Medical Applications of Micro-Electro-Mechanical Systems (MEMS) Technology - Biomaterials Science: An Integrated Clinical and Engineering Approach - page 78

FIGuRE 3.35 (See color insert.)
Illustration of one implementation of a cortical implant for visual prosthesis.
into the brain tissue. The microprobes stimulate the surrounding tissues
via injected electrical currents to provoke a series of luminous points
to appear (an array of pixels) in the field of vision of the blind person
(See Figure 3.36). The visual prosthesis system is composed of two distinct
subsystems: the implanted microprobe array and an external electronic
controller [73].
The implanted microprobe array is inserted into the visual cortex and
connected to the controller by a wire to receive the visual and control data
[75, 76]. Energy to power the microprobe array is also supplied through
the connecting wiring. More sophisticated systems connect the microprobe
array to the controller wirelessly using a radio frequency communica-
tion linkage. The implantable microprobe array contains all of the circuits
necessary to generate the electrical stimuli and to oversee the interface
between the microprobes and the surrounding biological tissue. A battery-
operated camera is positioned externally to capture and process the image
data as well as to generate a signal to electrically stimulate the implanted
microprobes.
Visual prosthetics based on cortical implants have been tested on sev-
eral patients and have demonstrated proof of principle. Patients with these
implants have been able to obtain some limited visual functionality, such