27 February 2013
Scientists from the Faculty of Biomedical Engineering at the Technion developed a novel approach towards non-invasive vision restoration in blind retinas, by combining holography and optogenetics – a rapidly developing field in neuroscience. The study is published in the multidisciplinary Journal, Nature Communications.
“Degenerative diseases of the outer retina are one of the major causes of blindness in the Western world,” says Professor Shy 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 Professor 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.
“Applications of this approach are not limited to vision restoration,” stresses Professor Shoham. “holographic stimulation strategies can permit flexible control of the activity of large cellular networks which artificially express light-sensitive channels, and pave the way towards new medical devices and scientific tools that can help “break” the brain’s neural code."
The research was funded by a European Research Council Starting Grant to Prof. Shoham.