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The success of a person directly depends on how quickly he orients himself in space and time. The key to this is, among other things, visual acuity. Technological progress and the rapid modern pace of life can cause visual impairment at a fairly young age. This is guarded by the world ophthalmology. Preventive diagnostics includes a huge range of procedures that allow you to monitor eye health.
One of these procedures is perimetry – the study of the boundaries of the visual field (peripheral vision), the indicators of which help ophthalmologists diagnose eye diseases, in particular, glaucoma or optic nerve atrophy. To measure the necessary parameters, doctors have modern diagnostic equipment in their arsenal, the examination of which is painless and without contact with the surface of the eyes, which reduces the risk of inflammation.
In case of any problems, it is recommended to consult a doctor without delay, and also not to neglect annual preventive examinations.
The concept of the boundaries of the field of view
Peripheral vision gives a person the ability to see and recognize a certain amount of objects around him. To check its quality, ophthalmologists use a technique for examining the boundaries of the visual field, which is called perimetry. The boundaries of the visual fields in medicine mean the visible space that the fixed eye can recognize. In other words, this is an overview that is available provided that the patient’s gaze is fixed on one point.
The quality of such a visual ability is directly dependent on the volume of points present in space, which are covered by the eye in a stationary state. The presence of certain deviations in the indicator obtained during perimetry gives the doctor reason to suspect a particular eye disease.
In particular, the definition of the boundaries of the field of view is necessary in order to find out what state the retina or optic nerve is in. Also, such a procedure is indispensable for identifying pathologies and diagnosing ophthalmic diseases, such as glaucoma, and prescribing effective treatment.
Indications for the procedure
In medical practice, there are a number of indications for which it is necessary to prescribe perimetry. So, for example, visual field impairment can be caused by the following reasons:
- Retinal dystrophy, in particular its detachment.
- Hemorrhages in the retina.
- Oncological formations on the retina.
- Optic nerve injury.
- Burns or eye injuries.
- The presence of certain ophthalmic diseases.
In particular, perimetry makes it possible to diagnose glaucoma with subsequent examination and clarification of this diagnosis, or to establish diseases associated with damage to the macula.
In some cases, information about perimetry data is required when applying for a job. With its help, the presence of increased attentiveness in an employee is checked. In addition, using this research method, it is possible to diagnose craniocerebral injuries, chronic hypertension, as well as strokes, coronary disease and neuritis.
Finally, the determination of the field of view helps to identify simulation moods in patients.
Contraindications for perimetry
In some cases, the use of perimetric diagnostics is contraindicated. In particular, this technique is not used in the case of aggressive behavior of patients or the presence of a mental disorder. The results are distorted not only by patients being in a state of alcoholic or drug intoxication, but also by the use of even minimal doses of alcoholic beverages. Contraindications to the determination of peripheral visual acuity are also mental retardation of patients, which does not allow following the doctor’s instructions.
If such a diagnosis is necessary in these cases, doctors recommend resorting to alternative methods of examination.
Methods of diagnosis
For perimetry in ophthalmic practice, several types of devices are used, which are called the perimeter. With their help, doctors track the boundaries of the field of view using specially developed methods.
Following are the main types of procedure. All of them are painless and non-invasive, and do not require any preliminary preparation from the patient.
Kinetic perimetry
This is a procedure that allows you to evaluate the dependence of the field of view on the size and color saturation of an object that is moving. This test implies the obligatory presence of a bright light stimulus in an object moving along predetermined trajectories. During the examination, points are fixed that cause a certain reaction of the eyes. They are entered in the form of perimetric research. Their connection at the end of the event makes it possible to identify the trajectory of the boundaries of the field of view. When conducting kinetic perimetry, modern projection perimeters with high measurement accuracy are used. With their help, the diagnosis of a number of ophthalmic pathologies is carried out. In addition to ophthalmic abnormalities, this research method makes it possible to detect some pathologies in the work of the central nervous system.
Static perimetry
In the course of static perimetry, a certain immovable object is observed with its fixation in a number of sections of the field of view. This diagnostic method allows you to set the sensitivity of vision to changes in the intensity of the image display, and is also suitable for screening studies. In addition, it can be used to determine the initial changes in the retina. As the main equipment, an automatic computer perimeter is used, which makes it possible to study the entire field of view or its individual sections. With the help of such equipment, a threshold or suprathreshold perimetric study is performed. The first of them makes it possible to obtain a qualitative assessment of the sensitivity of the retina to light, and the second allows to fix qualitative changes in the visual field. These indicators are aimed at diagnosing a number of ophthalmic diseases.
Campimetry
Campimetry refers to the evaluation of the central visual field. This study is carried out by fixing the eyes on white objects that move on a black matte screen – campimeter – from the center to the periphery. The doctor marks the points where objects temporarily fall out of the patient’s field of vision.
Amsper test
Another fairly simple method for assessing the central visual field is the Amsper test. It is also known as the Macular Retinal Degeneration Test. During the diagnosis, the doctor studies the reaction of the eyes when the gaze is fixed on an object placed in the center of the grid. Normally, all lattice lines should appear to the patient as absolutely even, and the angles formed by the intersection of the lines should be straight. In the event that the patient sees the image distorted, and some areas are curved or blurred, this indicates the presence of pathology.
Donders test
The Donders test allows you to very simply, without the use of any devices, determine the approximate boundaries of the field of view. When it is carried out, the gaze is fixed on the object, which they begin to move from the periphery to the center of the meridian. In this test, along with the patient, an ophthalmologist is also involved, whose field of view is considered normal.
Being at a distance of a meter from each other, the doctor and the patient must simultaneously focus on a certain object, provided that their eyes are at the same level. The ophthalmologist covers his right eye with the palm of his right hand, and the patient covers his left eye with the palm of his left hand. Next, the doctor brings his left hand from the temporal side (beyond the line of sight) half a meter from the patient, and begins, moving his fingers, to move the brush to the center. The moments are recorded when the eye of the subject catches the beginning of the appearance of the contours of the object that moves (the doctor’s hands) and its end. They are decisive for establishing the boundaries of the field of view for the patient’s right eye.
A similar technology is used to fix the outer boundaries of the field of view in other meridians. At the same time, for research in the horizontal meridian, the ophthalmologist’s brush is located vertically, and in the vertical – horizontally. Similarly, only in a mirror image, the visual field indicators of the patient’s left eye are examined. In both cases, the field of view of the ophthalmologist is taken as the standard. The test helps to establish whether the boundaries of the patient’s field of view are normal or whether their narrowing is concentric or sector-shaped. It is used only in cases where it is not possible to carry out instrumental diagnostics.
Computer perimetry
The greatest accuracy in the assessment is given by computer perimetry, for which a special computer perimeter is used. This state-of-the-art high-performance diagnostic uses programs to conduct a screening (threshold) study. Intermediate parameters of a number of examinations remain in the memory of the device, which makes it possible to conduct a static analysis of the entire series.
Computer diagnostics makes it possible to obtain a wide range of data on the state of vision of patients with the greatest accuracy. However, it does not represent anything complicated and looks like this.
- The patient is positioned in front of the computer perimeter.
- The specialist invites the subject to fix his gaze on the object that is presented on the computer screen.
- The patient’s eyes can see a number of marks moving randomly across the monitor.
- Having fixed his gaze on the object, the patient presses the button.
- Data on the results of the check are entered in a special form.
- At the end of the procedure, the doctor prints out the form and, after analyzing the results of the study, gets an idea about the state of vision of the subject.
In the course of the procedure according to this scheme, a change in the speed, direction of movement and colors of the objects presented on the monitor is provided. Due to the absolute harmlessness and painlessness, such a procedure can be repeated many times until the specialist is convinced that objective results of the study of peripheral vision are obtained. After the diagnosis, no rehabilitation is required.
Explanation of results
As noted above, the data obtained during the perimetric survey are subject to interpretation. Having studied the examination indicators entered on a special form, the ophthalmologist compares them with the standard indicators of statistical perimetry and assesses the state of the patient’s peripheral vision.
The following facts may indicate the presence of any pathologies.
- Cases of detection of loss of visual function from certain segments of the visual field. A conclusion about the pathology is made if the number of such violations exceeds a certain norm.
- The detection of scotoma – spots that prevent the full perception of objects – may indicate diseases of the optic nerve or retina, including glaucoma.
- The reason for the narrowing of vision (spectral, centric, bilateral) may be a serious change in the visual function of the eye.
When undergoing computer diagnostics, a number of factors should be taken into account that can distort the results of the examination and cause deviations from the normative parameters of perimetry. These include both features of the physiological structure of the appearance (lowered eyebrows and upper eyelid, high bridge of the nose, deep-set eyeballs), as well as significantly reduced vision, irritation or inflammation of blood vessels near the optic nerve, as well as poor-quality vision correction and even some types of frames.