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Visual
Prosthesis Market May Follow Uncharted Path
by James Cavuoto, editor
Several recent developments from research teams and commercial developers
working on visual prostheses have raised hopes and investor interest
in retinal implants and other strategies for restoring vision to blind
individuals. But a long road of testing, product cycles, clinician
acceptance, and reimbursement issues awaits players in this market
segment.
Earlier this year, Optobionics
Corp., which manufactures an artificial silicon retina, announced
results from its first six trials in human patients with retinitis
pigmentosa. Several patients reported improvement in their vision,
including the ability to see lights or shapes for the first time since
the onset of their disease. In part because of the positive publicity
it has garnered, Optobionics received an additional $20 million in
venture capital investment this year from Medtronic
and Polaris Ventures.
In February, investigators at USC implanted a permanent retinal implant
manufacured by Second Sight, Llc,
in a blind volunteer as the first step in a FDA-approved feasibility
trial. The retinal prosthesis measures 4 by 5 millimeters, and is
studded with 16 electrodes in a 4-by-4 array.
Unlike Optobionics’ ASR, which relies on passive photodetectors
for stimulation, the Second Sight device is intended to electrically
stimulate the retina (retinal ganglion cells). Visual signals from
a camera are sent to an implanted receiver, and a visual image is
then created by stimulating the appropriate electrodes on the surface
of the retina. The implant is directed at persons blind due to macular
degeneration or retinitis pigmentosa.
In previous acute, or temporary, human trials, blind patients reported
seeing spots of light, or simple patterns, as a result of the stimulation.
In the current trial, the device is intended to be a permanent implant
and barring complications will remain in place indefinitely.
Another commercial effort is Intelligent
Implants GmbH of Bonn, Germany. The company’s retinal implant
consists of an implanted retina stimulator based on an ultra-thin
microcontact foil, and a computational element called a retina encoder.
The encoder transforms visual patterns projected onto a photosensor
chip into a parallel stream of asynchronous stimulation pulses directed
to retinal ganglion cells. It incorpoates “spatio-temporal filters”
that process the visual signals. The filters can be individually tuned
to optimize visual perception during a learning phase.
Besides these commercial efforts, several research laboratories, including
teams at the Naval Research Laboratories, London’s University
College, the University of Houston, and NASA’s Space
Vacuum Epitaxy Center, are working on a retinal implant. The latter
effort has spun off an as-yet unnamed commercial venture to develop
a thin-film array of photodetectors as small as 5 microns each.
Many observers are looking to the cochlear implant segment of the
neural prosthesis market as a model for the development of the retinal
implant market. But there are many profound differences in the potential
retinal prosthesis market and the cochlear prosthesis market. To begin
with, the sheer complexity of the human visual system, and the massive
data rate involved, dwarfs the information load of most cochlear implants,
which feature fewer than 50 electrodes and data channels. The organization
of fibers in the optic nerve is much more poorly understood than in
the auditory nerve.
Second Sight’s president Robert Greenberg believes this is not
an insurmountable problem. He feels that a useful navigation or reading
aid for blind individuals could conceivably be constructed with an
array as small as25 by 25 electrodes, although no one has yet tested
this. And the NASA/University of Houston team believes they can construct
an implant with up to 100,000 detectors, because of the dense packing
of thin film sensors possible.
Another issue confronting efforts to stimulate the retina is the increase
in current density that necessarily accompanies decreased electrode
surface area. So as manufacturers struggle to build more densely packed
electrode arrays, they may face the problem of induced tissue damage
or component failure resulting from the increased current density.
Nonetheless, there are other factors that may work in favor of commercial
developers of retinal implants. For one, the degree of incapacitation
caused by blindness is much more profound than results from deafness,
and although there are various aids available for blind people, they
are generally not as restorative as options such as lip-reading, sign
language, and captioning available to the deaf community. Accordingly,
it is likely that blind individuals will exhibit less reticence in
electing to receive an implant than was encountered in the deaf community
in the early days of the cochlear implant. In fact, some commercial
firms working on retinal implants have found that they must tone down
their publicity efforts because of the massive amont of interest expressed
by potential recipients.
Moreover, there are a number of private and quasi-governmental agencies
active in the visual disabilities community, and these organizations
may be in a position to supplement government and VC funding for device
development. Indeed, it is conceivable that vendors of first-generation
retinal implants will gain revenue for their investigational units,
even before insurers approve reimbursement.
Manufacturers of retinal implants will need to be very careful to
not overpromise on the capabilities or the timetable of their devices.
Because of the intense public interest, a well publicized failure
or lack of meaningful results could erase all of the investor and
funding agency confidence built up during development. It might be
a wise strategy to position the first stage of development as visual
aids, with tangible goals such as the ability to read individual words,
a low-resolution computer screen, or carefully crafted signage. Once
these preliminary goals are met, the industry could work on the next
generation of more general purpose prostheses. |
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