title: Factors affecting the test-retest variability of Heidelberg retina tomograph and Heidelberg retina tomograph II measurements.
abstract: OBJECTIVE
  To evaluate the test-retest variability of stereometric parameter measurements made with the Heidelberg retina tomograph (HRT) and Heidelberg retina tomograph-II (HRT-II), and to establish which parameter(s) provided the most repeatable and reliable measurements with both devices. An investigation into the factors affecting the repeatability of the measurements of this parameter(s) was conducted.
  
  
  METHODS
  43 ocular hypertensive and 31 glaucoma subjects were recruited to a test-retest study. One eye from each subject underwent HRT and HRT-II imaging by two observers on each of two occasions within 6 weeks of each other. Lens grading was carried out by LOCS III grading and Scheimpflug camera generated densitogram analysis.
  
  
  RESULTS
  Rim area (RA) and mean cup depth measurements were found to be least variable. Both inter-test reference height difference and image quality had a strong relation (R(2)>0.5, p<0.0001) with inter-test RA difference and, together, are responsible for 70% of RA measurement variability. Image quality was influenced by lens opacity, cylindrical error, and age. Inter-test RA measurement differences were unrelated to the observer or visit interval.
  
  
  CONCLUSIONS
  RA represents an appropriate measure for monitoring glaucomatous progression. Reference height difference and image quality were the factors that most influenced RA measurement variability. Image analysis strategies that address these factors may reduce test-retest variability.
authors.affiliation: Glaucoma Research Unit, Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK.
authors.forename: N G
authors.initials: NG
authors.lastname: Strouthidis
authors.forename: E T
authors.initials: ET
authors.lastname: White
authors.forename: V M F
authors.initials: VM
authors.lastname: Owen
authors.forename: T A
authors.initials: TA
authors.lastname: Ho
authors.forename: C J
authors.initials: CJ
authors.lastname: Hammond
authors.forename: D F
authors.initials: DF
authors.lastname: Garway-Heath
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis* / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009898:Optic Disk / Q000473:pathology; D015203:Reproducibility of Results; D014054:Tomography / Q000379:methods*