Comparison between broadband and monochromatic photopic negative response in full-field electroretinogram in controls and subjects with primary open-angle glaucoma

A prospective, cross-sectional, case–control study was conducted to investigate the role of broadband and monochromatic photopic negative response (PhNR) of the full-field flash electroretinogram (ERG) in the evaluation of ganglion cell damage in primary open-angle glaucoma (POAG) subjects.

Subjects with POAG and age-matched normal subjects were recruited from the outpatient department of a tertiary eye care center in South India. A total of 25 patients with POAG and 50 age-matched normal subjects were recruited. ERG was recorded using broadband (3.5 cd.s/m² white stimulus on 10 cd/m² white background) and monochromatic (3.5 cd.s/m² red stimulus on 10 cd/m² blue background and 1 cd.s/m² blue stimulus on 10 cd/m² yellow background) stimuli.

The reduction in PhNR amplitude in POAG compared to normal individuals was higher in red-on-blue PhNR [26.37 µV; p < 0.001, confidence interval (CI) 19.34 to 33.4] as compared to broadband stimuli (16.41 µV; p < 0.001, CI 8.68 to 24.13), and blue on yellow (21.96 µV; p < 0.001, CI 10.12 to 33.8). Red-on-blue PhNR amplitudes correlated better with mean deviation (MD; r = − 0.66, p < 0.05), pattern standard deviation (PSD; r = − 0.4, p = 0.04), visual field index (VFI; r = − 0.58, p < 0.05), and retinal nerve fiber layer thickness (r = − 0.67, p < 0.05) in comparison with broadband and monochromatic blue-on-yellow PhNR. Receiver operating characteristic curve revealed largest area under the curve (0.89) in red-on-blue PhNR compared to broadband (0.76) and blue on yellow (0.74). The sensitivity and specificity was also higher in red-on-blue PhNR (72% and 80%, respectively) as compared to the other stimuli (sensitivity and specificity of broadband 0.68 and 0.7, blue on yellow 0.64 and 0.7, respectively).

Correlation of PhNR with Humphrey visual field parameters and retinal nerve fiber layer thickness showed that red-on-blue PhNR can be a useful additional tool for clinical assessment of retinal ganglion cell dysfunction in glaucoma patients. Red-on-blue PhNR was more sensitive as compared to white-on-white and blue-on-yellow PhNR in identifying ganglion cell dysfunction and correlates well with other structural and functional tests for glaucoma such as MD, PSD, VFI, and RNFL thickness.