title: Comparison of neuroretinal rim area measurements made by the Heidelberg Retina Tomograph I and the Heidelberg Retina Tomograph II.
abstract: OBJECTIVE
  To investigate the agreement between neuroretinal rim area (RA) measurements using the Heidelberg Retina Tomograph I (HRT Classic) and Heidelberg Retina Tomograph II (HRT II). To compare apparent RA changes in follow-up series of HRT II topographies when using either an HRT Classic or HRT II mean topography as baseline.
  
  
  METHODS
  Cross-sectional study and "no-change," short time series study.
  
  
  METHODS
  Forty-three ocular hypertensive and 31 primary open angle glaucoma subjects.
  
  
  METHODS
  Five HRT Classic and 5 HRT II examinations were acquired from 1 eye of each subject, across 2 visits within 6 weeks. For the cross-sectional study, follow-up RA measurements from HRT Classic and HRT II were compared, using the same HRT Classic mean topography as the baseline. The linear rates of RA change were compared in 2 short time series with either an HRT Classic or an HRT II mean topography as baseline, and 4 follow-up HRT II mean topographies. Intervals between topographies were arbitrarily set at 1 year for meaningful comparisons of rates. Rates of RA change over time were calculated by linear regression. Separate analyses were performed using 3 available reference planes (RP).
  
  
  METHODS
  Global and sectoral RA measurements in HRT Classic and HRT II mean topographies; linear rates of RA change.
  
  
  RESULTS
  HRT Classic minus HRT II mean differences (95% limits of agreement) were 0.09 (-0.17, 0.35) mm, 0.09 (-0.13, 0.32) mm, and 0.11 (-0.24, 0.46) mm for the Moorfields, 320 µm, and standard RPs, respectively (P<0.001 for all RPs, Wilcoxon rank sum test). In the time series, the mean differences (95% limits of agreement) of RA rates of change (HRT Classic baseline minus HRT II baseline) were -0.01 (-0.06, 0.03) mm/y, -0.01 (-0.06, 0.04) mm/y, and -0.0 (-0.09, 0.05) mm/y using the Moorfields, 320 µm, and standard RPs, respectively.
  
  
  CONCLUSIONS
  Although HRT software is backward-compatible, follow-up RA measurements made in the same eye using HRT Classic and HRT II devices display statistically and clinically meaningful systematic differences when HRT Classic topographies are used as a baseline.
authors.affiliation: *NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital and UCL Institute of Ophthalmology ‡Department of Optometry and Visual Science, City University London, London, UK †Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China §Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, NS, Canada.
authors.forename: Ya Xing
authors.initials: YX
authors.lastname: Wang
authors.forename: Neil
authors.initials: N
authors.lastname: O'Leary
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Strouthidis
authors.forename: Edward T
authors.initials: ET
authors.lastname: White
authors.forename: Tuan A
authors.initials: TA
authors.lastname: Ho
authors.forename: David F
authors.initials: DF
authors.lastname: Garway-Heath
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D018450:Disease Progression; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000175:diagnosis*; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D012160:Retina / Q000473:pathology*; D014054:Tomography; D014065:Tonometry, Ocular; D055815:Young Adult