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Long-Sheng Fan, Chia-He Chung, Frank Yang, Eunice Liu, Jasmine Lin, Zung-Hua Yang, Grace Teng, Chang-Hao Yang, Kea-Tiong Tang; A Center-Surround-Selectable, High-Acuity, Large-Field-of-View, Flexible Retinal Prosthesis. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1067.
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We previously reported a 4,096-pixel flexible retinal prosthesis generating bi-phasic electrical stimulations 30 μm in pitch to enable the possibility of high visual acuity (VA) and cover a field of view (FOV) around 10o. The pixel electrical output is a function of the light intensity on that pixel. However, retinal photo sensors influence retinal neurons across hundreds of micrometers, and the retinal networks exhibit a center-surround receptive field through lateral inhibition. Various stages of retina degeneracy may also need certain artificial restoration of such neural function through electronics. We target to implement a 16,328-pixel prosthesis that is selectable to have an electrical output consistent with the center-surround receptive field, and the chip covers up to 20o FOV with 30 μm pixel pitch, and conform to the surface of a 25 mm eyeball.
Since the ratio of the number of photo sensors to that of ganglion cells is low near the fovea, the center-surround characteristics is expected to be the key feature of the coding in this region. The new retinal prosthesis chip includes the option that the pixel electrical output from the pixel signal processing circuitry can be selected to be a function of the light intensities on neighboring pixels to a range of the typical receptive field in additional to the light intensity on that pixel. The primary weight matrix is a Laplacian Gaussian.
We have implemented a flexible 16,328-element retina chip 30 μm thick using a 180nm, flexible CIS technology. The electrodes are 10 μm in size and photo sensors 30 μm in pitch. The retina chip with a large FOV is 6 mm in size including multiplexing electronics for pixel characterizations and perfusion openings, and formed into a spherical-shaped patch during the packaging process. We have previously shown that the identical 10 μm-sized electrode arrays are capable of inducing RGC spiking in vitro, and details are under characterization.
This study demonstrates the feasibility to integrate a high-acuity, large-field-of-view, flexible retinal prosthesis in a spherical-shaped patch with the selectable feature to have an electrical output characteristic consistent with the center-surround receptive field using a 180 nm mixed-signal CMOS Image Sensor technology. Detailed characteristics of this retinal chip will be reported.
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