Electrical stimulation of the paralyzed orbicularis oculi in rabbit

Dysfunction of the seventh cranial nerve often results in facial paralysis and loss of the ability to blink the eye, which can lead to corneal scarring, diminished vision, and potential loss of the eye. This study investigated the potential of electrical stimulation of the orbicularis oculi muscle as a means of restoring blink function. An animal model of orbicularis paralysis was created by sectioning the seventh cranial nerve in rabbit. Twenty paralyzed and five normal rabbits were acutely implanted with a subcutaneous stimulating electrode near the margin of the upper eyelid. Biphasic current controlled stimulation pulses were delivered between implanted contacts at the medial and lateral edges of the eyelid. Strength-duration curves for lid twitch threshold were generated, and quantitative measurements of lid closure were made for systematically varied parameters including pulse amplitude, pulse width, number of pulses delivered, and duration of paralysis prior to stimulation. Normal rabbits achieved a greater degree of lid closure due to electrical stimulation than rabbits that had been surgically paralyzed. Of rabbits that had been paralyzed, those demonstrating evidence of at least partial reinnervation achieved a greater degree of lid closure than those demonstrating persistent denervation. Trains of 10 ms biphasic pulses delivered at 50 Hz were found to be the most effective means of eliciting lid closure for the range of parameters tested.