title: Choroidal blood flow decreases with age: an MRI study.
abstract: OBJECTIVE
  To verify that a visual fixation protocol with cued eye blinks achieves sufficient stability for magnetic resonance imaging (MRI) blood-flow measurements and to determine if choroidal blood flow (ChBF) changes with age in humans.
  
  
  METHODS
  The visual fixation stability achievable during an MRI scan was measured in five normal subjects using an eye-tracking camera outside the MRI scanner. Subjects were instructed to blink immediately after recorded MRI sound cues but to otherwise maintain stable visual fixation on a small target. Using this fixation protocol, ChBF was measured with MRI using a 3 Tesla clinical scanner in 17 normal subjects (24-68 years old). Arterial and intraocular pressures (IOP) were measured to calculate perfusion pressure in the same subjects.
  
  
  RESULTS
  The mean temporal fluctuations (standard deviation) of the horizontal and vertical displacements were 29 ± 9 μm and 38 ± 11 μm within individual fixation periods, and 50 ± 34 μm and 48 ± 19 μm across different fixation periods. The absolute displacements were 67 ± 31 μm and 81 ± 26 μm. ChBF was negatively correlated with age (R = -0.7, p = 0.003), declining 2.7 ml/100 ml/min per year. There were no significant correlations between ChBF versus perfusion pressure, arterial pressure, or IOP. There were also no significant correlations between age versus perfusion pressure, arterial pressure, or IOP. Multiple regression analysis indicated that age was the only measured independent variable that was significantly correlated with ChBF (p = 0.03).
  
  
  CONCLUSIONS
  The visual fixation protocol with cued eye blinks was effective in achieving sufficient stability for MRI measurements. ChBF had a significant negative correlation with age.
authors.affiliation: Research Imaging Institute, University of Texas Health Science Center , San Antonio, TX , USA .
authors.forename: Oscar San
authors.initials: OS
authors.lastname: Emeterio Nateras
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Harrison
authors.forename: Eric R
authors.initials: ER
authors.lastname: Muir
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Qi
authors.initials: Q
authors.lastname: Peng
authors.forename: Steven
authors.initials: S
authors.lastname: Chalfin
authors.forename: Juan E
authors.initials: JE
authors.lastname: Gutierrez
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Johnson
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Kiel
authors.forename: Timothy Q
authors.initials: TQ
authors.lastname: Duong
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002829:Choroid / Q000098:blood supply*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012039:Regional Blood Flow / Q000502:physiology*; D055815:Young Adult
keywords: Choroidal basal blood flow; eye tracking; high-resolution MRI; visual fixation