Agreement for detecting glaucoma progression with the GDx guided progression analysis, automated perimetry, and optic disc photography

Abstract

Purpose: To evaluate the ability of the GDx Variable Corneal Compensation (VCC) Guided Progression Analysis (GPA) software for detecting glaucomatous progression.

Design: Observational cohort study.

Participants: The study included 453 eyes from 252 individuals followed for an average of 46+/-14 months as part of the Diagnostic Innovations in Glaucoma Study. At baseline, 29% of the eyes were classified as glaucomatous, 67% of the eyes were classified as suspects, and 5% of the eyes were classified as healthy.

Methods: Images were obtained annually with the GDx VCC and analyzed for progression using the Fast Mode of the GDx GPA software. Progression using conventional methods was determined by the GPA software for standard automated achromatic perimetry (SAP) and by masked assessment of optic disc stereophotographs by expert graders.

Main outcome measures: Sensitivity, specificity, and likelihood ratios (LRs) for detection of glaucoma progression using the GDx GPA were calculated with SAP and optic disc stereophotographs used as reference standards. Agreement among the different methods was reported using the AC(1) coefficient.

Results: Thirty-four of the 431 glaucoma and glaucoma suspect eyes (8%) showed progression by SAP or optic disc stereophotographs. The GDx GPA detected 17 of these eyes for a sensitivity of 50%. Fourteen eyes showed progression only by the GDx GPA with a specificity of 96%. Positive and negative LRs were 12.5 and 0.5, respectively. None of the healthy eyes showed progression by the GDx GPA, with a specificity of 100% in this group. Inter-method agreement (AC(1) coefficient and 95% confidence intervals) for non-progressing and progressing eyes was 0.96 (0.94-0.97) and 0.44 (0.28-0.61), respectively.

Conclusions: The GDx GPA detected glaucoma progression in a significant number of cases showing progression by conventional methods, with high specificity and high positive LRs. Estimates of the accuracy for detecting progression suggest that the GDx GPA could be used to complement clinical evaluation in the detection of longitudinal change in glaucoma.

Figure 1

Example of a 48 year-old African-American patient suspected of having glaucoma based on high levels of intraocular pressure at the baseline. The optic disc at the baseline shows a slightly tilted disc with a normal appearance of the neuroretinal rim and a normal pattern of brightness and striations of the retinal nerve fiber layer (RNFL). During the follow-up, a new localized RNFL defect can be observed in the inferior temporal sector on the optic disc stereophotographs and the visual fields show a corresponding superior defect. All three maps of the GDx Guided Progression Analysis (GPA) report were able to detect RNFL loss in the same sector, in agreement with both conventional methods.

Figure 2

Example of a 56 year-old Caucasian male diagnosed with glaucoma and followed for almost 5 years under treatment. The figure shows an example of disagreement among methods for detection of change. The optic disc stereophotographs showed progressive retinal nerve fiber layer loss in the inferior temporal sector, with corresponding visual field loss. Even though the GDx shows pronounced the retinal nerve fiber layer damage at the corresponding position, the GDx Guided Progression Analysis (GPA) software was not able to identify significant worsening over time.

Figure 3

Venn diagram showing the number of exams classified as progressing by the GDx Guided Progression Analysis (GPA), standard achromatic perimetry GPA and expert clinician stereophotographs assessment.