We have obtained important results about stimulus parameters and percepts from 6 subjects implanted with our Model 1 retinal implant which has a 4x4 electrode array. This information directs the design of a higher resolution retinal prosthesis, which is being developed in collaboration with the Technology Thrusts and our corporate partner; Second Sight Medical Products, Inc. Specific achievements in the first three years include demonstration of an integrated interconnect scheme and a prototype 1000 channel electrode array design. We have invented a closed loop power control system and a 1000-channel stimulator chip has been designed and submitted for fabrication. We have implemented real-time image processing algorithms on multiple platforms and have begun to integrate these systems with data telemetry. Finally, we have implanted prototype systems in cadaveric pig and dog eyes. This includes image acquisition components to demonstrate surgical biocompatibility and mechanical fit.
Fundamental research projects in retinal prosthesis physiology are an essential element of our systems integration plan. For example, we have developed a novel method of measuring retinal response to electrical stimulation by using a custom built gene gun. This device propels nanometer size particles (coated with fluorescent indicators) into live retinal cells. We also have constructed multielectrode arrays with a layout similar to the proposed stimulating array. This will allow us to study stimulating channel interactions in isolated retina. Another isolated retina study involves analysis of the retinal response to natural images and the decomposition of that response into Volterra kernels. Such an analysis will lead to a further understanding of the system response of the retina and will allow us to create biomimetic stimulation strategies. From a biocompatibility standpoint, we have begun to study the response of retinal cells to electrical stimulation both in isolated cultured cells and in intact animal models. These studies will establish safe limits for electrical stimulation in the retina. Finally, we have begun to study the mechanical properties of the retina and other eye tissues. Our past experience with chronic implantation suggests that the mechanical damage to the retina is a significant concern for long-term implants. However, detailed knowledge of the mechanical properties of eye tissues is lacking, making it difficult to design electrode arrays whose mechanical properties match the retina. Thus, a study into the fundamental mechanical properties of eye tissues is needed to better design the electrode array. In summary, we have fundamental research projects in retinal electrophysiology, retinal neuropathology, and biomaterials that will provide a scientific basis for the retinal prosthesis systems design.
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