Subretinal photodiode retinal prosthesis is subretinally implanted in rat's eye.
(photo credit: PALANKER LAB)
A retinal implant that could restore vision in a resolution five times better than existing devices has been produced by an international teach that included researchers from Bar-Ilan University in Ramat Gan.
The development was described in a recent issue of Nature Medicine.
“The retinal implant – a 30-micrometer-thin, photovoltaic pixel array implanted beneath the retina – converts incoming infrared light into electric current – which stimulates the retinal neurons that remain functional, allowing them to send messages to the visual center of the brain.”
The paper’s main authors were Stanford University’s Henri Lorach, George Goetz and Daniel Palanker, and Alexander Sher of the University of California, Santa Cruz.
Additional contributions were made by BIU’s Dr. Yossi Mandel and researchers affiliated with the Institut de la Vision in Paris, the University of California, Santa Cruz, and Scotland’s University of Strathclyde.
As a clinical ophthalmologist, Mandel is an expert in the diagnosis, treatment and prevention of diseases that can lead to blindness. But as an experimental researcher with a doctorate in bio-engineering, he also sees things from a different, technological angle. He helped develop a model for measuring visual acuity in rats during his post-doctoral research at Stanford. “Since the rat cannot easily indicate if it sees the stimuli, we evaluated visual acuity using an approach that is routinely employed for young children or other nonverbal patients.” In this method, the clinician records brain activity in response to visual stimuli at various sizes.
“Retinal degenerative diseases destroy photoreceptors – the rods and cones that respond to light – but other parts of the eye usually remain healthy,” noted Mandel, a senior lecturer at BIU’s life sciences faculty and head of the ophthalmic science and engineering lab. Electrical measurement of neural activity in the visual cortex showed that the response evoked by this electrical stimulation resembles what occurs during normal vision.
The new implant represents a major improvement in “prosthetic” vision devices that may someday restore functional vision to patients suffering from degenerative diseases of the retina. Clinical trials, which will focus on patients blinded by a genetic disease called retinitis pigmentosa, are scheduled to begin in France next year.
According to Mandel, previous retinal prostheses have been successful in restoring limited vision, even in humans. But the new technology represents a breakthrough in the restoration of high visual acuity.
The small pixel size of the photovoltaic array – with each pixel measuring just 70 microns across – allows for the highly localized stimulation that, in turn, results in an unprecedented level of visual acuity.
“While existing systems achieve visual acuity up to about 20/1200, the current implant achieves correction to 20/250 – still a long way from perfect ‘20/20’ vision, but a major improvement nonetheless,” Mandel said “This is a level of acuity that would allow blind patients to make out the shape of objects and to see meaningful images.”
The implant has another advantage over previous technologies – its potential for use in minimally invasive vision therapy. “Other prostheses are powered by extraocular devices that are wired to a retinal electrode array and require complex surgeries,” Mandel said. “The current technology, on the other hand, is wireless, with light transmitted by special glasses stimulating the photovoltaic pixels positioned under the retina. While a sophisticated approach, for the patient, our system is far less complicated.”
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