Artificial Vision by Veit Peter Gabel

Author:Veit Peter Gabel
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Future Technologies

Current clinical trials have demonstrated the feasibility to restore some visual perception by stimulating the residual inner retina, despite ongoing retinal degeneration. These outstanding results call for the development of new technologies to improve further the resolution of stimulating electrodes in order to increase their number and density. Indeed, psychophysical experiments have concluded for the need of at least 600 pixels to allow independent locomotion, face recognition and text reading. Different electrode distributions were shown to increase the current focalization. These distributions includes bipolar stimulation [24], a quasimonopolar stimulation using a distant return electrode in a plane above hexapolar return electrodes surrounding each stimulating electrode [22], and a ground grid surrounding all stimulating electrodes [16]. The latter ground grid configuration was found interesting for both planar [16] and 3D implant designs [3, 4]. In fact, as demonstrated by Dijilas et al. 3D designs could encode more gray levels than planar arrays, even with a distant ground [3]. Interestingly, the recent photovoltaic retinal prosthesis, named PRIMA and under development at Pixium Vision with Pr Palanker (Stanford University), has already introduced such a ground grid [21] resulting in a high visual acuity in blind rats [19]. However, the advantage of ground grids relies on very conductive materials [16]. Therefore, the development of new materials, more stable and very conductive, appears as a promising challenge for the production of very dense electrode arrays with a high resolution. In this line of research, researchers have investigated the advantage of carbon-based materials such as graphene and diamond because they have a wider electrochemical window than metals. Both materials were found to be highly biocompatible for retinal neurons, which could grow directly on them [1, 2]. We also demonstrated the in vivo biocompatibility of diamond after having developed a process for the fabrication of flexible implants with a diamond coating [3]. The efficacy of these materials at stimulating electrode depending highly on their developed surfaces, introducing a nanostructure in the diamond coating using carbon nanotubes has further enhanced the material performances [7, 8]. We further showed that these performances were very important for neuronal interfaces [25]. These new nanostructured diamonds should therefore enhance the efficacy of retinal neuron stimulation achieved with classic diamond electrodes, which had been reported by others [6].

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