The Stanford Photovoltaic Subretinal Prosthesis
the Stanford Retinal Prosthesis device
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"It works like the solar panels on your roof, converting light into electric current," said Daniel Palanker, PhD, associate professor of ophthalmology and one of the paper's senior authors. "But instead of the current flowing to your refrigerator, it flows into your retina." Palanker is also a member of the Hansen Experimental Physics Laboratory at Stanford and of the interdisciplinary Stanford research program, Bio-X. The study's other senior author is Alexander Sher, PhD, of the Santa Cruz Institute of Particle Physics at UC Santa Cruz; its co-first authors are Keith Mathieson, PhD, a visiting scholar in Palanker's lab, and James Loudin, PhD, a postdoctoral scholar. Palanker and Loudin jointly conceived and designed the prosthesis system and the photovoltaic arrays.
The Stanford device uses near-infrared light, which has longer wavelength than normal visible light. It's necessary to use such an approach because people blinded by retinal degenerative diseases still have photoreceptor cells, which continue to be sensitive to visible light. "To make this work, we have to deliver a lot more light than normal vision would require," said Palanker. "And if we used visible light, it would be painfully bright." Near-infrared light isn't visible to the naked eye, though it is "visible" to the diodes that are implanted as part of this prosthetic system, he said.
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Retinal prostheses are based on the idea that there are other ways to stimulate those neurons.
The Stanford device uses near-infrared light, which has longer wavelength than normal visible light.
"The surgeon needs only to create a small pocket beneath the retina and then slip the photovoltaic cells inside it." What's more, one can tile these photovoltaic cells in larger numbers inside the eye to provide a wider field of view than the other systems can offer, he added.
Stanford University holds patents on two technologies used in the system, and Palanker and colleagues would receive royalties from the licensing of these patents.
The proposed prosthesis is intended to help people suffering from retinal degenerative diseases, such as age-related macular degeneration and retinitis pigmentosa.
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Daniel Palanker is a Professor in the Department of Ophthalmology and Director of the Hansen Experimental Physics Laboratory at Stanford University. He received MSc in Physics in 1984 from the Yerevan State University in Armenia, and PhD in Applied Physics in 1994 from the Hebrew University of Jerusalem, Israel.
Dr. Palanker is working on optical and electronic technologies for diagnostic, therapeutic, surgical and prosthetic applications, primarily in ophthalmology. These studies include laser-tissue interactions with applications to non-damaging retinal laser therapy and to ocular surgery with ultrafast lasers. In the field of electro-neural interfaces, Dr. Palanker is developing retinal prosthesis for restoration of sight to the blind and implants for electronic control of organs, including secretory glands and blood vessels. He is also working on interferometric imaging of neural signals.
Several of his developments are in clinical practice world-wide: Pulsed Electron Avalanche Knife (PEAK PlasmaBlade, Medtronic Inc.), Patterned Scanning Laser Photocoagulator (PASCAL, Topcon Inc.), OCT-guided Laser System for Cataract Surgery (Catalys, Johnson&Johnson), Neural stimulator for enhanced tear secretion (TrueTear, Allergan Inc.). Several others are in clinical trials: Smartphone-based ophthalmic diagnostics and monitoring (Paxos, DigiSight Inc.), Photovoltaic Retinal Prosthesis (PRIMA, Pixium Vision), Gene therapy of the retinal pigment epithelium (Ocular BioFactory, Avalanche Biotechnologies Inc).
Speaker's Biography: Daniel Palanker is an Associate Professor in the Department of Ophthalmology and in the Hansen Experimental Physics Laboratory at Stanford University. He received PhD in Applied Physics in 1994 from the Hebrew University of Jerusalem, Israel.
Dr. Palanker studies interactions of electric field with biological cells and tissues in a broad range of frequencies: from quasi-static to optical, and develops their diagnostic, therapeutic and prosthetic applications, primarily in ophthalmology.
Several of his developments are in clinical practice world-wide: Pulsed Electron Avalanche Knife (PEAK PlasmaBladeTM), Patterned Scanning Laser Photocoagulator (PASCALTM), and OCT-guided Laser System for Cataract Surgery (CatalysTM). In addition to laser-tissue interactions, retinal phototherapy and associated neural plasticity Dr. Palanker is working on electro-neural interfaces, including Retinal Prosthesis, electronic control of vasculature and of the glands.
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Stanford Researchers Develop Small Retinal Implant …
One characteristic of retinal conditions such as age-related macular degeneration is that while the photoreceptors themselves are lost, the neurons in the inner retinal layers largely survive. Hence a number of recent and well-reported trials of implanted prostheses that aim to restore some of the lost vision by electrically stimulating those neurons.Most of these have faced a set of inherent problems, including how to supply power to the implanted array; the need for intraocular cabling to deliver stimulation signals; and how to transfer the data rapidly enough to be effective. The need for an external camera can also prevent the patient from using natural eye movements to scan a scene.A team at has developed a possible solution, using a photovoltaic subretinal prosthesis in which silicon photodiodes receive power and data directly through pulsed near-infrared illumination, and electrically stimulate the neurons.The system uses a portable computer to processes video images captured by a head-mounted camera, and video goggles then project these images onto the prosthesis using pulsed infrared at 880 to 915 nm. Because LEDs cannot meet the brightness requirements involved, the infrared projection system makes use of an array of laser diodes coupled into a multimode fibre, to produce high-intensity illumination with reduced coherence.This design simplifies the implanted circuitry, and eliminates the need for a bulky external power source. It also enables patients to scan the visual scene with their own eyes, within the visual field of the goggles. The findings have been published in Nature Photonics.Thin and wireless
"The design uses video goggles to deliver both power and visual information directly to each pixel through pulsed near-IR illumination, eliminating the need for complex electronics and wiring schemes, and preserving the natural link between image perception and eye movement," said Stanford's James Loudin in the paper."We have demonstrated the plausibility of this design through successful in-vitro stimulation of healthy and degenerate rat retina with NIR light intensities at least two orders of magnitude below the ocular safety limit. We also demonstrate the possibility of high-resolution stimulation with retinal responses elicited by a single 70 micron bipolar pixel."Because the photovoltaic implant is thin and wireless, the surgical procedure is much simpler than in other retinal prosthetic approaches, and the system considerably reduces the bulk of the implanted components.In the lab trials, the Stanford team placed a rat retina between a photodiode array to receive the incoming signal, and a multi-electrode array (MEA) to stimulate the neurons. The MEA measured 1.7 mm2, while two sizes of photodiode array were constructed: 0.8 x 1.2 mm for implantation into rats, and 2 x 2 mm for potential use in larger animals."Surgeons should be much happier with us," commented Loudin, envisaging the practical use of the technology. "Other approaches require pretty big pieces of hardware to be stuck in the body, 1 to 2 cm in size. We have just the one implant." The demonstration reported in Nature Photonics is described by Loudin as proof-of-concept, and further work will be required on issues of biocompatibility, stability of the material and the development of safe surgical procedures.
How video goggles and a tiny implant could cure …
Daniel Palanker and his group at Stanford University havedeveloped an optoelectronic system for visual prosthesis that includes a subretinal photodiode array and an infrared imageprojection system mounted on video goggles. Information from thevideo camera is processed in a pocket PC and displayed on pulsednear-infrared (IR, 850-900 nm) video goggles. IR image isprojected onto the retina via natural eye optics, and activatesphotodiodes in the subretinal implant that convert light intopulsed bi-phasic electric current in each pixel. Charge injectioncan be further increased using a common bias voltage provided by aradiofrequency-driven implantable power supply Close proximity between electrodes and neural cells necessary forhigh resolution stimulation can be achieved utilizing effect ofretinal migration.
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