Artificial Retina Animation by Tun Min Soe
Narration by Yu-Chong Tai, Professor of Electrical Engineering
The Artificial Retina Project is a multi-institutional collaborative effort, headed by the U.S. Department of Energy, whose goal is to restore partial sight to people blinded by retinal diseases such as age-related macular degeneration and retinitis pigmentosa.
In normal vision, light enters the eye through the lens, which focuses the light as an image across the retina — a screen of photoreceptor cells (rods and cones) arrayed in a membrane across the back of the eye. These cells convert the light to electrical impulses that pass through the optic nerve to the brain.
Age-related macular degeneration (AMD) is a retinal disease affecting approximately 12 million people aged 60 or over in the United States, of whom 10 percent suffer severe vision loss each year. AMD is caused by fluid leakage or bleeding in the central area of the retina, causing gradual loss of central vision. Due to the brain’s capacity to compensate, this loss may go unnoticed in its early stages.
Retinitis pigmentosa is a genetic disorder that strikes people between the ages of 20 and 60. In contrast with AMD, it initially causes deterioration of peripheral vision rather than central vision. Approximately 500,000 people in the United States suffer from retinitis pigmentosa, of whom 20,000 are totally blind.
Designing an Artificial Retina
Although retinal diseases cause irreversible damage to the retina, the optic nerve and the brain remain intact. The plan of the Artificial Retina Project is not to restore function to the eye itself, but to use the retina essentially as a portal to the optic nerve. The system consists of three basic elements:
- a tiny electronic camera and microprocessor mounted on a pair of eyeglasses
- a small transmitter implanted behind the patient’s ear
- an implant studded with an array of microelectrodes that is tacked to the eye’s natural retina.
Power for the artificial retina comes from a wireless battery pack worn on the belt.
Images from the camera are converted to an electronic signal in the microprocessor and sent to the transmitter behind the patient’s ear. The transmitter relays the signal to the retinal implant, whose microprocessors send the image to the optic nerve as electronic pulses. The brain learns to interpret these pulses as sight.
Developing and implementing the artificial retina presents numerous, often conflicting challenges:
- Devices must be sufficiently safe, effective, and durable to provide a lifetime of use.
- The artificial retina must be compatible with the delicate tissues of the eye yet tough enough to survive in the eye’s salty interior.
- The artificial retina must also remain safely tacked to the natural retina — whose surface has the resilience of wet facial tissue — without shifting or causing damage.
- The device must operate at power sufficient to stimulate the electrodes, yet not produce heat at levels that might damage surrounding tissue.
- Image processing must take place in real time.
- Successful implantation requires development of innovative surgical procedures.
In 2002, Argus 1, the first artificial retina — a postage-stamp-sized device containing an array of 16 electrodes — was implanted into the eye of a man who had been blinded by retinitis pigmentosa for more than 50 years. Five additional patients with retinitis pigmentosa have received the device. All six patients regained the ability to distinguish light from dark, locate and describe the motion of objects, and count individual items.
Clinical trials for an improved device, Argus 2, began in January 2007. Argus 2 contains an array of 60 electrodes on an implant much smaller than that used in Argus 1. And time required for surgery has fallen from six hours to two. Argus 2 is expected to be the first artificial retina to become commercially available.
The greater number of electrodes is intended to improve resolution, much as increasing the number of dots per inch on a printed picture improves its sharpness and clarity.
A third-generation device is already in development, which will provide an array of 200 electrodes on a smaller, more flexible material that will conform to the shape of the eye. Ultimately, the DOE Artificial Retina Project anticipates an implant containing up to a thousand microelectrodes, with resolution that will allow patients to read large print, move without assistance, and recognize faces.
The Artificial Retina Project is now recruiting patients. For more information on this research and to find out more about enrolling in the clinical trial, visit http://artificialretina.energy.gov.