Stanford researchers have developed a solar-powered retinal implant that could one day be used to correct blindness. They show the implant can send visual signals to the brains of rats in a study published today in Nature Communications.
Diseases of the eye's retina are the most common cause of inherited blindness in children. At the other end of the age spectrum, macular degeneration in the retina afflicts nearly two million aged adults in the U.S.
Artificial retinal implants aren't a new development. Take the case of Barbara Campbell who received one of the first artificial retinal implants in 2009. A special microchip was inserted into the retina, located in the back of eye. The tiny device was wired to video camera eyeglasses and translates visual images into electrical signals that can be understood by the neurons in the eye. The developers of this early bionic eye, Second Sight Medical Products, won FDA-approval for the device earlier this year.
While this achievement bordered on miraculous, ophthalmologist and physicist Daniel Palanker of Stanford University believed there was room for improvement.
Second Sight's eye prosthetic is physically linked to the video eyeglasses by a cable, and 30 percent of patients report complications with the implant.
In addition, the microchip's sensors are placed on the surface of the retina, instead of inside the tissue where it can directly interact with neurons. The authors claim that this can lead to unwanted, spontaneous nerve signals.
To address these shortcomings of bionic implants, Palanker and his colleagues developed a solar-powered microchip that could be inserted into the sub-retinal layers of eye.
This device was placed adjacent to the neurons that send visual information to the brain, which should stimulate a more "natural" pattern of neural activity. Their retinal prosthetic is wireless, so its special set of video eyeglasses beams images directly into the microchip.
In this study, Palanker's team from the Hansen Experimental Physics Laboratory placed these second-generation implants into the retinas of rats with or without macular degeneration. The researchers found that the new bionic retinas could transmit images into the minds of rats, which was observed by measuring brain activity in the visual centers of the rodents' brains.
Brain activity returned to normal in rats with eye disease that were given these retinal implants.
While this technology is in its early phases, it could have several advantages over older retinal prosthetics. First, the surgery is less complex and doesn't require the permanent addition of circuitry to the head and face. The researchers also equipped the implant with better resolution, which could offer a greater range of sight to human recipients in the future.
Source: Mandel Y, Goetz G, Lavinsky D, et al. Cortical responses elicited by photovoltaic subretinal prostheses exhibit similarities to visually evoked potentials. Nature Communications. 2013.