Ganglion cell loss in early glaucoma, as assessed by photopic negative response, pattern electroretinogram, and spectral-domain optical coherence tomography.

Purpose: To evaluate discrimination ability of pattern electroretinography (PERG) and photopic negative response (PhNR) between early glaucoma and healthy controls, and their relationship with structural measurements using spectral-domain optical coherence tomography (SD-OCT).
Methods: Cross-sectional study with 34 patients with ocular hypertension (n = 7), suspect glaucoma (n = 17), and early glaucoma (n = 10), plus 24 age-matched controls. The following parameters were analyzed: P50 and N95 amplitude of the PERG, PhNR amplitude and PhNR/b-wave ratio, peripapillary retinal and macular nerve fiber layer (NFL) thicknesses, and ganglion cell complex (GCC) thickness. Data from only one eye per individual were included in the statistical analysis. Descriptive statistics, ANOVA, receiver operating characteristics (ROC) curves, and correlation tests were used for analysis of the variables.
Results: PERG N95 and PhNR amplitudes were significantly reduced in suspect and early glaucoma eyes versus controls. Significant differences across ocular hypertensive, suspect, and early glaucoma eyes were found for macular NFL and GCC thickness, but not for any of the ERG parameters. The mean PhNR amplitude did not differ across these groups and was already reduced on average by 46% in ocular hypertensive and early glaucoma eyes and by 52% in suspect glaucoma eyes. The P50 and N95 amplitudes showed similar reduction in suspect and early glaucoma eyes on average by 15 and 26%, respectively. Of the ERG parameters, PhNR amplitude distinguished best between glaucoma and control groups, with an area under ROC curve of 0.90 for suspect glaucoma, and 0.86 for early glaucoma. PhNR/b-wave ratio showed strongest association in suspect glaucoma eyes with peripapillary retinal (r, 0.61) and macular NFL (r, 0.76) thicknesses. In eyes with early glaucoma, peripapillary retinal NFL thickness correlated best with PhNR amplitude (r, 0.71) and PERG P50 amplitude (r, 0.67).
Conclusions: In eyes with suspect glaucoma, important decrease in PhNR amplitude is associated with small changes in peripapillary retinal and macular NFL thicknesses. These findings suggest that PhNR may be a useful and sensitive test in eyes with diagnostic dilemma, although further follow-up of such eyes is required for definitive confirmation.