The new device takes advantage of what is preserved.
The 2-by-2-millimeter chip that receives images is implanted in the part of the retina where photoreceptors have been lost. The chip is sensitive to infrared light projected from the glasses, unlike real photoreceptors that respond only to visible light.
“The projection is done by infrared because we want to make sure it’s invisible to the remaining photoreceptors outside the implant,” Palanker said.
The design means patients can use their natural peripheral vision along with the prosthetic central vision, which helps with orientation and navigation.
“The fact that they see simultaneously prosthetic and peripheral vision is important because they can merge and use vision to its fullest,” Palanker said.
Because the chip is photovoltaic, meaning it needs only light to generate electric current, it can operate wirelessly and be implanted under the retina. Previous eye prostheses required an external power source and a cable running out of the eye.
Reading again
The new trial included 38 patients older than 60 who had geographic atrophy due to age-related macular degeneration and worse than 20/320 vision in at least one eye.
Four to five weeks after implantation of the chip in one eye, patients began using the glasses. Though some patients could make out patterns immediately, all patients’ visual acuity improved over months of training.
“It may take several months of training to reach top performance — which is similar to what cochlear implants require to master prosthetic hearing,” Palanker said.
Of the 32 patients who completed the one-year trial, 27 could read and 26 demonstrated clinically meaningful improvement in visual acuity, which was defined as the ability to read at least two additional lines on a standard eye chart. On average, participants’ visual acuity improved by 5 lines; one improved by 12 lines.
The participants used the prosthesis in their daily lives to read books, food labels and subway signs. The glasses allowed them to adjust contrast and brightness and magnify up to 12 times. Two-thirds reported medium to high user satisfaction with the device.
Nineteen participants experienced side effects, including ocular hypertension (high pressure in the eye), tears in the peripheral retina and subretinal hemorrhage (blood collecting under the retina). None were life-threatening, and almost all resolved within two months.
Future visions
For now, the PRIMA device provides only black-and-white vision, with no shades in between, but Palanker is developing software that will soon enable the full range of grayscale.
“Number one on the patients’ wish list is reading, but number two, very close behind, is face recognition,” he said. “And face recognition requires grayscale.”
He is also engineering chips that will offer higher resolution vision. Resolution is limited by the size of pixels on the chip. Currently, the pixels are 100 microns wide, with 378 pixels on each chip. The new version, already tested in rats, may have pixels as small as 20 microns wide, with 10,000 pixels on each chip.
Palanker also wants to test the device for other types of blindness caused by lost photoreceptors.
“This is the first version of the chip, and resolution is relatively low,” he said. “The next generation of the chip, with smaller pixels, will have better resolution and be paired with sleeker-looking glasses.”
A chip with 20-micron pixels could give a patient 20/80 vision, Palanker said. “But with electronic zoom, they could get close to 20/20.”
Palanker is an affiliate with the Wu Tsai Neurosciences Institute.
Researchers from the University of Bonn, Germany; Hôpital Fondation A. de Rothschild, France; Moorfields Eye Hospital and University College London; Ludwigshafen Academic Teaching Hospital; University of Rome Tor Vergata; Medical Center Schleswig-Holstein, University of Lübeck; L’Hôpital Universitaire de la Croix-Rousse and Université Claude Bernard Lyon 1; Azienda Ospedaliera San Giovanni Addolorata; Centre Monticelli Paradis and L’Université d’Aix-Marseille; Intercommunal Hospital of Créteil and Henri Mondor Hospital; Knappschaft Hospital Saar; Nantes University; University Eye Hospital Tübingen; University of Münster Medical Center; Bordeaux University Hospital; Hôpital National des 15-20; Erasmus University Medical Center; University of Ulm; Science Corp.; University of California, San Francisco; University of Washington; University of Pittsburgh School of Medicine; and Sorbonne Université contributed to the study.
The study was supported by funding from Science Corp., the National Institute for Health and Care Research, Moorfields Eye Hospital National Health Service Foundation Trust, and University College London Institute of Ophthalmology.