Our ability to see depends on two factors: light-sensitive rods and cones in the retina, and the nerves that transmit signals from these cells to the brain (along with the brain itself, of course). When the rods and cones die, which can occur as the eye ages or in the retina-damaging eye disease retinitis pigmentosa, the nerves can sometimes still function—if they have a new, working sensor for light. To replace the rods and cones, previous treatments have used electronic implants, which require surgery, or gene therapy, which relies on injections deep into the eye. But in a new technique, all it takes to restore vision—at least partially—is a much less invasive injection of the chemical AAQ.
AAQ, which stands for acrylamide-azobenzene-quaternary ammonium, is a photoswitch: it changes shape when exposed to light. And when AAQ molecules bind to living cells, like the neurons that serve the eye, the chemical can make those cells light-sensitive as well. To test AAQ, researchers engineered mice with doomed rods and cones, which died while the mice were still young. Then they injected some of the rodents’ eyes with AAQ and placed the mice in a slim tube monitored by an infrared camera. Mice with vision shied away from the bright end, while blind ones were indifferent to the light. And two hours after an injection of AAQ, formerly blind mice avoided the illuminated end of the tube as well. Unfortunately, the effect wore off a few hours later. To make this a viable treatment, researchers will have to tweak either the AAQ delivery system to make it slowly release the chemical over time, or the molecule itself to make it last longer.
Even a slow-release formula of AAQ won’t be perfect. When researchers tested the retinal response of mouse eyes treated with the chemical, they found that AAQ helped cells pick up certain wavelengths more strongly than others, and it was less effective with dim light conditions. On the other hand, the eyes regained a high level of spatial resolution, responding even to tiny spots of light one ten-thousandth of a meter in radius. The new method may not perfectly restore vision, but it could at least bring the blind out of the darkness.
Image courtesy of Aaron Logan / Wikimedia Commons