Evaluation of inner retinal function at different stages of primary open angle glaucoma using the photopic negative response (PhNR) measured by RETeval electroretinography

Purpose: To investigate the objective function of the inner retinal layer in each stage of primary open angle glaucoma (POAG) using the photopic negative response (PhNR) measured by RETeval full-field electroretinography (ERG), and to identify which PhNR parameter is the most useful.

Methods: Ninety eyes of 90 patients with POAG (30 with mild POAG (mean deviation (MD) ≥ -6 dB) and 60 with moderate-to-advanced POAG (MD < -6 dB)) and 76 eyes of 76 control cases were examined. We investigated six PhNR parameters and their relationships with the results of the Humphrey 30-2 visual field test and the thickness of the circumpapillary retinal nerve fiber layer (cpRNFL) obtained from optical coherence tomography. The following PhNR parameters were assessed: base-to-trough (BT), peak-to-trough (PT), 72msPhNR, the W-ratio, P-ratio, implicit time (IT), and a-wave and b-wave amplitudes on ERG.

Results: All PhNR parameters other than IT significantly differed between the all POAG (all stages) and control groups and between the moderate-to-advanced POAG and control groups. BT and 72msPhNR in the mild POAG group, significantly differed from those in the control group. Regarding the relationships between PhNR parameters and the visual field and between these parameters and cpRNFL thickness, correlations were observed between all PhNR parameters, except PT and IT, and both the visual field and cpRNFL thickness in the all and moderate-to-advanced POAG groups. 72msPhNR correlated with cpRNFL thickness in the mild POAG group. The area under the receiver operating characteristic curve was greater for BT than for the other PhNR parameters in both the mild and moderate-to-advanced POAG groups. The discriminant linear function for examining the presence or absence of POAG and the threshold for diagnosis were quantitatively obtained as follows. Regarding BT: discriminant = 0.505 × BT + 2.017; threshold = positive for POAG, negative for no POAG; correct answer rate = 80.7%. Concerning 72msPhNR: discriminant = 0.533 × 72msPhNR + 1.553; threshold = positive for POAG and negative for no POAG; correct answer rate = 77.1%.

Conclusion: RETeval-measured PhNR parameters were useful for an objective evaluation of visual function in moderate-to-advanced POAG. BT appeared to be the most diagnostically useful parameter.