Toward an implantable functional electrical stimulation device to correct strabismus

Abstract

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...

Effects of Intracranial Trochlear Neurectomy on the Structure of the Primate Superior Oblique Muscle

“…From whatever cause, the relative preservation of the denervated SO fibers offers the possible opportunity of therapeutic rescue by later trochlear reinnervation, or some other modality, such as artificial electrical stimulation. 44 The monkeys whose anatomic findings are reported herein exhibited a complex evolution in strabismus over a period of 30 days, with a nonmonotonic variation in hypertropia over time. 22 Although some of the changes in strabismus might have been due to the mechanical effects of SO fiber atrophy and gross stretching of the SO belly, the present results indicate that gross mechanical changes were complete by 5 weeks after ITN, approximately the duration of the behavioral study.…”

A Programmable High-Voltage Compliance Neural Stimulator for Deep Brain Stimulation in Vivo

“…In recent decades, electrical stimulation devices have been increasingly used in clinical applications [ 1 , 2 , 3 , 4 ] and late-stage development of many traditional “medical” disorders [ 5 , 6 , 7 , 8 ]. In particular, deep brain stimulation (DBS) has become one of the most important therapies in functional neurosurgery.…”

A noninvasive electromagnetic perturbation approach to probe extraocular proprioception

“…1,5,7,8,16,21 In the past, two distinctive physiological approaches have been developed to manipulate proprioceptive signals: one is to mechanically displace the eye with a suction lens 2,7,20 or by having the subject manually press one of their eyes 1 ; the other is to perturb the proprioceptive representation by vibrating the extraocular muscle tendon 7,16 or electrically stimulating extraocular muscles. 22 We developed a new approach, employing an electromagnet (EM) technique to alter the rotation kinematics of a real-time model eye. This technique had rapid onset and was able to effectively alter the kinematics of eye rotations.…”