title: Inner retinal oxygen extraction fraction in rat.
abstract: OBJECTIVE
  Oxygen extraction fraction (OEF), defined by the ratio of oxygen consumption to delivery, may be a useful parameter for assessing the retinal tissue status under impaired circulation. We report a method for measurement of inner retinal OEF in rats under normoxia and hypoxia based on vascular oxygen tension (PO(2)) imaging.
  
  
  METHODS
  Retinal vascular PO(2) measurements were obtained in 10 rats, using our previously developed optical section phosphorescence lifetime imaging system. Inner retinal OEF was derived from retinal vascular PO(2) measurements based on Fick's principle. Measurements of inner retinal OEF obtained under normoxia were compared between nasal and temporal retinal sectors and repeatability was determined. Inner retinal OEF measurements obtained under normoxia and hypoxia were compared.
  
  
  RESULTS
  Retinal vascular PO(2) and inner retinal OEF measurements were repeatable (ICC ≥ 0.83). Inner retinal OEF measurements at nasal and temporal retinal sectors were correlated (R = 0.71; P = 0.02; n = 10). Under hypoxia, both retinal arterial and venous PO(2) decreased significantly as compared with normoxia (P < 0.001; n = 10). Inner retinal OEF was 0.46 ± 0.13 under normoxia and increased significantly to 0.67 ± 0.16 under hypoxia (mean ± SD; P < 0.001; n = 10).
  
  
  CONCLUSIONS
  Inner retinal OEF is a promising quantitative biomarker for the adequacy of oxygen supply for metabolism under physiologically and pathologically altered conditions.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, USA.
authors.forename: Pang-yu
authors.initials: PY
authors.lastname: Teng
authors.forename: Justin
authors.initials: J
authors.lastname: Wanek
authors.forename: Norman P
authors.initials: NP
authors.lastname: Blair
authors.forename: Mahnaz
authors.initials: M
authors.lastname: Shahidi
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000378:metabolism*; D008163:Luminescent Measurements; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D010313:Partial Pressure; D051381:Rats; D020318:Rats, Long-Evans; D012171:Retinal Vessels / Q000502:physiology*
chemical_list: D010100:Oxygen