Retinal Prosthetic Approaches to Enhance Visual Perception for Blind Patients

Abstract

Retinal prostheses are implantable devices that aim to restore the vision of blind patients suffering from retinal degeneration, mainly by artificially stimulating the remaining retinal neurons. Some retinal prostheses have successfully reached the stage of clinical trials; however, these devices can only restore vision partially and remain insufficient to enable patients to conduct everyday life independently. The visual acuity of the artificial vision is limited by various factors from both engineering and physiological perspectives. To overcome those issues and further enhance the visual resolution of retinal prostheses, a variety of retinal prosthetic approaches have been proposed, based on optimization of the geometries of electrode arrays and stimulation pulse parameters. Other retinal stimulation modalities such as optics, ultrasound, and magnetics have also been utilized to address the limitations in conventional electrical stimulation. Although none of these approaches have been clinically proven to fully restore the function of a degenerated retina, the extensive efforts made in this field have demonstrated a series of encouraging findings for the next generation of retinal prostheses, and these could potentially enhance the visual acuity of retinal prostheses. In this article, a comprehensive and up-to-date overview of retinal prosthetic strategies is provided, with a specific focus on a quantitative assessment of visual acuity results from various retinal stimulation technologies. The aim is to highlight future directions toward high-resolution retinal prostheses.

Micro-Fabrication of Components for a High-Density Sub-Retinal Visual Prosthesis

“…Another matter relating to mechanical properties of our implantable multi-electrode array components in particular was the channel count needed in order to be able to stimulate sufficient numbers of sites to have a reasonable likelihood of restoring “useful” vision. We estimated for our third-generation retinal prosthesis that at least 256 channels would be required, based on the findings of a number of teams in the field over the last 20+ years that have recently been reviewed [ 3 , 4 ]. Since no de-multiplexer was included in our system in a distal region near the stimulation sites beneath the retina, this meant that >256 individual traces or leads would need to be incorporated along the length of the array from the stimulator package containing the circuitry, to the electrode locations within the eye.…”

“…In that case, it was the limitations of the fabrication process for creating high temperature co-fired ceramic parts that determined the spacing. While it is true that high channel counts can and have been achieved, e.g., by the use of alternative, photodiode-based visual prosthesis designs, those approaches are entirely different, make use of the capabilities of silicon foundries used to create such devices, and have been reviewed elsewhere [ 3 , 4 ].…”

“…The retinal neural network is a part of the brain with well-understood anatomical and physiological organization. Patients with longstanding and profound blindness secondary to retinal disease have provided detailed feedback on perceptual responses to electrical stimulation of the retina, whether the stimuli were provided sub-retinally or epi-retinally [ 1 , 2 , 3 , 4 ]. Advances in micro-fabrication technology, electronics, materials, surgical techniques, and other research have enabled our Bionic Eye Technologies team (formerly known as the Boston Retinal Implant Project or BRIP) to build a 256+ channel retinal prosthesis to restore vision to patients who have lost vision due to degenerative diseases such as retinitis pigmentosa and age-related macular degeneration [ 5 ].…”

Editorial for the Special Issue on Micro/Nanofabrication for Retinal Implants

“…For future innovations in retinal prosthetics, comprehensive understanding of the current status is essential. In that sense, the review paper of Shim et al [ 6 ] is timely. They have systematically compared a broad array of existing methodologies for retinal stimulation.…”

“…In microelectronic approaches, stimulating electrodes have long been in two-dimensional planar shapes which typically touch the epi-/sub-retinal surface. Recently, these planar electrodes have been challenged by three-dimensional (3D) electrodes in diverse shapes [ 6 , 8 , 9 ]. In this Special Issue as well, the two articles by Shire et al and Seo et al [ 10 , 11 ] reported 3D pillar electrode structures.…”