Technology to Give Eyesight to the Blind
Dec 31, 2009 5:00 AM PT
This story was originally published on Nov. 2, 2009, and is brought to you today as part of our Best of ECT News series.
The Massachusetts Institute of Technology (MIT) has developed technology that could help fight blindness. It's aimed at the millions of people impacted by two of the major causes of blindness: age-related macular degeneration (AMD) and retinitis pigmentosa.
The MIT project is one of several that use a physical prosthesis -- a chip implanted directly into or onto the eyeball, coupled with a pair of electronic glasses that provide assistance.
Here's a rough description of how our eyes normally work: Light enters the eyeball and stimulates an array of microscopic rod and cone formations in the back of the eye. These process the images by converting their analog light signals into digital electro-chemical pulses.
The images are then sent to the brain through the optic nerve.
AMD and retinitis pigmentosa kill these rods and cones, so the light is not translated into electrical images. However, they do not affect the optic nerves leading to the brain.
The MIT project, led by electrical engineering professor John Wyatt, involves attaching a microchip to a patient's eyeball toward the outside of the affected eye. This microchip is attached to a 10-micron thick electrode array that goes through the white of the eye and lies up against the retina from behind, Wyatt told TechNewsWorld. The array is one-seventh the thickness of a human hair.
The implant consists of a 15-channel stimulator chip, a secondary power and data receiving coil, and discrete power supply components, all encapsulated in polydimethylsiloxane. Polydimethylsiloxane, also known as "PDMS," is a widely used silicon-based organic polymer. Optically clear, inert, non-toxic and non-inflammable, it is used in contact lenses and medical devices, among other things.
To work, the chips are assisted by a pair of glasses the patient wears and a device he or she carries in a pocket. A tiny camera is mounted on the hinge of one earpiece of the pair of spectacles. The earpiece will be on the same side as the patient's affected eye. The spectacles contain the primary data coil.
Images from the camera are sent through a wire attached to a battery and a signal processor that are in the patient's pocket. The processor translates the images into electromagnetic signals.
These signals are sent to the primary data coil in the spectacles, which transmits them wirelessly to a secondary data coil that has been surgically implanted around the patient's eyeball. The primary data coil also transmits power wirelessly to the secondary coil. The secondary power and data receiving coil consists of four gold wires. Two of the wires handle power and the other two handle data.
Wyatt said the power is sent at 125 KHz and data at 5 MHz. "We may go up to more than 5 MHz for data in our next design," he added.
The MIT team has conducted short-term trials on six people, lasting less than a day with the patient lying on a table. It plans to launch longer-term trials soon. "We didn't want to do any more acute trials because the real question here is how the visual cortex adapts to abnormal data, which is data that's not coming down the optic nerve," Wyatt explained.
In less than two years, MIT will have a device for which it will seek the Food and Drug Administration's approval to test on chronic patients, Wyatt said.
Causes of Blindness
Age-related macular degeneration, or AMD, is the leading cause of blindness in adults over the age of 55, according to the Foundation Fighting Blindness. "At this point, about 10 million Americans are affected by AMD, and that number is expected to double by 2020, as it's age-related," Angie Vasquez, the spokesperson for the foundation, told TechNewsWorld. "We need to find a cure before the numbers become an epidemic."
While lifestyle, diet and environmental factors can contribute to AMD, its main component is age.
While some victims go completely blind in childhood, others become legally blind in middle age; still others retain a degree of sight all their lives. Noted victims of retinitis pigmentosa include musician Stevie Wonder; former San Francisco Mayor Willie Brown; and Gordon Gund, co-owner of the San Jose Sharks ice hockey team.
Retinitis pigmentosa impacts 100,000 Americans and about 1.5 million people worldwide.
Other researchers are working on other approaches. Second Sight Medical Products uses a slightly method for eye prostheses, implanting the array of electrodes in the eyeball rather than locating it behind the retina. Other than that, the two approaches are very similar.
Second Sight, a privately owned company, has conducted trials on a total of 38 people worldwide. It is using 60-electrode arrays in the latest 32 trial subjects.
MIT has a lot of catching up to do, according to Brian Mech, vice president of business development at Second Sight. "There are other commercial efforts around the world that aren't as advanced as ours but are more advanced than MITs," Mech told TechNewsWorld.
"There are almost 70 people around the world who have participated in some sort of retinal prosthesis trial," Mech pointed out. "We've had our prostheses in patients for up to six years." Second Sight has the only active prosthesis that has been approved for a trial on humans by the FDA, according to Mech.
MIT's counter to that is that it's better to move slowly because of the risks involved to patients. "We started at roughly the same time as Second Sight, but we thought it was premature to get people to think of this work as salable," Joseph Rizzo, director of the Center for Innovative Visual Rehabilitation at the VA Boston Healthcare System, JP Campus, explained.
Rizzo, who works on the MIT project with Wyatt, told TechNewsWorld that the MIT team used the same epi-retinal approach as Second Sight for 10 years, then switched to the sub-retinal approach because it believed there were huge engineering and biocompatibility advantages.
"The surgery for the sub-retinal approach is more difficult but what we get back in return is worth the added effort," Rizzo explained. "We use a minimally invasive procedure with very little surgery inside the eye, and we believe that will make the product more bio-compatible."
Does It Work?
It's not yet clear how effective the prostheses will be. "We're spending a lot of time trying to find out what people see," Second Sight's Mech said. "The performance between patients is variable even though they all have the same device." Some patients see formless blobs while others see objects more clearly.
Second Sight's trial subjects all have retinitis pigmentosa, and the company is not sure why exactly they are responding differently to the implants. "It could be because they have different gene mutations causing the blindness, or the length of time they've been blind, or other factors," Mech said.
However, every subject has been able to see something. "Some subjects can read very large letters, and many have a significant improvement in orientation and mobility; they can detect, locate and recognize objects and detect motion."
Rizzo, who's with the VA, says the experiments will prove useful one way or another. "Many of the technologies we're developing are platform technologies that can be moved around," he explained. "They can also be used elsewhere in the body."