Assoc. Prof. Shy Shoham and team from the Faculty of Biomedical Engineering are researching a new approach to the artificial stimulation of blind retinas, developing devices that could bring more sight to the visually impaired. “Our work is at the interface of neuroscience and engineering,” he says. Shoham is pursuing the creation of external devices – such as goggles for the blind – that are able to remotely stimulate damaged sensory areas in order to restore the capacity of the brain to “see,” despite a damaged retina.

“The field of Neuroprosthetics involves the development of solutions for bypassing compromised neural systems,” says Shoham. “The goal is to interface with the nervous system.”

Their novel approach toward non-invasive vision restoration in blind retinas, by combining holography and optogenetics – a newly developing area in neuroscience, could be a first step toward noninvasive sight restoration in cases of degenerative retinal diseases. The study reporting a proof of principle for the new approach was published in the multidisciplinary journal, Nature Communications.

“Degenerative diseases of the outer retina are a major cause of blindness in the Western world,” says Assoc. Prof. Shoham. “These diseases are characterized by degeneration of the photoreceptors, which serve as light sensors, while downstream cellular levels in the retina, and specifically the retinal ganglion cells, are relatively well preserved. Artificial stimulation of these neurons constitutes a potential strategy for getting around the damaged retinal nerve cells. Restoring lost vision to basic functionality levels has become possible recently through invasive surgical insertion of artificial electronic implants that electrically stimulate surviving retina cells, similar to the snail-shaped cochlear implants used to treat the hearing impaired. Our approach is different and attempts to stimulate the surviving retinal cells without the need for direct implants onto the retina, and may eventually make surgery and implants redundant.”

“Our optogenetic approach relies on genetic expression of ion channels that are light sensitive (proteins derived from algae) in the ganglion cells of the retina,” explains Dr Inna Reutsky-Gefen, who studied the combination of holography and optogenetics and its application to blind retinas during her doctoral thesis under the mentoring of Shoham, and with assistance from additional study co-authors Lior Golan, Dr Nairouz Farah, Adi Schejter, Limor Tsur, and Dr Inbar Brosh.

“The ganglion cells are natively transparent and not light-responsive, but after expressing the channel, transform into light-sensors and may be capable of substituting the function of the photoreceptors. In order to create a coherent visual perception in the brain, we have to be able to activate a large number of neurons simultaneously, just as it works in normal visual processing. In addition, this needs to be achieved with high temporal and spatial precision in order to imitate normal retinal information processing. Our study findings demonstrate that optical stimulation of these cells, with the use of a unique holographic projector, enables simultaneous stimulation of a large group of cells with spatial precision at the level of single retinal cells, which is not possible with electrical stimulation. In this manner we demonstrated, in principle, the first ever holographic photo-stimulation capable of restoring cellular activity similar to intact retinal behavior, as a basis for sight rehabilitation developments.”

The holographic projection method developed in the study uses diffractive spatial light modulation to generate images at the focal plane. This approach is light-efficient and does not ”throw away” much of the light energy. The researchers emphasize that this efficiency will be particularly useful in more advanced phases, where it will be required to miniaturize the system into a portable component of a retinal “prosthetic” system, but it is too early to know when they will reach this stage.