August 15, 2012
Artificial Retina Could One Day Help Restore Sight
Connie K. Ho for redOrbit.com — Your Universe Online
Researchers have developed an artificial retina with the ability to restore normal vision based on its work on deciphering the retina´s neural code for brain communication. It´s the first of its kind — an effective prosthetic retina device that can accommodate for blindness in mice. The results of the project are a major breakthrough in working to restore vision for the blind.To begin, the scientists from Weill Cornell Medical College believe that they have solved the code for a monkey retina, which is similar to that of a human. They are looking to design and test a device that blind humans could utilize. The findings are detailed in a recent edition of the Proceedings of the National Academy of Science.
"It's an exciting time. We can make blind mouse retinas see, and we're moving as fast as we can to do the same in humans," explained Dr. Sheila Nirenberg, a professor in the Department of Physiology and Biophysics and in the Institute for Computational Biomedicine at Weill Cornell, in a prepared statement. The study's co-author is Dr. Chethan Pandarinath, who was a graduate student with Dr. Nirenberg and is currently a postdoctoral researcher at Stanford University.
Current prosthetics help blind users navigate with spots and edges of light. They focus on surviving cells, with electrodes implanted into a blind patient´s eye to situate ganglion cells that act as the retina´s output cells. The new device offers a code that could restore normal vision. Researchers describe the code as so accurate that individuals will be able to tell the difference between various facial features as well as offer animals the ability to record moving images in their mind. Nirenberg hopes that one day the blind can just wear a visor that will absorb light, change the light into a code with the use of computer chip, and then send an image to the brain.
In understanding sight, individuals are able to see images when light falls on photoreceptors in the surface of the retina. The retinal circuitry takes in the signals from the photoreceptors and changes them into a code of neural impulses. Ganglion cells pass the impulses to the brain. The brain can read the code of neural impulses and produce meaningful images.
“People have been trying to find the code that does this for simple stimuli, but we knew it had to be generalizable, so that it could work for anything – faces, landscapes, anything that a person sees," remarked Nirenberg in the statement.
According to Bloomberg, the researchers monitored healthy eyes to identity the equations that could convert light received by the retina to messages to the brain. Nirenberg realized that mathematical equations on a “chip” could be combined with a mini-projector. The chip, known as the “converter,” could change images that come into the eye into electrical impulses. This could change the electrical impulses into light impulses, allowing the light-sensitive proteins to pass the code to the brain. The researchers tested the system on a mouse with two prosthetic system, one that had the code and one that did not have the code.
"Incorporating the code had a dramatic impact," mentioned Nirenberg in the statement. "It jumped the system's performance up to near-normal levels – that is, there was enough information in the system's output to reconstruct images of faces, animals – basically anything we attempted."
They concluded that the patterns created by the blind retinas in mice were similar to the patterns produced by normal mouse retinas.
"The reason this system works is two-fold," reported Nirenberg in the statement. "The encoder – the set of equations – is able to mimic retinal transformations for a broad range of stimuli, including natural scenes, and thus produce normal patterns of electrical pulses, and the stimulator (the light sensitive protein) is able to send those pulses on up to the brain."
Moving forward, the investigators are looking to the test the retinal prosthetic in human clinical trials.
"This has all been thrilling," concluded Nirenberg in the statement. "I can't wait to get started on bringing this approach to patients."
The findings could affect 25 million people around the world who suffer from blindness related to disease of the retina. Diseases of the retina eliminate the photoreceptors and damage the associated circuitry. Drug therapies have only been able to assist a small part of the affected population. As such, prosthetic devices are seen as a viable option for the future.
“It´s a major step, it´s elegant, and it works,” Jonathan Victor, a professor in the department of neurology and neuroscience at Weill unaffiliated with the study, told Bloomberg.