National Geographic : 2016 Sep
46 national geographic • September 2016 one kind of patterned flashing as a person, another as a tree. She’s getting better at dis- tinguishing contrast in the dreaded task she calls the “50 shades of gray test” (it’s really seven). She can read a big high-contrast clockface at arm’s length. The week before I visited, she took a walk around Oxford with MacLaren’s team and found that she could tell, for the first time in years, a building ’s windows from its walls. Yet the gains are modest, and Lewis still does almost everything—dresses, bathes, moves around the house, gets the kids out the door, feeds Chopsy the dog, gets the mail—by feel and the fading sight of her good eye. Her bionic eye is taxing to use; she usually leaves it turned off. Such limits are to be expected with these early prototypes, says Eberhart Zrenner, the German eye surgeon who began developing the Alpha more than 20 years ago. “The idea was never to get full vision,” he says, “but to improve a patient’s ability to recognize objects and move around.” It’s doing that. Lewis again sees the lights of her Christmas tree. Zrenner describes a patient who can again read his own name; anoth- er who can again see the kitchen sink; another who beheld for the first time his fiancée’s face “and saw that it was laughing.” Nearly half the 29 patients who received a similar, previous version of the implant, he says, find it truly useful. Lewis also has found hers useful, and for this she is grateful. Even if it gets no better, she says, the chip’s often indecipherable image constitutes a miracle of sorts—light replacing dark. She ex- pects that as her left eye inevitably fails altogeth- er, this bionic eye, or perhaps a successor, will allow her to still do all the things she does now. She’s also glad to be part of this wild exper- iment. “My motivation is for my kids,” she says, both of whom see fine now but stand at increased risk of developing retinitis pigmento- sa, which is inheritable. “Anything I can do now can help people down the line.” MacLaren says the implant project is teaching valuable lessons. For starters, its demonstration that photodiodes can substitute for natural pho- toreceptors is a huge stride: In the exacting ma- chine that is the eye, we’ve fashioned a cog that fits, even if imperfectly. The devices also show that patients can learn to interpret new presen- tations of visual stimuli. In addition, MacLaren says, the implants show that “there’s still visu- al potential once the photoreceptors are gone, because the other nerves are still intact. This is something I never thought could be shown.” MacLaren says that these lessons learned are already spurring advances in the other two cutting-edge areas: gene therapy and stem cells. IN CALIFORNIA an eyeball dream team is run- ning a stem cell trial that evolved almost direct- ly from an implant. One of the leaders is Mark Humayun, a courteous, efficient, impeccably besuited man. Like MacLaren, Humayun seems to be running projects in every possible therapy for every part of the eye. His first big project was co-inventing the Argus II, which in the early 2010s became the first retinal implant to go to market. Like Zren- ner’s Alpha, the Argus uses an electrode array embedded in the back of the retina. But rather than collect light, this grid of just 60 electrodes pulls signals from a tiny eyeglass-mounted cam- era that relays them through a processing unit carried on a belt or in a bag. All this gear impos- es a stiffer set of limitations and demands than the Alpha does. In addition, the Argus’s external camera means that, unlike the Alpha, it cannot exploit the eyeball’s constant small movements, known as microsaccades, that play a mysterious but vital role in vision. Fitting that implant into people’s retinas, however, helped inspire the stem cell device Humayun is now developing. He and his fellow If experimental treatments restore only partial vision, that’s still a miracle for blind patients: light replacing dark.