title: Quantitative retinal and choroidal blood flow during light, dark adaptation and flicker light stimulation in rats using fluorescent microspheres.
abstract: OBJECTIVE
  The present study aimed to quantify retinal and choroidal blood flow (BF) during light, dark adaptation and flicker light stimulation using the microsphere technique.
  
  
  METHODS
  Adult male Sprague-Dawley rats were anesthetized with isoflurane. Eyes were dark (Group I, n = 8), light (Group II, n = 8) adapted or stimulated with 10 Hz flicker light (Group III, n = 10). Retinal and choroidal BF were measured by a previously established method, using a mixture of 8 µm yellow-green and 10 µm red fluorescent microspheres. The microspheres were counted ex vivo in the dissected retina and choroid and in the reference arterial blood under a fluorescent microscope.
  
  
  RESULTS
  The choroidal BF was 64.8 ± 29 µl/min (mean ± SD) during dark adaptation, not significantly different from that during light adaptation (66.0 ± 17.8 µl/min). The retinal BF was 13.5 ± 3.2 µl/min during 10 Hz flickering light stimulation, significantly higher than that during dark adaptation in the control fellow eyes (9.9 ± 2.9 µl/min). The choroidal BF values were not statistically different between flicker stimulation and dark adaptation. Retinal BF was 11.6 ± 2.9 µl/min during light adaptation. Dark adaptation did not increase retinal BF (Group I, 8.2 ± 2.4 µl/min; Group II, 9.9 ± 2.9 µl/min).
  
  
  CONCLUSIONS
  These findings argue against a dark-induced or flicker-induced functional hyperemia in the choroid as a result of the demands of the outer retina. Retinal BF was not higher during dark adaptation. Our data support the conclusion that the inner retina has a higher energy demand in flicker conditions relative to dark.
authors: Research Imaging Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA. shihy@unc.edu
authors: Yen-Yu I
authors: YY
authors: Shih
authors: Lin
authors: L
authors: Wang
authors: Bryan H
authors: BH
authors: De La Garza
authors: Guang
authors: G
authors: Li
authors: Grant
authors: G
authors: Cull
authors: Jeffery W
authors: JW
authors: Kiel
authors: Timothy Q
authors: TQ
authors: Duong
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002829:Choroid / Q000098:blood supply / Q000502:physiology; D003623:Dark Adaptation / Q000502:physiology*; D005425:Flicker Fusion / Q000502:physiology*; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D008297:Male; D008863:Microspheres; D008955:Models, Cardiovascular; D010775:Photic Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000502:physiology; D012160:Retina / Q000502:physiology; D012171:Retinal Vessels / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide