A US-based research team has
successfully demonstrated how dynamic stimulation of the visual cortex enables
blind and sighted people to see shapes, a technique that could one day be used
to convey entire visual scenes to patients. Neuroscientists and neurosurgeons
have long known that electrical stimulation of electrodes implanted in the
visual cortex using small currents produces the perception of a small flash of
light, known as a phosphene. This process could serve as the basis for a visual
cortical prosthesis (VCP), a device that could restore some visual abilities to
blind patients. Although some VCPs were tested in the 1960s and 1970s, they had
limited effectiveness and were constrained by the technology of the time. But
now a new wave of teams is attempting to produce a modern VCP, using improved
electrodes and better wireless data and power transfer technology. Two such
teams, based at Baylor College of Medicine (BCM) and the University of
California, Los Angeles (UCLA), have carried out clinical trials and tests of a
VCP device called Orion, produced by Second Sight Medical Products.
The results show that the Orion
device is a safe and effective means of providing patients with some visual
experience. Instead of treating the electrodes on the array like pixels in a
video display, and sending various current levels to all of them at once in an
attempt to convey a particular form or shape to the patient, the device instead
stimulates only the electrodes that outline the shape it is trying to convey,
and stimulates them in a rapid dynamic sequence. The Orion VCP system consists
of a camera, which captures an image of the visual scene in front of the
patient, a visual processing unit that the subject wears on their belt and
which performs some filtering of the camera image, and a transmitter worn on a
headset that delivers wireless data and power to a receiving coil implanted
under the skin. It also contains circuitry to handle the final conversion of
signals into currents to be sent to the electrodes, as well as the electrode
array itself, which consists of a flexible sheet with 60 embedded electrodes
that lies on the surface of the visual cortex. Looking ahead, the team hopes to
test its stimulation protocol in VCPs that have a greater number of implanted
electrodes.
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