-There is a growing interest in the development of a retinal prosthesis device based on a number of recent experiments demonstrating electrical stimulation of retinal tissue with single electrodes. An intraocular retinal prosthesis test device is currently under development at NRL/JHU. The microelectronic device has an image format of 80 X 40 unit cells interfaced to the retinal surface via an array of microwires in a glass matrix. The system architecture and technology development issues are discussed as well as the topic of biocompatibility. This test device will enable acute human experiments in an operating room environment to demonstrate a massively parallel interface between retinal tissue and a microelectronic array. Keywords -Retina, prosthesis, channel glass, multiplexer 1. INTRODUCTION Recent advances in the fields of microelectronics, neurophysiology, and retinal surgery have progressed to the point where an implantable visual prosthesis system, based on electrical stimulation, is now considered feasible. Currently a number of research projects around the world are aimed at developing prosthetic vision systems. The device discussed in this paper addresses the technical problem of positioning a high-density electrode array against the retina to achieve high-resolution retinal stimulation and perception of image sequences in the patient.The outermost layer of the sensory retina consists of photoreceptors; in the macular region, the photoreceptors are mostly cones (color-sensitive). The next layers of the sensory retina are the bipolar, amacrine, horizontal, and the ganglion cells. The axons of the ganglion cells form the optic nerve.Photoreceptor loss from diseases such as retinitis pigmentosa and age-related macular degeneration are the leading causes of legal blindness. Despite near-total loss of photoreceptors, there is relative preservation of the other retinal neurons. By stimulating the remaining functional retinal layers, it may be possible to restore visual perception.Initial experiments with intraocular stimulation, were performed by de Juan and Humayun several years ago [I]. Since that time, a number of research groups have begun the development of retinal prostheses [2,3,4,5,6,7,8]. Some groups are working toward a device that will be implanted on the epiretinal retinal surface while others are developing a subretinal implant.Epiretinal implantation has the advantage of leaving the retina intact by placing the implant in the vitreous cavity, a naturally existing and fluid-filled space. Studies at John Hopkins University Hospital have demonstrated that this array position is biocompatible [9]. Subretinal implantation of a retinal prosthesis essentially replaces the diseased photoreceptors with a microelectronic stimulator device. However, the surgical implantation requires detaching the retina, and the location of the device may be disruptive to the health of the retina.Section 2 gives an overview of the intraocular retinal prosthesis (IRP) concept and associated electrical stimul...