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Stefanie Freitag, Alexander Hunold, Matthias Klemm, Jens Haueisen; Simultaneous dynamic retinal vessel analysis and pulsed anodal transcranial electrical stimulation at the eye. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):760.
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© ARVO (1962-2015); The Authors (2016-present)
Variations in neuronal activity cause changes in blood flow, an effect that is part of the neurovascular coupling (NVC). In neurosciences transcranial electrical stimulation (TES) methods are used to provoke excitation or inhibition of neuronal activity in the human cortex. We propose to adapt these techniques to analyze the mechanisms of NVC in the retina using dynamic retinal vessel analysis. This study tested the hypothesis that pulsed anodal TES at the eye evokes changes in the dynamic retinal vessel response to flicker.
Retinal vessel reactions were observed in 13 healthy volunteers (23.8±1.6 years) using the Dynamic Vessel Analyzer (DVA) in two cases: (a) flicker light stimulation; (b) flicker light stimulation and simultaneous TES. To apply TES we developed a ring-shaped rubber electrode (ca. 37cm2) placed around one eye as the anode and a square rubber electrode (100cm2) at the occiput as the cathode. We applied anodal rectangular current pulses (frequency: 10Hz; current intensity: 800µA). The DVA measurements consisted of 60s baseline and two periods of 60s stimulation (application of flicker light or simultaneous flicker light and TES) followed by 120s observation. The retinal vessel responses were calculated by the DVA as the mean of the two measurement cycles and expressed in the stimulation induced dilation of the vessels compared to their baseline diameters. The maximum dilation of one arterial and venous vessel segment was measured in each subject under both stimulation conditions. Wilcoxon rank-sum test was used to compare the mean values of retinal vessel dilation for flicker light stimulation and simultaneous flicker light stimulation and TES.
At flicker light stimulation retinal vessels provided physiological reactions with a maximum arterial dilation of 3.9±1.6% and a maximum venous dilation of 6.0±2.1%. For simultaneous flicker light stimulation and TES maximum arterial dilation was significantly increased (5.5±1.7%; p=0.018), maximum venous dilation showed no significant change (6.6±2.1%; p=0.329).
The results confirm our hypothesis that pulsed anodal TES affects retinal vessel reactions to flicker light, especially shown in arterial reactions. Thus, the NVC in the retina can be modulated by electrical stimulation and observed using dynamic retinal vessel analysis.
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