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J.F. Rizzo, J.L. Wyatt, J. Loewenstein, S. Montezuma, D.B. Shire, L. Theogarajan, S.K. Kelly; DEVELOPMENT OF A WIRELESS, AB EXTERNO RETINAL PROSTHESIS . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3399.
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Purpose: A retinal prosthesis has the potential to restore vision to patients with retinal degeneration. We sought to develop an ab externo prosthesis in which only an ultra–thin membrane passed through the wall of the eye. This design was preferred because of the inherent advantages of biocompatibility. Methods: We chose to utilize an extraocular coil(s) for wireless communication, using a conformal method of attaching the coil(s) to the eye. We explored a variety of geometries by performing surgeries on rabbits and pigs, and by comparing preferred geometries to the dimensions of a human eye. Microfabrication techniques were used to create all but the coils and capacitors. A custom–designed stimulator circuit was made to permit discrete control of stimulating pulse characteristics for each electrode. Stimulus capabilities of the circuit provide considerably more charge than measured by performing parallel studies of cortical recordings following electrical retinal stimulation in rabbits (see H. Kaplan). Surgical methods are being developed in parellel to facilitate minimally traumatic positioning of the prosthesis (see J. Loewenstein). Results: A prototype was developed that has the functionality, dimensions and mechanical properties for use as an ab externo retinal prosthetic. Surgical methods to insert the stimulating electrode array are non–optimized but improving, with a current yield of success for a minimally invasive insertion of roughly 50%. Conclusions: The development of this prototype will permit studies on animals to assess the biocompatibility of long–term implantation and stimulation. This prototype, which is our first generation device, has design features to enhance biocompatibility, most notably an ultra–thin membrane that penetrates the sclera and a conformal design that eliminates tethering of the external components that might impinge on ocular rotation.
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