title: Oxygen saturation in human retinal vessels is higher in dark than in light.
abstract: OBJECTIVE
  Animal studies have indicated that retinal oxygen consumption is greater in dark than light. In this study, oxygen saturation is measured in retinal vessels of healthy humans during dark and light.
  
  
  METHODS
  The oximeter consists of a fundus camera, a beam splitter, a digital camera and software, which calculates hemoglobin oxygen saturation in the retinal vessels. In the first experiment, 18 healthy individuals underwent oximetry measurements after 30 minutes in the dark, followed by alternating 5-minute periods of white light (80 cd/m(2)) and dark. In the second experiment, 23 volunteers underwent oximetry measurements after 30 minutes in the dark, followed by light at 1, 10, and 100 cd/m(2). Three subjects were excluded from analysis in the first experiment and four in the second experiment because of poor image quality.
  
  
  RESULTS
  In the first experiment, the arteriolar saturation decreased from 92% +/- 4% (n = 15; mean +/- SD) after 30 minutes in the dark to 89% +/- 5% after 5 minutes in the light (P = 0.008). Corresponding numbers for venules are 60% +/- 5% in the dark and 55% +/- 10% (P = 0.020) in the light. In the second experiment, the arteriolar saturation was 92% +/- 4% in the dark and 88% +/- 7% in 100 cd/m(2) light (n = 19, P = 0.012). The corresponding values for venules were 59% +/- 9% in the dark and 55% +/- 10% in 100 cd/m(2) light (P = 0.065).
  
  
  CONCLUSIONS
  Oxygen saturation in retinal blood vessels is higher in dark than in 80 or 100 cd/m(2) light in human retinal arterioles and venules. The authors propose that this is a consequence of increased oxygen demand in the outer retina in the dark.
authors.affiliation: Department of Ophthalmology, University of Iceland/Landspítali University Hospital, Reykjavik, Iceland.
authors.forename: Sveinn Hakon
authors.initials: SH
authors.lastname: Hardarson
authors.forename: Samy
authors.initials: S
authors.lastname: Basit
authors.forename: Thora Elisabet
authors.initials: TE
authors.lastname: Jonsdottir
authors.forename: Thor
authors.initials: T
authors.lastname: Eysteinsson
authors.forename: Gisli Hreinn
authors.initials: GH
authors.lastname: Halldorsson
authors.forename: Robert Arnar
authors.initials: RA
authors.lastname: Karlsson
authors.forename: James Melvin
authors.initials: JM
authors.lastname: Beach
authors.forename: Jon Atli
authors.initials: JA
authors.lastname: Benediktsson
authors.forename: Einar
authors.initials: E
authors.lastname: Stefansson
mesh_terms: D000328:Adult; D003623:Dark Adaptation / Q000502:physiology*; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D012171:Retinal Vessels / Q000378:metabolism*
chemical_list: D010100:Oxygen