title: Semi-automated retinal vessel analysis in nonmydriatic fundus photography.
abstract: OBJECTIVE
  Funduscopic assessment of the retinal vessels may be used to assess the health status of microcirculation and as a component in the evaluation of cardiovascular risk factors. Typically, the evaluation is restricted to morphological appreciation without strict quantification. Our purpose was to develop and validate a software tool for semi-automated quantitative analysis of retinal vasculature in nonmydriatic fundus photography.
  
  
  METHODS
  matlab software was used to develop a semi-automated image recognition and analysis tool for the determination of the arterial-venous (A/V) ratio in the central vessel equivalent on 45° digital fundus photographs. Validity and reproducibility of the results were ascertained using nonmydriatic photographs of 50 eyes from 25 subjects recorded from a 3DOCT device (Topcon Corp.). Two hundred and thirty-three eyes of 121 healthy subjects were evaluated to define normative values.
  
  
  RESULTS
  A software tool was developed using image thresholds for vessel recognition and vessel width calculation in a semi-automated three-step procedure: vessel recognition on the photograph and artery/vein designation, width measurement and calculation of central retinal vessel equivalents. Mean vessel recognition rate was 78%, vessel class designation rate 75% and reproducibility between 0.78 and 0.91. Mean A/V ratio was 0.84. Application on a healthy norm cohort showed high congruence with prior published manual methods. Processing time per image was one minute.
  
  
  CONCLUSIONS
  Quantitative geometrical assessment of the retinal vasculature may be performed in a semi-automated manner using dedicated software tools. Yielding reproducible numerical data within a short time leap, this may contribute additional value to mere morphological estimates in the clinical evaluation of fundus photographs.
authors.affiliation: Mannheim Institute of Public Health, Social and Preventive Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Alexander Karl-Georg
authors.initials: AK
authors.lastname: Schuster
authors.forename: Joachim Ernst
authors.initials: JE
authors.lastname: Fischer
authors.forename: Urs
authors.initials: U
authors.lastname: Vossmerbaeumer
mesh_terms: D000328:Adult; D000465:Algorithms; D001794:Blood Pressure / Q000502:physiology; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009184:Mydriatics / Q000008:administration & dosage; D010781:Photography / Q000295:instrumentation / Q000379:methods*; D015203:Reproducibility of Results; D012161:Retinal Artery / Q000033:anatomy & histology*; D012169:Retinal Vein / Q000033:anatomy & histology*; D012984:Software; D055815:Young Adult
chemical_list: D009184:Mydriatics
keywords: central retinal vessel equivalents; epidemiology; fundus photography; hypertensive retinopathy; imaging analyser; retinal vessel