title: Flicker-induced retinal arteriole dilation is reduced by ambient lighting.
abstract: OBJECTIVE
  To investigate the impact of ambient room lighting on the magnitude of flicker light-induced retinal vasodilations in healthy individuals.
  
  
  METHODS
  Twenty healthy nonsmokers participated in a balanced 2 × 2 crossover study. Retinal vascular imaging was performed with the dynamic vessel analyzer under reduced or normal ambient lighting, then again after 20 minutes under the alternate condition. Baseline calibers of selected arteriole and venule segments were recorded in measurement units. Maximum percentage dilations from baseline during 20 seconds of luminance flicker were calculated from the mean of three measurement cycles. Within-subject differences were assessed by repeated measures analysis of variance with the assumption of no carryover effects and pairwise comparisons from the fitted model.
  
  
  RESULTS
  Mean (SD) maximum arteriole dilations during flicker stimulation under reduced and normal ambient lighting were 4.8% (2.3%) and 4.1% (1.9%), respectively (P = 0.019). Maximum arteriole dilations were (mean ± 95% confidence interval) 0.7% ± 0.6% lower under normal ambient lighting compared with reduced lighting. Ambient lighting had no significant effect on maximum venular dilations during flicker stimulation or on the baseline calibers of arterioles or venules.
  
  
  CONCLUSIONS
  Retinal arteriole dilation in response to luminance flicker stimulation is reduced under higher ambient lighting conditions. Reduced responses with higher ambient lighting may reflect reduced contrast between the ON and OFF flicker phases. Although it may not always be feasible to conduct studies under reduced lighting conditions, ambient lighting levels should be consistent to ensure that comparisons are valid.
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Noonan
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Dusting
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Thanh T
authors.initials: TT
authors.lastname: Nguyen
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Victoria, Australia Singapore Eye Research Institute and Department of Ophthalmology, National University of Singapore, Singapore.
authors.forename: Ryan E K
authors.initials: RE
authors.lastname: Man
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: William J
authors.initials: WJ
authors.lastname: Best
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Ecosse L
authors.initials: EL
authors.lastname: Lamoureux
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001160:Arterioles / Q000502:physiology / Q000528:radiation effects; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D012171:Retinal Vessels / Q000502:physiology / Q000528:radiation effects*; D014664:Vasodilation / Q000502:physiology / Q000528:radiation effects*; D014699:Venules / Q000502:physiology / Q000528:radiation effects
keywords: flicker light; functional imaging; neurovascular coupling; retinal blood flow