Development of Extraocular Muscle Prosthesis for Paralytic Strabismus

DESCRIPTION (provided by applicant): The ultimate goal of this Small Business Innovation Research project is to develop the first generation extraocular muscle prosthetic device designed to correct paralytic strabismus. The focus of Phase I of this project is to refine the design of the prosthesis and to test the limits of the device and its components. A method of measuring extraocular muscle forces will be developed and tested using an animal model. Furthermore, a short-term in vivo animal study to assess the biocompatibility of the device will be performed. A common ophthalmic complication encountered with increasing frequency in functional endoscopic sinus surgery (FESS) is the inadvertent amputation of the medial rectus muscle. Extraocular muscle dysfunction can also be manifested in cranial nerve palsies or vehicular trauma to the muscles. Consequently, the involved eye will assume a large angle exotropia, and the patient will experience debilitating diplopia and will be unable to adduct or abduct the involved eye. Conventional surgical options typically result in suboptimal outcomes as the eye is permanently tethered to a fixed primary position, limiting ocular movements and forcing the patient to adopt face turns to maintain binocular fusion. These major shortcomings call for the need of an alternative remedy in the form of a mechanical prosthetic device to obviate the fixed, locked primary position of the affected eye. The unique features of this extraocular muscle prosthesis include: 1) a coiled Nitinol spring that possesses inherent stiffness to counterbalance the passive forces of the antagonist eye muscles when the eye is in the primary position but also allows linear elasticity to permit eye movement initiated by an antagonist muscle. The spring also has inherent recoil tension to restore the eye back to the primary position upon relaxation of the antagonist muscle; 2) a novel biocompatible polymer, poly(styrene-block-isobutylene-block- styrene) or SIBS, that does not elicit significant inflammatory reaction or encapsulation when implanted and has a safety track record in coronary stent use. This biomaterial is extruded as a protective, elastic envelope that insulates the spring coil from the surrounding orbital tissues; and 3) a titanium, T-shaped bone plate that provides a firm metallic fixation point to the orbit and directs the prosthesis posteriorly from the muscle insertion site towards the apex of the orbit, coinciding with the axis of the paretic muscle that the prosthesis is designed to replace. PUBLIC HEALTH RELEVANCE: The goal of this project is to develop an extraocular muscle prosthetic device to correct complex eye muscle misalignment conditions in which effective therapy remains elusive. Conventional surgical options typically result in suboptimal outcomes as the eye is permanently tethered to a fixed position, unable to rotate. The device developed in this project is designed to permit eye rotations; the Extraocular Muscle Prosthesis is a novel prosthetic device comprised of a new polymeric biomaterial that is extremely biocompatible in the eye and has shown insignificant encapsulation compared to silicone rubber.