title: Inner Retinal Oxygen Extraction Fraction in Response to Light Flicker Stimulation in Humans.
abstract: OBJECTIVE
  Light flicker has been shown to stimulate retinal neural activity, increase blood flow, and alter inner retinal oxygen metabolism (MO2) and delivery (DO2). The purpose of the study was to determine the change in MO2 relative to DO2 due to light flicker stimulation in humans, as assessed by the inner retinal oxygen extraction fraction (OEF).
  
  
  METHODS
  An optical imaging system, based on a modified slit lamp biomicroscope, was developed for simultaneous measurements of retinal vascular diameter (D) and oxygen saturation (SO2). Retinal images were acquired in 20 healthy subjects before and during light flicker stimulation. Arterial and venous D (DA and DV) and SO2 (SO2A and SO2V) were quantified within a circumpapillary region. Oxygen extraction fraction was defined as the ratio of MO2 to DO2 and was calculated as (SO2A - SO2V)/SO2A. Reproducibility of measurements was assessed.
  
  
  RESULTS
  Coefficients of variation and intraclass correlation coefficients of repeated measurements were <5% and ≥0.83, respectively. During light flicker stimulation, DA, DV , and SO2V significantly increased (P ≤ 0.004). Oxygen extraction fraction was 0.37 ± 0.08 before light flicker and significantly decreased to 0.31 ± 0.07 during light flicker (P = 0.001).
  
  
  CONCLUSIONS
  Oxygen extraction fraction before and during light flicker stimulation is reported in human subjects for the first time. Oxygen extraction fraction decreased during light flicker stimulation, indicating the change in DO2 exceeded that of MO2. This technology is potentially useful for the detection of changes in OEF response to light flicker in physiological and pathological retinal conditions.
authors.forename: Anthony E
authors.initials: AE
authors.lastname: Felder
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: D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000528:radiation effects*; D010775:Photic Stimulation; D012160:Retina / Q000378:metabolism / Q000528:radiation effects*; D012171:Retinal Vessels / Q000378:metabolism / Q000528:radiation effects; D066167:Slit Lamp
chemical_list: D010100:Oxygen