title: Factors Determining Flicker-Induced Retinal Vasodilation in Healthy Subjects.
abstract: OBJECTIVE
  The purpose of this study was to analyze factors determining retinal arterial and venous responses to stimulation with diffuse luminance flicker in healthy subjects.
  
  
  METHODS
  We retrospectively analyzed results obtained in 374 healthy subjects who had previously participated in clinical studies in our department. A total of 153 subjects underwent a protocol in which flicker stimulation was delivered through the fundus camera at 8 Hz (protocol 1), separating measurement and stimulation light depending on the wavelength, and 221 subjects underwent a protocol in which diffuse luminance flicker was delivered at 12.5 Hz with high modulation depth (protocol 2). We investigated whether sex, systemic blood pressure, baseline vessel size, blood plasma concentration of fasting glucose and hematocrit, and serum concentration of cholesterol, triglycerides, creatinine and C-reactive protein influenced the retinal vascular response to flicker stimulation.
  
  
  RESULTS
  Flicker responses in arteries and veins were more pronounced in protocol 2 than in protocol 1 (P < 0.001, each). In both of the protocols the vascular response to stimulation with diffuse luminance flicker was larger in smaller vessels (P between 0.001 and 0.016). In protocol 2 the retinal arterial flicker response was negatively associated with cholesterol serum levels (P = 0.033); in protocol 1, only a tendency toward this effect was observed (P = 0.056).
  
  
  CONCLUSIONS
  The present analysis indicates that retinal arterial and venous responses to stimulation with diffuse luminance flicker depend on the way the stimulation is delivered through the fundus camera. In addition, the flicker response varied with vessel size, that is, the smaller the vessel width, the larger the flicker response. Finally, our data indicate that, even within the normal range, higher cholesterol serum levels are associated with lower hyperemic flicker responses.
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria 2Center of Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
authors.forename: Mozhgan
authors.initials: M
authors.lastname: Sharifizad
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Katarzyna J
authors.initials: KJ
authors.lastname: Witkowska
authors.affiliation: Center of Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
authors.forename: Gerold C
authors.initials: GC
authors.lastname: Aschinger
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Sabina
authors.initials: S
authors.lastname: Sapeta
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Rauch
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Doreen
authors.initials: D
authors.lastname: Schmidl
authors.affiliation: Center of Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
authors.forename: Rene M
authors.initials: RM
authors.lastname: Werkmeister
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Garhöfer
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria 2Center of Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002784:Cholesterol / Q000097:blood; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D012044:Regression Analysis; D012161:Retinal Artery / Q000502:physiology / Q000528:radiation effects*; D012169:Retinal Vein / Q000502:physiology / Q000528:radiation effects*; D012189:Retrospective Studies; D014664:Vasodilation / Q000502:physiology / Q000528:radiation effects*
chemical_list: D002784:Cholesterol