Electroretinography in idiopathic intracranial hypertension: comparison of the pattern ERG and the photopic negative response

Abstract

Purpose: To evaluate the relationship between electrophysiological measures of retinal ganglion cell (RGC) function in patients who have idiopathic intracranial hypertension (IIH).

Methods: The pattern electroretinogram (pERG) and photopic negative response (PhNR) were recorded from 11 IIH patients and 11 age-similar controls. The pERG was elicited by a contrast-reversing checkerboard. The PhNR, a slow negative component following the flash ERG b-wave, was recorded in response to a long-wavelength flash presented against a short-wavelength adapting field. The PhNR was elicited using full-field (ffPhNR) and focal macular (fPhNR) stimuli. Additionally, Humphrey visual field mean deviation (HVF MD) was measured and ganglion cell complex volume (GCCV) was obtained by optical coherence tomography.

Results: The ffPhNR, fPhNR, and pERG amplitudes were outside of the normal range in 45, 9, and 45% of IIH patients, respectively. However, only mean ffPhNR amplitude was reduced significantly in the patients compared to controls (p < 0.01). The pERG amplitude correlated significantly with HVF MD and GCCV (both r > 0.65, p < 0.05). There were associations between ffPhNR amplitude and HVF MD (r = 0.58, p = 0.06) and with GCCV (r = 0.52, p = 0.10), but these did not reach statistical significance. fPhNR amplitude was not correlated significantly with HVF MD or GCCV (both r < 0.40, p > 0.20).

Conclusions: Although the fPhNR is generally normal in IIH, other electrophysiological measures of RGC function, the ffPhNR and pERG, are abnormal in some patients. These measures provide complementary information regarding RGC dysfunction in these individuals.

Keywords: Electroretinogram; Idiopathic intracranial hypertension; Pattern electroretinogram; Photopic negative response.

Figure 1

Waveforms obtained for the ffPhNR (top), fPhNR (middle), and pERG (bottom). Each trace represents a response from an IIH subject and the gray region represents the range of responses from the visually-normal subjects.

Figure 2

Distribution of amplitudes. Amplitudes for each IIH subject are represented by the symbols (corresponding to those given in Table 1) and the gray regions represent the range of amplitudes obtained from the visually-normal subjects; horizontal black bars indicate the normal mean. In the top panel, data are shown for the ffPhNR (1^st data set) and the fPhNR (2^nd data set). The 3^rd and 4^th data sets represent the b-wave normalized ffPhNR and fPhNR, respectively. The normalized data are plotted with respect to the right y-axis. The lower panel shows amplitudes for the pERG P50, N95, and P50+N95 amplitudes, respectively. The normalized N95/P50 amplitude is plotted with respect to the right y-axis.