Interobserver agreement and intraobserver reproducibility of the subjective determination of glaucomatous visual field progression

Abstract

Purpose: To determine the extent of interobserver agreement and intraobserver reproducibility of the subjective determination of visual field progression with achromatic automated static perimetry in eyes with glaucoma, and to determine the impact of access to Glaucoma Progression Analysis (GPA) data on interobserver agreement.

Design: Retrospective, observational case series.

Participants: Five glaucoma subspecialists from 5 different academic medical centers.

Methods: Five visual field tests from each of 100 eyes of 83 patients being monitored for glaucoma were retrospectively identified and subjectively and independently evaluated by the 5 glaucoma subspecialists. Each set of visual fields was classified regarding progression as "none," "questionable," "probable," or "definite." More than 1 month later, the same expert observers reevaluated the same sets of visual field tests to allow determination of intraobserver reproducibility. A final subjective evaluation regarding progression was performed 3 months later, at which time the expert observers had access to the GPA printout.

Main outcome measures: The level of interobserver agreement and intraobserver reproducibility was estimated using kappa statistics on the raw classification data and also on dichotomized data in which "none" and "questionable" progression were reclassified together as nonprogressed and " probable" and "definite" were reclassified as progressed.

Results: Intraobserver reproducibility was good to excellent (kappa = 0.62-0.78) for the raw data and moderate to good (kappa = 0.58-0.71) for the dichotomized data. Interobserver agreement was moderate (kappa = 0.45; 95% confidence interval [CI], 0.35-0.55) for the raw classification data and also for dichotomized data (kappa = 0.55; 95% CI, 0.46-0.64). Access to the GPA printout did not significantly change the level of interobserver agreement.

Conclusions: Five glaucoma experts had good to excellent reproducibility of the determination of visual field progression compared with earlier evaluation of the same field sets. Agreement among the experts with each other was only moderate, and did not improve when each had access to GPA results. .