Inner–retinal contributions to the multifocal pattern electroretinogram

Abstract

Abstract: : Purpose: To determine the inner–retinal contributions to the multifocal pattern electroretinogram (mPERG) and also to study the effects of age on these responses. Methods: mPERGs were recorded with a VERIS system (EDI) using DTL fiber electrodes from 4 anesthetized cynomologous monkeys before and after blocking inner–retinal activity with tetrodotoxin (TTX) and NMDA and from 60 normal human subjects (21–80 yrs). Stimuli consisted of counterphase–modulated triangular patterns arranged in 61–scaled hexagons with mean luminance 100cd/m.sq and 100% contrast. The entire stimulus array subtended 31 deg vertically and 37 deg horizontally at a viewing distance of 48 cms. The monitor frame rate was 75Hz, M–sequence exponent 15 with 1 frame/M–step and amplifier cut off frequencies 3 and 100Hz. The first slice of the second order kernel (2K) responses were analyzed. Results: The 2K responses showed prominent naso–temporal variations, primarily in the form of a slow negative potential that was prominent in the nasal but not in the temporal field. Following intravitreal injection of TTX and NMDA the naso–temporal variations disappeared and a significant response remained that was uniform in shape across the visual field. The mPERG responses from normal human subjects also showed naso–temporal variations. While the response amplitude at each location decreased with age the response timing was unaltered. Conclusions: The second order kernel responses of the mPERG of humans and non–human primates contain prominent contributions from inner–retinal neurons. Unlike the standard PERG that is dominated by retinal ganglion cell contributions the mPERG responses contains large contributions from retinal neurons proximal to the retinal ganglions cells.

Keywords: electroretinography: clinical • ganglion cells • visual fields