Steady-state electroretinograms and pattern electroretinograms in pigs

Abstract 

Background: Electroretinograms (ERG) or pattern-electroretinograms (PERG) could be valuable for the quantification of potential damage to the pig retina by experimental erbium:YAG laser treatment. We therefore performed a normative study of ERGs and PERGs in pigs. Methods: We recorded ERGs and PERGs under general anaesthesia in two experiments. In experiment 1 we examined eight eyes from six pigs of 20–25 kg body weight; in experiment 2 we examined four eyes from four pigs of 40–45 kg body weight. We used flash and checkerboard stimuli. In experiment 1, the stimulus parameters were mean luminance 48.3 cd/m² for checkerboard stimuli, 96.6 cd/m² for ERG, check sizes of 4°, 8°, and 16°, temporal frequencies were 16 Hz for ERG and 8 rev/s for PERG. Three measurements were repeated after two weeks. Stimulus parameters for experiment 2 were luminance 175 (350) cd/m², check sizes 1.6°, 3.2°, 6.7°, and 16°, temporal frequencies 6.3 Hz for ERG and 8 rev/s for PERG. Recordings were subjected to Fourier analysis.

Results: In experiment 1 the mean ERG amplitude was 1.02±0.89 µV with a coefficient of variation of 42% for repeat sessions. The mean PERG amplitudes were 0.53±0.25 µV for 16° checks, 0.36±0.21 µV for 8°, and 0.25±0.17 µV for 4°. The mean coefficient of variation between two measurements was 103% for 16° checks, 24% for 8°, and 116% for 4°. In experiment 2 the mean ERG amplitude was 9.72±3.96 µV. The mean PERG amplitudes were 0.77±0.50 µV for 16° checks, 0.09±0.16 µV for 6.7°, 0.07±0.13 µV for 3.2°, and 0.08±0.09 µV for 1.6°.

Conclusions: It was possible to record ERGs and PERGs in pigs. However, the ERG amplitudes were small; PERG amplitudes were even smaller in both groups and cannot be reliably recorded. A problem for both ERG and PERG was the high intra-individual and interindividual variability. Therefore, only very extensive damage to the retina by vitrectomy or Er:YAG laser treatment might lead to a significant change in the ERG or PERG amplitudes.