Contemporary approaches to visual prostheses

Abstract

Visual prostheses serve to restore visual function following acquired blindness. Acquired blindness (as opposed to congenital blindness) has many causes, including diseases such as retinitis pigmentosa, glaucoma, and macular degeneration, or trauma such as caused by automobile accident or blast damage from explosions. Many of the blindness-causing diseases target the retina or other ocular structure. Often, despite the loss of sensitivity to light, the remainder of the visual pathway is still functional, enabling electrical devices to deliver effective and meaningful visual information to the brain via arrays of electrodes. These arrays can be placed in any part of the early visual pathway, such as the retina, optic nerve, lateral geniculate nucleus, or visual cortex. A camera or other imaging source is used to drive electrical stimulation of remaining healthy cells or structures to create artificial vision and provide restoration of function. In this review, each approach to visual prostheses is described, including advantages and disadvantages as well as assessments of the current state of the art. Most of the work to-date has been targeting stimulation of (a) the retina, with three devices approved for general use and two more in clinical testing; (b) the lateral geniculate nucleus, with efforts still in the pre-clinical stage; and (c) the cortex, with three devices in clinical testing and none currently approved for general use despite the longest history of investigation of the three major approaches. Each class of device has different medical indications, and different levels of invasiveness required for implantation. All contemporary devices deliver relatively poor vision. There has been remarkable progress since the first proof-of-concept demonstration that used stimulation of the primary visual cortex, with the field exploring all viable options for restoration of function. Much of the progress has been recent, driven by advances in microelectronics and biocompatibility. With three devices currently approved for general use in various parts of the world, and a handful of additional devices well along in the pipeline toward approval, prospects for wide deployment of a device-based therapy to treat acquired blindness are good.

Dynamic Stimulation of Visual Cortex Produces Form Vision in Sighted and Blind Humans

“…The pioneering early attempt of Brindley and Lewin was the first to accomplish wireless stimulation but was impeded by technological limitations, especially the inability to fabricate miniature electrode arrays and control them with portable transmitters and receivers (Brindley and Lewin, 1968). Recent advances in wireless microelectronics have renewed interest in VCPs, with at least four neuroengineering groups currently developing devices that are either in or rapidly approaching the clinical trial stage (Lowery, 2013;Mirochnik and Pezaris, 2019;Roelfsema et al, 2018;Troyk, 2017). Despite these advances, the stimulation Article paradigm underlying VCPs has not changed.…”

“…Because of the retinotopic organization of the visual cortex, implanting an array of multiple electrodes at different locations within this cortical map allows for the creation of multiple phosphenes, with each stimulated electrode contributing a phosphene at one predictable visual field location (Bosking et al, 2017a;Tehovnik and Slocum, 2013). Recent advances in biomedical engineering have resulted in wirelessly powered and controlled devices containing dozens of electrodes that can be implanted in the visual cortex, leading to a worldwide resurgence in efforts to develop a clinically useable VCP (Lowery, 2013;Mirochnik and Pezaris, 2019;Roelfsema et al, 2018;Troyk, 2017).…”

Degeneration-Dependent Retinal Remodeling: Looking for the Molecular Trigger

“…Blocking or reducing hyperactivity unmasks light responses, opening a therapeutic window to enhance vision in patients suffering from RP, AMD and other photoreceptor degeneration diseases. In patients that are completely blind, restoration of vision might be possible through photo-pharmacology (Tochitsky et al, 2018), optogenetics (Baker and Flannery, 2018) or prosthetic devices (Mirochnik and Pezaris, 2019). However, low signal-to-noise ratio will result in poor visual restoration, regardless of the method employed.…”

Deep Learning-Supported Cytoarchitectonic Mapping of the Human Lateral Geniculate Body in the BigBrain

“…For example, routine Magnetic Resonance Imaging (MRI) studies often lack sufficient contrast and/or spatial resolution and could benefit from such atlas data. Current studies on the implementation of electrically stimulated prostheses in the visual cortex aim to restore part of the vision in blind people by multiple stimulations of electrodes to percept light [26,27], where such maps could be applied in the future to increase the localization accuracy. The investigation of the pathomechanisms of diseases where the visual pathway is affected, such as Multiple Sclerosis or glaucoma could be supported by the maps [28,29].…”