Loss of the low-frequency component of the global-flash multifocal electroretinogram in primate eyes with experimental glaucoma

Abstract

Purpose. To study relationships between glaucoma-sensitive components identified with frequency-domain analysis of global- flash multifocal electroretinogram (mfERG), regional retinal nerve fiber layer thickness (RNFLT), and local visual field sensitivity (VS). Methods. Eleven macaque monkeys, including four controls and seven with unilateral laser-induced trabecular meshwork scarification and ocular hypertension, were observed with optical coherence tomography (OCT), full-field light-adapted flash ERG, 103-hexagon global-flash mfERG (MFOFO), and static perimetry. The effects of experimental glaucoma on mfERG were assessed in the frequency domain. Relations between root mean square (RMS) amplitude of a glaucoma-sensitive frequency range and peripapillary RNFLT (standard 12° OCT circular scan), and between RMS amplitude and VS were studied. Results. Experimental glaucoma led to a dramatic and consistent power loss in the low-frequency (<25 Hz) band of mfERG. The RMS of this low-frequency component (LFC) correlated significantly with the regional RNFLT. The r 2 of linear fits was 0.39 (P < 0.001) for cross-sectional group data and 0.60 after correction for intersubject variability. The r 2 of linear fits for longitudinal data from individual animals was as high as 0.78 (P < 0.001). Local LFC RMS amplitude also correlated significantly with interpolated VS for hexagons. The r 2 for exponential fits of hexagon LFC RMS amplitudes (inner three rings) versus VS (dB) was 0.29 to 0.52 (P < 0.001) for the group and up to 0.95 in individuals. Conclusions. The significant correlations between regional measures of global-flash mfERG, RNFLT, and VS suggest that LFC RMS amplitude provides a useful index for objective quantification of local RGC function and monitoring of early changes in glaucoma. © 2011 The Association for Research in Vision and Ophthalmology, Inc.