Beta-zone parapapillary atrophy and multifocal visual evoked potentials in eyes with glaucomatous optic neuropathy

Abstract

We investigated changes in multifocal visual evoked potential (mfVEP) responses due to beta-zone parapapillary atrophy (ßPPA). Patients with glaucomatous optic neuropathy (GON) with or without standard achromatic perimetry (SAP) abnormalities were referred for mfVEP testing during a 2-year period. Eyes with good quality optic disc stereophotographs and reliable SAP results were included. The mfVEP monocular mean latency delays (ms) and amplitudes (SNR) were analyzed. Age, SAP mean deviation (MD), pattern standard deviation (PSD), and spherical equivalent (SE) were analyzed in the multivariate model. Generalized estimated equations were used for comparisons between groups after adjusting for inter-eye associations. Of 394 eyes of 200 patients, 223 (57%) had ßPPA. The ßPPA eyes were older (59.6 ± 13.7 vs. 56.5 ± 13.7 year, P = 0.02), more myopic (-4.0 ± 3.5 vs. -1.3 ± 3.5 D, P < 0.01), and had poorer SAP scores (MD: -4.9 ± 5.2 vs. -2.6 ± 5.2 dB, P < 0.01; PSD: 4.3 ± 2.9 vs. 2.5 ± 3.0 dB, P < 0.01). By univariate analysis, mean latencies were longer in ßPPA eyes (6.1 ± 5.3 vs. 4.0 ± 5.5 ms, P < 0.01). After adjusting for differences in SE, age, and SAP MD, there was no significant difference between the two groups (P = 0.09). ßPPA eyes had lower amplitude log SNR (0.49 ± 0.16 vs. 0.56 ± 0.15, P < 0.01), which lost significance (P = 0.51) after adjusting for MD and PSD. Although eyes with ßPPA had significantly lower amplitudes and prolonged latencies than eyes without ßPPA, these differences were attributable to differences in SAP severity, age, and refractive error. Thus, ßPPA does not appear to be an independent factor affecting mfVEP responses in eyes with GON.

Fig. 1

The mfVEP stimulus (VERIS Dart Board 60 with Pattern, Electro-diagnostic Imaging, Inc. (EDI, San Mateo, CA))

Fig. 2

a mfVEP monocular latency plots. In the latency probability plots, each tested sector of the retina tested is represented by a dot. Black dots represent sectors with normal latencies. Gray dots represent sectors with responses too small to accurately measure the latency. Colored sectors (blue in OD plot, red in OS plot) represent sectors with increased latencies significant at either the 5% (>1.96 SD, desaturated color) or 1% (>2.58 SD, saturated color) level compared to normal values. For example, the inferior hemifield OS has six sectors with increased latency, five of which are significant at the 5% level (desaturated, i.e., pink color), and one of which is significant at the 1% level (saturated, i.e., red color). In this same hemifield, there are five gray dots (inadequate data) and 19 black dots (normal latencies). b mfVEP monocular amplitude plots. The superior hemifield OS (red) has seven sectors with decreased amplitude, five of which are significant at the 5% level, and two of which are significant at the 1% level. In this same hemifield, there are 23 black boxes (normal amplitudes)