Origin of the fast oscillation in the electroretinogram of the macaque.

To investigate the origin of the fast oscillation, a phenomenon in the electroretinogram evoked with stimulus frequencies of about 8 mHz (a period time of about 2 min), we recorded responses from retina and pigment epithelium in the macaque. Micropipettes were placed in the subretinal space and in the vitreous close to the retina; the reference electrode was in the orbit behind the eye. Thus, simultaneous recordings were obtained of the trans-epithelial, the trans-retinal and the trans-tissue (vitreal) potential. At 10 mHz the trans-retinal and the trans-epithelial responses are of about equal magnitude but of opposite phase, resulting in a small and rather variable vitreal potential. The origin of the fast oscillation evoked with repetitive stimuli lies in subtle differences between retinal and pigment epithelial potentials, in which a pigment epithelial event plays an important role. For single stimuli lasting 60 s again the trans-epithelial and trans-retinal responses were of equal magnitude and opposite polarity. The epithelial responses were found to return more quickly towards the baseline than the retinal responses. In vitreal recordings this causes a trough between the c-wave and the light peak which is referred to as the "trough" fast oscillation. Most of the "trough" fast oscillation is caused by a pigment epithelial event. In view of the complexity of the fast oscillation evoked with repetitive stimuli it might be difficult to relate pathology to specific neuro-epithelial structures.