Page 364 - Handbook of Biomechatronics

358 Lilach Bareket et al.

visual cortex to induce phosphenes was indicated by several investigations in
the early 1920s (L€owenstein and Borchardt, 1918; Krause, 1924; Foerster,
1929). Brindley and Lewin, followed by Dobelle and coworkers have dem-
onstrated that chronically implanted electrodes in the visual cortex could
potentially offer limited restoration of visual sensations (Brindley and
Lewin, 1968; Dobelle and Mladejovsky, 1974; Dobelle et al., 1974;
Klomp et al., 1977). These pioneering efforts opened the door to the pos-
sibility of restoring visual perception via prosthetic devices.
Since these early breakthroughs, tremendous efforts have been invested
in translation of visual prostheses from the experimental to the clinical
stage. Current visual prostheses include three main functionalities: (1) an
implanted electrode array to stimulate neurons along the visual pathway,
(2) a component to capture the visual scene, and (3) an image-processing
unit. The image-processing unit transduces the captured image into a pat-
tern of stimulation signals that are transferred to the implanted chip. Three
retinal devices have already obtained regulatory approvals: the Argus II
device (Second Sight Medical Products, United States) received regulatory
approval for marketing in Europe (CE mark; 2011), the United States (FDA
approval, humanitarian device exemption; 2013) and Canada (2015), and
the Alpha IMS prosthesis (Retina Implant AG, Germany) and IRIS II
(Pixium Vision SA, France) which gained CE certification in 2014 and
2016, respectively. Patients implanted with retinal devices show improve-
ment in visually guided performance tasks including recognition and dis-
crimination of objects, following a marked trail, grasping objects, and
reading. The new generation of visual cortical devices is currently in the
experimental or preclinical phase of development, with clinical trials
planned within the next several years. The basic device architecture of a
camera, vision processing computer, and electrode interface with the brain
underpins the design of the new generation cortical visual prosthetics but the
difference is the application of computer chips, microelectronic circuit
design, new materials, microelectrodes wireless engineering, and advanced
manufacturing and neurosurgical techniques.
In this chapter, we review the progress in visual bionics, focusing on ret-
inal and cortical prostheses. We describe state-of-the-art devices undergoing
preclinical or clinical trials. Next, we discuss current technological chal-
lenges that need to be addressed. Finally, we highlight progress in next-
generation technologies, including alternative implantation sites along the
visual pathway.