Human vision. Types of vision: day, twilight and night. Monocular and binocular vision. Visual acuity. Differences in male and female vision

Anisometropia is a concept that characterizes different vision in the eyes. With a disease, the optical system of the body cannot refract the rays correctly, and each eye has a different optical power. With such a pathology, the task of selecting corrective optics becomes more complicated, so patients need to look for a special approach. If the problem is not corrected in time, a complication such as astigmatism may develop.

Why does it occur?

The causes of the development of the disease are divided into two groups:

• congenital;
• acquired.

More common are congenital forms of anisometropia, which are hereditary in nature. In infants, the disease is not outwardly manifested and initially has an asymptomatic course. But with age, the manifestations become brighter, and the disease progresses. The degree of development depends on the timeliness of the diagnosis and the correctness of the correction.

The causes of the acquired form of the disease are divided into 3 groups:

• cataract that progresses and cannot be treated;
• complication after surgical intervention;
• disturbance of accommodation in old age.

Acquired forms develop faster than congenital ones, which contributes to early diagnosis, staging correct diagnosis and taking corrective action. In most cases, the congenital form is genetic in nature, so they talk about the hereditary nature of the pathology. If it's time to start proper care behind the eyes and pick up corrective gymnastics, then the development of the disease can be slowed down or even stopped.

Separately, an idiopathic form of different vision in the eyes is distinguished, in which it is impossible to identify the causes of the pathology. Diagnosis can only be made after complete examination an ophthalmologist and a geneticist who will help rule out other causes. According to statistics, the idiopathic form is very rare.

How to understand?

The sensations of a person who has different vision depends on the degree of difference in the clarity of sight between the eyes. The classification of the difference in optical power is shown in the table:

With a low degree of difference, there are no symptoms.

Since the eyes of a patient diagnosed with anisometropia see differently, the organ of vision that has a higher optical power, takes over the function of vision. The other eye, in turn, ceases to function and eventually ceases to see. Patients are poorly oriented in the environment and are unable to clearly distinguish objects. Also, patients do not see well, the image is blurred, which makes them squint and strain their eyesight, so the eyes get tired, and the sharpness decreases.

Diagnostic methods

A doctor is consulted only when the loss of vision noticeably affects the patient's well-being. A person may not remember when and under what circumstances the discomfort began. It is important for the doctor to clarify the presence of such problems in the next of kin. The prognosis between the congenital and acquired form is different and, accordingly, the methods of correction may differ.

The ophthalmologist will prescribe examination methods, such as:

• Determination of acuity using tables for each eye separately and jointly.
• Perimetry - the study of the boundaries of the visual fields on both sides.
• Determination of the refractive power on the right and left using the skiascopy method and the establishment of the degree of anisometropia.
• Ophthalmoscopy and ophthalmometry - examination of the fundus and measurement of the curvature of the cornea.

When the question arises of what is the name of different vision in the eyes, the answer will be one: anisometropia. This pathological condition occurs when the optical system loses its ability to refract rays. That is, the visual organs with such a disease have different optical power. Anisometropia may be accompanied by the development of astigmatism. Of course, the disease is provoked by certain factors, and without proper treatment causes complications.

When a person is violated visual functions, effective methods of correction are selected. This refers to the use of glasses and lenses.

But if different vision is found in the eyes, corrective optics is not always able to help. It's all about the reasons due to which anisometropia occurs - a disease for which the presence of different vision in the eyes is just characteristic.

In order to form a correct and unblurred image, it is necessary to intersect in the focus of the retina parallel rays emanating from the object. If this process is disturbed, a decrease in visual acuity is observed.

When the difference in refractive power in the eyes is one or two diopters, binocular vision won't suffer much. But if the indicators differ significantly more, then the development of refractive anisometropia should be expected. Moreover, refraction in one eye can be observed normal, and in the other it will be abnormal. But, basically, the pathology affects both eyes.

It is advisable to eliminate anisometropia in time, otherwise the patient may face dangerous consequences:

• strabismus;
• amblyopia (when, due to inactivity of the eye, its visual functions are lost).

Causes and types of the disease

It is impossible to ignore the state when the visual apparatus is subjected to various lesions.

You should be aware that different vision in the eyes can have different reasons:

• congenital;
• acquired.

Usually, doctors diagnose a pathology of a congenital nature.

Acquired anisometropia becomes when:

1. Cataract progression is observed.
2. There are consequences of a negative nature after the surgical intervention on the organs of vision.

If we talk about hereditary predisposition, then in babies up to a year the disease is asymptomatic. With age, the symptoms become more pronounced. Manifestations will depend on the degree of the disease.

She happens:

• weak (the difference between the eyes is a maximum of 3 diopters);
• medium (the difference can reach six diopters);
• strong (over 6 diopters).

In addition, anisometropia occurs:

• refractive (characterized by the presence of the same length of the axis of the eyes and the difference in refraction);
• axial (respectively, there is a difference in the length of the axis, but refraction is not impaired);
• mixed (both the first and second parameters have differences).

If the degree is weak, the disorders are almost not felt. With the formation of pathology of the highest degree, a violation of binocular vision occurs. There is no clear image. It is difficult for the patient to navigate in space. Often visual loads provoke excessive eye fatigue.

In which eye there is a strong lesion, he, accordingly, suffers more. In other words, its activity will be suppressed by the brain. As a result - the development of amblyopia.

Another consequence is strabismus, which is provoked by a weakening of the rectus muscle of the affected eye and its deviation to the side.

Diagnostic methods and therapy

Making a diagnosis requires:

1. Visometry (tables are used to determine the level of sharpness).
2. Perimetry (due to a certain device, the boundaries of the visual fields are revealed).
3. Refractometry.
4. Skiascopy (with the help of a light beam and a mirror, the refractive power is determined).
5. Ophthalmoscopy (a doctor using an ophthalmoscope examines the bottom of the eye).
6. Ophthalmometry (the radius of curvature of the cornea is determined with an ophthalmometer).
7. The study of binocular vision (using a synoptophore, a four-point color test).

The way in which the pathology will be eliminated is determined by the level and type of refractive disorders. Usually, visual dysfunction is corrected with glasses or contact lenses. But this method is not suitable for every patient. It is necessary that the difference in refractive power is not more than 3 diopters.

The selection of lenses is carried out for each specific case separately. It is necessary to wear them correctly and periodically undergo an examination by an ophthalmologist, receiving the necessary consultations from him.

A patient who uses lenses may suffer from:

• epithelial edema;
• keratitis;
• damage to the cornea.

If a conservative methods turned out to be useless, the doctor decides to perform laser surgery. It is also prescribed to patients who have a high degree of illness. After surgery, a week or two should pass for improvement to become apparent.

Do not panic when anisometropia is diagnosed. With timely detection, the problem can be completely eliminated, especially if a mild degree of the disease is present.

Causes of different eyesight

Greetings, dear friends, readers of my blog! I often hear people complain that one eye sees worse than the other. What causes different vision in the eyes (anisometropia)? What is it connected with? And, most importantly, what needs to be done to prevent this from happening to you? I will try to answer these and other questions in my article.

Important Organs

The eyes are one of important organs person. After all, thanks to the eyes, we receive most of the information from the world around us. Despite this, often when vision deteriorates, we do not begin to worry. Some people think that visual impairment is due to age or overwork.

Indeed, visual impairment is not always associated with the disease. This can be facilitated by fatigue, lack of sleep, constant work at the computer and other reasons. And, indeed, sometimes in order to normalize vision, you just need to relax, do exercises for the eyes. Gymnastics can help improve vision and train eye muscles. But if, nevertheless, the exercises did not help, and the vision continues to fall, then you need to see a doctor.

What are the causes of different eyesight?

When people's eyesight falls, they try to correct it with the help of
glasses or lenses. But it happens that vision deteriorates in only one eye. Such symptoms can appear both in a child and in older people. When a person has unilateral visual impairment, his life becomes uncomfortable. Well, if the difference in vision is not very great. What if it's big? Varying visual acuity can lead to strain eye muscles, headaches and other problems.

The causes of different vision in the eyes can be both congenital and acquired. Most often, people have congenital (hereditary) anisometropia. So, for example, if a person in the family already had anisometropia, then most likely this disease can develop in the next generation. But it must be taken into account that in childhood it may not manifest itself at first, and in the future, it happens, it leads to bad consequences.

And it doesn’t matter at all which eye of the parents sees worse: this disease in a child can manifest itself in any eye.

One of the causes of visual impairment in children is huge pressure at school, watching TV for a long time, excessive hobby computer games. As a result, only one eye begins to see worse from excessive overvoltage. Most often this is preceded by headaches, severe fatigue, nervous tension. In adults, the cause may be a previous illness or surgery.

How do we feel it?

Images on the retina become different sizes due to asymmetrical projection. In such a situation, one eye usually captures the picture better than the other. Images become blurry, may merge. The perception of what is seen is distorted, it can double. The surrounding world is perceived as blurry and fuzzy. This can lead to the fact that a person is difficult to orient himself in space, he has a slow reaction to any external stimuli.

"Lazy" eye

In order to somehow compensate for this deformation, our brain reflexively, as it were, “turns off” the eye that sees poorly. After some time, he may completely stop seeing. In medicine, there is even a special term - "lazy eye" (amblyopia).

What to do?

Anisometropia is usually treated in two ways. The first is wearing telescopic glasses or corrective lenses. But I would like to emphasize that in no case should you choose glasses or lenses on your own without the advice of a doctor. On the contrary, this can only worsen the situation. In addition, this can lead to microtrauma of the cornea, and, as a result, to infection in the eye, inflammatory processes and edema.

Ophthalmologists confirm that with a disease such as anisometropia, it can be difficult to find a correction.

The second method is surgical. It is resorted to only in extreme cases, when all other methods do not work. Most often this happens at the stage of a chronic disease. The operation is done with a laser.

And only on prescription. This operation has some limitations and contraindications. So, for example, after surgical intervention you can’t put a lot of stress on your eyes, you need to try to exclude concussions and any injuries, because all this can again provoke a disease.

I note that in children amblyopia can be corrected quite well. But first you need to get rid of the cause of the drop in vision in the eye, and then make this eye work again. Often, for this, doctors advise using occlusion - that is, try to exclude the second, healthy, well-seeing eye from the visual process.

It is necessary to select treatment strictly individually. It all depends on the age of the person, the type of pathology and the stage of development of the disease.

The best treatment is exercise for the eyes!

One of the means of preventing anisometropia can be exercises for the eyes, reducing (or completely eliminating) watching TV, working on a computer, alternating mental and physical activity, walking on fresh air. Remember that any disease is easier to prevent than to cure!

I wish you, dear readers of my blog, good health, a keen eye and rich, bright colors! Let everything you see around you bring only joy and positive, which will subsequently lead to success! See you on my blog!

Farsightedness in children is a visual impairment when the child cannot clearly distinguish objects located near. In this case, "far" vision remains normal. Farsightedness is also called "hypermetropia" and is almost inextricably linked to astigmatism.

Description of the disease

farsightedness low degree, which develops in young children, is usually the norm, since such a period is characterized by the active maturation of the body, when eye structures are just beginning to form. Often, by the age of 4, the “defect” in question disappears on its own. If this does not happen, then appropriate treatment is prescribed.

Another thing is the reserve of farsightedness. If this margin is higher age norm, then the child constantly strains his eyes. If the margin is higher, then there is a high probability of developing myopia. For this reason, all pediatric ophthalmologists first of all pay attention to the stock of farsightedness.

Important: 6-7 years up to 10 years is the border between the norm and pathology. According to the opinions and opinions of experts, if after these years the child continues to experience hyperopia, myopia or astigmatism, then treatment is required, during which, as a rule, glasses are used. The need for such a gradation is due to the significant stress that the child's vision will be subjected to at school, which can provoke the rapid progression of the disease.

Physiological farsightedness in children from one to 10 years old has a value within 3 diopters. When large indicators are found at the first comprehensive examination which is held in one year old, early treatment is necessary to avoid numerous complications in the future.

Children's farsightedness - enough insidious disease, the signs of which seem completely harmless at first glance:

• rapid fatigue of the child;
• lack of normal school performance, which is expressed in poor grades;
• restless sleep;
• frequent whims;
• lack of focus.

When found at small child combination of these symptoms, you should seek medical advice. It should be borne in mind that a regular eye test will not be able to detect farsightedness, which is why it is advisable to seek help from a pediatric ophthalmologist who will help you choose the appropriate glasses.

Diagnosis of the stock of farsightedness will be possible by checking visual acuity during visual loads near and far from objects. Due timely diagnosis there is a high probability of preventing the occurrence of various complications in the form of strabismus or amblyopia, which is a lazy eye syndrome.

In the case of further progression of the disease, there is a violation of the outflow of intraocular fluid, which, in turn, can provoke glaucoma, which is typical for young patients.

Symptoms

Timely detection of children's farsightedness, myopia and astigmatism is hampered by the inability of the child to complain about poor eyesight. This is especially true for children under one year old. Then parents need to be more careful and pay attention to indirect signs. So, for example, the toys that the baby plays with can say a lot: if he prefers large objects, and small ones cause irritation in him, this is a reason to think.

In addition to the signs associated with vision, the following features in the behavior of the child can be observed:

• often rubs eyes;
• blinking frequently;
• increased irritability and capriciousness may alternate with isolation;
• high fatigue;
• pain in the head, having regular manifestations;
• general poor health;
• refusal of activities related to the implementation at close range.

Most common cause hyperopia, myopia and astigmatism in young children is a hereditary predisposition when there is a congenital pathology. However, the pathology may develop genetic reasons. So, its development is facilitated by the length of the eyeball less than normal or too flat the cornea, which makes the refractive power too weak. These factors can be combined.

Each age is characterized by its own norms of farsightedness and its reserve:

• six months to a year - 3 diopters. In the absence of pathology, this indicator independently decreases;
• 1-4 years - farsightedness should decrease to 2 diopters;
• 5-6 years - 1-1.5 diopters is considered the norm.

By the age of 7 and up to 10 years, farsightedness is transformed into normal vision.

A child can experience 3 degrees of farsightedness:

1. Weak. Values ​​reach 2 diopters. In the process of contraction of the ciliary muscle, the lens acquires a large bulge, and the focus of the radiation refraction falls directly on the retina, which makes the child's vision perfect: he sees well near and far. However, constant stress provokes frequent delivery of pain in the head, eye fatigue, neurosis and backlog in school.
2. Average. It is 2-5 diopters. With such values, the child sees well at a distance, but poorly at close range.
3. High. It is above 5 diopters. Vision is significantly reduced. Children have difficulty seeing objects near and far.

With the development of moderate and severe farsightedness, the functions of the cellular part of the cerebral cortex responsible for vision gradually decrease, since it is not able to identify a clear image, which causes the absence of full-fledged cellular development. Thus, there is a decrease in visual acuity, which is fraught with amblyopia.

The reasons

The main causes of farsightedness in young children are mainly associated with natural physiology, when a number of anatomical disorders in the structure of the eye are observed:

• short eye axis;
• insufficient curvature of the cornea;
• an incorrectly positioned lens or a change in its shape.

These facts strongly influence farsightedness in children. The reasons can also be associated with a hereditary predisposition or congenital pathology, as well as the peculiarities of the course of pregnancy:

• poor nutrition of a pregnant woman;
• constant or frequent stress;
• unfavorable environmental situation.

Prevention

Prevention of farsightedness in children consists in observing a number of simple rules:

1. Lighting mode

It is necessary to properly regulate visual loads. When reading or drawing, it is not recommended to use fluorescent lamps. Also, special attention should be paid to limited TV viewing or computer games: the child must maintain a sufficient distance from the screen and not watch too contrasting images.

2. Mode of visual and physical activity

A positive effect is achieved if you alternate watching TV with outdoor recreation. It is also necessary to remember about eye gymnastics.

3. Gymnastics

Gymnastic exercises for the eyes, according to the reviews of numerous mothers, are very useful for hyperopia, myopia and astigmatism. Exercises should be carried out after half an hour of visual stress. More than 10 are currently known effective exercises to correct farsightedness.

4. Complete nutrition

Proper nutrition plays a key role in eye health. It should be balanced and include proteins, vitamins and trace elements. It is also possible to use vitamins for the eyes.

Types of treatment

Treatment of farsightedness in children can be different and depend on the degree of development of the pathology:

1. Glasses or lenses

• children under school age and suffering from farsightedness are prescribed glasses with "plus" lenses. In this case, glasses are issued according to certain indications.
• children 7 years of age and older, up to 10 years of age who have average degree pathology, glasses are prescribed only for "myopic" work. In the presence of high degrees, there is a need for glasses or contact lenses designed for permanent wear;
• children with already developed vision, whose age exceeds 10 years, need special glasses that will allow them to achieve high visual acuity and a clear image of objects.

In older children age category Farsightedness, nearsightedness and astigmatism can be treated with contact lenses. However, points also remain relevant.

2. Surgery

Surgical correction of vision for farsightedness, myopia and astigmatism is applied after 18 years, since that is when it ends active growth eyes. Mainly used hardware treatment:

• laser stimulation of the ciliary muscle;
• electrical stimulation;
• color impulse therapy.

These correction methods are needed to eliminate spasms, reduce fatigue, and also train vision in strabismus.

Important: many doctors with the development of farsightedness, myopia and astigmatism allow surgery on the eyes of children after 10 years. However, according to the opinion of the famous pediatrician, Dr. Komarovsky, this age is critical, since there is a high probability of damage to vital eye structures.

Summary

Farsightedness, like myopia, as well as astigmatism, is not a sentence. Reviews show that the disease can be successfully treated in 8 out of 10 patients.

Prevention or correction of vision becomes possible through simple gymnastics for the eyes:

As you know, any gymnastics and physical exercises require pre-workout. In this case, the goal is to relax the muscles of the eyeball. To complete this exercise you need:

Exercise 2. Basic

Such gymnastics, according to reviews, will simultaneously get rid of farsightedness and contribute to the normal blood circulation of the eyes and cervical spine, problems with which arise in the case of prolonged work in a sitting position. So you need to do the following:

• in a sitting position, you need to look at the tip of the nose;
• nose in the air should draw imaginary numbers or lines;
• the eyes must follow him;
• The ideal exercise time is 10 minutes.

Here you need:

• place fingers at eye level;
• spread your fingers and try to see objects in front through them;
• slowly turn your head from side to side without spreading your fingers.

Gymnastics of this type will consolidate the effect of the main exercise.

As you can see, for the correction of farsightedness, as well as myopia and astigmatism, there are many gymnastics for the eyes. The only thing is that you need the desire and a little time.

Is farsightedness a plus or a minus?

With farsightedness, it is impossible to see the nearest objects, but distant objects are clearly visible. This is because the light flux is not focused strictly on the retina, but is collected behind it.

To correctly answer the question posed in the title, you need to know the principle of operation visual system and its possible problems.

The structure of the eye

The visual system is one of the most complex human body. Interacting with the cerebral cortex, the eyes convert light rays into visible images.

Each of the dozens of elements of the vision system performs a specific function.

Light reflected by objects hits the cornea. It focuses the incoming rays and refracts them. Through a chamber filled with a colorless liquid, light rays reach the iris, in the center of which the pupil is located. Only the central rays pass through its opening, and the rest are filtered out by the pigment cells of the iris.

The stream of rays hits the lens. This is a lens that focuses light rays more accurately. Through the vitreous body, the rays penetrate the retina, which is a kind of screen for projecting an image upside down. The object is displayed directly in the macula - the center of the retina responsible for visual acuity.

Processing the information flow, retinal cells encode it into electromagnetic impulses, much like when creating a digital photo. Through the optic nerve, impulses act on the part of the brain in which the process of perceiving the picture is completed.

The opaque membrane that covers the outside of the eyeball is called the sclera. It does not participate in the processing of the flow of light rays.

Farsightedness and myopia problems

Pathologies of the visual system can appear regardless of age or are congenital. Some diseases arise in connection with impaired functioning of the optic nerve or retina. Most diseases are caused pathological changes refractive characteristics, in which the outlines of objects lose their clarity and are no longer distinguished by the eye.

"Cons" and "pluses" indicate the degree of refraction of light beams - at an increased angle or insufficiently.

With myopia (or myopia), a person does not distinguish objects distant from the eyes, but his near vision is in order. You can safely sew and read, but not see the name of the street across the road. Myopia not only reduces visual acuity, but also causes fatigue eye, burning sensation and headache.

Serious vision pathologies do not allow to conduct full image life. However, it is more difficult to live with myopia than to put up with farsightedness. But there is one good news for these pathologies: they are corrected by modern surgical methods and the laser method.

Does "minus" or "plus" correct farsightedness?

An anomaly in refractive power (scientifically called refraction) needs to be corrected with suitable lenses. With the help of "positive" lenses, refraction occurs so that the light rays are focused as expected, directly on the retina. The required curvature of the lens is chosen depending on the degree of hypermetropia.

So, the answer to the question is obvious: with farsightedness, “positive” glasses are needed.

Especially the decrease in vision manifests itself after 30 years, when there is a weakening of accommodation - the ability of the eye to adjust to focus when shifting the gaze from a distant to a near object. About 10 percent of the population suffers from hypermetropia.

The values ​​of the degree of farsightedness required for the selection of glasses:

Thus, "plus" means the number of diopters needed to correct vision. Converging lenses matched to the patient's glasses should partially replenish the functionality of the lens. They are called "positive", therefore, they speak of farsightedness as a "plus". Myopia uses "minus" glasses that scatter light.

To alleviate the condition with pathological farsightedness, contact lenses or glasses will help, which are recommended to be selected in the specialist's office, and not in a street tent.

After age 40, it usually develops age-related farsightedness, which in medical reference books called presbyopia. It is caused by the loss of elasticity of the lens, which weakens the ability of the eye to change focus while looking at a distant object from a near one.

Signs, causes and symptoms of farsightedness

The main sign of hypermetropia is poor visibility at close range. But distant objects are considered in detail. Over time, the lens loses its accommodative properties, and pathology develops.

Farsightedness symptoms include:

• constant fatigue of the visual organs during work or reading;
• deterioration in far or near vision;
• increased inflammation of the eyes and conjunctivitis;
• strabismus in a small child.

The disease develops when the eyeball is too short, or the cornea is flattened. For these reasons, the light flux cannot be refracted sufficiently to focus on the retina. Therefore the image visible object focuses behind the retina, and not on it, as it should be normal.

Newborn children have hypermetropia, as they have a reduced eyeball on the so-called front-rear axle. When the baby grows up, vision becomes normal. Otherwise, there is congenital pathology, which is expressed in the insufficient power of refraction of light by the cornea or lens.

In older people, the lens can no longer change its curvature smoothly, and therefore, when reading, they are forced to move the book away for some distance.

Farsightedness occurs for the following reasons:

1. Heredity. If the eyeball is shortened, then the longitudinal axis of the eye is also shortened.
2. Age. The refractive properties of the eye are insufficient for full functioning.

Sometimes these reasons can be combined.

Diagnosis and treatment of farsightedness

An appeal to an ophthalmologist is necessary at the first sign of a decrease in visual acuity. Diagnostics will take place approximately in the following sequence:

1. The level of vision changes is examined using the tables of Orlova, Golovin or Sivtsev.
2. The fundus is checked using a special mirror or ultrasound.

To avoid vision problems, you need:

• choose the right lighting;
• by using special gymnastics according to the Bates method, train the muscles of the eyes;
• correctly correct vision;
• exercise and eat well.

The main medical methods for the treatment of farsightedness:

1. Wearing glasses and lenses.
2. Correction with a laser beam (for patients over 18 years old).
3. Lens implantation through surgery.

The goal of treating the disease is to restore the ability of the eyes to focus the visible image on the retina itself.

Practice shows that in most people in the period from forty to fifty years, farsightedness occurs: the lens thickens and provokes defocusing of vision. But the development of the disease can be stopped by correcting the course of the abnormal process.

Age-related farsightedness used to be considered incurable disease and corrected only by wearing "plus" glasses. Later they began to produce surgical operations by implanting a special lens, with the help of which near and far vision is restored. A multifocal lens is placed in place of the removed lens through a very small incision. Within some fifteen minutes after the operation, the ability of the eyes to distinguish near objects is noticeably restored.

Using microsurgery methods that were not available before, it is possible to restore vision completely.

Today the most common following methods therapy for farsightedness:

Description

Hyperopia, progressing at a rapid pace, is corrected by implantation artificial lens or an additional actual lens. These procedures are considered safe for health, since the risk is minimal. But many patients believe that a one percent risk is a strong argument against laser correction and continue to wear glasses or corrective lenses.

Non-traditional treatment of farsightedness

Traditional medicine recipes for stimulation visual apparatus It is recommended to be treated with an infusion of marsh calamus herb. Lemongrass grass should also help in solving this problem.

An unconventional method for correcting vision problems was developed by Dr. Norbekov. It includes simple sets of exercises for the eyes, articular gymnastics, control of one's own posture and positive emotions.

Video - Presbyopia: age-related farsightedness

human vision(visual perception) - the ability of a person to perceive information by converting the energy of electromagnetic radiation of the light range, carried out by the visual system.

Light signal processing begins on the retina, then photoreceptors are excited, visual information is transmitted and transformed in neural layers with the formation of a visual image in the occipital lobe of the cerebral cortex.

According to various sources, from 80% to more than 90% of information a person receives through vision. [ ]

Encyclopedic YouTube

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✪ Human vision

✪ Human body. Eye (Oculus). Vision.

✪ 10 MISSIONS ABOUT VISION

✪ Vision recovery Treatment film Vision improves immediately after watching this film

✪ RETURN VISION by restoring elasticity to the EYE MUSCLES / acupressure and eye exercises

Subtitles

General information

because of a large number stages of the visual perception process individual characteristics are considered from the point of view of different sciences - optics (including biophysics), psychology, physiology, chemistry (biochemistry). At each stage of perception, distortions, errors, and failures occur, but the human brain processes the information received and makes the necessary adjustments. These processes are of an unconscious nature and are implemented in a multi-level autonomous correction of distortions. Thus, spherical and chromatic aberrations, blind spot effects are eliminated, color correction is carried out, a stereoscopic image is formed, etc. In cases where subconscious information processing is insufficient or excessive, optical illusions arise.

Spectral sensitivity of the eye

In the process of evolution, light-sensitive receptors have adapted to solar radiation reaching the Earth's surface and propagating well in the water of the seas and oceans. The Earth's atmosphere has a significant transparency window only in the wavelength range of 300-1500 nm. In the ultraviolet region, transparency is limited by the absorption of ultraviolet by the ozone layer and water, and in the infrared region, by absorption by water. Therefore, the relatively narrow visible region of the spectrum accounts for more than 40% of the solar radiation energy near the surface.

The human eye is sensitive to electromagnetic radiation in the wavelength range of 400-750 nm ( visible radiation) . The retina of the eye is also sensitive to shorter wavelength radiation, but the sensitivity of the eye in this region of the spectrum is limited by the low transparency of the lens that protects the retina from destructive action ultraviolet.

Physiology of human vision

color vision

The human eye contains two types of light-sensitive cells (photoreceptors): highly sensitive rods and less sensitive cones. The rods function in relatively low light conditions and are responsible for the operation of the night vision mechanism, however, they provide only a color-neutral perception of reality, limited by the participation of white, gray and black colors. Cones work at higher light levels than rods. They are responsible for the mechanism of daytime vision, distinctive feature which is the ability to provide color vision.

Light with different wavelengths stimulates different types of cones differently. For example, yellow-green light stimulates L and M-type cones equally, but stimulates S-type cones to a lesser degree. Red light stimulates L-type cones much more strongly than M-type cones, and S-type cones do not stimulate almost at all; green-blue light stimulates M-type receptors more than L-type, and S-type receptors a little more; light with this wavelength also stimulates the rods most strongly. Violet light stimulates S-type cones almost exclusively. The brain perceives combined information from different receptors, which provides a different perception of light with different wavelengths.

Per color vision humans and monkeys respond with genes encoding light-sensitive opsin proteins. According to supporters of the three-component theory, the presence of three different proteins that respond to different lengths waves, is sufficient for color perception. Most mammals have only two of these genes, so they have two-color vision. In the event that a person has two proteins encoded by different genes that are too similar, or one of the proteins is not synthesized, color blindness develops. N. N. Miklukho-Maclay established that the Papuans of New Guinea, living in the thick of the green jungle, lack the ability to distinguish green color.

The red light-sensitive opsin is encoded in humans by the OPN1LW gene.

Other human opsins encode the OPN1MW, OPN1MW2, and OPN1SW genes, the first two of which encode proteins that are sensitive to light at medium wavelengths, and the third is responsible for the opsin that is sensitive to the short-wavelength part of the spectrum.

The need for three types of opsins for color vision has recently been proven in experiments on squirrel monkeys (saimiri), males of which were cured of congenital color blindness by introducing the human opsin gene OPN1LW into their retinas. This work (along with similar experiments in mice) showed that the mature brain is able to adapt to the new sensory capabilities of the eye.

The OPN1LW gene, which encodes the pigment responsible for the perception of red, is highly polymorphic (85 alleles were found in a sample of 256 people in a recent work by Virrelli and Tishkov), and about 10% of women who have two different alleles of this gene actually have an additional type color receptors and some degree of four-component color vision. Variations in the OPN1MW gene, which encodes the "yellow-green" pigment, are rare and do not affect the spectral sensitivity of the receptors.

The OPN1LW gene and genes responsible for the perception of light from medium length waves are located in tandem on the X chromosome, and non-homologous recombination or gene conversion often occurs between them. In this case, gene fusion or an increase in the number of their copies in the chromosome can occur. Defects in the OPN1LW gene are the cause of partial color blindness, protanopia.

The three-component theory of color vision was first expressed in 1756 by M. V. Lomonosov, when he wrote "about the three matters of the bottom of the eye." A hundred years later, it was developed by the German scientist G. Helmholtz, who does not mention the famous work of Lomonosov "On the Origin of Light", although it was published and briefly presented in German.

In parallel, there was an opponent color theory of Ewald Gering. It was developed by David Hubel and Thorsten Wiesel. They received the 1981 Nobel Prize for their discovery.

They suggested that the brain does not receive information about red (R), green (G) and blue (B) colors at all (Jung-Helmholtz color theory). The brain receives information about the difference in brightness - about the difference between the brightness of white (Y max) and black (Y min), about the difference between green and red colors (G - R), about the difference between blue and yellow colors (B - yellow), and yellow ( yellow = R + G) is the sum of red and green flowers, where R, G and B are the brightness of the color components - red, R, green, G, and blue, B.

We have a system of equations - K h-b \u003d Y max - Y min; K gr \u003d G - R; K brg = B - R - G, where K b-w, K gr , K brg - functions of the white balance coefficients for any lighting. In practice, this is expressed in the fact that people perceive the color of objects in the same way when different sources lighting (color adaptation). Opponent theory generally better explains the fact that people perceive the color of objects in the same way under extremely different light sources, including different color light sources in the same scene.

These two theories are not entirely consistent with each other. But despite this, it is still assumed that the three-stimulus theory operates at the level of the retina, however, the information is processed and the brain receives data that is already consistent with the opponent's theory.

Binocular and stereoscopic vision

Maximum pupil changes for healthy person- from 1.8 mm to 7.5 mm, which corresponds to a change in pupil area by 17 times. However, the actual retinal illuminance range is limited to 10:1, not 17:1, as would be expected based on changes in pupil area. In fact, the illuminance of the retina is proportional to the product of the pupil area, the brightness of the object and the transmittance of the eye media.

The contribution of the pupil to the adjustment of the sensitivity of the eye is extremely insignificant. The entire range of brightness that our visual mechanism is capable of perceiving is enormous: from 10 −6 cd m −2 for a fully dark adapted eye to 10 6 cd m −2 for a fully light adapted eye. The mechanism of such a wide range of sensitivity lies in the decomposition and restoration of photosensitive pigments in the photoreceptors of the retina - cones and rods.

The sensitivity of the eye depends on the completeness of adaptation, on the intensity of the light source, the wavelength and angular dimensions of the source, as well as on the duration of the stimulus. The sensitivity of the eye decreases with age due to the deterioration of the optical properties of the sclera and pupil, as well as the receptor link of perception.

Maximum sensitivity in daylight ( daytime vision) lies at 555-556 nm, and with a weak evening/night ( twilight vision/night vision) shifts towards the violet edge of the visible spectrum and is located at 510 nm (it fluctuates within 500-560 nm during the day). This is explained (the dependence of a person’s vision on the lighting conditions when he perceives multi-colored objects, the ratio of their apparent brightness - the Purkinje effect) by two types of light-sensitive elements of the eye - in bright light, vision is carried out mainly by cones, and in weak light, only sticks are preferably used.

Visual acuity

Ability various people to see larger or smaller details of an object from the same distance with the same shape of the eyeball and the same refractive power of the diopter eye system is due to the difference in the distance between the sensitive elements of the retina and is called visual acuity.

Visual acuity is the ability of the eye to perceive separately two points located at some distance from each other ( detail, fine grain, resolution). The measure of visual acuity is the angle of view, that is, the angle formed by the rays emanating from the edges of the object in question (or from two points A and B) to the nodal point ( K) eyes. Visual acuity is inversely proportional to the visual angle, that is, the smaller it is, the higher the visual acuity. Normally, the human eye is capable of separately perceive objects, the angular distance between which is not less than 1 ′ (1 minute).

Visual acuity is one of the most important functions of vision. Human visual acuity is limited by its structure. The human eye, unlike the eyes of cephalopods, for example, is a reversed organ, that is, light-sensitive cells are under a layer of nerves and blood vessels.

Visual acuity depends on the size of the cones in the region. yellow spot, retina, as well as a number of factors: refraction of the eye, pupil width, transparency of the cornea, lens (and its elasticity), vitreous body (which make up the light refracting apparatus), the state of the retina and optic nerve, age.

The inversely proportional value of visual acuity and / or light sensitivity is called the resolution of the simple (naked) eye ( resolving power).

line of sight

Peripheral vision (field of view) - determine the boundaries of the field of view when projecting them onto a spherical surface (using the perimeter). The field of view is the space perceived by the eye when the gaze is fixed. The visual field is a function of the peripheral parts of the retina; its condition largely determines the ability of a person to freely navigate in space.

Visual field changes are caused by organic and/or functional diseases visual analyzer: retina, optic nerve, visual pathway, CNS. Violations of the visual field are manifested either by a narrowing of its boundaries (expressed in degrees or linear values), or by the loss of its individual sections (hemianopsia), the appearance of scotoma.

binocularity

Looking at an object with both eyes, we see it only when the axes of vision of the eyes form such an angle of convergence (convergence) at which symmetrical clear images on the retinas are obtained in certain corresponding places of the sensitive yellow spot (fovea centralis). Thanks to this binocular vision, we not only judge the relative position and distance of objects, but also perceive relief and volume.

The main characteristics of binocular vision are the presence of elementary binocular, deep and stereoscopic vision, stereo vision acuity and fusional reserves.

The presence of elementary binocular vision is checked by dividing some image into fragments, some of which are presented to the left, and some to the right eye. An observer has elementary binocular vision if he is able to compose a single original image from fragments.

The presence of deep vision is checked by presenting silhouette, and stereoscopic - random dot stereograms, which should cause the observer to have a specific experience of depth, which differs from the impression of spatiality based on monocular features.

The sharpness of stereo vision is the reciprocal of the threshold of stereoscopic perception. The threshold of stereoscopic perception is the minimum detectable disparity (angular displacement) between parts of a stereogram. To measure it, the principle is used, which is as follows. Three pairs of figures are presented separately to the left and right eyes of the observer. In one of the pairs, the positions of the figures coincide, in the other two, one of the figures is shifted horizontally by a certain distance. The subject is asked to indicate the figures arranged in ascending order of relative distance. If the figures are in the correct sequence, then the level of the test increases (the disparity decreases), if not, the disparity increases.

Fusion reserves - conditions under which there is a possibility of motor fusion of the stereogram. Fusion reserves are determined by the maximum disparity between parts of a stereogram, at which it is still perceived as a three-dimensional image. To measure fusion reserves, the principle opposite to that used in the study of stereovision acuity is used. For example, the subject is asked to combine two vertical stripes into one image, one of which is visible to the left and the other to the right eye. At the same time, the experimenter begins to slowly separate the bands, first with convergent and then with divergent disparity. The image begins to split in two at the disparity value , which characterizes the observer's fusion reserve.

Binocularity can be impaired in strabismus and some other eye diseases. At severe fatigue there may be temporary strabismus caused by the turning off of the driven eye.

Contrast sensitivity

Contrast sensitivity - the ability of a person to see objects that differ slightly in brightness from the background. Contrast sensitivity is evaluated using sinusoidal gratings. An increase in the contrast sensitivity threshold can be a sign of a number of eye diseases, and therefore its study can be used in diagnosis.

Vision adaptation

The above properties of vision are closely related to the ability of the eye to adapt. Adaptation of the eye - adaptation of vision to different conditions lighting. Adaptation occurs to changes in illumination (distinguish between adaptation to light and darkness), color characteristics of lighting (the ability to perceive white objects as white even with a significant change in the spectrum of incident light).

Adaptation to light occurs quickly and ends within 5 minutes, adaptation of the eye to darkness is a slower process. The minimum brightness that causes the sensation of light determines the light sensitivity of the eye. The latter increases rapidly in the first 30 minutes. stay in the dark, its increase practically ends in 50-60 minutes. The adaptation of the eye to darkness is studied using special devices - adaptometers.

A decrease in the adaptation of the eye to darkness is observed in some eye (retinitis pigmentosa, glaucoma) and general (A-avitaminosis) diseases.

Adaptation is also manifested in the ability of vision to partially compensate for defects in the visual apparatus itself (optical defects of the lens, retinal defects, scotomas, etc.)

Processing of visual information

The phenomenon of visual sensations that are not accompanied by the processing of visual information is called the phenomenon of pseudo-blindness.

visual disturbances

lens defects

The most massive drawback is the discrepancy between the optical power of the eye and its length, leading to a deterioration in the visibility of close or distant objects.

farsightedness

Farsightedness is called such an anomaly of refraction, in which the rays of light entering the eye are focused not on the retina, but behind it. In light forms of the eye with a good margin of accommodation, it compensates for the visual deficiency by increasing the curvature of the lens with the ciliary muscle.

With stronger farsightedness (3 diopters and above), vision is poor not only near, but also far, and the eye is not able to compensate for the defect on its own. Farsightedness is usually congenital and does not progress (usually decreases by school age).

With farsightedness, glasses are prescribed for reading or constant wear. For glasses, converging lenses are selected (they move the focus forward to the retina), with the use of which the patient's vision becomes the best.

Presbyopia, or age-related farsightedness, is somewhat different from farsightedness. Presbyopia develops due to the loss of elasticity of the lens (which is a normal result of its development). This process starts at school age, but a person usually notices a decrease in near vision after the age of 40. (Although at 10 years old, emmetropic children can read at a distance of 7 cm, at 20 years old - already at least 10 cm, and at 30 - 14 cm, and so on.) Senile farsightedness develops gradually, and by the age of 65-70 a person already completely loses the ability to accommodate, the development of presbyopia is completed.

Myopia

Myopia is an anomaly of refraction of the eye, in which the focus moves forward, and an already defocused image falls on the retina. With myopia, the further point of clear vision lies within 5 meters (normally it lies in infinity). Myopia is false (when, due to overstrain of the ciliary muscle, its spasm occurs, as a result of which the curvature of the lens remains too large for distance vision) and true (when the eyeball increases in the anterior-posterior axis). In mild cases, distant objects are blurred while near objects remain sharp (the farthest point of clear vision lies quite far from the eyes). In cases of high myopia, significant reduction vision. Starting at about -4 diopters, a person needs glasses for both distance and close range, otherwise the object in question must be brought very close to the eyes. However, precisely because a near-sighted person brings an object close to his eyes for good image sharpness, he is able to distinguish finer details of this object than a person with normal vision.

AT adolescence myopia often progresses (the eyes are constantly straining to work near, which is why the eye grows in length compensatory). The progression of myopia sometimes takes a malignant form, in which vision drops by 2-3 diopters per year, sclera stretching is observed, dystrophic changes retina. AT severe cases there is a danger of detachment of the overstretched retina during physical exertion or a sudden impact. Stopping the progression of myopia usually occurs by the age of 25-30, when the body stops growing. With rapid progression, vision by that time drops to -25 diopters and below, very much crippling the eyes and sharply disrupting the quality of far and near vision (all that a person sees is blurry outlines without any detailed vision), and such deviations are very difficult to fully correct by optics: thick spectacle glasses create strong distortions and reduce objects visually, which is why a person does not see well enough even with glasses. In such cases, the best effect can be achieved with the help of contact correction.

Despite the fact that hundreds of scientific and medical works have been devoted to the issue of stopping the progression of myopia, there is still no evidence of the effectiveness of any method of treating progressive myopia, including surgery (scleroplasty). There is evidence for a small but statistically significant reduction in the rate of increase in myopia in children with eye drops atropine and (absent in Russia) eye gel pirenzipine [ ] .

With myopia, they often resort to laser correction vision (impact on the cornea using laser beam to reduce its curvature). This method of correction is not completely safe, but in most cases it is possible to achieve a significant improvement in vision after surgery.

Myopia and farsightedness defects can be overcome with glasses, contact lenses, or rehabilitation courses of gymnastics.

Astigmatism

Astigmatism is a defect in the optics of the eye, caused by an irregular shape of the cornea and (or) the lens. In all people, the shape of the cornea and lens differs from the ideal body of rotation (that is, all people have astigmatism of one degree or another). In severe cases, the stretching along one of the axes can be very strong, in addition, the cornea may have curvature defects caused by other causes (wounds, infectious diseases, etc.). With astigmatism, light rays are refracted from different strength in different meridians, as a result of which the image is distorted and sometimes fuzzy. In severe cases, the distortion is so strong that it significantly reduces the quality of vision.

Astigmatism is easy to diagnose by examining with one eye a sheet of paper with dark parallel lines - by rotating such a sheet, the astigmatist will notice that the dark lines are either blurred or become clearer. Most people have congenital astigmatism up to 0.5 diopters, which does not bring discomfort.

This defect is compensated for by spectacles with cylindrical lenses having different horizontal and vertical curvature and contact lenses (hard or soft toric), as well as spectacle lenses with different optical power in different meridians.

retinal defects

color blindness

If the perception of one of the three primary colors falls out or is weakened in the retina, then the person does not perceive any color. There are "color-blind" for red, green and blue-violet. Rarely is paired, or even complete color blindness. More often there are people who cannot distinguish red from green. Such a lack of vision was called color blindness - after the English scientist D. Dalton, who himself suffered from such a color vision disorder and first described it.

Color blindness is incurable, inherited (linked to the X chromosome). Sometimes it occurs after some eye and nervous diseases.

Color-blind people are not allowed to work related to driving vehicles on public roads. Good color perception is very important for sailors, pilots, chemists, mineralogists, artists, therefore, for some professions, color vision is checked using special tables.

scotoma

Scottoma (gr. skotos- darkness) - a spot-like defect in the field of vision of the eye, caused by a disease in the retina, diseases of the optic nerve, glaucoma. These are areas (within the field of view) in which vision is significantly impaired or absent. Sometimes a blind spot is called a scotoma - an area on the retinacorresponding to the optic nerve head (the so-called physiological scotoma).

Absolute scotoma (eng. absolute scotomata) - an area in which there is no vision. Relative scotoma (eng. relative scotoma) - an area in which vision is significantly reduced.

You can assume the presence of scotoma yourself by conducting a study using the Amsler test.

Other defects

• Day blindness - a sharp decline vision in conditions of excessive illumination, insufficient adaptation to bright light. Typical reasons day blindness are cone degeneration, achromatopsia, and taking the anticonvulsant drug trimethadione.
• Nyctalopia A disorder that makes it difficult or impossible to see in low light conditions. The cause of nyctalopia is beriberi or hypovitaminosis, as well as. Symptomatic nyctalopia is observed in diseases of the retina and optic nerve.

Ways to correct visual impairments

The desire to improve vision is associated with an attempt to overcome both visual defects and its natural limitations.