Ganglion Cell–Inner Plexiform Layer Change Detected by Optical Coherence Tomography Indicates Progression in Advanced Glaucoma

Purpose To examine the performance of Guided Progression Analysis (GPA; Carl Zeiss Meditec, Dublin, CA) in spectral-domain optical coherence tomography (OCT) in detecting progressive thinning of ganglion cell–inner plexiform layer (GCIPL) and retinal nerve fiber layer (RNFL) in glaucoma. Design Longitudinal, observational study. Participants A total of 196 eyes of 123 primary open-angle glaucoma patients (mean follow-up, 5.0 years). Methods Macular GCIPL and peripapillary RNFL thicknesses were measured by Cirrus HD-OCT (Zeiss, Dublin, CA), and progressive GCIPL and RNFL thinning were assessed by GPA. The reference standard of glaucoma progression was determined by visual field (VF) progression. Glaucomatous eyes were classified into mild (117 eyes) or moderate to advanced (79 eyes) groups based on VF defects. Ganglion cell–inner plexiform layer and RNFL thinning rates were compared between progressors and nonprogressors. Visual field survival estimates in eyes with and without progressive GCIPL and RNFL thinning were evaluated by Kaplan–Meier survival analysis and compared with the log-rank test. Main Outcome Measures Progressive GCIPL and RNFL thinning assessed by OCT GPA. Results Seventy-six eyes (38.8%) and 43 eyes (21.9%) demonstrated progressive GCIPL and RNFL thinning, respectively, and 48 eyes (24.5%) were classified as progressors by reference standard. The rate of change in the average GCIPL thickness was significantly higher in progressors (–1.05±0.98 μm/year for mild glaucoma and −0.66±0.30 μm/year for moderate to advanced glaucoma) than in nonprogressors (–0.47±0.54 μm/year for mild glaucoma and −0.31±0.50 μm/year for moderate to advanced glaucoma), regardless of glaucoma severity ( P < 0.05). Eyes with progressive GCIPL thinning had lower VF survival estimates than eyes without, regardless of glaucoma severity. However, the rate of change in the average RNFL thickness did not differ significantly in moderate to advanced glaucoma ( P = 0.765; –0.26±0.55 μm/year for progressors and −0.33±0.92 μm/year for nonprogressors), and VF survival estimates did not differ significantly between eyes with and without progressive RNFL thinning in moderate to advanced glaucoma ( P = 0.781). Conclusions Ganglion cell–inner plexiform layer GPA provides a new approach for evaluating glaucoma progression. It may be more useful for detecting progression in the advanced stages of glaucoma than RNFL GPA.