PURPOSE-To investigate the feasibility of electrically stimulating the lateral rectus muscle to recover its physiologic abduction ability in cases of complete sixth cranial (abducens) nerve palsy.METHODS-In the feline lateral rectus muscle model, the effects of a charge-balanced, biphasic, current-controlled stimulus on the movement of the eye were investigated while stimulation frequency, amplitude, and pulse duration was varied. Eye deflection was measured with a force transducer. Denervated conditions were simulated by injection of botulinum toxin A.RESULTS-Three chemically denervated and 4 control lateral rectus muscles were analyzed. In control lateral rectus muscles, the minimum fusion frequency was approximately 170 Hz, and the maximum evoked abduction was 27°. The minimum fusion frequency was unchanged after 4 weeks of chemical denervation. Stimulation of chemically denervated lateral rectus muscle resulted in 17° of abduction. For both innervated and chemically denervated lateral rectus muscle, frequencies greater than 175 Hz yielded very little increase in abduction. Modulating amplitude produced noticeable movement throughout the tested range (0.2 to 9 mA). CONCLUSIONS-Results from the feline lateral rectus muscle showed that electrical stimulation is a feasible approach to evoke a contraction from a denervated lateral rectus muscle. The degree of denervation of the feline lateral rectus muscle was indeterminate. Varying the stimulation amplitude allowed greater eye movement. It is very likely that both frequency and amplitude must be modulated for finer control of static eye position.Congenital or acquired anomalous innervation and palsy of the extraocular muscles may result in severe amblyopia, loss of stereopsis, marked deficits in binocular visual fields, and diplopia. 1 The goal of strabismus treatment is to restore fusion and stereopsis and to enlarge A complete extraocular muscle palsy results in permanent denervation and muscle atrophy, which limits the outcome from surgical intervention on the affected muscle. Surgical correction is challenging and outcomes are limited, with many patients requiring several surgical procedures to reach alignment in the primary position.Several techniques have been described to remobilize a denervated striate muscle, including nerve-to-nerve anastomosis, neuromuscular pedicle transfer, and functional electrical stimulation (FES). [2][3][4][5][6][7][8][9][10][11] The use of FES has long been proposed as a potential treatment for restoring motor function of denervated motor systems. 2,4-11 Recent success has been noted in the ability of FES to allow paraplegics to gain the ability to stand. 5,6,9 FES may protect muscles from atrophy, promote muscle reinnervation from appropriate native motoneurons, and reconnect a muscle to the original endplate and its nerve fiber without interrupting the natural course of reinnervation and the potential for spontaneous recovery. [12][13][14][15][16][17][18] The validity of this approach has been demonstrated in humans.Z...