Photopic Negative Response as a Marker for Optic Neuropathy using a Handheld Electroretinogram Device

Abstract

Purpose : The Photopic Negative Response(PhNR) is a ERG measure that derives from the retinal ganglion cells(RGCs). The purpose of this study is to use a handheld non-mydriatic electroretinogram(ERG) device with skin electrodes(RETeval/LKC) to determine if there is a difference PhNR between eyes with and without optic neuropathy(ON) as well as to determine association between ERG parameters and other structural and functional measures of the RGCs.

Methods : The handheld device was used to administer full field stimulation(red flashes at 3.4Hz over a blue background) adjusted for pupil diameter and record ERG waveforms using a skin electrode in 152 eyes(72 chronic non-glaucomatous ON, 80 control) of 96 subjects(56% female, ages 22-71 years). Custom MATLAB software was used to evaluate PhNR amplitude, P-ratio(PhNR_amp/B_amp), and W-ratio((B_amp–PhNR_amp)/(B_amp–A_amp)). Optical coherence tomography measures of optic nerve structure[Retinal nerve fiber layer(RNFL) thickness, Ganglion cell layer(GCL) thickness (Cirrus/Zeiss)] and optic nerve functional measures[Humphrey Visual Field mean deviation(HVF-MD)] were extracted from medical records where available(65 eyes, 50 chronic non-glaucomatous ON and 15 control). Logistic generalized estimating equations(GEE) were used to model ON status as a function of ERG measures. Linear GEE were used to model ERG measures as a function of structural and other functional measures of the RGCs.

Results : ON was associated with smaller PhNR(OR=.500 for 1µV change vs. control,[.344,.727],p<.0005, logistic GEE) and larger W-ratio(OR=2.34 for .1 unit change vs control,[1.13,4.88],p=.023, logistic GEE). P-ratio was not different(p=.193,logistic GEE). Among subjects with structural and functional data, PhNR was linearly associated with RNFL thickness(p=.015), GCL thickness(p=.001), and HVF-MD(p<.0005). W-ratio was association with RNFL thickness(p=.033), GCL thickness(p=.001), and HVF-MD(p<.0005). P-ratio was associated with GCL thickness(p=.026) and HVF-MD(p=.008), but not RNFL(p=.09).

Conclusions : A portable ERG device using a non-mydriatic stimulation protocol and skin electrodes measured PhNR amplitude decrease in ON vs controls. PhNR was associated with other functional and structural measures of RGCs. PhNR measured in this manner may have clinical application to detecting and measuring the severity of ON.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.