Implantable Retinal Prosthesis Research Articles

Demonstration of multi-point stimulation with AC-driven CMOS chips for retinal prosthesis

We demonstrated a multi-point stimulation system using CMOS chips designed for distributed implantable retinal prostheses. The CMOS chip integrates current sources and electrode selection circuits. This integration enables stimulation current control from multiple electrodes with minimal wires. In this study, we constructed a validation system with 49 electrodes capable of visually observing stimulation current outputs. The validation results show that it is possible to configure stimulation conditions in approximately 9.3 μs per electrode, and we demonstrated the ability to complete one frame, including the stimulation time, within approximately 11 ms. We also demonstrated parallel current stimulation from multiple electrodes using an in vitro experiment.

Implantable AC-driven CMOS chip for distributed multichip retinal prosthesis capable of high-rate stimulation

Implantable retinal prostheses are stimulation devices used to compensate for the light sensitivity loss of retinal cells. In this study, we propose and demonstrate a novel method to significantly reduce the setting time for the stimulation conditions of a retinal prosthesis chip capable of multi-electrode stimulation. The efficiency of the control method is increased while using only two wires, as in our previous work. The chip comprises an 8 bit ID and 7 electrodes, and the stimulation current value can be set from 50 to 1550 μA. The fabricated chip requires only 32 pulses to set the stimulation conditions, which is approximately 1/65 of that of our previous chip. Furthermore, it is equipped with a complementary metal–oxide–semiconductor rectifier to enable it to be driven by a rectangular AC power supply. The effectiveness of the chip is demonstrated by setting the stimulation conditions at approximately 18 μs per electrode at a clock frequency of 2.3 MHz.

Stereoscopic Distance Filtering Plus Thermal Imaging Glasses Design.

The authors present the development of eyewear that incorporates stereoscopic and thermal imaging cameras for the purpose of highlighting objects/views of interest. Image processing algorithms that simplify complex elements in a scene have the ability to improve the utility of blind and low vision aids. Thermal imaging can be used to highlight important objects such as people or animals, while stereoscopic imaging can be used to filter background imagery beyond a certain distance. The methods used have been successful in providing utility to retinal prosthesis users. The stereoscopic camera systems involved strict requirements on the relative orientation of the cameras for calibrated distance filtering. A mechanical design is presented that fixes the relative camera locations on a 3D printed titanium structure that can float in the frame to maintain orientations even when the eyewear is flexed during wearing. Clinical Relevance - The design presented has utility in improving perceived spatial resolution in implantable retinal prostheses, implantable visual cortical prostheses, direct-vision prostheses, and wearable low vision aids.

(Invited, Digital Presentation) Development of 3D-Stacked Artificial Retina Chip with 3DIC/TSV and Advanced Packaging Technology

3DIC/TSV is the most promising candidate for high-performance and low-power computing devices. They have many advantages such as short wiring length, small pin capacitances, high packing density, ultra-parallel operation. Among several types of 3D-IC technologies, multiple chips-to-wafer (MCtW) stacking can stack known-good chips fabricated with different technologies and sizes, leading to a true 3D heterogeneous system. We have developed a fully implantable retinal prosthesis with a 3D-stacked artificial retina (AR) chip. In the 3D-stacked AR chip, the photoreceptor chip and stimulus current generator with image processing circuits are vertically stacked and electrically connected by many TSVs. Furthermore, advanced packaging technology like FOWLP is being developed to implement multiple AR chips in a flexible substrate to obtain a wide viewing angle. This leads to small chip size, lightweight, large fill-factor, high resolution, and high quality of life patients.

Study of Al-doped ZnO Transparent Stimulus Electrode for Fully Implantable Retinal Prosthesis with Three-dimensionally Stacked Retinal Prosthesis Chip

Study of Al-doped ZnO Transparent Stimulus Electrode for Fully Implantable Retinal Prosthesis with Three-dimensionally Stacked Retinal Prosthesis Chip

Design and Simulations of an Energy Harvesting Capable CMOS Pixel for Implantable Retinal Prosthesis

A new pixel is designed with the capability of imaging and energy harvesting for the retinal prosthesis implant in 0.18 µm standard Complementary Metal Oxide Semiconductor technology. The pixel conversion gain and dynamic range, are 2.05 $$\upmu{\text{V}}/{\text{e}}^{ - }$$ and 63.2 dB. The power consumption 53.12 pW per pixel while energy harvesting performance is 3.87 nW in 60 klx of illuminance per pixel. These results have been obtained using post layout simulation. In the proposed pixel structure, the high power production capability in energy harvesting mode covers the demanded energy by using all available p-n junction photo generated currents.

Future Developments in Retinal Prostheses

Implantable retinal prostheses for the blind are already in use. In blind subjects suffering from retinitis pigmentosa (RP), these systems are able to induce phosphenes. However, the measurable gain in vision is limited. This is due to degeneration in the retina itself and to the technology, which is used in the currently available systems. Research groups and companies are working on solutions and prototypes to improve the outcome of electrical stimulation in the visual system. One improvement will be to enlarge the electrode array in order to restore a larger visual field. A second approach is to enlarge the number of electrodes and to place them at a higher density to improve the spatial resolution of the system. A third concept is to develop a recording unit within the electrode array to analyse ganglion cell behaviour underneath the electrode. This information can than be used to optimise the stimulation pattern. Not only retinal prostheses are under development but also systems to stimulate the retina from the suprachoroidal space, to directly stimulate the optic nerve or the lateral geniculate body or even the primary visual cortex.

A multi-scale computational model for the study of retinal prosthetic stimulation.

An implantable retinal prosthesis has been developed to restore vision to patients who have been blinded by degenerative diseases that destroy photoreceptors. By electrically stimulating the surviving retinal cells, the damaged photoreceptors may be bypassed and limited vision can be restored. While this has been shown to restore partial vision, the understanding of how cells react to this systematic electrical stimulation is largely unknown. Better predictive models and a deeper understanding of neural responses to electrical stimulation is necessary for designing a successful prosthesis. In this work, a computational model of an epi-retinal implant was built and simulated, spanning multiple spatial scales, including a large-scale model of the retina and implant electronics, as well as underlying neuronal networks.

A wearable real-time image processor for a vision prosthesis

Rapid progress in recent years has made implantable retinal prostheses a promising therapeutic option in the near future for patients with macular degeneration or retinitis pigmentosa. Yet little work on devices that encode visual images into electrical stimuli have been reported to date. This paper presents a wearable image processor for use as the external module of a vision prosthesis. It is based on a dual-core microprocessor architecture and runs the Linux operating system. A set of image-processing algorithms executes on the digital signal processor of the device, which may be controlled remotely via a standard desktop computer. The results indicate that a highly flexible and configurable image processor can be built with the dual-core architecture. Depending on the image-processing requirements, general-purpose embedded microprocessors alone may be inadequate for implementing image-processing strategies required by retinal prostheses.

A Comparison of Two and Three Dimensional Dipole Antennas for an Implantable Retinal Prosthesis

The feasibility is investigated using three dimensional folded dipole antennas as a data-telemetry implantable receiving antenna in a dual-unit retinal prosthesis to restore partial vision to the blind. Three dimensional designs are explored in an effort to enhance certain antenna characteristics such as bandwidth and maximum gain while reducing the planar footprint size in comparison to its two dimensional equivalent. The current vector alignment between the three dimensional layers are examined through folding and rotating the dipole arms with respect to each other to fully optimize the antenna's characteristics. The performance of the 2D and 3D antennas were compared in simulations and further examined by fabricating and characterizing the performance in a transmit/ receive system in air and inside eye phantoms. Results show that three-dimensional antennas can provide larger bandwidth while being physically smaller than the correspondent two-dimensional ones, thus providing larger channel capacity that could lead to a system with an increased number of stimulating electrodes.

Cortical Activation Via an Implanted Wireless Retinal Prosthesis

To demonstrate local cortical activations in the primary visual cortex of the cat as a result of retinal electrical stimulation by means of a completely wireless-controlled, implantable retinal prosthesis in a series of acute experiments. The transfer of energy to drive the device and signals to activate any combination of 25 retinal electrodes was achieved completely wirelessly by an external transmitter positioned in front of the eye. Individually configured electrical stimuli were applied via any combination of 25 electrodes, on sending the necessary pulse parameters to the implant. Placement of the implant onto the retinal surface was achieved after lensectomy and vitrectomy in the cat. Fixation was performed with a retinal tack. Cortical activation patterns were recorded by means of optical imaging of intrinsic signals. Implantation and fixation were successfully performed in three cats. Wireless activation of the implant by radiofrequency was demonstrated by recording of stimulus artifacts from the sclera. Local activation of the visual cortex measured by optical imaging of intrinsic signals revealed a shift of cortical response that was well correlated with a change in the position of the activated retinal electrodes. The results demonstrate the retinotopic activation of the visual cortex using a completely wireless, remote-controlled retinal implant.

A method and technical equipment for an acute human trial to evaluate retinal implant technology

This paper reports on methods and technical equipment to investigate the epiretinal stimulation of the retina in blind human subjects in acute trials. Current is applied to the retina through a thin, flexible microcontact film (microelectrode array) with electrode diameters ranging from 50 to 360 µm. The film is mounted in a custom-designed surgical tool that is hand-held by the surgeon during stimulation. The eventual goal of the work is the development of a chronically implantable retinal prosthesis to restore a useful level of vision to patients who are blind with outer retinal degenerations, specifically retinitis pigmentosa and macular degeneration.