title: Comparison of subjective and objective methods to determine the retinal arterio-venous ratio using fundus photography.
abstract: OBJECTIVE
  To assess the inter and intra observer variability of subjective grading of the retinal arterio-venous ratio (AVR) using a visual grading and to compare the subjectively derived grades to an objective method using a semi-automated computer program.
  
  
  METHODS
  Following intraocular pressure and blood pressure measurements all subjects underwent dilated fundus photography. 86 monochromatic retinal images with the optic nerve head centred (52 healthy volunteers) were obtained using a Zeiss FF450+ fundus camera. Arterio-venous ratios (AVR), central retinal artery equivalent (CRAE) and central retinal vein equivalent (CRVE) were calculated on three separate occasions by one single observer semi-automatically using the software VesselMap (ImedosSystems, Jena, Germany). Following the automated grading, three examiners graded the AVR visually on three separate occasions in order to assess their agreement.
  
  
  RESULTS
  Reproducibility of the semi-automatic parameters was excellent (ICCs: 0.97 (CRAE); 0.985 (CRVE) and 0.952 (AVR)). However, visual grading of AVR showed inter grader differences as well as discrepancies between subjectively derived and objectively calculated AVR (all p<0.000001).
  
  
  CONCLUSIONS
  Grader education and experience leads to inter-grader differences but more importantly, subjective grading is not capable to pick up subtle differences across healthy individuals and does not represent true AVR when compared with an objective assessment method. Technology advancements mean we no longer rely on opthalmoscopic evaluation but can capture and store fundus images with retinal cameras, enabling us to measure vessel calibre more accurately compared to visual estimation; hence it should be integrated in optometric practise for improved accuracy and reliability of clinical assessments of retinal vessel calibres.
authors.affiliation: Aston University, School of Life and Health Sciences, Birmingham, UK. Electronic address: R.Heitmar1@aston.ac.uk.
authors.forename: Rebekka
authors.initials: R
authors.lastname: Heitmar
authors.affiliation: Aston University, School of Life and Health Sciences, Birmingham, UK.
authors.forename: Angelos A
authors.initials: AA
authors.lastname: Kalitzeos
authors.affiliation: Topcon Corporation USA, NJ, USA; Toronto Western Hospital, Department of Ophthalmology and Vision Sciences, Toronto, Canada.
authors.forename: Sunni R
authors.initials: SR
authors.lastname: Patel
authors.affiliation: Aston University, School of Life and Health Sciences, Birmingham, UK.
authors.forename: Diana
authors.initials: D
authors.lastname: Prabhu-Das
authors.affiliation: Aston University, School of Life and Health Sciences, Birmingham, UK.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Cubbidge
mesh_terms: D000704:Analysis of Variance; D002983:Clinical Competence; D005654:Fundus Oculi; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D015588:Observer Variation; D009887:Ophthalmoscopy / Q000379:methods*; D010781:Photography / Q000379:methods*; D015203:Reproducibility of Results; D012171:Retinal Vessels / Q000033:anatomy & histology* / Q000502:physiology
keywords: Análisis semi-automatizado; Arterio-venous ratio; Central retinal artery equivalent; Central retinal vein equivalent; Diámetro de los vasos de la retina; Equivalente de la arteria retiniana central; Equivalente de la vena retiniana central; Graduación visual; Ratio arterio-venoso; Reproducibilidad; Reproducibility; Retinal vessel diameter; Semi-automated analysis; Visual grading