Changes in the electroretinogram and visual evoked potentials during general anaesthesia.

Ten patients (one male and nine females), aged 33.2+/-12.0 years, were given electrophysiological studies before and during general anaesthesia. A mixture of thiopentone sodium, halothane, and nitrous oxide was used for anaesthesia. Electroretinogram (ERG) and visual evoked potentials (VEP) were recorded with scalp electrodes, and an averaging technique was used to improve signal-noise ratio. The recordings were made under standard conditions 15 to 20 min after induction of the anaesthesia. The amplitudes of the a- and b-waves of the ERG were significantly diminished whereas their latencies remained unchanged. The peak-to-peak amplitudes of the early components N1 and P2 of the VEP were significantly lowered, and the latencies of N0, P1, and N1 were prolonged by anaesthesia. These modifications are suggested to reflect metabolic changes in the sensitive layers of the retina and in the optic tract.