title: Test-retest variability in structural and functional parameters of glaucoma damage in the glaucoma imaging longitudinal study.
abstract: OBJECTIVE
  To determine the test-retest variability in perimetric, optic disc, and macular thickness parameters in a cohort of treated patients with established glaucoma.
  
  
  METHODS
  In this cohort study, the authors analyzed the imaging studies and visual field tests at the baseline and 6-month visits of 162 eyes of 162 participant in the Glaucoma Imaging Longitudinal Study (GILS). They assessed the difference, expressed as the standard error of measurement, of Humphrey field analyzer II (HFA) Swedish Interactive Threshold Algorithm fast, Heidelberg retinal tomograph (HRT) II, and retinal thickness analyzer (RTA) parameters between the two visits and assumed that this difference was due to measurement variability, not pathologic change. A statistically significant change was defined as twice the standard error of measurement.
  
  
  RESULTS
  In this cohort of treated glaucoma patients, it was found that statistically significant changes were 3.2 dB for mean deviation (MD), 2.2 for pattern standard deviation (PSD), 0.12 for cup shape measure, 0.26 mm for rim area, and 32.8 microm and 31.8 microm for superior and inferior macular thickness, respectively. On the basis of these values, it was estimated that the number of potential progression events detectable in this cohort by the parameters of MD, PSD, cup shape measure, rim area, superior macular thickness, and inferior macular thickness was 7.5, 6.0, 2.3, 5.7, 3.1, and 3.4, respectively.
  
  
  CONCLUSIONS
  The variability of the measurements of MD, PSD, and rim area, relative to the range of possible values, is less than the variability of cup shape measure or macular thickness measurements. Therefore, the former measurements may be more useful global measurements for assessing progressive glaucoma damage.
authors.affiliation: Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA. hjampel@jhmi.edu
authors.forename: Henry D
authors.initials: HD
authors.lastname: Jampel
authors.forename: Susan
authors.initials: S
authors.lastname: Vitale
authors.forename: Yulan
authors.initials: Y
authors.lastname: Ding
authors.forename: Harry
authors.initials: H
authors.lastname: Quigley
authors.forename: David
authors.initials: D
authors.lastname: Friedman
authors.forename: Nathan
authors.initials: N
authors.lastname: Congdon
authors.forename: Ran
authors.initials: R
authors.lastname: Zeimer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003941:Diagnostic Techniques, Ophthalmological / Q000592:standards*; D018450:Disease Progression; D005260:Female; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D015203:Reproducibility of Results; D012165:Retinal Ganglion Cells / Q000473:pathology; D014054:Tomography / Q000379:methods; D014786:Vision Disorders / Q000175:diagnosis*; D058609:Visual Field Tests / Q000592:standards; D014794:Visual Fields