retinal degenerative diseases

Photovoltaic retinal implant could restore functional sight, researchers say

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Photovoltaic retinal implant could restore functional sight, researchers say
The wireless retinal implants convert light transmitted from special glasses into electrical current, which stimulates the retina’s bipolar cells. 

A team led by Stanford University researchers has developed a wireless retinal implant that they say could restore vision five times better than existing devices.

 Results in rat studies suggest it could provide functional vision to patients with , such as or .

A paper describing the implant was published online April 27 in Nature Medicine.

“The performance we’re observing at the moment is very encouraging,” said Georges Goetz, a lead author of the paper and graduate student in electrical engineering at Stanford. “Based on our current results, we hope that human recipients of this implant will be able to recognize objects and move about.”

Retinal degenerative diseases destroy photoreceptors—the retina’s rods and cones—but other parts of the eye usually remain healthy. The implant capitalizes on the electrical excitability of known as bipolar cells. These cells process the photoreceptors’ inputs before they reach ganglion cells, which send retinal signals to the brain. By stimulating bipolar cells, the implant takes advantage of important natural properties of the retinal neural network, which produces more refined images than the devices that skip these cells.

Made of silicon, the implant is composed of hexagonal photovoltaic pixels that convert light transmitted from special glasses worn by the recipient into electrical current. These electrical pulses then stimulate the retina’s , triggering a neural cascade that reaches the brain.

Clinical trial planned

So far, the team has tested the device only in animals, but a clinical trial is planned next year in France, in collaboration with a French company called Pixium Vision, said Daniel Palanker, PhD, professor of ophthalmology and a senior author of the paper. Initially, patients blinded by a genetic disease called retinitis pigmentosa will be included in the study.

Existing retinal prostheses are powered by extraocular devices wired to the retinal electrode array, which require complex surgeries, and provide visual acuity up to about 20/1,200. This new photovoltaic implant could be a big improvement because its small size, modularity and lack of wires enable a minimally invasive surgery. Vision tests in rats have shown it restores to an equivalent of 20/250.

Next, Palanker and his team plan to further improve acuity by developing chips with smaller pixels. To ensure the signals reach the target neurons, they plan to add a tiny prong to each electrode that will protrude into the target cell layer.

“Eventually, we hope this technology will restore vision of 20/120,” Palanker said. “And if it works that well, it will become relevant to patients with .”

 

Abstract

Patients with retinal degeneration lose sight due to the gradual demise of photoreceptors. Electrical stimulation of surviving retinal neurons provides an alternative route for the delivery of visual information. We demonstrate that subretinal implants with 70-μm-wide photovoltaic pixels provide highly localized stimulation of retinal neurons in rats. The electrical receptive fields recorded in retinal ganglion cells were similar in size to the natural visual receptive fields. Similarly to normal vision, the retinal response to prosthetic stimulation exhibited flicker fusion at high frequencies, adaptation to static images and nonlinear spatial summation. In rats with retinal degeneration, these photovoltaic arrays elicited retinal responses with a spatial resolution of 64 ± 11 μm, corresponding to half of the normal visual acuity in healthy rats. The ease of implantation of these wireless and modular arrays, combined with their high resolution, opens the door to the functional restoration of sight in patients blinded by retinal degeneration.

Source: Nature

Potential new approaches to treating eye diseases

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Potential new approaches to treating eye diseases
These are high magnification images representing immunochemistry of IL-33 (green), Iba1 (red), and GFAP (yellow) in the central retina of a control eye and lesion and nonlesion areas of an AMD eye. The bright-field (BF) images show RPE loss in the AMD lesion site. Bars, 50 µm. Credit: Xi et al., 2016

Potential new approaches to treating eye diseases such as age-related macular degeneration (AMD) are described in a new study, “IL-33 amplifies an innate immune response in the degenerating retina,” in the February Journal of Experimental Medicine.

 AMD is a leading cause of vision impairment in old age, and is caused by the degeneration of cells in the retinal layer of the eye. Retinal cell death can be induced by phagocytic immune cells that infiltrate the tissue in response to injury or infection, but the molecular signals that trigger phagocyte invasion are largely unknown. A team of researchers led by Hongkang Xi and Menno van Lookeren Campagne, of the Department of Immunology at Genentech, Inc., in South San Francisco, Calif., discovered that a pro-inflammatory signaling protein, or cytokine, called IL-33, plays a key role in recruiting phagocytes to damaged retina and inducing .

Working with rats and mice, Xi and colleagues found that specialized called Müller glial cells release IL-33 in response to retinal injury. The cytokine then binds to its receptor on the surface of the Müller cells and induces the release of additional inflammatory proteins that attract phagocytes to the damaged retina. Blocking the IL-33 receptor inhibited this process and prevented injury-induced retinal degeneration.

The researchers also found that IL-33 levels are increased in the retinas of AMD patients, suggesting that the same pathway may occur in humans. Inhibiting IL-33 may therefore help treat AMD and other .

“This study for the first time shows increased expression of IL-33 in AMD and further demonstrates a role for glia-derived IL-33 in the accumulation of myeloid cells in the outer retina, loss of photoreceptors, and functional impairment of the retina in preclinical models of retina stress,” the authors note.

New insight into eye diseases

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New insight into eye diseases
This image shows how transferred genes activate the stem cell properties of normally dormant retinal cells.

Many diseases that lead to blindness, such as glaucoma and macular degeneration, are caused by the death of certain cells in the human retina that lack the ability to regenerate. But in species such as zebrafish these cells, known as Muller glial cells (MGs), do serve as retinal stem cells that are capable of generating new cells.

 In a new study, a research team led by Associate Professor of Ophthalmology Bo Chen investigated whether the regenerative power of cells in zebrafish could be recreated in mammals, specifically mice.

The research team transferred genes into MGs to activate the stem cell properties of these normally dormant cells, causing them to reproduce and make other types of .

The strategy could be developed into a therapeutic tool, Chen said. “In the future we are hoping to manipulate these cells to replenish any lost retinal neurons, either in diseased or physically damaged retinas,” he noted. “Potentially, it’s a therapy to treat many different .”