title: Reliability of retinal vessel calibre measurements using a retinal oximeter.
abstract: BACKGROUND
  Summarised retinal vessel diameters are linked to systemic vascular pathology. Monochromatic images provide best contrast to measure vessel calibres. However, when obtaining images with a dual wavelength oximeter the red-free image can be extracted as the green channel information only which in turn will reduce the number of photographs taken at a given time. This will reduce patient exposure to the camera flash and could provide sufficient quality images to reliably measure vessel calibres.
  
  
  METHODS
  We obtained retinal images of one eye of 45 healthy participants. Central retinal arteriolar and central retinal venular equivalents (CRAE and CRVE, respectively) were measured using semi-automated software from two monochromatic images: one taken with a red-free filter and one extracted from the green channel of a dual wavelength oximetry image.
  
  
  RESULTS
  Participants were aged between 21 and 62 years, all were normotensive (SBP: 115 (12) mmHg; DBP: 72 (10) mmHg) and had normal intra-ocular pressures (12 (3) mmHg). Bland-Altman analysis revealed good agreement of CRAE and CRVE as obtained from both images (mean bias CRAE = 0.88; CRVE = 2.82).
  
  
  CONCLUSIONS
  Summarised retinal vessel calibre measurements obtained from oximetry images are in good agreement to those obtained using red-free photographs.
authors.affiliation: Aston University, School of Life and Health Sciences, Aston Triangle, Birmingham, B4 7ET, UK. R.Heitmar1@aston.ac.uk.
authors.forename: Rebekka
authors.initials: R
authors.lastname: Heitmar
authors.affiliation: Aston University, School of Life and Health Sciences, Aston Triangle, Birmingham, B4 7ET, UK.
authors.forename: Angelos A
authors.initials: AA
authors.lastname: Kalitzeos
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000379:methods*; D010781:Photography / Q000379:methods; D015203:Reproducibility of Results; D012161:Retinal Artery / Q000033:anatomy & histology*; D012169:Retinal Vein / Q000033:anatomy & histology*; D055815:Young Adult