Seeing the light through an artificial retina

Retinitis pigmentosa patient makes visual gains with retinal stimulation system

Model of retinal simulation system Source: Second Sight

Barbara Campbell is seeing the world with new eyes. The 56-year-old, who has been blind for years due to retinitis pigmentosa, can now make her way to her apartment building doorway unassisted by her cane and more thanks to an artificial retina. The artificial retina is helping to return some limited vision, according to Lucian V. Del Priore, M.D., professor of ophthalmology, Columbia University, New York, who implanted the device for Ms. Campbell.
The device, dubbed the Argus II Retinal Stimulation System (Second Sight, Sylmar, Calif.), was developed by Mark S. Humayun, M.D., professor of ophthalmology, biomedical engineering, and cell and neural biology, Doheny Eye Institute, University of Southern California, Los Angeles. It consists of a 2 mm-2.5 mm electrode array, an electronics package, and a pair of eyeglasses with a camera mounted on the frame to capture real time images, as well as a small module to digitize the images, worn around the waist. “The transmitter is actually on the eyeglasses,” Dr. Del Priore said. “The receiver is placed underneath the conjunctiva and they communicate with each other.”
Implantation of the artificial retina is intricate. “The device is put into the vitreous cavity through the pars plana and then a retinal tack is used to hold it in place along the retinal surface,” Dr. Del Priore said. “The device itself is actually connected by a cable to an electronics package.” The electronics package is sutured in a position so that it’s on the outside of the sclera but underneath the conjunctiva and is placed on the temporal side. “When a patient wears eyeglasses, the glasses have a camera on them,” Dr. Del Priore said. A digitized form of this image is wirelessly relayed back to the retina.

Letdown period

Results with this device, however, are not instantaneous; significant training is needed. “When the whole thing is powered up, the camera looks at a sample object, for example a square, and then we ask the patient what he perceives,” Dr. Del Priore said. “If the patient says it looks like a square that has been squashed on one side then we can manipulate the information in such a way that it stretches the square so that the patient perceives the right image.” In addition, the patient must be trained on how to properly use the device. As a result, after implantation of the artificial retina there can be a letdown period. “The next day the patient doesn’t see anything because the device has only been in place for 24 hours,” Dr. Del Priore said. “The patient hasn’t undergone any visual training and it takes awhile because there’s an extensive visual rehabilitation period involved.” Patients must spend one day a week for three years learning how to use the device.
Dr. Del Priore likens the process to having hip surgery. “You’re not going to walk right away and if you don’t do the rehab, you’re probably not going to walk at all on the hip,” he said.
Making visual leaps

Prior to implantation of the artificial retina, Ms. Campbell had been blind for many years. “She essentially lost all of her functional vision when she was in her 30s,” Dr. Del Priore said. “She had had a progressive decline from the time when she was first diagnosed, which was in late adolescence, up until that point.”
After months of working with the device, however, Ms. Campbell began to make significant strides. She can now maneuver her way straight through a white door on a black wall during an ambulatory test and can do the same in everyday life. “She subjectively describes being able to see her apartment building at night and being able to see the light in the doorway of her building,” Dr. Del Priore said. “She walks toward it knowing where it is without using her cane or other ancillary cues.” Ms. Campbell can also now see other things. “She’s starting to see traffic lights and can see objects moving, like a bus,” Dr. Del Priore said. “She’s also starting to see letters.” These are, however, quite large—in the range of 20/8000. “These are letters that are the size of a wall basically,” Dr. Del Priore said. “But still, it’s the first time that she has seen anything like that in 20 years.”
In addition, Ms. Campbell also recently had a telling real world experience showing how much of a difference the device can make. “She was walking in Central Park when all of a sudden her vision went dark,” Dr. Del Priore said. “She thought that maybe the retinal chip had moved or something, but it turned out that a baseball cap had fallen over and blocked the camera.”
Overall, Dr. Del Priore sees the device as an exciting one. “I think that it’s really fabulous and interesting technology,” he said. However, he does acknowledge that it is unlikely to be a cure all. “I think that it’s going to have its limitations in terms of the final visual acuity that patients can achieve and the final resolution.” However, going forward Dr. Del Priore envisions that the technology will get smaller and improve. “For the near future, I think that this has a place in treating patients who have medical conditions where they essentially have no vision at all,” he said. “I think that it’s only going to get better with time.”

Editors’ note: Dr. Del Priore has no financial interests related to his comments.

Contact information

Del Priore: 908-625-0395, ld394@columbia.edu