There’s a relay race in your eye that allows you to see. It begins when light hits the rod and cone cells in your retina, triggering a cascade of electrical signals. These pass through other types of cell in later layers and eventually to ganglion cells, which convey the signals to the brain.

In many eye diseases, the first stage of the relay—the light-sensing rods and cones—gradually die. The rest of the visual system is intact, but since it can’t respond to light, the world blackens.

Many scientists have tried to solve this problem by creating stand-ins for the lost light sensors. Two groups have developed implantable chips that do the same job: detect light and send out electrical