title: Automatic retinal oximetry.
abstract: OBJECTIVE
  To measure hemoglobin oxygen saturation (SO(2)) in retinal vessels and to test the reproducibility and sensitivity of an automatic spectrophotometric oximeter.
  
  
  METHODS
  Specialized software automatically identifies the retinal blood vessels on fundus images, which are obtained with four different wavelengths of light. The software calculates optical density ratios (ODRs) for each vessel. The reproducibility was evaluated by analyzing five repeated measurements of the same vessels. A linear relationship between SO(2) and ODR was assumed and a linear model derived. After calibration, reproducibility and sensitivity were calculated in terms of SO(2). Systemic hyperoxia (n = 16) was induced in healthy volunteers by changing the O(2) concentration in inhaled air from 21% to 100%.
  
  
  RESULTS
  The automatic software enhanced reproducibility, and the mean SD for repeated measurements was 3.7% for arterioles and 5.3% venules, in terms of percentage of SO(2) (five repeats, 10 individuals). The model derived for calibration was SO(2) = 125 - 142 . ODR. The arterial SO(2) measured 96% +/- 9% (mean +/- SD) during normoxia and 101% +/- 8% during hyperoxia (n = 16). The difference between normoxia and hyperoxia was significant (P = 0.0027, paired t-test). Corresponding numbers for venules were 55% +/- 14% and 78% +/- 15% (P < 0.0001). SO(2) is displayed as a pseudocolor map drawn on fundus images.
  
  
  CONCLUSIONS
  The retinal oximeter is reliable, easy to use, and sensitive to changes in SO(2) when concentration of O(2) in inhaled air is changed.
authors.affiliation: Department of Ophthalmology, University of Iceland, National Univbersity Hospital, Reykjavik, Iceland.
authors.forename: Sveinn Hakon
authors.initials: SH
authors.lastname: Hardarson
authors.forename: Alon
authors.initials: A
authors.lastname: Harris
authors.forename: Robert Arnar
authors.initials: RA
authors.lastname: Karlsson
authors.forename: Gisli Hreinn
authors.initials: GH
authors.lastname: Halldorsson
authors.forename: Larry
authors.initials: L
authors.lastname: Kagemann
authors.forename: Ehud
authors.initials: E
authors.lastname: Rechtman
authors.forename: Gunnar Már
authors.initials: GM
authors.lastname: Zoega
authors.forename: Thor
authors.initials: T
authors.lastname: Eysteinsson
authors.forename: Jon Atli
authors.initials: JA
authors.lastname: Benediktsson
authors.forename: Adalbjorn
authors.initials: A
authors.lastname: Thorsteinsson
authors.forename: Peter Koch
authors.initials: PK
authors.lastname: Jensen
authors.forename: James
authors.initials: J
authors.lastname: Beach
authors.forename: Einar
authors.initials: E
authors.lastname: Stefánsson
mesh_terms: D006801:Humans; D018496:Hyperoxia / Q000378:metabolism; D010092:Oximetry / Q000295:instrumentation*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology; D010108:Oxyhemoglobins / Q000378:metabolism; D015203:Reproducibility of Results; D012161:Retinal Artery / Q000378:metabolism*; D012169:Retinal Vein / Q000378:metabolism*; D012680:Sensitivity and Specificity
chemical_list: D010108:Oxyhemoglobins; D010100:Oxygen