Scientists are marrying tiny but powerful solar cells to goggles used for playing popular video games to come up with a contraption that would give “sight” to those who lost vision. The artificial retina, fabricated by researchers at Stanford University in the US , has fewer implanted components and does not require complicated surgical procedures. More importantly, this retinal prosthesis is self-powered, and hence does not need wires and coils, which are essential to supply power to existing “bionic” eyes.
A paper that appeared online in the journal Nature Photonics yesterday claimed that the prosthesis, which works on the same principle that allows solar cells to produce electricity using sunlight, offers several advantages over commercially available retinal implants which have been shown to restore a level of vision in the blind.
All these contraptions, including the latest one, benefit those who have become blind because of retinal degenerative diseases such as age-related macular degeneration — a leading cause of blindness among people who are 55 years or above — or retinitis pigmentosa, a type of inherited blindness, which is particularly common in tropical countries. Both these conditions lead to a destruction of photo receptors — the cells in the retina — that perceive light patterns and pass them on to the brain in the form of nerve impulses.
A large number of research groups all over the world have been in a race to develop an effective artificial eye. Such visual prostheses are in different stages of development. A Swiss firm — Second Sight Medical Products — already has a commercially available bionic eye called Argus II Retinal Prosthesis System in the European market. Very recently, Retina Implant, a Germany-based medical devices company, embarked on clinical trials to test a new chip-based retinal implant technology.
Though estimated to cost US$ 30,000, the Argus II bionic eye leaves much to be desired. Its one millimetre by one millimetre chip, implanted at the back of the retina, accommodates an array of 60 electrodes versus the Stanford contraption's 178 electrodes.
“We need at least 1,000 electrodes to make reading and face recognition possible,” says James Loudin, the first author of the Nature Photonics paper. Loudin, a postdoctoral student with Daniel Palanker of the Department of Ophthalmology at Stanford, took up research into this bionic eye as part of his doctoral work several years ago. With prostheses currently available, at best people can be perceived by their contours. Those who have an implanted bionic eye can easily identify sidewalks on a road and read letters which are 6 inches in size, he says. Loudin expects the Stanford prosthesis to be better, but doesn’t want to hazard a guess as to how much better. “We will never know till we test it in humans,” Loudin told KnowHow.
As of now, the scientists demonstrated the potential of the device by generating electrical stimulation in healthy and degenerated rat retina. “The next step would be to understand the resolution of the vision offered by the prosthesis,” Loudin says. As for testing it in humans, Loudin says, “We have to first find a commercial partner who can take us through further testing and development.” The Stanford retinal prosthesis, undoubtedly, has several advantages.
It works like this: a camera mounted on the goggles captures images, which are then processed by a portable computer. These signals are sent back to the goggles which then beams them onto the retinal implant as near-infrared radiation (which is very close to red colour in the visual spectrum, but invisible to the naked eye). Infrared is chosen because normal light is too dim to produce sufficient signals to directly stimulate neurons. Infrared rays produce signals that are 1000 times stronger, yet safe for the eye, says Loudin.
When the signals fall on the retinal implant, which has as many as 178 photodiodes on 1 mm X 1mm array, they are converted into impulses that can be carried to the brain. “There on, we exploit the principles of natural vision,” says Loudin.