The Perimetry comprises several procedures in ophthalmology that are used to determine the limits of the field of vision and the sensitivities of the visual system and which play a role in particular for the aptitude test of professional groups such as pilots.
With each perimetry, the person examined covers one eye and fixes a certain point in space with the open eye, whereby in the course of the examination different light stimuli appear at different points in space, which the person examined can either register or not perceive. Perimetric methods can be divided into kinetic and static methods, with the kinetic methods moving the light stimuli from the peripheral field of vision of the patient to the center of the field of vision, while with static methods they are presented statically in one place and only change the intensity.
What is the perimetry?
The ophthalmologist understands perimetry as a systematic measurement of the visual field, in which the external and internal limits of the visual field and the sensitivities of the visual system are determined using a perimeter and light stimuli. Various individual methods fall into the field of perimetry. A basic distinction is that between kinetic and static investigation methods.
In addition to finger perimetry, contour perimetry and threshold perimetry are among the best-known methods. The former is the fastest and easiest type of perimetry. While perimetric processes were not automated in the beginning, nowadays they are increasingly controlled by machines. With this goal in mind, Hans Goldmann began developing a kinetic perimeter as early as 1945. Around 30 years later, Franz Fankhauser developed a system that later became the first computer-controlled and static perimeter.
Function, effect & goals
The perimetry plays a role especially for aptitude tests. In this regard, the area of application that should be mentioned in particular is the airworthiness test of pilots. However, perimetric methods are also used to diagnose visual defects, as this allows a distinction to be made whether a visual disorder is related to the brain or the optic nerve.
For this reason, perimetric methods for diagnosing eye diseases such as glaucoma have now become the standard. The individual steps in the process depend on which method is used. Ultimately, in the course of each perimetric method, optical stimuli are given one after the other, each of which appears at different points in the room. One eye is always examined. The other eye remains covered and does not have its turn until the examination of the first has been completed. During the examination, the doctor documents the patient's perception of stimuli and records the individual data of the perception, depending on the location and the intensity of the stimulus that appeared.
The eye must remain static during the perimetric examination, that is, the patient is asked to fix a single point in space that he or she will not lose sight of during the entire procedure. From the recordings, the doctor creates a systematic image of the visual field, which he then compares with a standard visual field. The differences between the individual procedures mentioned are primarily in the effort involved. In the parallel experiment, also known as finger perimetry, the doctor and patient sit across from each other and look at each other.
The doctor inserts an object from the peripheral visual field into the central visual field and compares his own perception with the patient's perception. With static perimetry, on the other hand, the person being examined sits in front of a screen and fixes a point of light on the center of the screen with his open eye. During the course of the examination, the screen shows points of light at various points, which the examinee marks as perceived by pressing a button. If the patient has not perceived a stimulus, the system increases the stimulus intensity. If this does not lead to the desired result either, the perimeter changes the place of the displayed stimulus. This procedure takes about ten to 20 minutes for each eye. The doctor then evaluates the data recorded in this way and compares the result with a standard finding.
In contrast to this static method, the light points in kinetic perimetry move from the periphery into the patient's central field of vision. The system measures the point in time from which the patient can see them. Both finger and contour perimetry are kinetic methods. The static method, on the other hand, includes threshold perimetry, which can only be carried out with a high-tech electronic device.
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The results of a perimetry depend heavily on the cooperation of the person examined. This means that perimetric methods are not absolutely objective methods and sometimes produce questionable results for patients who are unwilling to work.
For example, perimetry on a child may be less reliable than the same procedure on an adult subject. For the patient, perimetric methods are not associated with any risks or side effects, as all methods are non-invasive. Since perimetric examinations require absolute concentration, some patients find the examination to be extremely strenuous and in some cases significantly longer than it actually takes.
Despite this subjective feeling, finger perimetry in particular requires little effort and is considered a particularly simple and time-saving examination method. On the whole, however, the doctor now uses kinetic perimetry significantly less than the static method.
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