Can we restore sight by turning nerve cells into light sensors? What resonates with me about this remarkable study by José-Alain Sahel and colleagues in the New England Journal of Medicine, and the accompanying editorial by Nobel laureate Karl Deisseroth, is the possibility of restoring function even after the cells responsible for vision have been lost. In 10 individuals with advanced retinitis pigmentosa, an inherited disease that destroys the retina's light-sensing cells, researchers used optogenetics, a technique that introduces light-sensitive proteins into surviving nerve cells, combined w/ special goggles that translate visual information into light signals. Six of the 10 participants experienced clinically meaningful improvements in light sensitivity, and several demonstrated improvements in detecting or locating objects. This was a small, early-phase safety study, not a cure for blindness, and adverse events remind us that considerable work remains. What excites me most is the larger implication Deisseroth highlights: optogenetics is moving from a revolutionary laboratory tool toward a potential human therapy. We may not always need to replace every neuron lost to disease. Sometimes we may be able to reprogram surviving circuits to recover meaningful function. For those of us working in Parkinson's disease and deep brain stimulation, this is an especially powerful concept. The future of neurology may depend not only on protecting neurons, but also on learning how to restore the functions of circuits that survive. nejm.org/doi/full/10.1056/NE…