title: Retinal vascular calibre and response to light exposure and serial imaging.
abstract: OBJECTIVE
  To investigate whether retinal vessel calibre measurements on optical retinal photography are affected by light and dark exposure prior to photography and whether the vessel calibre changes during an imaging sequence of several images.
  
  
  METHODS
  Digital optical retinal photographs were obtained from 32 healthy adults in two separate image sequences of six images during 1 min; one sequence with 10 min of dark exposure and one with 10 min of light exposure prior to imaging. Retinal arteriolar and venular calibres were measured computer-assisted and summarized as central retinal artery and vein equivalents (CRAE and CRVE). Outcome measures were difference in calibres after prior light versus prior dark exposure and difference in calibre during each of the two imaging sequences.
  
  
  RESULTS
  CRVE was wider with prior light exposure (2.7%, p = 0.0001), comparing the first image in each image sequence. Within each sequence, there was a venular dilatation from first to last image, both with prior light exposure (1.7%, p = 0.0003) and prior dark exposure (3.1%, p < 0.0001), with the change less pronounced with prior light exposure (p = 0.0164). CRAE showed no significant change in either outcome.
  
  
  CONCLUSIONS
  Retinal venular calibre was wider with light exposure prior to imaging and increased slightly during the imaging sequences, less pronounced after prior light than dark exposure. Measurement error due to these effects will probably be reduced by avoiding dark prior to imaging, and a possible bias effect of endothelial dysfunction may possibly be reduced by measuring calibre on an image taken early in the image sequence.
authors.affiliation: Brain and Circulation Research Group, Department of Clinical Medicine, Faculty of Health Sciences, University of Tromsø, Tromsø, NorwayDepartment of Ophthalmology, Nordland Hospital, Bodø, NorwayDepartment of Ophthalmology, Odense University Hospital, Odense, DenmarkDepartment of Neurology and Neurophysiology, University Hospital of North Norway, Tromsø, Norway.
authors.forename: Therese
authors.initials: T
authors.lastname: von Hanno
authors.forename: Anne Katrin
authors.initials: AK
authors.lastname: Sjølie
authors.forename: Ellisiv B
authors.initials: EB
authors.lastname: Mathiesen
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D003623:Dark Adaptation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007429:Intraocular Pressure / Q000502:physiology; D008027:Light; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D010781:Photography; D012039:Regional Blood Flow; D012161:Retinal Artery / Q000502:physiology* / Q000528:radiation effects; D012169:Retinal Vein / Q000502:physiology* / Q000528:radiation effects; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult
keywords: dark; imaging; light; retinal arterioles; retinal venules; vascular calibre