Flash-stimulated Visual Evoked Potential in Beagle Dogs: Effect of Mydriasis, Stimulated Side of Eye and Reproducibility

Abstract

Objective: The aim of this study was to investigate the effect of mydriasis, and the stimulated eye, and the reproducibility of flash-stimulated visual evoked potential (fVEP) in Beagle dogs. Procedures: fVEP was recorded from both eyes of 7 healthy beagles before and after mydriasis from both eyes. fVEP recording was performed with a portable VEP system under the sedation. Plate type electrodes were used as recording, reference, and ground electrodes were placed at inion, nasion, and temporal positions, respectively. fVEP was recorded in each eye of each dog in a dimly lit room, and 128 repetitions were averaged. White flash stimulation was performed with 1.5 Hz and 3.0 cd·s/m² with an fVEP stimulator. The stimulator was set 2 cm from the subject's eye. The latencies of N2 and P2 in the fVEP component and the amplitude of between N2 and P2 (N2-P2) were measured. To evaluate the reproducibility, VEP was recorded from the same dogs again, 7 days later. Results: fVEP responses after mydriasis showed significantly shortened latencies (N2: -32%, P2: -19%) and increased amplitude (N2-P2: +60%) compared with those before mydriasis. There were no significant differences in fVEP responses between the left and right stimulated eyes. Reproducibility of the latencies of N2 and P2 was observed. Conclusion: fVEP in dogs should be recorded with mydriasis, and latency should be used to evaluate the response by our method, because of its reproducibility. Comparing the responses obtained from each eye might be useful to find a lesion site.