title: Retinal venous oxygen saturation increases by flicker light stimulation.
abstract: OBJECTIVE
  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 μm and 228 ± 20 μm at baseline increased statistically significant to a maximum of 202 ± 19 μm (P < 0.0005) and 242 ± 17 μm (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.
authors.affiliation: Department of Ophthalmology, University of Jena, Jena, Germany. martin.hammer@med.uni-jena.de
authors.forename: Martin
authors.initials: M
authors.lastname: Hammer
authors.forename: Walthard
authors.initials: W
authors.lastname: Vilser
authors.forename: Thomas
authors.initials: T
authors.lastname: Riemer
authors.forename: Fanny
authors.initials: F
authors.lastname: Liemt
authors.forename: Susanne
authors.initials: S
authors.lastname: Jentsch
authors.forename: Jens
authors.initials: J
authors.lastname: Dawczynski
authors.forename: Dietrich
authors.initials: D
authors.lastname: Schweitzer
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D005260:Female; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008297:Male; D010092:Oximetry; D010100:Oxygen / Q000378:metabolism*; D010775:Photic Stimulation; D012039:Regional Blood Flow / Q000528:radiation effects; D012160:Retina / Q000528:radiation effects*; D012161:Retinal Artery / Q000502:physiology; D012169:Retinal Vein / Q000502:physiology*; D014664:Vasodilation / Q000502:physiology
chemical_list: D006454:Hemoglobins; D010100:Oxygen