Modification of the Heidelberg retinal flowmeter to record pattern and flicker induced blood flow changes

We tested a prototype stimulator interfaced with a commercially available scanning laser ophthalmoscope designed to measure retinal capillary perfusion (Heidelberg Retina Flowmeter (HRF)). The add-on stimulator optically superimposed the image of a monitor display on to the subject's retina coaxially with the imaging optics of the HRF. The purpose of the study was to determine if flicker and pattern stimulation presented in this manner could evoke changes in retinal perfusion that could be measured by the HRF.

The prototype stimulator projected 55 degrees visual angle circular fields of homogeneous flicker, alternating checkerboard, and multi-focal m-sequence hexagonal patterns on the retina of 10 human subjects during acquisition of images by the HRF.

Images were successfully acquired and processed. HRF perfusion values during flicker and pattern stimulation were not significantly different from control values.

Results of the present study and a previously published study showing a flicker-induced increase in the HRF perfusion values are contradictory. Retinal perfusion measured by the HRF were not affected by flicker and pattern stimulation delivered through the prototype device. These data are not consistent with a large flicker or pattern induced increase in retinal perfusion. The instrumental modification appears promising. However, the raster scan stimulation technique or some other aspect of stimulation or image acquisition may account for the different results in the present study and previous studies in our laboratory and in the laboratories of other investigators.