Perimetry

As perimetry (from Greek peri " around " metron " dimension" ) is referred to in ophthalmology systematic survey of the visual field.

Goal of the study is on the one hand, to determine the outer and inner boundaries of the field, and on the other hand, to determine the sensitivity of the visual system in the perceived space. The devices used for this purpose is called a perimeter.

During the examination, visual stimuli are successively presented at different locations of the room. The perception of these stimuli depending on their location and their strength will be logged. In order to preserve the spatial relationship of the test sites, the examined eye must continually fix a central point. From the study protocol, a schematic image of the visual field can be constructed then. The fellow eye must be covered throughout the course of the examination, for example, with an eye patch. The results are usable as a rule only in good cooperation of the examinee.

Basically, to distinguish static from kinetic investigation process. In the former, the stimulus is invariably present in one place and increased in intensity until the examinee indicates a perception. In the latter, in their intensity constant stimuli from outside the field boundaries are moved into the suspected visual field and considered the place of perception as the boundary of the field for the given stimulus intensity.

The brightness of the visual stimuli and the background investigation are in the range of sensitivity of the cones ( photopic vision ). Central scotoma can complicate the fixation of the patient. But they are ausmessbar both the Konturperimetrie and with the threshold perimetry in size and depth.

Methods of investigation

Fingerperimetrie

The Fingerperimetrie (synonym: Konfrontationsperimetrie or confrontation visual field) is a kinetic process, which has the advantage to make qualitative statements about the external borders of the visual field without extensive technical equipment. The examiner compares the outer limits of his own field of vision with those of the subjects. Examiner and subject sit for over, each cover an opposite eye and fix each other, for example the nose of the other. The finger of the examiner is led from the outside into the field, the subject explains when he notices the fingers. The Fingerperimetrie is suitable only for determining gross visual field defects, error prone, and provides no information about the sensitivity distribution within the field.

Konturperimetrie

The Konturperimetrie (synonym: Goldmann perimetry, isopters perimetry ) is the classical method of perimetry, also kinetically. The patient's head is in a projection perimeter ( hemisphere, according to Goldmann ). The test point is projected into the ball, and is mechanically coupled to a guide pin, that the position of the test point is transferred to a flat sheet of paper. Size and brightness of the test point can be chosen independently. The result of Goldmann perimetry represents the visual field similar to a map with contour lines dar. as curves of equal sensitivity

Threshold perimetry ( computerized perimetry )

The threshold perimetry (synonym: computerized perimetry ) is a static method, which requires extensive, electronically controlled device. The subject looks into an optical system - usually also a hemisphere over the light spots of different position and brightness of computer control are projected. The respondent confirmed each detected stimulus by pressing a button. With the aid of sophisticated applications that rely on statistical methods, both the entire extent of the field and the state of selected areas under various issues can be examined. The results can be further processed directly for electronic documentation.

Before the introduction of computerized threshold perimetry static perimetry was performed manually as Profilperimetrie. As investigation unit was, for example, a perimeter of Goldmann - type used (see Konturperimetrie ). The light stimuli offered were not moved, but increased by a slider in their intensity. This study was usually limited because of the expense, only one or a few meridians of the visual field, so that the result is a profile of the visual field map was created.