The therapy uses chemicals known as photoswitches, which change shape when hit with light, to open the channels that activate retinal cells. Treated mice can distinguish between steady and flashing light, while dogs with late-stage retinal degeneration also regain some sensitivity to light.

The procedure starts with an adeno-associated virus. Some retina cells in blind mice survive after disease kills the rod and cone photoreceptors, but they won't work on their own. The virus inserts a gene that instructs the cells to produce a modified version of a common glutamate receptor ion channel. Then photoswitches are attached to the newly-formed ion channels, akin to a glutamate amino acid dangling on a light-sensitive string. When light hits a photoswitch, it forces an ion channel open, thereby turning the retinal neurons on and off many times a second.

The researchers are able to insert the gene into almost all of the million or so retinal ganglion cells, which should restore useful vision. The success of this therapy will vary somewhat, however, depending on whether it targets early or late-stage retinal degeneration.