Electronic Visual Prosthesis Research Articles

Flexible ultrasound-induced retinal stimulating piezo-arrays for biomimetic visual prostheses

Electronic visual prostheses, or biomimetic eyes, have shown the feasibility of restoring functional vision in the blind through electrical pulses to initiate neural responses artificially. However, existing visual prostheses predominantly use wired connections or electromagnetic waves for powering and data telemetry, which raises safety concerns or couples inefficiently to miniaturized implant units. Here, we present a flexible ultrasound-induced retinal stimulating piezo-array that can offer an alternative wireless artificial retinal prosthesis approach for evoking visual percepts in blind individuals. The device integrates a two-dimensional piezo-array with 32-pixel stimulating electrodes in a flexible printed circuit board. Each piezo-element can be ultrasonically and individually activated, thus, spatially reconfigurable electronic patterns can be dynamically applied via programmable ultrasound beamlines. As a proof of concept, we demonstrate the ultrasound-induced pattern reconstruction in ex vivo murine retinal tissue, showing the potential of this approach to restore functional, life-enhancing vision in people living with blindness.

Implantation of electronic visual prosthesis for blindness restoration

Loss of sight significantly degrades the quality of human life. Various methods for restoring the vision of blind patients have been studied and range from biological ways to electronic devices. Ever since a visual prosthesis device demonstrated that electrical signals have the beneficial effect of generating phosphenes, their subsequent development has progressed rapidly. Implantation of an electronic prosthetic device in a visually-impaired person allows the individual to recognize the phase and movement of an object. In addition, several commercially approved prosthetic devices have demonstrated successful long-term stability. However, there are some challenges that need to be solved. In this work, we assess the current technology levels of retinal prosthesis devices (categorized by implant location), and then suggest possible directions for future retinal prosthesis devices.

Bionic vision: system architectures – a review

The concept of an electronic visual prosthesis has been investigated since the early 20th century. While the first generation of long-term implantable devices were defined by the turn of the millennium, the greatest progress has been achieved in the past decade. This review describes the current state of the art of visual prosthesis investigated by more than two dozen active groups in this field of research. The focus is on technological solutions in regard to long-term safety of materials, electrode–tissue interfaces and encapsulation technologies. Furthermore, we critically assess the maximum number of stimulating electrodes each technological approach is likely to provide.

Visual Prosthesis

Electronic visual prostheses have demonstrated the ability to restore a rudimentary sense of vision to blind individuals. This review paper will highlight past and recent progress in this field as well as some technical challenges to further advancement. Retinal implants have now been tested in humans by four independent groups. Optic nerve and cortical implants have been also been evaluated in humans. The first implants have achieved remarkable results, including detection of motion and distinguishing objects from a set. To improve on these results, a number of research groups have performed simulations that predict up to 1000 individual pixels may be needed to restore significant functions such as face recognition and reading. In order to achieve a device that can stimulate the visual system in this many locations, issues of power consumption and electronic packaging must be resolved.

Region-of-interest processing for electronic visual prostheses

Electronic visual prostheses, or “bionic eyes,” are likely to provide some coarse visual sensations to blind patients who have these systems implanted. The quality of artificially induced vision is anticipated to be very poor initially. Research described explores image processing techniques that improve perception for users of visual prostheses. We describe visual perception experiments undertaken with 192 normally sighted viewers to simulate artificially induced vision expected from emerging electronic visual prosthesis designs. Several variations of region-of-interest (ROI) processing were applied to images that were presented to subjects as low-resolution 25×25 binary images. Several additional processing methods were compared to determine their suitability for use in automatically controlling a zoom-type function for visual prostheses. The experiments show that ROI processing improves scene understanding for low-quality images when used in a zoom application.

Elektronische Sehprothesen

Currently, no treatment is available for progressive retinal dystrophies. The fabrication of an implantable visual prosthesis seems to be possible now as a result of advances in the fabrication of extremely small micro-systems and their encapsulation in biocompatible materials. The development of implantable visual prostheses is based on the fabrication of remotely controlled microelectrode arrays which have to be implanted in different target regions of the visual system. Prototypes of such systems have already been implanted in animal experiments and also in pilot trials in humans. Four concepts are pursued: 1. epiretinal implant -- fixation onto the inner retinal surface; 2. subretinal implant -- implantation within the subretinal space; 3. optic nerve stimulator -- cuff electrode placed around the optic nerve; 4. cortical prosthesis -- implantation of surface electrodes in the region of the visual cortex. All these concepts have already been applied in pilot trials in humans. The results show some promising visual perception. The use of implantable electronic visual prostheses will become a possible option in the treatment of currently untreatable retinal dystrophies. Further basic research initiatives are necessary as well as further human trials to characterize the stimulation parameters and to improve the currently available devices.

Transscleral implantation and neurophysiological testing of subretinal polyimide film electrodes in the domestic pig in visual prosthesis development**The first two authors (H G Sachs and Th Schanze) contributed equally to this paper.

Loss of photoreceptor function is responsible for a variety of blinding diseases, including retinitis pigmentosa. Advances in microtechnology have led to the development of electronic visual prostheses which are currently under investigation for the treatment of human blindness. The design of a subretinal prosthesis requires that the stimulation device should be implantable in the subretinal space of the eye. Current limitations in eye surgery have to be overcome to demonstrate the feasibility of this approach and to determine basic stimulation parameters. Therefore, polyimide film-bound electrodes were implanted in the subretinal space in anaesthetized domestic pigs as a prelude to electrical stimulation in acute experiments. Eight eyes underwent surgery to demonstrate the transscleral implantability of the device. Four of the eight eyes were stimulated electrically. In these four animals the cranium was prepared for epidural recording of evoked visual cortex responses, and stimulation was performed with sequences of current impulses. All eight subretinal implantation procedures were carried out successfully with polyimide film electrodes and each electrode was implanted beneath the outer retina of the posterior pole of the operated eyes. Four eyes were used for neurophysiological testing, involving recordings of epidural cortical responses to light and electrical stimulation. A light stimulus response, which occurred 40 ms after stimulation, proved the integrity of the operated eye. The electrical stimuli occurred about 20 ms after the onset of stimulation. The stimulation threshold was approximately 100 µA. Both the threshold and the cortical responses depended on the correspondence between retinal stimulation and cortical recording sites and on the number of stimulation electrodes used simultaneously. The subretinal implantation of complex stimulation devices using the transscleral procedure with consecutive subretinal stimulation is feasible in acute experiments in an animal model approximating to the situation in humans. The domestic pig is an appropriate animal model for basic testing of subretinal implants. Animal experiments with chronically implanted devices and long-term stimulation are advisable to prepare the field for successful human experiments.

Electronic visual prosthesis.

Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are incurable diseases that result in profound vision loss due to degeneration of the light sensing photoreceptors. However, the discovery that direct electrical stimulation of the retinal neurons creates visual sensation has inspired prosthetic devices aimed to restore useful vision in RP/AMD patients. The approach to one such electronic visual prosthesis is described in this article. The prosthesis consists of an external unit and an internal unit. The communication link has three components--power and data transfer from the external to the internal unit, and data transfer from the internal to the external unit. A novel method of integrating power transfer and back telemetry is described here. The goal is to design a stimulator chip with a small area with low power consumption. This chip, capable of stimulating 60 dedicated electrodes, is fabricated using AMI 1.2 microm process technology and the results are presented. Improvements in the design to increase the number of outputs to 1,000 have been discussed. The new circuit is aimed at increasing the circuit density, reducing power per stimulus, and meeting the requirements more closely than the previous designs. The results of the designed chip are presented.

The bionic eye (electronic visual prosthesis): A review

The concept of a visual prosthesis for the blind or partially sighted is not a new one. Indeed, for more than three decades this technology based treatment for blindness has appeared imminent. Despite the concerted efforts of numerous physicians, scientists and engineers, the successful application of a useful visual prosthesis remains elusive. The present review will endeavour to describe past efforts, investigate the present state of the art and indicate the obstacles that must be overcome in order to bring an electronic visual prosthesis to fruition.