Pulsed Electrical Stimulation of the Human Eye Enhances Retinal Vessel Reaction to Flickering Light

Abstract

Recent studies indicate therapeutic benefits of electrical stimulation in cases of specific ophthalmic diseases that are associated with dysfunctional ocular microcirculation. This suggests effects of electrical stimulation on vascular functions. In the present study, we investigated the effects of electrical stimulation on retinal vessel reactions using dynamic vessel analysis (DVA). Eighty healthy subjects were randomly assigned to one of three groups receiving electrical stimulation with different current intensities: 400 μA (n = 26); 800 μA (n = 27); 1200 μA (n = 27). The electrode montage for electrical stimulation consisted of a ring-shaped active electrode surrounding one eye and a square return electrode at the occiput. Rectangular, monophasic, positive current pulses were applied at 10 Hz for a duration of 60 s per stimulation period. DVA was used to observe the stimulation-induced reactions of retinal vessel diameters in response to different provocations. In three DVA measurements, three stimulus conditions were investigated: flicker light stimulation (FLS); electrical stimulation (ES); simultaneous electrical and flicker light stimulation (ES+FLS). Retinal vasodilation caused by these stimuli was compared using paired t-test. The subjects receiving electrical stimulation with 800 μA showed significantly increased retinal vasodilation for ES+FLS compared to FLS (p < 0.05). No significant differences in retinal vessel reactions were found between ES+FLS and FLS in the 400 and 1200 μA groups. No retinal vasodilation was observed for ES for all investigated current intensities. The results indicate that positive pulsed electrical stimulation of an adequate intensity enhances the flicker light-induced retinal vasodilation.

Advantages of imaging photoplethysmography for migraine modeling: new optical markers of trigemino‐vascular activation in rats

“…Despite the fact that the OIS marker did not demonstrate any notable sensitivity to the test drugs, it is of undoubted interest as an indicator of the quality of electrical stimulation of trigeminal afferents, which makes it possible to exclude the receipt of fake results. It is known that OIS is proportional to the total blood volume in tissues [ 37 ], while the electrical stimulation leads to a local increase in the volumetric blood flow velocity, i.e., hyperemia in the irritated area [ 52 – 54 ]. By monitoring OIS during each trial of CCW electrical stimulation, it is possible to control the quality of the electrode contact with CCW, which is critical for efficient stimulation of trigeminal afferents.…”

Effects of Ocular Direct Current Stimulation on Full Field Electroretinogram

“…The current stimulation was performed with a direct current of 800 μA over a duration time of 5 min. The current intensity was chosen to be higher than the mean phosphene threshold of healthy subjects ( Freitag et al, 2019 ). In order to avoid skin irritation under stimulation electrodes and transient current sensation, the current was linearly ramped on (Fade-In) over 5 s at the beginning of the current stimulation and was ramped down linearly (Fade-Out) for 5 s at the end of the stimulation.…”

The Effects of an Ocular Direct Electrical Stimulation on Pattern-Reversal Electroretinogram

“…The stimulation current was increased from 0 to 500 µA in 5 s at the start of the stimulation to prevent transient sensations. The current intensity (500 µA) was chosen such that it is slightly above the mean flicker response of healthy subjects (Freitag et al, 2019). The direct current was kept constant for 5 min and was subsequently ramped down in 5 s.…”

“…The stimulation parameters such as frequency, current strength, and configuration of the stimulation electrodes vary widely in the literature. The stimulation induced processes within the retina and visual pathways are not fully understood yet (Freitag et al, 2019(Freitag et al, , 2020.…”