Effects of changes in systemic blood pressure on the electroretinogram of the cat: evidence for retinal autoregulation.

Systemic blood pressure was increased and decreased in anesthetized cats by intravenous infusion of angiotensin and by gradual exsanguination, respectively. The b- and c-wave amplitudes of the electroretinogram were used as indicators of activity of the inner retina and outer retina with pigment epithelium, which are supplied by the retinal and choroidal circulations, respectively. The amplitude of the b-wave remained stable during increases in mean arterial blood pressure (MABP) up to 225 mm Hg but decreased rapidly if the MABP was lowered below 55 mm Hg. This wide range of stability of the b-wave is likely to be brought about by autoregulation of the blood supply to the inner retina. No such stability was seen in the c-wave, the amplitude of which changed inversely to increases or decreases in the MABP. The c-wave thus appears to respond to changes in choroidal blood flow. The data provide new electrophysiologic evidence for autoregulation of the retinal vasculature and suggest that choroidal blood flow may influence the amplitude of the c-wave.