Patients with retinal degeneration lose sight due to gradual demise of photoreceptors. Electrical stimulation of
the surviving retinal neurons provides an alternative route for delivery of visual information. Subretinal photovoltaic
arrays with 70μm pixels were used to convert pulsed near-IR light (880-915nm) into pulsed current to stimulate the
nearby inner retinal neurons. Network-mediated responses of the retinal ganglion cells (RGCs) could be modulated by
pulse width (1-20ms) and peak irradiance (0.5-10 mW/mm<sup>2</sup>). Similarly to normal vision, retinal response to prosthetic
stimulation exhibited flicker fusion at high frequencies, adaptation to static images, and non-linear spatial summation.
Spatial resolution was assessed in-vitro and in-vivo using alternating gratings with variable stripe width, projected with
rapidly pulsed illumination (20-40Hz). In-vitro, average size of the electrical receptive fields in normal retina was
248±59μm – similar to their visible light RF size: 249±44μm. RGCs responded to grating stripes down to 67μm using
photovoltaic stimulation in degenerate rat retina, and 28μm with visible light in normal retina. In-vivo, visual acuity in
normally-sighted controls was 29±5μm/stripe, vs. 63±4μm/stripe in rats with subretinal photovoltaic arrays,
corresponding to 20/250 acuity in human eye. With the enhanced acuity provided by eye movements and perceptual
learning in human patients, visual acuity might exceed the 20/200 threshold of legal blindness. Ease of implantation and
tiling of these wireless arrays to cover a large visual field, combined with their high resolution opens the door to highly
functional restoration of sight.
Novel technologies are constantly under development for vision restoration in blind patients. In some of these techniques, such as photodiode implants or optogenetics based treatment, a glasses mounted optical projection system projects the visual scene onto the retina. The desired projection system is characterized by a relatively high power density, a localized retinal stimulation area and compatibility for wavelengths that are specific for the technology at hand. The challenges of obtaining such a projection system are not only limited by developing the tools and the apparatus for testing the visual performance of artificial retina, but also devising the technique and the methodology for training and testing the behaving animals using this tool. Current research techniques used for evaluation of visual function in behaving animals utilize computer screens for retinal stimulation, and therefore do not fulfill the requirements of the evaluation of retinal implant performance or optogenetics based treatment (inefficient power and no wavelength flexibility). In the following work we will present and evaluate a novel projection system that is suited for behavioral animal studies and meet the requirements for artificial retinal stimulation. The proposed system is based on a miniature Digital Mirror Device (DMD) for pattern projection and a telescope for relaying the pattern directly onto the animal eye. This system facilitates the projection of patterns with high spatial resolution at high light intensities with the desired wavelength and may prove to be a vital tool in natural and artificial vision performance research in behaving animals.
Over a million people in US alone are visually impaired due to the neovascular form of age-related macular degeneration (AMD). The current treatment is monthly intravitreal injections of a protein which inhibits Vascular Endothelial Growth Factor, thereby slowing progression of the disease. The immense financial and logistical burden of millions of intravitreal injections signifies an urgent need to develop more long-lasting and cost-effective treatments for this and other retinal diseases. Viral transfection of ocular cells allows creation of a “biofactory” that secretes therapeutic proteins. This technique has been proven successful in non-human primates, and is now being evaluated in clinical trials for wet AMD. However, there is a critical need to down-regulate gene expression in the case of total resolution of retinal condition, or if patient has adverse reaction to the trans-gene products. The site for genetic therapy of AMD and many other retinal diseases is the retinal pigment epithelium (RPE). We developed and tested in pigmented rabbits, an optical method to down-regulate transgene expression in RPE following vector delivery, without retinal damage. Microsecond exposures produced by a rapidly scanning laser vaporize melanosomes and destroy a predetermined fraction of the RPE cells selectively. RPE continuity is restored within days by migration and proliferation of adjacent RPE, but since the transgene is not integrated into the nucleus it is not replicated. Thus, the decrease in transgene expression can be precisely determined by the laser pattern density and further reduced by repeated treatment without affecting retinal structure and function.
We have developed a photovoltaic retinal prosthesis, in which camera-captured images are projected onto the retina using pulsed near-IR light. Each pixel in the subretinal implant directly converts pulsed light into local electric current to stimulate the nearby inner retinal neurons. 30 μm-thick implants with pixel sizes of 280, 140 and 70 μm were successfully implanted in the subretinal space of wild type (WT, Long-Evans) and degenerate (Royal College of Surgeons, RCS) rats. Optical Coherence Tomography and fluorescein angiography demonstrated normal retinal thickness and healthy vasculature above the implants upon 6 months follow-up. Stimulation with NIR pulses over the implant elicited robust visual evoked potentials (VEP) at safe irradiance levels. Thresholds increased with decreasing pulse duration and pixel size: with 10 ms pulses it went from 0.5 mW/mm<sup>2</sup> on 280 μm pixels to 1.1 mW/mm<sup>2</sup> on 140 μm pixels, to 2.1 mW/mm<sup>2</sup> on 70 μm pixels. Latency of the implant-evoked VEP was at least 30 ms shorter than in response evoked by the visible light, due to lack of phototransduction. Like with the visible light stimulation in normal sighted animals, amplitude of the implant-induced VEP increased logarithmically with peak irradiance and pulse duration. It decreased with increasing frequency similar to the visible light response in the range of 2 - 10 Hz, but decreased slower than the visible light response at 20 - 40 Hz. Modular design of the photovoltaic arrays allows scalability to a large number of pixels, and combined with the ease of implantation, offers a promising approach to restoration of sight in patients blinded by retinal degenerative diseases.
Non-compressible hemorrhages are the most common preventable cause of death on battlefield or in civilian traumatic
injuries. We report the use of sub-millisecond pulses of electric current to induce rapid constriction in femoral and
mesenteric arteries and veins in rats. Extent of vascular constriction could be modulated by pulse duration, amplitude
and repetition rate. Electrically-induced vasoconstriction could be maintained at steady level until the end of
stimulation, and blood vessels dilated back to their original size within a few minutes after the end of stimulation. At
higher settings, a blood clotting could be introduced, leading to complete and permanent occlusion of the vessels. The
latter regime dramatically decreased the bleeding rate in the injured femoral and mesenteric arteries, with a complete
hemorrhage arrest achieved within seconds. The average blood loss from the treated femoral artery was about 7 times
less than that of a non-treated control. This new treatment modality offers a promising approach to non-damaging
control of bleeding during surgery, and to efficient hemorrhage arrest in trauma patients.