Now engineers have tested a new nano-scale system that could be implanted onto a patient's retina to respond to light by directly stimulating the neurons that send visual signals to the brain. Unlike other systems, the new device wouldn't require any external sensors, and can provide a much higher resolution.

Two of the most promising bionic eyes in development are the Argus II, built by Second Sight, and a similar system created by researchers at Bionic Vision Australia. Both of these prosthetics involve first implanting electrodes into the eye, then connecting them to external sensors that can be worn like glasses. Light signals from these camera-like sensors are translated into electrical impulses and sent to the implants to stimulate the neurons at the retina, which in turn send the visual information to the brain by way of the optic nerve.