title: Comparison of Common Retinal Vessel Caliber Measurement Software and a Conversion Algorithm.
abstract: OBJECTIVE
  To compare three commonly used retinal vessel caliber measurement software systems, and propose an algorithm for conversion between measurement systems.
  
  
  METHODS
  We used 120 retinal photographs to evaluate the agreement between three commonly used software (Retinal Analysis [RA], Integrative Vessel Analysis [IVAN], and Singapore I Vessel Assessment [SIVA]). Bland-Altman plots were used to evaluate agreement of retinal arteriolar (central retinal artery equivalent, CRAE) and venular (central retinal vein equivalent, CRVE) calibers. Pearson's correlation was used to assess the associations between systemic factors and retinal vessel calibers, and Z-test was used to compare the strength of the correlation coefficients across the three software systems. An algorithm was created to convert measurements, with pairedt-test performed to evaluate the differences between SIVA-measured retinal calibers and SIVA-approximates converted from RA- and IVAN-measurements using the algorithm.
  
  
  RESULTS
  Differences between SIVA- and RA-measured calibers (CRAE: mean difference [MD] = -21.8 μm, 95% limits of agreement [LOA], -47.3 to 3.7 μm; CRVE: MD = -7.7 μm, 95% LOA, -28.0 to 12.6 μm), SIVA- and IVAN-measured calibers (CRAE: MD = -6.7 μm, 95% LOA, -23.8 to 10.4 μm; CRVE: MD = -18.2 μm 95% LOA, -36.7 to 0.4 μm) were large. However, the strength of correlations between systemic factors with SIVA-measured retinal calibers was not significantly different to that measured using RA and IVAN (P≥ 0.332). SIVA-approximates converted from RA and IVAN measurements using the proposed algorithm was not significantly different from SIVA-measured calibers (P≥ 0.20).
  
  
  CONCLUSIONS
  Absolute measurements of retinal vessel calibers vary between three common software systems but associations with systemic factors were similar.
  
  
  CONCLUSIONS
  The proposed algorithm allowed conversions of RA and IVAN measurements to SIVA-approximates. This conversion is important for future data pooling and establishment of normative values for retinal vascular caliber measurements.
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore ; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore.
authors.forename: WanFen
authors.initials: W
authors.lastname: Yip
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore ; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore.
authors.forename: Yih Chung
authors.initials: YC
authors.lastname: Tham
authors.affiliation: School of Computing, National University of Singapore, Singapore.
authors.forename: Wynne
authors.initials: W
authors.lastname: Hsu
authors.affiliation: School of Computing, National University of Singapore, Singapore.
authors.forename: Mong Li
authors.initials: ML
authors.lastname: Lee
authors.affiliation: University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Ronald
authors.initials: R
authors.lastname: Klein
authors.affiliation: University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Klein
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore ; Department of Neurology, Brain Center Rudolf Magnus, University Medical Center Utrecht, the Netherlands ; Ophthalmology and Visual Sciences Academic Clinical Programme, Duke-NUS Graduate Medical School, National University of Singapore, Singapore.
authors.forename: Mohammad Kamran
authors.initials: MK
authors.lastname: Ikram
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore ; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore ; Ophthalmology and Visual Sciences Academic Clinical Programme, Duke-NUS Graduate Medical School, National University of Singapore, Singapore.
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore ; Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong.
authors.forename: Carol Yim-Lui
authors.initials: CY
authors.lastname: Cheung
keywords: epidemiology; retinal vasculature; retinal vessels