title: The Heidelberg retina tomograph Glaucoma Probability Score: reproducibility and measurement of progression.
abstract: OBJECTIVE
  To evaluate the reproducibility of the Heidelberg retina tomograph (HRT) Glaucoma Probability Score (GPS) and assess its potential for monitoring progression.
  
  
  METHODS
  Evaluation of diagnostic tests in a randomized, controlled clinical trial.
  
  
  METHODS
  For reproducibility, we included 43 ocular hypertensive (OHT) and 31 glaucoma subjects. For progression, we included 198 OHT and 21 control subjects.
  
  
  METHODS
  To study reproducibility, global GPS values were generated for HRT images acquired in a test-retest study. Images were acquired at 2 visits within 6 weeks of each other, by 2 different observers. To study progression, GPS values were generated for HRT images acquired prospectively (1993-2001). Linear regression of GPS against time was performed, with progression defined as a significant negative slope (P<0.05). Criterion specificity was estimated from the number of improving subjects (significant positive slope) and the number of progressing controls. Visual field (VF) progression in the same subjects was assessed using 3-omitting pointwise linear regression of sensitivity over time.
  
  
  METHODS
  Reproducibility of GPS was assessed using Bland-Altman analysis (mean difference, 95% limits of agreement). Progression was assessed by the number of OHT subjects identified as progressing, and by agreement with VF progression.
  
  
  RESULTS
  Reproducibility of GPS was better at its extremes (-0.01+/-0.20 for GPS 0-0.30, and 0.02+/-0.09 for GPS 0.78-1.00) than in its mid range (0.07+/-0.54 for GPS 0.30-0.78). Estimated criterion specificity ranged from 95.2% (95% confidence interval, 76.1%-99.9%) to 96.8% (93.2%-98.5%). Twenty-five OHT subjects (12.6%) progressed by GPS, with 11 of the 25 (5.6%) also progressing by VF; 26 subjects (13.1%) progressed by VF alone.
  
  
  CONCLUSIONS
  Changes in HRT GPS values between 0.30 and 0.78 should be interpreted with caution because the index has poorer reproducibility in this range. The global GPS progression algorithm performs at least as well as previously described rim area-based HRT progression strategies.
  
  
  BACKGROUND
  Proprietary or commercial disclosure may be found after the references.
authors.affiliation: NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom. nicholas.strouthidis@btinternet.com
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Strouthidis
authors.forename: Shaban
authors.initials: S
authors.lastname: Demirel
authors.forename: Ryo
authors.initials: R
authors.lastname: Asaoka
authors.forename: Claudio
authors.initials: C
authors.lastname: Cossio-Zuniga
authors.forename: David F
authors.initials: DF
authors.lastname: Garway-Heath
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003941:Diagnostic Techniques, Ophthalmological; D018450:Disease Progression; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis* / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009798:Ocular Hypertension / Q000175:diagnosis / Q000503:physiopathology; D011336:Probability; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014054:Tomography / Q000379:methods; D014794:Visual Fields / Q000502:physiology; D055815:Young Adult