A loss of photoreceptor cells caused by retinal degenerative diseases often results in complete blindness. Zhuo-Hua Pan of Wayne State University School of Medicine in Detroit and colleagues explored the possibility of converting nonphotosensitive (or inner) retinal neurons into photosensitive cells in mice to see if they could restore retinas that lack rods and cones by making them sensitive to light. Photoreceptor cells in the retina convert light signals to electrical signals that are relayed through other retinal neurons to the brain. As reported in the April 6 issue of Neuron, the researchers injected a harmless virus that contained channelrhodopsin-2, which is a light-sensitive protein found in green algae, into the eyes of mice. They wanted to see if the protein would make the retinal neurons sensitive to light. To directly observe the expression of the light-sensitive proteins, the researchers tagged them with GFP. Three to four weeks after the injection, bright fluorescence was seen in retinal neurons under either a Zeiss fluorescence microscope equipped with exciter, dichroic and emission filters and with a CCD camera or a Leica confocal microscope. The fluorescence was still detected even 12 months after injection, with no major changes in the retina. The researchers believe that their results indicate that the microbial-type channel proteins may provide a potential strategy for restoring the vision in patients suffering from photoreceptor degeneration. They hope that further studies will evaluate which types of retinal diseases may benefit from this potential treatment strategy.