Visual impairment overtakes a person at any age. Modern gadgets contribute to the development of eye diseases. Prevention helps maintain human health. Determination of visual fields is an important study in identifying eye diseases. Modern equipment allows painless diagnosis.
What is the field of view
The space that is visible with a fixed eye is called the field of view. Depth of field of vision is determined by the retina. With a normal rate, a person can freely navigate in space. If the field is disturbed, then the patient does not see what is happening near him, cannot quickly determine the distance, experiences dizziness and headaches.
The determination of visual fields is included in the list of frequent examinations by an ophthalmologist. When detecting a decrease in the field, they search for the cause. This may be a violation of the structure of the eye or the development of a functional disease. A decrease in indicators indicates a malfunction of the retina, central nervous system or visual analyzer.
How to determine the field of view
Determination of the visual field in a person reveals a narrowing or loss of individual boundaries. How narrowed the vision is calculated in degrees. If a scotoma (a blind spot in the field of view) became the cause of the change in boundaries, then its indicators are determined in degrees or linear values.
Field of view - all points of space that one eye sees, looking motionless forward. In this case, the eye sees only a focused point, peripheral parts of the retina are responsible for everything else. In a place where there is no field of view, the retina that receives light has a defect.
To determine the periphery in ophthalmology, devices are used that are called the perimeter. With their help, the doctor conducts an examination according to certain methods. The main methods for determining the fields of view:
- control;
- kinetic;
- static;
- with double frequency.
An ophthalmologist examines each eye separately. One eye must be closed with a shield, and the second should be looked at a certain point, informing the doctor about the appearance of a certain object in the field of vision.
Control diagnostics
The control technique for determining the field of view gives an error in the measurement, but can be used in any conditions. It is used provided that the high accuracy of the data obtained is not needed or as a preliminary examination to prescribe more accurate diagnostic studies.
The patient and the doctor are located on each other at a distance of 50–70 cm. One eye of the subject is closed with a shield or palm, the second eye is fixed on the control point. The doctor moves an object in space, usually a pencil or pen. The subject moves perpendicular to the visual line at a distance of about 30 cm. The analysis is carried out horizontally from the ear, from behind the nose, and vertically.
This method is used in the diagnosis of children, because it does not require long-term attention. In children, the indicators are 10 ° less than in adults. It is recommended to determine the visual field in children no earlier than 4 months, until this time, children do not have stable fixation. The child's gaze is held on a bright subject and oscillates on the periphery. As soon as the child looks at a moving object, note the field of view.
Kinetic Perimetry
With the kinetic method, the perimeter to determine the field of view is examined in 8 meridians. The test object moves along the surface from the periphery to the center.
To obtain reliable results, you should not look away from a given point. The speed of the test object is 2 ° per 1 second. If a person has low vision, then the study is carried out without glasses.
In medical centers, manual or computer perimetry is used. For manual diagnostics, the Ferster perimeter is used, where white objects move on a fixed arc.
Hemispherical perimeters are more convenient to use due to the background brightness, which increases the accuracy of diagnosis. Thus, the determination of visual fields occurs at different levels from its base. Kinetic perimetry is used to determine significant changes due to a detected disease. With the development of glaucoma, more accurate information gives the method of static perimetry.
Static method
Determination of the peripheral field of view by the static method implies the detection of light sensitivity using blinking objects. The examination uses instruments that allow you to work in semi-automatic mode.
Modern devices have 25-30 programs in their arsenal. You can set the size, brightness and sequence of points. Using the method, a threshold and screening strategy is determined. In the first case, a long concentration of attention is required and more time is spent, but the accuracy of the result will be high. The screening test has less sensitivity and can reduce the time of diagnosis.
Perimeters are a hemisphere with programs for studying the central field of vision, detecting glaucoma, determining peripheral vision, etc.
If necessary, use combined options. First, an approximate determination of the visual fields occurs, and then, in the areas of decline, the parameters are detected with high accuracy. This approach allows you to reduce time and increase the reliability of the result.
Double Frequency Diagnostics
In the double frequency method, the white and black stripes that the patient examines change with a high frequency. Depending on whether the patient sees or not, in some areas black bars are diagnosed. The technique is effective for detecting in the early stages of the disease of the optic nerve, retina and detection of glaucoma.
To detect glaucoma using this method, 5 signs were selected according to which a diagnosis is made. Determining the average sensitivity deficit is the main indicator of the survey. Thanks to this, it is possible to diagnose up to 96% of the development of the disease at an early stage.
Indications for the procedure
Perimetry is performed as prescribed by an ophthalmologist. The doctor conducts the simplest control method directly in the office based on the patient's complaints. If there are doubts about the decrease in visual fields or diagnosis, the patient is sent for further diagnosis.
The change in the field of view occurs for the following reasons:
- eye diseases, disruption in the operation of the optic nerves;
- retinal detachment;
- burn or injury to the eye;
- oncological neoplasms of the visual organ;
- retinal hemorrhage.
When passing the commission for some types of work, perimetry may be required. This verifies employee attention and responsiveness. Using perimetry, latent traumatic brain injuries, chronic hypertension, strokes and neuritis are detected.
Perimetric contraindications
There are practically no contraindications for determining the visual fields. It is not carried out in case of aggressive behavior of the patient or the presence of a sick mental disorder.
The doctor will refuse to diagnose a person in alcohol or drug intoxication. Even with a small consumption of alcohol-containing drinks, the results may be distorted, in this case, the examination is contraindicated.
It is impossible to determine the field of view if a person has a mental retardation and cannot follow the doctor’s instructions. In this case, alternative methods of examination should be carried out.
Deciphering the results
The data obtained during the survey should be correctly decrypted. Perimetric data are entered on a special form and compared with standard indicators. Situations indicating the presence of pathologies:
- In some segments of the field of view, a person does not see an object.
- Identification by cattle that interfere with full sight. A possible cause is a disease of the optic nerve or retina.
- General narrowing of vision. Depending on the zone (central, spectral, bilateral), a diagnosis is made. As a rule, the functioning of the eyes is reduced due to mechanical damage.
During the diagnosis, factors that can affect the change in the field of view should be taken into account:
- deep set eyes;
- low eyebrows;
- high nose bridge;
- severe vision loss;
- inflammation of the eyes;
- infectious diseases.
The ophthalmologist identifies the reason why the vision has narrowed. If the reason lies in eye diseases, then prescribes treatment or further diagnosis. In diseases of the nervous system should be observed by a neurologist.