title: Measuring retinal vessel tortuosity in 10-year-old children: validation of the Computer-Assisted Image Analysis of the Retina (CAIAR) program.
abstract: OBJECTIVE
  To examine the agreement of a novel computer program measuring retinal vessel tortuosity with subjective assessment of tortuosity in school-aged children.
  
  
  METHODS
  Cross-sectional study of 387 retinal vessels (193 arterioles, 194 veins) from 28 eyes of 14 children (aged 10 years). Retinal digital images were analyzed using the Computer Assisted Image Analysis of the Retina (CAIAR) program, including 14 measures of tortuosity. Vessels were graded (from 0 = none; to 5 = tortuous) independently by two observers. Interobserver agreement was assessed by using kappa statistics. Agreement with all 14 objective measures was assessed with correlation/regression analyses. Intersession repeatability (comparing morning and afternoon sessions) of tortuosity indices was calculated.
  
  
  RESULTS
  Interobserver agreement of vessel tortuosity within one grade was high (kappa = 0.97), with total agreement in 56% of grades and 42% differing by +/-1 grade. Tortuosity indices based on subdivided chord length methods showed strong log-linear associations with agreed subjective grades (typically r > 0.6; P < 0.001). An approach that averages the distance from the vessel to chord length along the length of the vessel showed best agreement (r = 0.8; P < 0.0001). Tortuosity measures based on curvature performed less well. Intersession repeatability of the vessel to chord technique was good, differing by values equivalent to <1 in subjective grade.
  
  
  CONCLUSIONS
  Tortuosity indices based on changes in subdivided chord lengths showed optimal agreement with subjective assessment. The relation of these indices to ethnicity and cardiovascular risk factors in childhood should be examined further, as these indices may be a useful indicator of early vascular function.
authors.affiliation: Division of Community Health Sciences, St. George's, University of London, London, United Kingdom. cowen@sgul.ac.uk
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Owen
authors.forename: Alicja R
authors.initials: AR
authors.lastname: Rudnicka
authors.forename: Robert
authors.initials: R
authors.lastname: Mullen
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Barman
authors.forename: Dorothy
authors.initials: D
authors.lastname: Monekosso
authors.forename: Peter H
authors.initials: PH
authors.lastname: Whincup
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Ng
authors.forename: Carl
authors.initials: C
authors.lastname: Paterson