Activating the levator to elevate the eyelid

Abstract

To demonstrate in an animal model the feasibility of elevating the eyelid in a functionally useful manner by chronically stimulating the levator palpebrae superioris (LPS) muscle with an implanted electrode. Five rabbits were implanted with electrodes designed to stimulate the nerve innervating the LPS near its entry to the muscle. Bipolar platinum electrodes in a silicone rubber envelope with silicone-sleeved, PTFE-coated platinum lead wires were used to provide long-term stimulation with bipolar square-wave pulse trains of 0.18-0.80mA and 200Hz at a duty cycle of 8seconds on and 2seconds off. Explanted electrodes were examined for damage, and stimulated tissues were evaluated for abnormalities by light microscopy. We achieved mean lid elevation of 1.6mm, approaching the diameter of the light-adapted pupil, with 0.5mA stimulus. Stimulus currents below 1.0mA produced no signs of discomfort. Three animals with which we attempted daily stimulation, averaged 16.1hours per week. Experiments lasted 22weeks on average. Lid lifting with a well-implanted platinum electrodes was stable, with no apparent tissue or electrode damage after as long as 29.1weeks. Stable, functionally useful eyelid lifting was achieved with stimulation currents that caused no apparent discomfort or damage to muscles or nerves. A simple, discrete bipolar electrode was effective and survivable.