The results of a new UC Berkeley study may offer some hope for the nearly 40 million people who suffer from blindness worldwide. In a recent paper published in the journal Neuron, researchers led by Professor Richard Kramer of the department of Molecular and Cell Biology have shown that a simple chemical, known as AAQ, can restore light sensitivity to the retina for prolonged periods of time. AAQ—or acrylamide-azobenzene-quaternary ammonium when spelled out in its full, tongue-twisting form—is a small molecule that acts as a “photoswitch,” responding to light by making neurons in the retina more or less excitable and likely to fire. This switching can replace the action of dead, degenerated or missing (due to genetic mutation) rods and cones, the normally photoactive cells in the vertebrate eye. By injecting AAQ directly into the eyes of blind mice with fully degenerated rods and cones, Kramer’s group showed its ability to restore both the electrical firing of neurons in the retina, as well as light-induced behavioral responses. In particular, the treated mice showed pupils that contract in response to light and also avoided bright light, much like fully seeing animals. “The first time we observed them responding to light, it blew us away,” says Kramer.
Perhaps most exciting about the efficacy of AAQ as a retinal photoswitch is the simplicity and reversibility of treatment. Other current remedies for the loss of visual acuity, while also promising, require highly invasive or permanent procedures to restore sight, and typically target only a fraction of the retina. “AAQ is able to render nearly every cell in the retina light sensitive,” says Alexandra Polosukhina, the lead author of the study. Requiring only a minor injection and fully reversible, treatment with AAQ is also much less risky for the prospective patient. Eventually, an even less invasive slow release pill could be viable. Despite its promise, however, Polosukhina is careful to stress the early stage of this research. “It’s still a little too soon to guess exactly what type of vision AAQ and related compounds could restore,” she cautions. “Nevertheless, they could someday allow for contrast sensitivity, object recognition, and a better standard of living for individuals suffering from blindness.”