Nearly ten million people suffer from a form of strabismus in the United States alone, with 2-4% of the population developing strabismus within the first six years of life [1]. During this period, the visual system is extremely susceptible to developmental problems from strabismus, such as amblyopia. Lesions to the sixth cranial nerve, or abducens nerve, results in selective paralysis of the ipsilateral lateral rectus muscle, which causes convergent strabismus. Symptoms of sixth nerve palsy include loss of horizontal eye control, convergent strabismus, and functional loss of sight in the affected eye. In moderate cases, the medial rectus is treated with Botulinum toxin to effectively balance horizontal eye muscle forces. In severe cases, the superior and inferior rectus muscles are surgically re-inserted laterally, followed by physical therapy and minimal recovery of horizontal eye motility. Our approach involves reanimating the lateral rectus based on force measurements from the opposing medial rectus. Previous studies have indicated that a relationship exists between horizontal rectus muscle force and eye position and velocity. An innovative implantable stimulation device exploiting this relationship can lead to reanimation of lateral rectus tissue and recovery of horizontal eye control. A feasibility study involving implantable muscle force transducers (MFT), control electronics, and long-term stimulating electrodes is a necessary precursor to the development of this device. We have developed a unique laboratory setting to study the feasibility of reanimating the lateral rectus muscle, using non-human primates as the subjects for our experiments. The subjects will perform visual tasks in this environment, while eye position and muscle force output can be recorded. Eye position is accurately obtained through pickup of an implanted scleral search coil in generated differential electromagnetic fields. Muscle force is directly measured with implanted muscle force transducers (MFT). The lateral rectus muscle will be temporarily dennervated through metered injections of Botox, and will be stimulated with implanted electrodes using the MFT frame as a platform. The final implanted device will encompass the stimulation control system, which will be optimized in individual tests within our laboratory setting.
| Velez, Federico G; Isobe, Jun; Zealear, David et al. (2009) Toward an implantable functional electrical stimulation device to correct strabismus. J AAPOS 13:229-35.e1 |
