The Artificial Retina

Tuesday, July 1, 2014
Close-up of a human eye.

In this era of “seeing” robots and “bionic” body parts, patients sometimes ask about the possibility of an artificial electronic retina. Such a device was approved last year by the FDA, providing rudimentary vision for blind patients and the hope that future advances in the technology will help even more people who have lost vision.

The name of the device is the Argus II, manufactured by Second Sight Medical Products. It uses a small electronic chip surgically implanted onto 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.

Currently, 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.

Patients who have lost central vision due to age-related macular degeneration would not likely 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 may increase the level of vision. Second Sight is planning to increase the number of electrodes to 240 in a future model.  The German company Retinal Implant, has begun clinical testing with a 1,500-pixel device. For reference, a healthy human eye has the equivalent of approximately 1 million “pixels.”

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.

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 visual cortex, the part of the brain responsible for seeing.

Another approach is to use gene therapy to deliver light sensitive molecules to the retina. In retinitis pigmentosa, the light sensitive photoreceptors die. However, the neurons that receive signals from the photoreceptors remain functioning. Making these remaining cells sensitive to light can effectively bypass the photoreceptors, restoring some degree of vision in animal models. How this type of vision will compare to that provided by chip implants is not yet known.

The fact that electronic retinal implants are already approved for use in patients with retinitis pigmentosa and gene therapy for human blindness is in advanced clinical trials bodes well for future vision restoration or protection for people with retinal diseases.

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