Steady-state electroretinograms and pattern electroretinograms in pigs

Background: Electroretinograms (ERG) or pattern-electroretinograms (PERG) c ould be valuable for the quantification of potential damage to the pig reti na by experimental erbium:YAG laser treatment. We therefore performed a nor mative 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 examin ed four eyes from four pigs of 40-45 kg body weight. We used flash and chec ker board stimuli. In experiment 1, the stimulus parameters were mean lumin ance 48.3 cd/m(2) for checkerboard stimuli, 96.6 cd/m2 for ERG, check sizes of 4 degrees, 8 degrees, and 16 degrees, temporal frequencies were 16 Hz f or ERG and 8 rev/s for PERG. Three measurements were repeated after two wee ks Stimulus parameters for experiment 2 were luminance 175 (350) cd/m2, che ck sizes 1.6 degrees, 3.2 degrees, 6.7 degrees, and 16 degrees, temporal fr equencies 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 muV with a coefficient of variation of 42% for repeat sessions. Th e mean PERG amplitudes were 0.53 +/-0.25 muV for 16 degrees checks, 0.36 +/ -0.21 muV for 8 degrees, and 0.25 +/-0.17 muV for 4 degrees. The mean coeff icient of variation between two measurements was 103% for 16 degrees checks , 24% for 8 degrees, and 116% for 4 degrees. In experiment 2 the mean ERG a mplitude was 9.72 +/-3.96 muV. The mean PERG amplitudes were 0.77 +/-0.50 m uV for 16 degrees checks, 0.09 +/-0.16 muV for 6.7 degrees, 0.07 +/-0.13 mu V for 3.2 degrees, and 0.08 +/-0.09 muV for 1.6 degrees. Conclusions: It wa s possible to record ERGs and PERGs in pigs. However, the ERG amplitudes we re small; PERG amplitudes were even smaller in both groups and cannot be re liably recorded. A problem for both ERG and PERG was the high intra-individ ual and interindividual variability. Therefore, only very extensive damage to the retina by vitrectomy or Er:YAG laser treatment might lead to a signi ficant change in the ERG or PERG amplitudes.