The US Department of Energy’s Office of Biological and Environmental Research is funding a three-year, $9 million project that will investigate restoring sight to the blind.
The research will be carried out by DOE labs, including Sandia, Oak Ridge, Argonne, Lawrence Livermore and Los Alamos National Laboratories. Other team members include the University of Southern California, North Carolina State University and private company, Second Sight.
The idea is to create 1,000 points of light through 1,000 MEMs (microelectromechanical systems) electrodes. The electrodes will be positioned on the retinas of those blinded by diseases such as age-related macular degeneration and retinitis pigmentosa.
These diseases damage rods and cones in the eye that normally convert light to electrical impulses, but leave intact the neural paths to the brain that transport electrical signals. Eventually the input from rods and cones ceases, but 70 to 90 percent of nerve structures set up to receive those inputs remain intact.
‘The aim is to bring a blind person to the point where he or she can read, move around objects in the house, and do basic household chores,’ said Sandia National Laboratories’ project leader Kurt Wessendorf. ‘They won’t be able to drive cars, at least in the near future, because instead of millions of pixels, they’ll see approximately a thousand. The images will come a little slowly and appear yellow. But people who are blind will see.’
The plan is to use a tiny camera and radio frequency transmitter lodged in the frame of a patient’s glasses to transmit information and power to modules placed within the eyeball. The modules will be linked to retinal nerves that will send electrical impulses to the brain for processing.
The Sandia approach is to attach a MEMs chip on the retina (within the vitreous humour of the eyeball) made of LIGA (a German acronym for lithography, electroplating and moulding, which makes small parts of metal, plastic, or ceramics) and surface micromachined silicon parts.
The idea is to directly stimulate some of the nerve endings within the retina to produce images good enough to read large print and to distinguish between objects in a room.
‘Compared to the elegance of the original biological design, what we’re doing is extremely crude,’ said Wessendorf. ‘We are trying to build retinal implants in the form of electrode arrays that sit on the retina and stimulate the nerves that the eye’s rods and cones formerly served.’
‘We’ll use a crude, shotgun approach that fires groups of nerves. In the long run, of course, we’d like to stimulate each individual nerve,’ said Sandia manager Mike Daily.
‘Integrating microdevices into the human eye is incredibly challenging because of the need for high-reliability operation over decades in a saline environment,’ said Daily. ‘BioMEMs interfaces and biocompatibility issues drive much of the effort, particularly in the packaging of the microsystem.’ ‘Packaging’ is said to refer to sealing and securing a microdevice in place and linking it electronically and physically with its environment.
Counterintuitively, the rods and cones of the retina lie beneath nerves, not above them, which makes it slightly easier to connect directly to the nerves.
‘The tissue housing the nerves is relatively clear. We’re investigating which electronic waveforms will best stimulate these nerves, ‘ said Wessendorf. One problem, he said, is that ‘If we excite a nerve with electrons, we don’t know exactly how that compares to the electrochemical response of light on a healthy retina.’
There are other issues, he said. For one, the retina can’t handle much pressure. Sandia Labs favour spring-loaded electrodes that insure good electrode contact with minimal force. Also, protein fouling can mess up delicate interfaces intended to transmit electrical impulses.
Other problems include biocompatibility – the problem of rejection of alien matter by the body – and long-term reliability.
Over a five-year period, said Dean Cole, a biomedical engineer who directs the project at DOE’s Office of Biological and Environmental Research in Washington, the project will begin with goggles and move in the direction of corneal implants, aiming to prepare five patients for the procedure before the project’s end. After that, he said, ‘The FDA will say they want 100 patients for long-term studies and DOE will get out and leave the project in the hands of industry.’