title: Choroidal oximetry with a noninvasive spectrophotometric oximeter.
abstract: OBJECTIVE
  The purpose of the study was to establish a new technology to measure hemoglobin oxygen saturation in human choroidal vasculature with a noninvasive spectrophotometric oximeter.
  
  
  METHODS
  The fundus camera-based oximeter captures dual-wavelength oximetry images of the fundus and calculates optical density ratio (ODR), which is inversely related to hemoglobin oxygen saturation. Sixteen healthy and lightly pigmented individuals were imaged during normoxia and six during both normoxia and pure oxygen breathing (hyperoxia). ODR was measured for choroidal vessels, vortex veins, and retinal arterioles and venules.
  
  
  RESULTS
  ODR was 0.10 ± 0.10 (mean ± SD) for choroidal vessels, 0.13 ± 0.12 for vortex veins, 0.22 ± 0.04 for retinal arterioles, and 0.50 ± 0.09 for retinal venules. Inhalation of pure oxygen lowered ODR levels in all vessel types; the decrease was 0.035 ± 0.028 in choroidal vessels (P = 0.029, paired t-test), 0.022 ± 0.017 in the retinal arterioles (P = 0.022, paired t-test), and 0.246 ± 0.067 in retinal venules (P = 0.0003, paired t-test).
  
  
  CONCLUSIONS
  The ODR can be measured noninvasively in the choroidal vessels of lightly pigmented individuals and is significantly lower in choroidal vessels than in retinal arterioles. This may suggest higher oxygen saturation but is also compatible with the reduced contrast of choroidal vessels at both wavelengths that is expected from scattering of light within the choroid. The decrease of ODR during hyperoxia was significant for all vessel types, which confirms that the oximeter is sensitive to changes in oxygen saturation in both choroidal and retinal vessels.
authors.affiliation: Department of Ophthalmology, Landspitali University Hospital, Reykjavik, Iceland.
authors.forename: Jona Valgerdur
authors.initials: JV
authors.lastname: Kristjansdottir
authors.forename: Sveinn Hakon
authors.initials: SH
authors.lastname: Hardarson
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Harvey
authors.forename: Olof Birna
authors.initials: OB
authors.lastname: Olafsdottir
authors.forename: Thorunn Scheving
authors.initials: TS
authors.lastname: Eliasdottir
authors.forename: Einar
authors.initials: E
authors.lastname: Stefánsson
mesh_terms: D000328:Adult; D001160:Arterioles / Q000502:physiology; D002829:Choroid / Q000098:blood supply*; D005260:Female; D006801:Humans; D018496:Hyperoxia / Q000503:physiopathology; D008297:Male; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000008:administration & dosage / Q000097:blood*; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000378:metabolism; D012161:Retinal Artery / Q000502:physiology; D012169:Retinal Vein / Q000502:physiology; D013053:Spectrophotometry / Q000295:instrumentation; D014699:Venules / Q000502:physiology
chemical_list: D010108:Oxyhemoglobins; D010100:Oxygen
keywords: choroid; hyperoxia; optical density; oxygen; retina