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M. Hammer, W. Vilser, T. Riemer, F. Liemt, S. Jentsch, J. Dawczynski, D. Schweitzer; Retinal Vessel Diameter and Oxygen Saturation in Response to Luminance Flicker Stimulation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1391.
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© ARVO (1962-2015); The Authors (2016-present)
Luminance flicker stimulation of the photoreceptors is known to increase retinal blood flow. Elevated blood velocity was determined using laser Doppler velocimetry and increased vascular diameters during flicker were observed by measurements with the Retinal Vessel Analyzer (RVA). Oxygen supply seems to be the target of the auto - regulation of retinal blood flow. Thus, we investigated the oxygen saturation in retinal arterioles and venules along with their diameters.
Dual - wavelength (548 nm and 610 nm) fundus images were taken in 20 healthy volunteers (mean age: 25.5 ± 2.3 years) before (baseline) and immediately after monochromatic (567 - 587 nm) luminance flicker stimulation (12.5 Hz, modulation depth: 1:20). Diameters and oxygen saturation (2 - wavelength optical oximetry) were determined and averaged for all arterioles and venules in an annular area centered at the optic disk ("ARIC" - grid).
Mean venular and arteriolar diameters of 108.2 µm and 89.0 µm at baseline increased to 111.8 nm and 91.7 nm after flicker respectively. The arterial dilation was statistically significant (p=0.027). While the mean arterial oxygen saturation remained constant (92.8%), the venous saturation increased by flicker stimulation from 57.6 % to 59.9 %. Thereby, the individual arterio - venous oxygen saturation difference decreased significantly (p=0.045) from 35.1% to 32.9 %.
In agreement with earlier investigations, the vessel dilation, found here, indicates an elevation of retinal blood flow by luminance flicker stimulation. This increase of the flow should meet the enhanced metabolic need of the neural retina under a physiological stimulus. However, the significant decrease of the arterio - venous oxygen saturation difference possibly indicates an over - compensation of this need by the retinal auto - regulation in the healthy eye.
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