Skip to comments.Visions for the future
Posted on 09/07/2002 1:51:56 PM PDT by Tumbleweed_Connection
UCLA researchers have helped to develop a "vision chip" which can help some blind patients see again.
The development is good news for one in four Americans over the age of 64, who suffer from a now curable form of blindness according to the Macular Degeneration Research Foundation.
In humans, normal vision starts when an image passes through the eyeball and into the retina at the back of the eye. The retina contains photoreceptors which break down the image and creates the corresponding neural stimulus, or signals, to the brain.
In many blind patients, the retina degenerates and the photoreceptors no longer function, leading to blindness.
The vision chip works by replacing the function of the eye's retina, acting like a photoreceptor which processes images and sends the correct signals to the brain to form an image.
"In some people, the nerves still work, but the retina is dead," said professor Warren Grundfest, chair of the biomedical engineering department at UCLA. "With this technology, electrodes are implanted in the back of the (patient's) eye, which is controlled by a very complex system."
The system was developed from research led by Second Sight, a 4-year old company in Valencia, Calif.
It consists of a tiny video camera mounted onto a pair of glasses to capture images. These images are then processed by a tiny computer to prepare the visual information for the prosthetic chip implanted in the patient's eye.
The signals are then sent via radio frequencies to the retina chip, which receives the signals (acting like photoreceptors).
The chip finally sends corresponding electrical pulses through tiny electrodes connected to the chip, which stimulate neural responses to the brain, forming an image the blind patient sees.
The first such retina prosthesis was implanted into a patient five months ago at the Retina Institute at USC Medical Center.
"We have been working with the patient to determine the best way to electrically stimulate his completely blind retina," said Dr. Robert Greenberg, President and CEO of Second Sight.
Currently, the vision chip in the patient's eye uses a simple two-dimensional 4x4 matrix to simulate vision. The patient can only see lines and shapes created by the low-resolution array.
"It allows for crude vision such as identifying orientation of objects and movements," Greenberg said.
But Greenberg believes higher resolution arrays will help future patients see with more detail.
"A 1,000 electrode device (30x30 matrix) would provide a level of vision that most of us would consider adequate for everyday tasks," Greenberg said. "Even 100 electrodes would allow the identification of faces."
Greenberg is working with UCLA electrical engineering professor Jack Judy on increasing the resolution of the current low-resolution array.
Judy has experimented with micromachining the electrodes to increase their effective surface areas and reduce their size on the integrated circuit, allowing for more electrodes on the chip and better resolution.
"The whole concept is the miniaturization of things," Judy said. "I'm focusing on miniaturizing the electrodes on the retina chip but there are limitations on their size."
In order to stimulate the neurons in the retina, the electrodes must be able to deliver a certain amount of current. Decreasing the size of the electrodes and keeping the current constant will increase the current density. If the current density increases beyond a threshold density, electrochemical reactions will occur.
"You will have certain problems (past the threshold current density)," Judy said. "It can cause hydrolysis (gas bubbles) or even corrode the metal."
Judy and Greenberg are still experimenting with several methods to increase the number of electrodes on the chip.
Greenberg is confident they will succeed.
"Our effort with Professor Judy is an important path that may allow such (high-resolution) arrays," Greenberg said. "I am sure we will achieve this goal by one of the methods being pursued."
I'm aware of the developments yet know nothing about nerve degeneration possibly contributing to the impairment.
Camera in the eye could help the blind to see again By Roger Highfield, Science Editor (Filed: 07/09/2002)
Enabling the blind to see - a task once thought the province of miracles - is the goal of an ambitious £6 million programme launched by the United States government.
A team of scientists is working on a device, consisting of a tiny camera and radio transmitter lodged in the frame of a patient's spectacles 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.
Diseases such as age-related macular degeneration and retinitis pigmentosa damage the rods and cones in the eye that normally convert light to electrical impulses, but leave intact the nerve pathways to the brain.
Eventually the input from rods and cones ceases, but up to 90 per cent of nerve structures set up to receive their signals remain intact.
The team aims to create 1,000 points of light through 1,000 minute electrodes positioned on the retinas of those blinded by diseases. Counterintuitively, the rods and cones of the retina lie beneath nerves, not above them, which makes connecting the device easier.
The team, which includes Sandia National Laboratories, New Mexico, four other national labs, a private company and two universities, has been funded by the Department of Energy's Office of Biological and Environmental Research.
"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 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 one thousand. The images will come a little slowly and appear yellow. But people who are blind will see."
The silicon chip should be able to stimulate directly 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," concedes Mr 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."
The plan is to achieve a 10-by-10 electrode array this year and 33-by-33 arrays by 2004.
Mike Daily, manager of Sandia, said there were several hurdles to overcome. These include how to make devices that will work in a saline environment; cope with protein fouling that can upset delicate interfaces intended to transmit electrical impulses; how to cope with rejection; and long-term reliability. Over a five-year period, the project will begin with goggles and move in the direction of corneal implants, aiming, if all goes well, to prepare five patients for implants.
The project began in February when Prof Mark Humayun, of the University of Southern California implanted a permanent retinal prosthesis known as the "eye chip" in a patient as part of a trial.
The 4mm by 5mm chip is studded with 16 electrodes in a 4-by-4 array. "Each electrode can excite a lot of nerve cells," said Prof Humayun.
Signals from a video camera are sent to the electrode array attached to the retina via the receiver implanted behind the patient's ear. The signal will then be recreated by stimulating the appropriate electrodes.