National Geographic : 2016 Sep
40 national geographic • September 2016 running an experimental treatment on one eye can usually use the other as a control—and as a backup in case something goes awry. The eye is also tough. Within the eye’s spheri- cal refuge, the immune system restrains itself in a way that makes the eye “immune privileged,” tol- erant of invaders that might cause troublesome inflammation in other organs. This means you can more safely try a remedy in the eye, such as gene therapy, that might wreak havoc elsewhere. Neuroscientists love the eye because “it’s the only place you see the brain without drilling a hole,” as one put it to me. The retina, visible through the pupil, is basically a bowl of neurons tied to the brain by the optic nerve; the eye as a whole is an “outpouching of the brain,” formed during fetal development by stretching away from it. Like the eye, the brain enjoys immune privilege, so treatments that work in the eye may readily transfer to the brain or spinal cord. These advantages take on extra importance because experimental strategies now focused on the eye may drive future treatments for the whole human organism. Gene therapy offers the promise of fixing faulty genes that cause illness- es of all kinds. Stem cells offer the promise of re- placing entire tissue structures; bionic implants may replace failing organs. The eye is becoming a window not just to the soul, but also to the pos- sibilities—and limits—of therapeutic approach- es on which medicine is betting its future. IMAGINE A HIGH-CONTRAST, low-resolution, flickering black-and-white picture—a down- grade from the first television images of the 1920s—and you’ve imagined something close to what Rhian Lewis sees with her bionic eye. Lewis, 50, of Cardiff, Wales, has retinitis pig- mentosa, a disease in which photoreceptors die because of a gene deficiency and vision dims from the periphery. Over time the tunnel of sight shrinks to nothing—“ like a dimmer switch slowly going dark,” Lewis says. The condition struck Lewis early. While still crawling, she wouldn’t leave a room if it meant going into an unlit hall; she once ran head- long into a barbwire fence. She nonetheless got through school and college; tended bar by knowing the precise location of every bottle, glass, and tap pull; and later, even as her right eye completely failed, worked 20 years in a book and stationery shop by memorizing every sec- tion and learning to tell pens apart by the feel of their barrels or packages. Since the bookstore closed, she has mostly stayed home raising her twins, who are now in their late teens. In June 2015 she went to Oxford Eye Hos- pital, lay on a table, surrendered to anesthesia, and, 10 hours later, awoke with a bionic eye. In what was “without doubt the most complex op- eration I’ve ever done,” says surgeon Robert MacLaren, the Oxford team slipped between her retina’s delicate layers a freckle-size micro- chip laden with 1,600 tiny photodiodes. Mac- Laren’s clinical trial is exploring whether this chip, known as the Alpha, can replace the dead photoreceptors (the famous rods and cones) in the center of Lewis’s retina by translating light into bursts of current that the existing neural network will relay to the brain. When they turned on the device, Lewis told me last November, “I couldn’t believe it. Sud- denly—oh, my God—there’s something there.” But what? Her brain interpreted the chip’s electrical signals not as objects or scenes, but as strongly contrasting flashes and shimmers. “Not an image as such,” she says, “just sort of an awareness that there’s a difference.” Since then she’s been learning to interpret these bursts of light as sight. This includes for- mal training at MacLaren’s lab that “is like tri- ple maths,” she says, laughing. “I hate it.” But it’s paying off. She has learned to recognize Roughly one in every 200 people on Earth—39 million of us—can’t see. Another 246 million have reduced vision.