on which letters are drawn. The letters on the top lines have the greatest parameters. To the bottom of the table, they gradually decrease. If the patient has 100% vision, that is, his visual acuity is 1.0, he can distinguish the top line from a distance of 50 m. To make out the lower letters, you will 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. To do this, you can use outdoor lighting devices, but it is better to place a poster in the Rota device, equipped with mirrored walls, with the help of which uniform lighting is provided.
The cabinet should also be sufficiently lit. Each eye is tested individually. The eye that is not involved in the study is covered with a palm or a special white shield.
Identification of normal vision
How is visual acuity determined? First, the patient should sit in a chair located five meters from the table. Diagnosis usually begins with the right eye, and then the doctor switches to the left. The doctor suggests that the subject name the letters located in line 10 in order. If the answers are correct, the doctor sets 100% vision, that is, 1.0. This indicator is considered normal.
If the patient reads the letters uncertainly or makes mistakes, the test is continued by 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 appropriate notes in the certificate or card. Usually they are presented as follows: Vis OD and Vis OS. These characters are decrypted very simply. The first indicator concerns the right eye, and the second - the left. If visual acuity is adequate on both sides, then the number 1.0 will be near these signs.
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 a decrease. As a result, the doctor will select an optical correction device for the patient - contact lenses or glasses.
Sometimes people can distinguish the 11th and 12th line. This skill correlates with a visual acuity rating of 1.5 and 2.
Decreased visual acuity
And what does vision mean minus 1? Probably, every person on Earth at least once in his life felt tired in his eyes, which instantly reflected in the 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 normal sleep.
Then you need to seek help from doctors who will make an accurate diagnosis and give recommendations for reconstructing lost vision. And so, you have passed all the tests in a reliable ophthalmological clinic, and the doctor told you that your vision is minus 1. Do not rush to deceive yourself or panic. Doctors believe that this is an initial stage myopia, ordinary people say that this is a weak myopia. So what is it? We will answer the question further.
What is eye refraction ?
What do the concepts of minus and plus mean? These are the standards for diopters - units in which eye refraction is measured. Refraction refers to the location of the eye relative to the retina. There are three types of refraction:
- Hypermetropia - the placement of focus behind the retina, that is, farsightedness. It is indicated by the word "plus".
- Emmetropia is vision without refraction disorders when the focus is placed on the retina. In this case, the refraction is 0.
- Myopia - the focus is in front of the retina, which causes distortion of visibility in the distance, blurry images 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:
- Strong myopia - up to -15 diopters.
- Average myopia is up to -6 diopters.
- Weak myopia - up to -3 diopters.
It is known that with a vision of -1 a person loses up to 10% of his vision. This norm is not critical, but everyone wants to be healthy. If you take care of your vision, you can reconstruct it to a state of emmetropia.
Twilight Vision Disorder
What is a twilight vision disorder? This ailment has been known to medicine since ancient times and was called hemeralopia. Doctors do not distinguish between its degrees (the disease is either there or it is not), but ophthalmologists are sure that the disorder of twilight vision significantly reduces the quality of life, which sometimes has fatal consequences.
Hemeralopia is also called night blindness. This visual disturbance 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 the following symptoms:
- narrowing of the fields of vision and transformation of light adaptation;
- decreased vision with disturbance of areal orientation at night.
Sometimes problems with the contemplation of blue and yellow are associated with this symptomatology.
Both men and women suffer from hemeralopia equally. But when women begin menopause and endocrine corrections occur in the body, they have a slightly higher risk of night blindness. Interestingly, Australian Aborigines have a natural increased vigilance, especially at night. Scientists have found that in these people visual acuity reaches 400%.
The peoples of the North see better in the dark. This skill has been formed for centuries, because in the North there are very few sunny days. That is why their eyes have adapted to such a situation “historically”. In winter, when daylight hours become too short, the problem of hemeralopia is exacerbated.
Why does night blindness develop?
Scientists have conducted many tests, with the help of which they found out that a violation of twilight vision can cause just hypovitaminosis. A 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.
Vitamin A is known to be involved in photoreception mechanisms. With its deficiency, the retina sticks are destroyed, and it is their dysfunction that is the first sign of hemeralopia. This pathology is detected using electroretinography, dark adaptometry and scotometry.
Doctors among the probable reasons call latent illnesses of the body: anemia, general exhaustion, pregnancy or glaucoma. Sometimes this disease appears if a person has had chickenpox or measles in childhood, and may be associated with hereditary moments. Often the cause of its occurrence is ailments of the retina, liver, optic nerve, sunburn, chronic alcoholism, exposure to the body of toxins. In general, hemeralopia develops when the human body has a deficiency of vitamins PP, A and B2. Congenital night blindness, as a rule, manifests itself in youthful early childhood or childhood.
Binocular vision test
And what is a binocular vision test? Violation of this vision can be suspected when, pouring boiling water from a kettle into a cup, you pour it past a container. An easy experiment can also help verify this feature. Vertically above at a distance of 30-50 cm from the face at eye level, you need to place the index finger of the left hand. Next, you need to try with the same finger, but of the right hand, to quickly get into the end of the left, moving from top to bottom.
If this trick was a success the first time, we can assume that binocular vision is in order. If the finger goes farther or closer, then a disorder of this vision can be suspected. If a person has divergent or convergent squint, then, naturally, he has no vision of this kind.
Doubling is also a criterion for the disorder of binocular vision, more precisely synchronous, although if it is absent, this does not mean that binocular vision exists. Doubling appears in such cases:
- With paralytic strabismus caused by disturbances in the nerve device, which controls the activity of the oculomotor muscles.
- If one eye is displaced from its usual position. This happens with the deliberate (artificial) displacement of the eyeball by the finger through the eyelid, with the progression of the dystrophic process in the fat pad of the orbit near the eye or with neoplasms.
Confirm the presence of the vision we are considering can be as follows:
- The test subject must look at a point in the distance.
- One eye should be lightly pressed through the lower eyelid with the finger pointing up. Next, they trace what happens to the picture.
- If a person has full binocular vision, then vertical ghosting will appear. The single image is bifurcated, and the picture goes up.
- When pressure on the eye ceases, a single visual image should be restored again.
- If during the experiment double vision is absent and the picture does not transform, then the nature of vision is monocular. In this case, the eye that has not been displaced works.
- If there is no double vision, but at the moment of displacement of the eye a single picture is shifted, then the nature of vision is also monocular, and the eye that has been displaced acts.
You can conduct another experiment. To do this, the subject must look at some point in the distance. Let him cover one eye with his palm. If after this the fixed point moves, the nature of the vision is monocular, and with open eyes only the one that covered is functioning. If this point disappears, then the nature of vision with the same eye is also monocular, and the eye, which was not covered, does not see at all.
In order to have a visual perception of the depth of space and really contemplate a three-dimensional picture, our brain must use visual data obtained 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 an additional “noise”.
Binocular vision is important not only for long distances, but also for activities in the middle distance or near. This can be, for example, needlework, reading, working for a PC, writing. A binocular disorder can lead to headaches, increased fatigue, poor general condition, and even vomiting and nausea.