In this era of “seeing” robots and “bionic” body parts, patients sometimes ask about the possibility of an electronic retina. Recent publications in the journals Nature and Scientific American describe an exciting advance: the development of an artificial eye with tiny light-sensing nano-wires. These wires can be packed into the artificial eye even more tightly than the light-sensing photoreceptor cells in natural eyes. While this is a breakthrough, it will take years to determine how to best connect this artificial eye to the optic nerve (which sends vision signals to the brain), or directly to the visual cortex in the back of the brain.
Retinal implants, which substitute for dead photoreceptors in patients with age-related macular degeneration or retinitis pigmentosa, have been developed. One such device, the Argus II, was approved by the FDA in 2013, providing rudimentary vision for blind patients and the hope that future advances in the technology will help even more patients.
The approved device was manufactured by Second Sight Medical Products, and uses a small electronic chip surgically implanted onto the surface of the retina. The patient wears glasses containing a small video camera that wirelessly transmits images to the chip. The images look like multiple white spots of light.
In the Argus II, the resolution is limited, as the device has 60 pixels. It can enable patients with the progressive, hereditary disease retinitis pigmentosa, who previously could see little or no light, to read large letters, determine the location of moving objects or people, and detect street curbs. For reference, a healthy human eye has about 1 million “pixels.”
Patients who have lost central vision due to age-related macular degeneration would not be likely to experience much benefit from an Argus II because their peripheral vision is still better than that provided by the device. However, further advances in chip technology are providing better resolution.
A device called the “Prima” was recently implanted under the retina of a patient with advanced AMD at University of Pittsburgh Medical Center. It is activated by infrared light projected be special glasses. It has 378 electrodes, so it could provide more pixels than the Argus.
Another device from a company called Nano Retina also uses glasses that deliver infrared light to a chip. Unlike the Prima, but like the Argus II, the Nano Retina is positioned on top of the retina. A couple have of patients in Europe have received the implant in a clinical trial.
In addition to having limited numbers of pixels, the implants also lack the information processing that occurs in layers of neurons within the retina. Despite these limitations, some patients have reported improved visual experiences provided by the chips over time, as they learn to interpret the novel light patterns provided by the chips, which stimulate the healthy neurons on the surface of the retina.
Other Approaches to Restore Vision
In addition to improved retinal implants, additional approaches to restoring vision are being tested. In one approach, rather than stimulate the retina, an electronic chip directly stimulates the part of the brain responsible for seeing, the visual cortex, located in the back of the head. Second Sight, the company that made the Argus II retinal implant, is now focusing on making a brain implant, and a few patients have received such implants in clinical trials. They report having some rudimentary vision restored, and even being able to play a “PacMan” like game.
Another approach is to use gene therapy to deliver light sensitive molecules to the retina. In retinitis pigmentosa and AMD, the light-sensitive photoreceptors die. However, the neurons that receive signals from the photoreceptors remain. Making these remaining cells sensitive to light can bypass the photoreceptors, restoring some degree of vision in experimental animals. How this type of vision will compare to that provided by chip implants is not yet known.
The fact that electronic retinal implants and gene therapy have been approved by the FDA for specific retinal degenerative diseases bodes well for future vision restoration or protection for people with retinal diseases.
Author: Joshua Dunaief, MD, PhD, Scheie Eye Institute, University of Pennsylvania