For a sighted person, the loss of vision represents much more than a physical impairment. It means a loss of their accustomed independence: the end of driving to work, reading the local newspaper, even simple pleasures like playing catch. Through a new center based at Wayne State University, a multidisciplinary team of Detroit-area researchers and clinicians has begun work they hope will return a level of autonomy to the growing number of men and women who are facing the limitations of life without sight.

Dr. Auner, director of WSU's Smart Sensor lab, has already developed prototype devices that may help people see.

"To be able to come up with something to help the large pool of people with very low vision - that would be one of the most exciting advances in the history of medicine," said Gary Abrams, MD. Dr. Abrams is director of WSU's new Ligon Research Center of Vision at the Kresge Eye Institute, which he heads as professor and chair of ophthalmology. The Ligon Center is beginning to test implants that could restore at least partial vision to those people who were once sighted but now have extremely low vision. These are men and women who once had normal vision, but now see no more than dull, unrecognizable blotches of light and dark. 

"This center is important, because its purpose is to do research and development in the exciting new area of artificial vision," Dr. Abrams said. "We're attempting to provide sight for people who have lost it." 
Center researchers and clinicians are beginning to develop miniature implants to take the place of damaged portions of the visual system. In particular, they hope to use an electronic implant to stimulate vision in damaged portions of the retina, which is in the inside back wall of the eye. If a patient's retina or optic nerve is too badly damaged for a retinal implant to work, researchers hope to bypass the damaged area and directly stimulate the visual cortex, which is located in the upper back part of the brain.

The Ligon Center (pronounced LIGG-un) is unusual in several aspects, Dr. Abrams said. Unlike other research groups that have begun to consider artificial vision from the viewpoint of either clinicians in one medical field or researchers in one laboratory, the Ligon Center comprises both clinicians and researchers from many disciplines. Specialists in ophthalmology, neurosurgery, neuroscience, and engineering are all involved. 

In addition, the research team is tackling retinal and cortical implants at the same time. "We're probably one of the few places investing heavily in both areas, and we feel that there's a major advantage to that," Dr. Abrams said. By experimenting in the laboratory with both of these critical parts of the visual system, he and the other researchers believe they will learn more about how the system works and how implants can be used most successfully.

"The retinal implant is something that would be particularly useful for someone with retinal degeneration," Dr. Abrams said, although he noted that the implants may eventually help patients who are experiencing macular degeneration or some forms of trauma. "Retinal degeneration is a genetic condition in which the photoreceptors - the visual cells of the outer retina - prematurely degenerate and die. In this group of patients, the inner retina and its cells, called the bipolar and ganglion cells, usually remain relatively normal." Normally, he said, light causes the photoreceptor cells to transmit chemical stimuli called neurotransmitters, which trigger the bipolar and ganglion cells, ultimately sending the visual signal to the brain's visual cortex. 

Dr. Iezzi, a biomedical engineer and vitreoretinal surgeon, is the main bridge between biological and hardware efforts related to implants.

Raymond Iezzi, MD, director of the retinal implant project, is a vitreoretinal surgeon, a faculty member in the WSU ophthalmology department, and a biomedical engineer. He described the retinal implant as a melding of man and machine. "We are attempting to micromachine, if you will, an electrode array and a computer chip or processor that would electrically stimulate the retinal ganglion cells, which may remain viable in a variety of retinal degenerative diseases." This array in the implant would essentially sidestep the damaged outer retina, replacing the absent neurotransmitter signaling with the artificial electrical stimulus. 

Beyond a detailed understanding of the anatomy of the eye, Dr. Iezzi said, the researchers have to learn more about how to select materials and make devices that will be compatible with human tissue for many, many years. 

"Once we've tackled those issues, we also have to actually talk in the language of the brain. We have to be able to communicate with the neural tissue. That requires processing a visual picture into a series of impulses like those that the retinal ganglion cells would normally anticipate from the photoreceptor cells." To do that, he envisions a microcamera - perhaps mounted on a pair of eyeglasses - that will take pictures of the outside world. The implanted electrode array will then receive the pictures and transform them into ensembles of encoded pulses that travel from the ganglion and/or bipolar cells to the brain. Finally the brain must be able to translate the pulses into an accurate reproduction of the original picture.

Despite the considerable work that needs to be done, Drs. Abrams and Iezzi believe that the retinal implant is an achievable goal. Some steps are already under way. "We're beginning laboratory testing of components early in 2000, and we expect to be testing components on humans within the next two years," Dr. Iezzi said. 

Dr. Abrams added, "As far as implantation of devices, certainly we're capable of building the device, but the timing will depend on how quickly things develop after the initial testing."

Dr. McAllister is leading the research on cortical implants.

J.P. "Pat" McAllister, PhD, director of the cortical implant project and WSU professor of neurosurgery, is similarly optimistic about the cortical implant. These implants, he explained, would help people who have experienced damage to the entire retina or to other significant parts of the visual system, such as the optic nerve. 

Dr. Abrams noted that cortical implants would be particularly beneficial for patients with diabetic retinopathy or glaucoma, and those who have many types of trauma-induced vision loss. "In these cases, the visual systems have been damaged to such a degree that the best and perhaps only hope of restoring vision is through the visual cortex."

Electrode arrays in the preliminary implant.

Basically, a cortical implant would receive visual signals from an external, electronic sensor, and then process them into information that the cortex could translate into a recognizable picture. In other words, the implant would bypass all of the defective portions of the visual system and directly stimulate the brain's vision hub.

Through the current work, Dr. McAllister said the research team hopes to determine how the cortex normally responds to visual signals and use that knowledge to refine the implant's responses and mimic the normal state. "I actually got inspired by watching some of the other types of projects that are similar to this, like the cochlear implants that let deaf people hear," he said. "They're very sophisticated and have the same kinds of tuning problems we're facing."

One of the most challenging areas of the cortical implant research lies in developing computer processors that can match the so-called plasticity of the brain. Over time, Dr. McAllister explained, the brain adapts and responds differently to stimuli. The processor in the implants will have to be similarly plastic.

"We're probably going to have to reconfigure the visual world and update that representation over time as the patient becomes more experienced with the devices," Dr. Iezzi added. "Eventually, we want these patients to be able to see letters and see forms, and that's going to require a significant scientific breakthrough."

For the majority of the engineering work, the artificial-vision projects will rely on its researchers in the WSU Department of Electrical and Computer Engineering. The engineering group includes Gregory Auner, PhD, and other scientists in the Smart Sensors and Integrated Devices Laboratory. "That lab is really empowering us to make an intelligent approach to this problem," Dr. Iezzi said. "When you consider that the eye is smaller than an inch in diameter, and that we need to implant a whole series of electronics and electrodes inside of that little space, you can see that building these things is not a trivial task. Greg's lab is unique in that it truly has technology that is not available anywhere else in the world to fabricate the actual devices that we will be testing."

Dr. Auner said his lab is investigating three approaches to the development and design of the device. "One approach is to make a passive array without batteries or anything like that. The material and geometry of the device, which is implanted behind the retina, is stimulated by the light coming into the eye. The device then stimulates the neural tissue. At least that's the theory."

The second route is an electrode array that would attach to the retina. "It would have some microelectronics that would communicate with a CCD (charge-coupled device) camera - like a type of TV camera. The camera would transmit images that the array would process to create an imaging system." Finally, he said, they are considering a CCD camera that would transmit signals to a cortical implant. "This last one is a very futuristic option, and a long-term one."

Dr. Auner believes the first approach shows the most promise right now. "Here, a photon of light comes in, it's absorbed on one end of these little pixel arrays and it develops a proportional charge on the other side, which is in contact with the neural tissue in the retina. The charge would stimulate the neural tissue." Researchers in his lab have already made a prototype device.

Although challenging, the work is exciting, Dr. Auner remarked. "These microelectrodes are not something that existed before. They're new technology. We even had to develop the processing, which is a special excimer-laser micromachining process, in order to make these very, very special geometry electrodes out of these materials. And we've done that. There are no other electrodes in existence like these."

Before actual implantation begins, they will be using a "test bed" developed by Dr. Iezzi to simulate a human or animal visual system and determine how well the array works. With the test bed, they will be able to transmit visual stimuli to hundreds of neurons, and then to record and analyze their responses simultaneously. Dr. Iezzi said, "Once we understand how the ensemble of neurons responds to normal patterns of visual stimulation in a sighted animal, then we're going to have to recreate those patterns of activity in the brain using an electrical stimulator I'm designing. That stimulator is going to interface with the electrode array that Dr. Auner is designing." The neurosurgery team will implant the array in the cortex, while the retinal team will implant it in the retina. 

Dr. Abrams says patient testing of vision devices can begin within two years.

"A lot of components will have to come together, but this is an achievable goal," Dr. Iezzi asserted.
While Dr. Abrams is equally enthusiastic about the future of artificial vision, he cautioned that the work is still in its early stages. "I don't think that people should expect that they're going to get their normal vision back. Our initial goal is to provide ambulatory vision, and then vision that's good enough so the person can read. Those two goals are achievable. Further than that, however, we have no idea what would be possible."

He added, "This work on artificial vision is interesting, it's exciting, and it's something that could be of major benefit. It's something we really look forward to working on every day."