Factor structure and ammonia-related modulation of the human retinal oscillatory potentials

Objective: To investigate in man the factor structure of retinal oscillator y potentials (OPs) to full-field luminance stimulation (0.9-9.5 cd.s.m(-2)) and the correlation with the spontaneous fluctuations of plasma ammonia. Methods: Six male healthy volunteers were studied. Five OP recordings and a mmonia determinations (GLDH method) were obtained for each subject at 2 h i nterval during an 8 h experimental session. A standard factor analysis was applied on the OP latency (time from stimulus to peak) and amplitudes value s. Results: Two consecutive factors on latencies and two factors on amplitudes were identified. consistent with reported differences between the earlier and later OP waves. The model explained a large portion of the OP variance. Both factors on latencies and factor 1 on amplitudes were directly correla ted to the stimulus intensity and the ammonia plasma concentration in the 1 5.8-39.5 mu mol/l range. Factors 1 and 2 on latencies decreased and factor 1 on amplitude increased at increasing stimulus intensities. The latency fa ctors decreased and the amplitude factor increased with increasing ammonia concentration. Factor 2 on amplitudes did not correlate with the stimulus i ntensity or ammonia concentration. Conclusions: The factor structure further supports the evidence of function al differences between early and late OP waves. The observed correlation co nceivably reflects a role of ammonia in the modulation of retinal electroph ysiology in physiological conditions and potentially accounts for spontaneo us variability in otherwise controlled electrophysiological studies. (C) 20 01 Elsevier Science Ireland Ltd. All rights reserved.