Methods for studying central vision. Peripheral and central vision: features

Central vision– the central area of ​​visible space. The main purpose of this function is the perception of small objects or their details. This vision is the highest and is characterized by the concept of “visual acuity”. Central vision is provided by the cones of the retina, which occupy the fovea in the macula area.

As you move away from the center, visual acuity decreases sharply. This is explained by changes in the density of neuroelements and the characteristics of impulse transmission. The impulse from each cone of the fovea passes through separate nerve fibers through all parts of the visual pathway.

Visual acuity (Visus) – the ability of the eye to distinguish two points separately with a minimum distance between them, which depends on the structural features of the optical system and the light-receiving apparatus of the eye.

Points A and B will be perceived separately if their retinal images b and a are separated by one unexcited cone c. This creates a minimum light gap between two separately lying cones. The diameter of the cone c determines the value of maximum visual acuity. The smaller the diameter of the cones, the higher the visual acuity. The image of two points, if they fall on two adjacent cones, will merge and will be perceived as a short line.

Angle of view– the angle formed by the extreme points of the object under consideration (A and B) and the nodal point of the eye (O). Nodal point- a point in the optical system through which rays pass without refraction (located at the posterior pole of the lens). The eye sees two points separately only if their image on the retina is not less than an arc of 1’, i.e. the visual angle must be at least one minute.

Methods for studying central vision:

1) Using special Golovin-Sivtsev tables– optotypes – contain 12 rows of specially selected characters (numbers, letters, open rings, pictures) of different sizes. The creation of optotypes is based on an international agreement on the size of their details, distinguishable at a visual angle of 1 minute, while the entire optotype corresponds to a visual angle of 5 minutes. The table is designed to study visual acuity from a distance of 5 m. At this distance, the details of the optotypes of the tenth row are visible at a viewing angle of 1', therefore the visual acuity of the person distinguishing the optotypes of this row will be equal to 1. If the visual acuity is different, then determine in which row of the table the subject distinguishes the signs . In this case, visual acuity is calculated According to the Snellen formula: Visus = d / D, where d is the distance from which the study is carried out, D is the distance from which the normal eye distinguishes the signs of this row (indicated in each row to the left of the optotypes). For example, a subject reads the first row from a distance of 5 m, a normal eye distinguishes the signs of this row from 50 m, which means Visus = 5/50 = 0.1. The table is constructed using the decimal system: when reading each subsequent line, visual acuity increases by 0.1 (except for the last two lines).

If the visual acuity of the subject is less than 0.1, then the distance from which he casts the optotypes of the first row is determined, and then visual acuity is calculated using the Snellen formula. If the visual acuity of the subject is below 0.005, then to characterize it, indicate at what distance he is counting fingers. For example, Visus = counting fingers by 10 cm.

When vision is so poor that the eye does not distinguish objects, but perceives only light, visual acuity is considered equal to light perception: Visus = 1/¥ with correct (proectia lucis certa) or incorrect (proectia lucis incerta) light projection. Light projection is determined by directing a beam of light from an ophthalmoscope into the eye from different sides.

In the absence of light perception, visual acuity is zero (Visus = 0) and the eye is considered blind.

2) An objective method for determining visual acuity based on optokinetic nystagmus– using special devices, the subject is shown moving objects in the form of stripes or a chessboard. The smallest object size that causes involuntary nystagmus corresponds to the visual acuity of the eye being examined.

In infants, visual acuity is determined approximately by determining whether the child's eye fixes large and bright objects or by using objective methods.

Visual acuity is a parameter that determines the ability of the visual organ to recognize two points located at a minimum distance (until they merge together). This function is the main characteristic of central vision and depends on the characteristics of the optical properties of the eye and its ability to perceive light. The unit of measurement for this parameter is considered to be 1 unit, which is the norm.

The highest visual acuity is observed in the area of ​​the central fovea of ​​the retina; as you move away from it, this parameter decreases significantly.

Visual acuity is poorly developed in children in the first months of life, but over time (by 4-5 years) it significantly increases (indicator 0.8-1). The maximum value is reached by adolescence, after which this function decreases significantly (by 50-60 years).

Methods for assessing central visual acuity

Visual acuity is assessed. Visual acuity is determined using special tables that show icons (letters and circles for adults, drawings for children) of different sizes. The most popular are the tables of Sivtsev-Golovin, Frolov, Orlova, etc.

Research methodology

The subject is located at a distance of five meters from the table. First, the right eye is examined (the patient closes the left with a special shutter), then the left. On the Sivtsev-Golovin table there are twelve lines with letters or symbols, the largest ones on top, the smallest ones on the bottom. Normally (with a vision indicator of 1 unit), the patient should see the tenth line from a distance of 5 meters.

If the subject does not see even the top line from 5 meters, he must be gradually brought closer to the table until he sees the largest symbols. In such cases, visual acuity is determined by the formula:

Where V is visual acuity, d is the distance from which the patient can distinguish the table icons, D is the distance from which a person with normal vision sees this line

Objective methods

The method described above is a subjective method for determining visual acuity, because based on the testimony of the subject, who in some cases may be interested in the results of the examination (for example, conscripts).

There are also objective methods for determining visual acuity; the most popular is based on a phenomenon called optokinetic nystagmus. The subject is shown moving objects of various sizes using special devices. The minimum size of an object to which involuntary eye movements (nystagmus) is determined corresponds to a certain indicator of central visual acuity.

The eyes allow you to see not only those objects that are directly in front of you, but also to the sides. This is called peripheral vision.

Human central and peripheral vision allows us to see certain areas of space, which provide visual fields. Fields are characterized by the viewing angle when the eyes are stationary. Depending on the position of the object in relation to the retina, different colors are perceived from different angles.

Central vision is that which is provided by the central part of the retina and allows you to see small elements. Visual acuity depends specifically on the functioning of this part of the retina.

Peripheral vision is not only those objects on which the eye on the side of it is focused, but also blurred neighboring objects, moving objects, etc. around this object. This is why peripheral vision is so important: it ensures a person’s orientation in space, his ability to navigate the environment.

Peripheral vision is better developed in women, and central vision in men. The angle of peripheral vision in humans is approximately 180 0 when viewed in a horizontal plane and about 130 0 in a vertical plane.

Determination of central and peripheral vision is possible using both simple and complex methods. The study of central vision is carried out using the well-known Sivtsev tables with letters of different sizes arranged in a column. Visual acuity in both eyes can be 1 or even 2, although the norm is considered when reading 9 lines of the table.

Methods for determining peripheral vision

Using a simple method does not require special tools or equipment. The study is carried out as follows: for this, the nurse and the patient close different eyes, sitting face to face to each other. The nurse moves her hand from right to left, and the patient must say when he sees it. The fields are determined for each eye separately.

For other detection methods, a special apparatus is required that will allow you to quickly and effortlessly examine each part of the retina, determine the visual field, and viewing angle. For example, campimetry, which is carried out using a sphere. However, this method is only suitable for examining a small part of peripheral vision.

The most modern method for determining visual fields is dynamic perimetry. This is a device that contains a picture that has different brightness and sizes. The person just puts his head on the device, and then it takes the necessary measurements.

Quantitative perimetry is used to detect glaucoma even at an early stage.

There is also visocontrast perimetry, which consists of gratings formed by black-and-white and colored stripes of different diameters and sizes. With a normal retina without abnormalities, the grating is perceived in its original form. If there are violations, then there is a violation of the perception of these structures.

Human visual field testing requires some preparation for perimetry procedures.

• When checking one eye, it is necessary to carefully close the other so as not to distort the results.
• The study will be objective if the person’s head is located opposite the desired mark.
• In order for the patient to orient himself with what he needs to say, he is shown moving marks and told about how the procedure will take place.
• If the field of view of color is determined, then it is necessary to record the indicator at which the color on the mark is clearly determined. The results obtained are applied to the section of the form, where normal indicators are written next to it. If areas of loss are identified, they are sketched.

Peripheral vision impairment

The so-called cones and rods are responsible for central and peripheral vision. The former are all directed to the central part of the retina, the latter - along its edges. Impaired peripheral vision is usually a symptom of pathological processes due to eye injury, inflammatory processes of the membranes of the eye.

Physiologically, certain areas of the visual field that fall out of view are distinguished; they are called scotomas. They can occur due to the onset of a destructive process in the retina and are determined by identifying objects in the field of view. In this case, they speak of a positive scotoma. It will be negative if a study using a device is necessary to determine it. Atrial scotoma appears and disappears. It is usually caused by cerebral vascular spasm. When a person closes his eyes, he sees circles or other elements of different colors that may extend beyond the limits of peripheral vision.

In addition to examining the presence of a scotoma, there is a classification based on the location of the spot: peripheral, central or paracentral.

Loss of visual angle can occur in various ways:

1. Tunnel vision is the loss of the field of vision down to a small central area.
2. Concentric narrowing is said to occur when the fields narrow evenly on all sides, leaving a small figure of 5-10 0. Since central vision is preserved, visual acuity may remain the same, but the ability to navigate the environment is lost.
3. When central and peripheral vision is lost symmetrically on both sides, this is most often due to a tumor.
4. If an anatomical structure such as the decussation of the visual pathways, or chiasm, is affected, the visual fields will be lost in the temporal region.
5. If the optic tract is affected, then in both eyes, field loss will occur on the corresponding side (right or left).

Causes of visual field loss

Loss of part of the field can occur due to a number of reasons:

• glaucoma or other retinal pathology;
• the appearance of a tumor;
• swelling of the optic nerve and dystrophic changes in the retina.

Glaucoma is manifested by the appearance of darkening in the pupil area, and loss of both central and peripheral vision may occur. It leads to complete loss of vision as the pathology progresses, since it is characterized by the death of the optic nerve. The cause of this disorder is increased intraocular pressure. Age, usually after 40 years, also becomes a provoking factor. With glaucoma, vision is impaired in the nasal area.

Glaucoma usually begins with pain in the eyes, flickering of floaters, and eye fatigue even with slight strain. Further propagation of the process causes difficulties when trying to examine certain areas of the picture. The process can affect one eye, but more often affects both eyes.

Tumor processes in the tissues of the eye at the initial stage are manifested by loss of part of the vision, up to 25%. In addition, the presence of a tumor can be suspected if there is a sensation of a foreign body, pain and stinging in the eyes.

When swelling of the nerve and dystrophic changes in the retina appear, the loss of a person’s peripheral vision occurs evenly and does not exceed 5-10 degrees.

Development of peripheral vision

Not everyone understands the purpose of training lateral vision, but taking into account the fact that it determines the activity of the brain and trains attention, it will not hurt anyone to develop lateral vision. Receiving indirect information about objects allows you to process it and store it in memory, even if this information is not immediately used.

You can develop central and peripheral vision with the help of auxiliary exercises:

The central part of the view is blocked, which forces the eye to concentrate on those objects that are in the periphery. Periodically, the object in the center is removed so that concentration on the side objects occurs at the request of the person.

The second exercise trains vision using a table in which the numbers are arranged randomly. There may be different numbers of them. In the center of the table there is a red dot, looking at which you need to count the numbers in order. You should start with a table with a small number of numbers, moving on to more. The search can be carried out over time, gradually reducing it, which will stimulate you to improve your results.

Visual acuity. The ability of the eye to perceive small details of objects at a great distance or to distinguish two points visible at a minimum angle, i.e. at a minimum distance from each other, determines visual acuity.

More than 250 years ago, Hooke and then Donders determined that the smallest visual angle at which the eye can distinguish two points is one minute. This visual angle value is taken as the international unit of visual acuity.

Visual acuity, at which the eye can distinguish two points with an angular distance of 1, is considered normal and equal to 1.0 (one).

At a visual angle of 1, the image size on the retina is 0.0045 mm, i.e. 4.5 µm. But the diameter of the cone body is also 0.002-0.0045 mm. This correspondence confirms the opinion that for the separate sensation of two points, it is necessary to stimulate the light-sensing receptors (cones) in such a way that two such elements are separated by at least one element on which the light beam does not fall. However, visual acuity equal to one is not the limit. In some nationalities and tribes, visual acuity reaches 6 units. Cases are described when visual acuity was equal to 8 units; there is a phenomenal report about a person who could count the satellites of Jupiter. This corresponded to a visual angle of 1", i.e. visual acuity was 60 units. High visual acuity is more often found in residents of flat, steppe regions. About 15% of people have visual acuity equal to one and a half to two units (1.5-2. 0).

The highest visual acuity is provided only by the region of the central zone of the retina; on both sides of the foveola it quickly decreases and already at a distance of more than 10° from the central fovea of ​​the macula it is only 0.2. This distribution of normal visual acuity in the center and periphery of the retina is of great importance for clinical practice and in the diagnosis of many diseases.

It must be borne in mind that due to insufficient differentiation of the visual-nervous apparatus, visual acuity in children in the first days, weeks and even months is very low. It develops gradually and reaches its possible maximum by an average of 5 years. The works of domestic and foreign authors, as well as our own observations using objective methods based on the phenomenon of optokinetic nystagmus, indicate that the acuity

Conditioned reflex studies have proven that in the first month of a child’s life, his vision, as a result of underdevelopment of the cerebral cortex, is subcortical, hypothalamic, primitive, protopathic, diffuse light perception. The development of visual perception manifests itself in newborns in the form of tracking. This is an innate function; tracking continues for seconds. The child's gaze does not stop at objects. From the second week of life, fixation appears, that is, a more or less long delay of gaze on an object while moving it at a speed of no more than 10 cm/s. Only by the second month, due to the functional improvement of cranial innervation, eye movements become coordinated, as a result of which synchronous tracking-fixation appears, i.e., prolonged binocular fixation of gaze.

Object vision begins to appear in children from about the 2nd month of life, when the child reacts vividly to the mother’s breast. By 6-8 months, children begin to distinguish simple geometric shapes, and from 1 year of age or later they can distinguish drawings. At the age of 3, visual acuity equal to one is found on average in 5-10% of children, at the age of 7 in 45-55%, at the age of 9 in 60%, at the age of 11 in 80% and at 14- summer in 90% of children.

The resolution of the eye, and therefore, to a certain extent, visual acuity, depends not only on its normal structure, but also on fluctuations of light, the number of quanta falling on the photosensitive part of the retina, clinical refraction, spherical and chromatic aberration, diffraction, etc. For example , the resolution of the eye is higher when 10-15 quanta (photons) hit the retina and the frequency of light flickers is up to 4 periods per second. The lowest resolution of the eye corresponds to 3-5 quanta, 7-9 periods, and the critical one corresponds to 1-2 quanta and a frequency of 30 periods per second. It should be especially noted that the distinct perception of an object by the eye depends not only on the characteristics of light, it is composed of unconditioned reflex motor acts of the eye. One of them is drift, which takes seconds, the second is tremor with a period of tenths of a second, and the third is jumps (up to 20°) lasting hundredths of a second.

Visual perception is impossible with constant lighting (no flickering) and immobility of the eyes (no drift, tremor and jumps), since in this case impulses from the retina to the subcortical and cortical visual centers disappear. In the first months of a child’s life, the volume of all these motor acts of the eye is extremely small, but with the formation and development of subcortical and cortical visual and oculomotor centers, they improve and by the second year of life they become relatively complete.

Central vision allows you to get a clear picture of the central area of ​​the image. This function of the eye has the highest resolution and is responsible for the concept of visual acuity.

Visual acuity is determined by measuring the distance between two points that the eye is able to distinguish as two different objects. This indicator directly depends on the individual parameters of the structure of the optical system, as well as the light-receiving apparatus of the eyeball. The angle that is formed as a result of connecting the extreme points and the nodal point is called the visual angle.

Decreased visual acuity can occur for various reasons. Among the following, three large groups can be distinguished:

1. Pathology associated with anomaly is the most extensive group. It includes hypermetropia and myopia. In this case, the use of special glasses helps restore visual acuity.
2. The second reason for decreased visual acuity includes clouding of the media of the eyeball, which normally transmit light rays without hindrance.
3. The third group combines various pathologies of the optic nerve and, as well as higher centers of vision and pathways.

It should be noted that throughout life, visual acuity undergoes physiological changes. Thus, visual acuity reaches its maximum by 5-15 years, and then there is a gradual decrease up to 40-50 years.

Methods for diagnosing central vision

To determine the patient’s visual acuity, the doctor performs. Normal visual acuity is a condition in which a person is able to distinguish two points that, together with the nodal point, form one degree. For convenience, opticians use not the angle formed by the dots to measure visual acuity, but the inverse value. That is, in practice relative units are used. The normal value is the indicator that is obtained with a distance between points of one degree. In other words, we can say that the smaller the angle between the points, the higher the visual acuity, and vice versa. Based on these parameters, tables have been developed that are used in practical ophthalmology to determine visual acuity. There are different types of tables, but all are based on a certain set of optotypes (test objects).

In the practice of opticians and ophthalmologists, there are concepts of minimally distinguishable, visible and recognizable. During visometry, the patient must see the optotype itself, distinguish the details of the optotype and recognize the picture (letter, sign, etc.). Optotypes are projected onto a screen or display. The optotype can be letters, pictures, numbers, stripes, circles. Each optotype has a specific structure, which allows you to distinguish details (thickness of lines, spaces) from a certain distance at an angle of 1 minute, and the entire optotype - 5 minutes.

The international optotype is the Landolt ring, which has a break of a certain size. In Russia, tables with Sivtsev-Golovin optotypes, which are represented by letters of the alphabet, are most often used. Each table has 12 rows with optotypes of various sizes. At the same time, the size of the optotypes in one row is the same. From the top row to the bottom there is a uniform gradual decrease in size. In the first ten rows, the step is 0.1 units, which measure visual acuity. The last two rows differ by another 0.5 units. Therefore, if the patient can distinguish the fifth row, then his visual acuity is 0.5 diopters, the tenth - 1 diopter.

In order to accurately determine visual acuity using the Sivtsev-Golovin tables, the patient should be placed at a distance of five meters, while the lower edge of the table should be 1.2 meters above the floor. With normal vision, a patient can distinguish row 10 optotypes from a distance of five meters. That is, his visual acuity is 1.0. Each row ends with a symbol that displays visual acuity, that is, on the 10th row it is 1.0. To the left of the optotypes there are other symbols that indicate the distance from which the optotypes can be read with 1.0 vision. So to the left of the optotypes of the first row there is a value of 50 meters.

To determine visual acuity, the doctor uses the Siellen-Deuders formula, in which vision is defined as the ratio of the distance from which the patient can determine the optotypes of the table and the distance from which he should normally see this series.

To determine visual acuity in an office of non-standard size, that is, if the patient is located at a distance of less than 5 meters from the table, it is enough to substitute the data into the formula. So, with a distance from the table to the patient of 4 m, if the patient can only read the fifth row of the table, his visual acuity will be 4/10, that is, 0.4.

In some people, visual acuity exceeds standard values ​​and is 2.0 and 1.5, or more. They can easily distinguish the characters of the 11th and 12th rows of the table from a distance of 5 meters. If the patient cannot read even the first row, then the distance to the table should be gradually reduced until the optotypes of the first row become distinguishable.

The similarity of the thickness of the fingers with the lines of the optotypes of the first line allows the approximate determination of visual acuity to be used by demonstrating the doctor’s spread fingers. In this case, it is advisable to demonstrate your fingers against a dark background. For example, with visual acuity less than 0.01, the patient can count fingers from a distance of 10 cm. Sometimes the patient cannot count fingers, but can see hand movements directly in front of the face. With minimal vision, there is light perception, which can be with correct or incorrect light projection. Light projection can be determined by directing rays from an ophthalmoscope directly into the eyeball at various angles. If light perception is completely absent, then visual acuity is defined as zero, and the eye is considered blind.

To determine the visual acuity of children, Orlova tables are used. In them, optotypes are represented by drawings depicting animals or other objects. Before starting the study, you should bring the child to the table and allow him to study all the presented optotypes, so that later it will be easier for him to distinguish between them.

If vision is below 0.1, then Polyak optotypes are used to diagnose it. They are represented by line texts or Landolt rings. They are shown at close range to determine appropriate visual acuity. They are also used in medical and social examinations and in the military medical commission, which are carried out to determine fitness for service or during the assignment of a disability group.
Objective methods for determining the visual acuity of patients are studies that are based on optoclistic. Using special devices, the patient is shown special moving objects (chessboard, stripes). At the smallest object size that provokes involuntary nystagmus, visual acuity is determined.

Rules for studying central vision

To reliably determine visual acuity during an examination, a number of important principles should be observed:

1. Vision must be determined separately for each eye, that is, monocularly. The examination usually begins with the right eye.
2. During the examination, both eyes must be kept open, while the free eye is covered with a special shield (sometimes with the palm of your hand). It is important that there is no impact on the eyes, and the possibility of intentional or unintentional involvement of the free eye in the study is excluded. Also, no light should enter the palpebral fissure from the side.
3. The study should be carried out in the correct position of the head, gaze and eyelids. You cannot tilt your head to any shoulder, turn it, or tilt it forward or backward. It is also not allowed to squint, as in case of myopia the results may be improved.
4. The time factor is also important to consider during the examination. During normal clinical work, the exposure time should be 2-3 seconds, and during control and experimental studies - 4-5 seconds.
5. Optotypes in tables must be demonstrated using a pointer, which is placed directly under the required optotype (at a short distance from it).
6. The examination should begin from the tenth row, and it is advisable to demonstrate the optotypes not sequentially, but separately. If visual acuity is obviously lower, then the examination should begin from the top row in order to gradually reach the required size of optotypes.

Visual acuity is finally assessed based on the series in which the patient was able to correctly name all the proposed optotypes. In this case, one mistake is allowed in 3-6 rows, and in 7-10 rows you can make two mistakes. All of these errors should be recorded in the physician's note.

At close range, to determine visual acuity, you can use a special table, which is placed at a distance of 33 cm from the patient. If the patient does not even see the top row, then his visual acuity is less than 0.1. For further research, the distance is reduced until the patient sees the optotypes of the first row. In some cases, cut tables are used, with individual optotypes of the first row gradually brought closer to the patient to determine visual acuity.