[Fundus-oriented perimetry. Evaluation of a new visual field examination method for detecting angioscotoma].

BACKGROUND

Conventional automated perimeters usually work with a given set of grids and thus are normally not adapted to individual conditions. This fact restricts efficiency of this method not only for any single examination but also for follow-up studies.

MATERIALS AND METHODS

A new method (patent pending) is introduced which superimposes an individual perimetric grid--corrected in respect to orientation, position and size--onto a patient's fundus image. A recently developed software realizes this procedure in a comfortable manner: the digitized fundus image is loaded into the computer by e.g. photo-CD or disc, depicted on a control monitor and mirrored if necessary. Assuming a central fixation, the foveola is translationally shifted to the center of the perimetric grid by the help of a crosshair. The blind spot which has been previously determined with kinetic perimetry is then superimposed onto the optic disc of the fundus image using a rotation and zoom function. In this way, it is possible to adapt the perimetric grid directly to the underlying individual fundus findings: thus, stimuli can be spatially concentrated or more frequently tested in special regions of interest. Additionally, test points can be dragged away from delicate positions to avoid artifacts. Examinations were carried out on a high resolution colour VDU of the Tübingen Electronic Campimeter (TCC). Alternatively, suited bowl perimeters can be used.

RESULTS

In order to test the precision of the superimposing procedure, fundus oriented perimetry was performed to detect angioscotomata in 13 ophthalmologically normal subjects. Using dark stimuli (12'), visual field defects in the expected region, caused by retinal vessels, could be detected in 7 cases (= 54%). The resulting attenuation of differential light sensitivity in this circumscribed region was up to 12 dB.

CONCLUSIONS

By means of a morphologically adapted, individual arrangement of stimulus locations fundus-oriented perimetry enables detection of even minute (angio-) scotomata.