97th DOG Annual Meeting 1999



P. Janknecht, T. A. Wesendahl, T. Otto, M. Bach

Purpose: We intend to ablate epiretinal membranes and the internal limiting membrane by an Er:YAG laser. It is possible that this therapy causes harm to the retina. Quantifying such a functional damage in animals necessitates Ganzfeld-ERG or Pattern-ERG (PERG) measurements. We present normal data for pigs.

Method: We examined Ganzfeld-ERG and PERG using DTL-electrodes in pigs (20-25 kg) in general anaethesia. ERG Ganzfeld and PERG checkerboard was presented using a computer monitor the reflexion of which was centered on the cornea of the pigs. Depth of the anaethesia was adapted so that the animals looked straight forward. The check size of the chequerboard stimuli (16 rps) was 4°, 8° and 16°; the mean luminance 48,3 cd/m2, the contrast 100% and the field size 32 x 27°. Some (P)ERG measurements were done successively. If both were adequate, there Fourierc spectra were averaged. For further analysis only those spectra were used which showed a significant 16º-checkerboard response in Fourier transformation.

Results: We were able to record a Ganzfeld-ERG or PERG in 8 animals. The mean of the amplitude was 1,02±0,89 µV for Ganzfeld-ERG. In PERG the amplitude in 16º, 8º, and 4º caro size was 0,53±0,25 µV, 0,36±0,21 µV, and 0,25±0,17 µV, respectively. Three pigs were examined in a two week´s interval. The coefficient of variation (CV) between first and second measurement was 63% for Ganzfeld-ERG and in 16º, 8º and 4º PERG 43%, 123%, and 89%, respectively.

Conclusion: In general amplitudes were small and disappointingly showed a larger interindividual and intraindividual variation than in humans. The small amplitudes imply that visual acuity in (young) pigs is not too good. Damage after laser therapy is probable only if amplitudes before and afterwards differ by more than 2*CV, i.e. in Ganzfeld-ERG by more the 0.62 µV on the average. We had the impression that the depth of the anaethesia influences amplitudes significantly.

Department of Ophthalmology, University of Freiburg