Retina Code Helps in Restoring Normal Vision

The researchers at the Cornell Medical College have made remarkable advances in longstanding efforts to restore vision. They have deciphered mouse retina's neural code and coupled this information to a novel prosthetic device to restore sight to blind mouse.

This new approach provides hope for the 25 million people worldwide who suffer from blindness due to diseases of the retina. 

The new device provides the code to restore normal vision and the code is so accurate that it permits the facial features to be distinguished and also allow animals to track moving images.

The lead researcher, Dr. Sheila Nirenberg, a professor in the Department of Physiology and Biophysics and in the Institute for Computational Biomedicine at Weill Cornell said, "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. Because drug therapies help only a small fraction of this population, prosthetic devices are their best option for future sight. "This is the first prosthetic that has the potential to provide normal or near-normal vision because it incorporates the code."

Nirenberg and her co-author Chethan Pandarinath (a former Cornell graduate student now conducting postdoctoral research at Stanford University School of Medicine) report their work in the Proceedings of the National Academy of Sciences. 

The study author's explain that blindness is often caused by diseases of the retina that kill the photoreceptors and destroy the associated circuitry, but typically, in these diseases, the retina's output cells are spared.

Current prosthetics generally work by driving these surviving cells. Electrodes are implanted into a blind patient's eye, and they stimulate the ganglion cells with current.

There's another critical factor that is Nirenberg highlighted, "Not only is it necessary to stimulate large numbers of cells, but they also have to be stimulated with the right code -- the code the retina normally uses to communicate with the brain."

According to the researchers the pattern of light that falls on to the retina had to be converted into general code a set of equations that would convert light patterns into a general code, a set of equations that successfully converts the light patterns into patterns of electrical pulses. It is important that the code is generalizable, so that it could work for anything faces, landscapes, anything that a person sees.

By incorporating the code right into their prosthetic device's chip Nirenberg and Pandarinath generated the kind of electrical and light impulses that the brain understood.

The entire approach was tested on the mouse. The researchers built two prosthetic systems -- one with the code and one without. "Incorporating the code had a dramatic impact," Nirenberg says. "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."

"The reason this system works is two-fold," Nirenberg says. "The encoder's 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. What these findings show is that the critical ingredients for building a highly-effective retinal prosthetic the retina's code and a high resolution stimulating method are now, to a large extent, in place,"

This new devices has to still undergo human clinical trials especially to test the safety of the gene therapy component, which delivers the light sensitive protein.