Argus IIconsists of an array of 60 electrodes that are surgically imlanted and attached to the retina.
A device called Argus II is currently being developed by engineers at five U.S. Department of Energy laboratories and four universities. A private company, Second Sight Medial Products Inc., is marketing the bionic eye. The high-density microelectronic-tissue hybrid device aims to restore sight to people blinded by diseases such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP).
People with AMD and RP are blind because retinal photoreceptors called rods and cones degenerate and lose function. According to Mark Humayun, M.D., an ophthalmologist at the Doheny Eye Institute at the University of Southern California, rods and cons are cells that capture light and transmit it into electrical signals. The signals are passed through underlying retinal cells and down the optic nerve to the brain, where visual images are formed.
自2001年以来，美国能源部已在人工视网膜项目上花费了6300万美元。资金定于2010年结束。该计划的目的是用摄像机替换丢失的轻型收集棒和锥体被摄像机捕获以电刺激视网膜的部分未被疾病破坏。
“ Argus II is a three-part system designed to transmit information about the physical environment directly to an individual’s retina, thus bypassing the photoreceptors that have been damaged,” says Humayun. It consists of an array of 60 electrodes that are surgically implanted and attached to the retina.
“The electrodes conduct information acquired from an external camera mounted on a pair of eyeglasses,” Humayun points out. A battery pack worn on a belt powers the system. “The implant has been designed to last many years, but can be safely removed if necessary,” explains Humayun.
The metal traces forming the electrodes are less than 10 micrometer thick. The electrode array is embedded in a soft biocompatible polymer to allow it to conform to the curvature of the retina.
Stimulation is done with a thin, flexible metal electrode array that has been patterned on soft plastic material similar to a contact lens. The delicate, electrical stimulation of the retina needs to be performed in the eye’s saltwater environment without shorting out any electronic components. Another challenge engineers face is finding a bioadhesive that can be used to attach the microelectrode array to the surface of the retina.
Engineers at Lawrence Livermore National Laboratory are addressing those challenges and developing an advanced ocular surgical tool that allows ophthalmologists to implant microelectrode arrays with minimal tissue damage.
The 60-electrode Argus II 设备已经植入了世界各地29名患者。未来几年将提供更新的更高分辨率模型。第三代设备将具有200多个电极。但是，研究项目的长期目标是开发配备1000多个电极的仿生眼，这将允许面部识别。
Because that density is beyond conventional packaging technology, it creates a wide variety of engineering challenges. For instance, the compact size of the artificial retina’s electronics package makes it difficult to mechanically and electrically interconnect the microelectronics inside.
Researchers at Sandia National Laboratories are developing state-of-the-art packaging technology to assemble and integrate the microelectronic components with the thin-film electrode array. Biocompatibility issues are driving much of this effort, requiring the high-density interconnects to be insulated with a nonconductive film to prevent moisture and ionic and biological contamination from causing device failure.
The artificial retina’s custom-designed integrated circuit (IC) is the system’s brain. Its job is to take signals from the external camera and convert them into stimuli that are transferred to the electrode array. The IC performs this function via a series of interconnected, nanosize nodes.
桑迪亚（Sandia）的IC设计工程师肖恩·皮尔森（Sean Pearson）说：“当前实现较高电极电流的方法涉及与大量粘结线和其他互连的组装。”“这使该设备乏味构建，并且很难产生完整的功能。”
Pearson and his colleagues are developing a dual-sided IC to simplify how data are routed and to better integrate the electronics package with the electrode array. “We’re using one side to bring the signals in and the other side to put them out,” Pearson points out.
For the electronics substrate, the engineers are using a Sandia-patented MEMS technique to selectively etch away parts of the silicon chip or add new structural layers to create tiny features that cannot be made any other way. This micromachining process allows wiring of the electrical connections through the chip for access to both sides.
“By using that bottom surface, which adds interconnect space instead of eliminating it, we’re able to get higher interconnect densities,” thereby allowing the number of electrodes on the array to be increased without making the device bigger, says Murat Okandan, a microsystems engineer at Sandia.
