title: Visual field progression in glaucoma: what is the specificity of the Guided Progression Analysis?
abstract: OBJECTIVE
  To estimate the specificity of the Guided Progression Analysis (GPA) (Carl Zeiss Meditec, Dublin, CA) in individual patients with glaucoma.
  
  
  METHODS
  Observational cohort study.
  
  
  METHODS
  Thirty patients with open-angle glaucoma.
  
  
  METHODS
  In 30 patients with open-angle glaucoma, 1 eye (median mean deviation [MD], -2.5 decibels [dB]; interquartile range, -4.4 to -1.3 dB) was tested 12 times over 3 months (Humphrey Field Analyzer, Carl Zeiss Meditec; SITA Standard, 24-2). "Possible progression" and "likely progression" were determined with the GPA. These analyses were repeated after the order of the tests had been randomly rearranged (1000 unique permutations).
  
  
  METHODS
  Rate of false-positive alerts of "possible progression" and "likely progression" with the GPA.
  
  
  RESULTS
  On average, the specificity of the GPA "likely progression" alert was high-for the entire sample, the mean rate of false-positive alerts after 10 follow-up tests was 2.6%. With "possible progression," the specificity was considerably lower (false-positive rate, 18.5%). Most important, the cumulative rate of false-positive alerts varied substantially among patients, from <1% to 80% with "possible progression" and from <0.1% to 20% with "likely progression." Factors associated with false-positive alerts were visual field variability (standard deviation of MD, Spearman's rho = 0.41, P<0.001) and the reliability indices (proportion of false-positive and false-negative responses, fixation losses, rho>0.31, P≤0.10).
  
  
  CONCLUSIONS
  On average, progression criteria currently used in the GPA have high specificity, but some patients are more likely to show false-positive alerts than others. This is a natural consequence of population-based change criteria and may not matter in clinical trials and studies in which large groups of patients are compared. However, it must be considered when the GPA is used in clinical practice where specificity needs to be controlled for individual patients.
authors.affiliation: Ophthalmology and Visual Sciences, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada. Electronic address: paul@dal.ca.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Artes
authors.affiliation: Ophthalmology and Visual Sciences, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada; Biostatistics, Institute of Population Health, Faculty of Medical and Human Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Neil
authors.initials: N
authors.lastname: O'Leary
authors.affiliation: Ophthalmology and Visual Sciences, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Marcelo T
authors.initials: MT
authors.lastname: Nicolela
authors.affiliation: Ophthalmology and Visual Sciences, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Balwantray C
authors.initials: BC
authors.lastname: Chauhan
authors.affiliation: Optometry and Visual Science, City University London, United Kingdom.
authors.forename: David P
authors.initials: DP
authors.lastname: Crabb
mesh_terms: D000368:Aged; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D058609:Visual Field Tests / Q000379:methods* / Q000592:standards; D014794:Visual Fields / Q000502:physiology