Abstract
PURPOSE: 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 a retinal vessel analyzer. Oxygen supply may be the target of
the regulation of retinal blood flow. Thus, the oxygen saturation (SO(2)) in
retinal arterioles and venules was investigated along with their diameters.
METHODS: Dual-wavelength (548 nm and 610 nm) fundus images were taken in 19
healthy volunteers (mean age, 26 +/- 2.5 years) before (baseline) and during
luminance flicker stimulation (12.5 Hz; modulation depth, 1:25). Retinal vessel
SO(2) (dual-wavelength optical oximetry) and diameters (central retinal arterial
and venous equivalents CRAE and CRVE) were determined. RESULTS: CRAEs and CRVEs
of 193 +/- 20 mum and 228 +/- 20 mum at baseline increased statistically
significant to a maximum of 202 +/- 19 mum (P < 0.0005) and 242 +/- 17 mum (P <
0.0005), respectively, under flicker stimulation. Although the arterial SO(2)
remained unchanged at 98\%-99\%, an increase of the venous saturation from 60\% +/-
5.7\% to 64\% +/- 5.9\% (P < 0.0005) was found. CONCLUSIONS: 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. The augmentation of venous oxygenation may indicate a
higher capillary oxygen concentration, necessary to provide a sufficient
diffusion rate of oxygen from the capillaries to the inner retinal tissue.
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