Differential recovery of the electroretinogram, visually evoked cortical potential, and electrically evoked cortical potential following vitrectomy: implications for acute testing of an implanted retinal prosthesis.

To determine the extent to which electrophysiologic tests of the afferent visual pathway are affected by vitrectomy, the procedure was performed in 15 eyes of 11 adult Dutch-belted rabbits. An electroretinogram (ERG), visually evoked cortical potential (VECP), and electrically evoked cortical potential (EECP) were obtained preoperatively and sequentially after surgery. For electrical stimulations, biphasic impulses were delivered to the retina. Post-vitrectomy declines of 49, 25, and 41% from the median baseline amplitudes and increases of 13, 18, and 17% from the median baseline latency values were found for ERG, VECP, and EECP, respectively. At 90 min, 13 to 30% of eyes still had an amplitude more than 10% below baseline on at least one of the three tests, whereas 10 to 47% of eyes had an abnormal latency more than 10% above baseline on at least one of the three tests. Amplitudes were more likely than latencies to return to near baseline, but for eyes that remained subnormal, the decline was greater for amplitudes than latencies. Significant alterations in retinal function, manifested by declines in amplitudes and increases in latencies of the ERG, VECP, and EECP, persist in a large proportion of eyes up to 90 min post-vitrectomy.