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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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