Attaining higher resolution visual prosthetics: a review of the factors and limitations

Abstract

Visual prosthetics is an expanding subfield of functional electrical stimulation which has gained increased interest recently in light of new advances in treatments and technology. These treatments and technology represent a major improvement over prior art, but are still subject to a host of limitations which are dependent on the manner in which one approaches the topic of visual prosthetics. These limitations pose new research challenges whose solutions are directly applicable to the well-being of blind individuals everywhere. In this review, we will outline and critically compare major current approaches to visual prosthetics, and in particular retinal prosthetics. Then, we will engage in an in-depth discussion of the limitations imposed by current technology, physics, and the underlying biology of the retina to highlight several of the challenges currently facing researchers.

Prototype chemical synapse chip for spatially patterned neurotransmitter stimulation of the retina ex vivo

“…Yet, this technology is unable to restore high-resolution naturalistic vision due to the characteristics of the electrical current distribution through a large array of electrodes. Two fundamental limitations of electrical stimulation are its inability to: (1) selectively stimulate various retinal neurons as the natural retinal circuitry does, and (2) enable high resolution distributed stimulation since one needs a large array of tiny electrodes to cover the fine retinal cellular mosaic 10 . Therefore, it is worthwhile to explore alternative strategies and agents that could stimulate the retina more effectively by engaging visual pathways biomimetically.…”

“…However, the vision restored by these prostheses is still well above the legal blindness limit and advancing their capability to further improve the quality of vision has proven difficult due to inherent limitations of electrical stimulation. Specifically, electrical charge density limitations restrict both the size of microelectrodes and the current that can be safely applied to avoid tissue damage 10 . As a result, electrical stimulation of the retina relies on large, widely separated electrodes that stimulate large regions of the retina, which necessarily limits the visual acuities these devices can restore to levels far above the legal blindness limit 6,10 .…”

“…Specifically, electrical charge density limitations restrict both the size of microelectrodes and the current that can be safely applied to avoid tissue damage 10 . As a result, electrical stimulation of the retina relies on large, widely separated electrodes that stimulate large regions of the retina, which necessarily limits the visual acuities these devices can restore to levels far above the legal blindness limit 6,10 . Second, though electrical stimulation parameters have been optimized to evoke functional RGC responses, electrical current, being an unnatural stimulus, activates all types of retinal cells, including their axons, indiscriminately and creates confusing perceptions in patients 3,10,11 .…”

“…As a result, electrical stimulation of the retina relies on large, widely separated electrodes that stimulate large regions of the retina, which necessarily limits the visual acuities these devices can restore to levels far above the legal blindness limit 6,10 . Second, though electrical stimulation parameters have been optimized to evoke functional RGC responses, electrical current, being an unnatural stimulus, activates all types of retinal cells, including their axons, indiscriminately and creates confusing perceptions in patients 3,10,11 . Therefore, while current electrical prostheses provide some useful vision to patients, there is a definite need for an alternative stimulation strategy capable of restoring high resolution and more naturalistic vision.…”

Neuro-robotics Paradigm for Intelligent Assistive Technologies

“…Some improvements in auditory performance of people with hearing loss can be obtained with cochlear implants (Simmons et al, 1965;Blume, 1999;Loizou, 1999;Spelman, 1999;Marsot-Dupuch et al, 2001). Retinal implants can be realized in the attempt to regain lost visual functionality (Eiber et al, 2013).…”