Features

Millions of people with diseases that starve eye tissue and nerves of oxygen may avoid blindness with a procedure developed by researchers at the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL), the University of Southern California, and the University of Tennessee.

The technique uses “smart” prosthetic implants to provide oxygen to retinal tissue being deprived of oxygen because of restricted blood flow. This condition occurs mostly in patients with diabetic retinopathy, which is caused by changes in the blood vessels of the retina. Those with diabetic retinopathy at first may not notice changes to their vision. But over time, diabetic retinopathy can get worse and cause vision loss.

With the artificial retina, a miniature camera mounted in eyeglasses captures images and wirelessly sends the information to a microprocessor hat converts the data to an electronic signal and transmits it to a receiver on the eye.The receiver sends the signals through a cable to the micro electrode array, stimulating it to emit pulses. The artificial retina bypasses defunct photoreceptor cells and transmits electrical signals directly to the retina’s remaining viable cells. The pulses travel to the optic nerve and,ultimately, to the brain, which perceives patterns of light and dark spots corresponding to the electrodes stimulated.(U.S. DOE)
The procedure involves surgically implanting a feedback-controlled three-electrode electrolysis system that stimulates production of oxygen near the retina. The electrodes provide small amounts of current in very short pulses — about 200 microseconds. This results in a rapid production of oxygen and suppressed production of chlorine, which is potentially harmful. By using three electrodes and a feedback loop made possible by implanting a “ground” electrode behind the patient’s ear, the team is able to maintain constant pH in the area being treated. At the same time, any pH drift can be exported to a surface-accessible region where it can be easily dealt with.

This new technique builds upon the DOE’s successful artificial retina project begun in 2004 at ORNL in which Elias Greenbaum and his colleagues at ORNL’s Chemical Sciences Division were joined by Dr. Mark Humayun of the Doheny Eye Institute and Keck School of Medicine at the University of Southern California, and Dan Close of the University of Tennessee.

Project History

The DOE’s Artificial Retina Project is a collaborative, multiinstitutional effort to develop an implantable microelectronic retinal device that restores useful vision to people blinded by retinal diseases. The ultimate goal of the project is to restore reading ability, facial recognition, and unaided mobility in people with retinitis pigmentosa and age-related macular degeneration.

Described as a group of inherited eye diseases that affect the retina, RP causes degeneration of the photoreceptor cells that enable sight by capturing and processing light. Normal vision begins when light enters and moves through the eye to strike specialized photoreceptor (light-receiving) cells in the retina called rods and cones. These cells convert light signals to electric impulses that are sent to the optic nerve and the brain. Retinal diseases like age-related macular degeneration and RP destroy vision by annihilating these cells.

With the artificial retina device, a miniature camera mounted in eyeglasses captures images and wirelessly sends the information to a microprocessor (worn on a belt) that converts the data to an electronic signal and transmits it to a receiver on the eye. The receiver sends the signals through a tiny, thin cable to the microelectrode array, stimulating it to emit pulses. The artificial retina device bypasses defunct photoreceptor cells and transmits electrical signals directly to the retina’s remaining viable cells. The pulses travel to the optic nerve and, ultimately, to the brain, which perceives patterns of light and dark spots corresponding to the electrodes stimulated. Patients learn to interpret these visual patterns.

Three models are now in development or testing. Model 1, with 16 electrodes in a one-inch package, has been implanted in six patients. Each of these previously blind individuals has since been able to detect light, identify objects in the surrounding environment, and even perceive motion.

Clinical trials for a second, more compact device with 60 electrodes are underway with U.S. Food and Drug Administration (FDA) permission. A third, far less invasive and higher-resolution model is under development. Second Sight Medical Products manufactured the Model 1 and Model 2 devices (the latter with DOE contributions), and will integrate DOE technologies into the third design.

The second-generation retinal prosthesis is designed to last a lifetime and contains 60 electrodes embedded in a tiny array. The array is surgically attached to the retinal surface and used in conjunction with an external camera and video-processing system to provide rudimentary sight to the implanted subjects. Fitting neatly into the eye’s socket, the new prosthesis is only about a quarter of the size of the original retinal implant, thereby dramatically reducing surgery and, potentially, recovery times.

A third implant model under development will have more than 200 electrodes and use more advanced materials than those in the two previous models. A special coating, only a few microns thick, will replace the bulky sealed package used in the other models. Additionally, the new model will be constructed of flexible materials that conform to the shape of the inner eye and will be many times smaller than earlier models.

Eventually, the DOE collaborators hope to produce a 1,000-electrode device that potentially could restore enough sight to enable facial recognition and even the ability to read large print, in addition to unaided mobility.

For more information on the DOE’s Artificial Retina Project, visit http://artificialretina.energy.gov/