Electrophysiological study of the denervated orbicularis oculi muscle in dogs

This study investigated the elctrophysiology of the denervated orbicularis oculi muscle and its clinical application. Orbicularis oculi muscle denervation was achieved by complete transection of the seventh nerve in ten dogs. The parameters studied were the electrical requirements needed to cause a minimal perceptible contraction (twitch) and a complete eyelid closure (blink). Twitch and blink curves were generated. The findings are summarized as follows: (1) Minimum intensities for direct twitch of denervated orbicularis oculi muscle were significantly lower than intensities of normal orbicularis oculi muscle twitch (p < 0.01) when long stimulus duration (5 to 400 ms) was used. (2) Minimum intensities for direct blink of denervated orbicularis oculi muscle were not significantly different from stimulus intensities for blink of normal orbicularis oculi muscle if long stimulus duration (5 to 400 ms) was used. Twitch and blink curves could be used to clinically follow the orbicularis oculi muscle movement return after operations performed in patients affected by lagophthalmos.