title: Photoplethysmographic measurement of various retinal vascular pulsation parameters and measurement of the venous phase delay.
abstract: OBJECTIVE
  Retinal vein pulsation properties are altered by glaucoma, intracranial pressure (ICP) changes, and retinal venous occlusion, but measurements are limited to threshold measures or manual observation from video frames. We developed an objective retinal vessel pulsation measurement technique, assessed its repeatability, and used it to determine the phase relations between retinal arteries and veins.
  
  
  METHODS
  Twenty-three eyes of 20 glaucoma patients had video photograph recordings from their optic nerve and peripapillary retina. A modified photoplethysmographic system using video recordings taken through an ophthalmodynamometer and timed to the cardiac cycle was used. Aligned video frames of vessel segments were analyzed for blood column light absorbance, and waveform analysis was applied. Coefficient of variation (COV) was calculated from data series using recordings taken within ±1 unit ophthalmodynamometric force of each other. The time in cardiac cycles and seconds of the peak (dilation) and trough (constriction) points of the retinal arterial and vein pulse waveforms were measured.
  
  
  RESULTS
  Mean vein peak time COV was 3.4%, and arterial peak time COV was 4.4%. Lower vein peak occurred at 0.044 cardiac cycles (0.040 seconds) after the arterial peak (P = 0.0001), with upper vein peak an insignificant 0.019 cardiac cycles later. No difference in COV for any parameter was found between upper or lower hemiveins. Mean vein amplitude COV was 12.6%, and mean downslope COV was 17.7%.
  
  
  CONCLUSIONS
  This technique demonstrates a small retinal venous phase lag behind arterial pulse. It is objective and applicable to any eye with clear ocular media and has moderate to high reproducibility. ( http://www.anzctr.org.au number, ACTRN12608000274370.).
authors.affiliation: Lions Eye Institute, University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: William H
authors.initials: WH
authors.lastname: Morgan
authors.affiliation: Statistics and Bioinformatics Group, Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.
authors.forename: Martin L
authors.initials: ML
authors.lastname: Hazelton
authors.affiliation: Statistics and Bioinformatics Group, Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.
authors.forename: Brigid D
authors.initials: BD
authors.lastname: Betz-Stablein
authors.affiliation: Lions Eye Institute, University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Dao-Yi
authors.initials: DY
authors.lastname: Yu
authors.affiliation: Neurofinity, School of Surgery, University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Christopher R P
authors.initials: CR
authors.lastname: Lind
authors.affiliation: Lions Eye Institute, University of Western Australia, Nedlands, Western Australia, Australia Neurofinity, School of Surgery, University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Vignesh
authors.initials: V
authors.lastname: Ravichandran
authors.affiliation: Lions Eye Institute, University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Philip H
authors.initials: PH
authors.lastname: House
mesh_terms: D000368:Aged; D005260:Female; D005901:Glaucoma / Q000503:physiopathology*; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009884:Ophthalmodynamometry / Q000379:methods; D009900:Optic Nerve / Q000098:blood supply / Q000502:physiology; D017156:Photoplethysmography / Q000379:methods*; D011673:Pulsatile Flow / Q000502:physiology*; D012161:Retinal Artery / Q000503:physiopathology; D012169:Retinal Vein / Q000503:physiopathology*; D012170:Retinal Vein Occlusion / Q000503:physiopathology*
keywords: glaucoma; retina; retinal blood flow