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Ophthalmology and Optometry
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Retina Changes Its "Language" with Changing Brightness PDF
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Ophthalmology and Optometry
Wednesday, 17 December 2014

A study at the University of Tübingen highlights the intricate nature of visual responses. The findings may help to improve digital cameras as well as visual prosthetics.

Our visual abilities are astonishing: we can see in extreme situations, from a stroll under the starry sky to a ski-run in glaring sunlight. We do this effortlessly, much smoother and more stable than even the most modern digital cameras. Scientists knew that the first steps of visual processing already occur inside our eyes: The retina does not only harbor the light-sensitive receptor cells, but it also processes the incoming information and transmits it as an intricate pattern of activity via the optic nerve to the brain.

A new study now shows that this process is much more complex than previously thought. Scientists of the Werner Reichardt Centre for Integrative Neuroscience (CIN) and Bernstein Center for Computational Neuroscience at the University of Tübingen, together with colleagues from the University of Manchester, showed that the activity patterns sent to the brain – the "language" of the retina – fundamentally depends on the ambient light level in our environment. When light conditions change, the retina speaks a different language. The study was published on 8 Dec 2014 in the journal Nature Neuroscience.

 
Human Eye Can Potentially See Infrared Light PDF
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Ophthalmology and Optometry
Thursday, 11 December 2014

infrared lightAn international team of researchers has found that under certain conditions, the retina can sense infrared light after all. Using cells from the retinas of mice and people, and powerful lasers that emit pulses of infrared light, the researchers found that when laser light pulses rapidly, light-sensing cells in the retina sometimes get a double hit of infrared energy. When that happens, the eye is able to detect light that falls outside the visible spectrum.

The findings are published Dec. 1 in the Proceedings of the National Academy of Sciences (PNAS) Online Early Edition. Collaborators include scientists in U.S., Poland, Switzerland and Norway. The research was initiated after scientists on the research team reported seeing occasional flashes of green light while working with an infrared laser. Unlike the laser pointers used in lecture halls or as toys, the powerful infrared laser the scientists worked with emits light waves thought to be invisible to the human eye.

Normally, a particle of light, called a photon, is absorbed by the retina, which then creates a molecule called a photopigment, which begins the process of converting light into vision. In standard vision, each of a large number of photopigments absorbs a single photon. But packing a lot of photons in a short pulse of the rapidly pulsing laser light makes it possible for two photons to be absorbed at one time by a single photopigment, and the combined energy of the two light particles is enough to activate the pigment and allow the eye to see what normally is invisible.

Although the researchers are the first to report that the eye can sense light through this mechanism, the idea of using less powerful laser light to make things visible isn’t new. The two-photon microscope, for example, uses lasers to detect fluorescent molecules deep in tissues. And the researchers said they already are working on ways to use the two-photon approach in a new type of ophthalmoscope, which is a tool that allows physicians to examine the inside of the eye. The idea is that by shining a pulsing, infrared laser into the eye, doctors might be able to stimulate parts of the retina to learn more about its structure and function in healthy eyes and in people with retinal diseases such as macular degeneration.

 
Nanotubes May Restore Sight to Blind Retinas PDF
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Ophthalmology and Optometry
Wednesday, 10 December 2014

The aging process affects everything from cardiovascular function to memory to sexuality. Most worrisome for many, however, is the potential loss of eyesight due to retinal degeneration.

New progress towards a prosthetic retina could help alleviate conditions that result from problems with this vital part of the eye. An encouraging new study published in Nano Letters describes a revolutionary novel device, tested on animal-derived retinal models, that has the potential to treat a number of eye diseases. The proof-of-concept artificial retina was developed by an international team led by Prof. Yael Hanein of Tel Aviv University (TAU)'s School of Electrical Engineering and head of the University's Center for Nanoscience and Nanotechnology and including researchers from TAU, the Hebrew University of Jerusalem, and Newcastle University.

The researchers combined semiconductor nanorods and carbon nanotubes to create a wireless, light-sensitive, flexible film that could potentially replace a damaged retina. The researchers tested the new device with chick retinas which were not yet light sensitive to prove that the artificial retina is able to induce neuronal activity in response to light.

Patients with age-related macular degeneration (AMD), which usually affects people age 60 or older who have damage to a specific part of the retina, will stand to benefit from the nanotube device if it is proved compatible in animals over the long term.

According to TAU doctoral student and research team member Dr. Lilach Bareket, there are already medical devices that attempt to treat visual impairment by sending sensory signals to the brain. While scientists are trying different approaches to develop an implant that can "see" light and send visual signals to a person's brain, to counter the effects of AMD and related vision disorders, many of these approaches require the use of metallic parts and cumbersome wiring or result in low resolution images. The researchers set out to make a more compact device.

"In comparison with other technologies, our new material is more durable, flexible, and efficient, as well as better able to stimulate neurons," said Prof. Hanein. "We hope our carbon nanotube and semiconductor nanorod film will serve as a compact replacement for damaged retinas."

"We are still far away from actually replacing the damaged retina," said Dr. Bareket. "But we have now demonstrated that this new material stimulates neurons efficiently and wirelessly with light. If you compare this to other devices based on silicon technology, which require wiring to outside energy or light sources, this is a groundbreaking new direction."

 
Australian Researchers Find New Laser Therapy Slows Down AMD PDF
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Ophthalmology and Optometry
Friday, 21 November 2014

AMDA new, low impact low energy laser treatment for patients with early age-related macular degeneration (AMD) has produced positive results by reducing indicators of the disease. Researchers from the University of Melbourne found unlike other laser treatments, this new faster laser did not result in damage to the retina, the sensitive light detecting tissue at the back of the eye.

Associate Professor Erica Fletcher from the Department of Anatomy and Neuroscience said this was the first report detailing how this new laser treatment may improve eye health in those with AMD. In the early stages, the disease is characterised by the presence of small fatty deposits called drusen and thickening in a membrane at the back of the eye.

Published in Journal of the Federation of American Societies for Experimental Biology (FASEB), the study explores how this laser may help in limiting retinal disease, showing that it improved the health of important supporting cells at the back of the eye.

"These findings suggest treating people with AMD with this new nanosecond laser reduces signs of the disease. Importantly, unlike other lasers currently used to treat eye disease, the nanosecond laser does not result in damage to the sensitive retina," she said.

The study also showed evidence that nanosecond laser treatment in one eye can also produce positive effects in the other untreated eye. This raises the possibility that monocular treatment may be sufficient to treat disease in both eyes. AMD affects one in seven people over the age of 50 with the incidence increasing in age. It is responsible for 48 per cent of severe vision loss in Australia with an estimated 17,700 new cases each year.

This research was conducted in collaboration with the Centre for Eye Research Australia (CERA) through the ongoing Laser intervention in Early Age-related macular Degeneration (LEAD) study. The laser is manufactured in Australia by Ellex.

 
DNA Sequencing Helps Identify Genetic Defects in Glaucoma PDF
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Ophthalmology and Optometry
Thursday, 20 November 2014

Scientists from the University of Liverpool have sequenced the mitochondrial genome in glaucoma patients to help further understanding into the genetic basis for the disease.

Glaucoma is a major cause of irreversible blindness, affecting more than 60 million people worldwide, increasing to an estimated 79.6 million people by 2020. It is thought that the condition has genetic origins and many experiments have shown that new sequencing approaches could help understand how the condition develops.

Studies on primary open-angle glaucoma – the most common form of glaucoma – have shown that mutations in mitochondria, the energy generating structures in all cells, could give valuable insight into how to prevent the disease.

Using new gene sequencing techniques, called massively parallel sequencing, the Liverpool team have produced data on the mitochondrial genome taken from glaucoma patients from around the world.

The impact that mitochondrial gene change has on disease progression has been difficult to fully determine as cells in the human body can contain mixtures of healthy and mutated mitochondrial genes. Using this new technology, however, the researchers aim to support the delivery of personalised medicines to identify drugs that will target mutated mitochondria.

Professor Colin Willoughby, from the University's Institute of Ageing and Chronic Disease, explains: "Understanding the genetic basis of glaucoma can direct care by helping to determine the patient’s clinical risk of disease progression and visual loss. Increasing evidence suggests that mitochondrial dysfunction results in glaucoma and drugs that target mitochondria may emerge as future therapeutic interventions. Further studies on larger glaucoma numbers of patients are required to firmly establish the link between genetic defects in the mitochondrial genome and glaucoma development. Our research, however, has demonstrated that massively parallel sequencing is a cost-effective approach to detect a wide spectrum of mitochondrial mutations and will improve our ability to understand glaucoma, identify patients at risk of the disease or visual loss and support the development of new treatments."

The research is published in Genetics Medicine and supported by the British Council for the Prevention of Blindness.

 
New Properties of Microbes That Cause Conjunctivitis Discovered PDF
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Ophthalmology and Optometry
Monday, 17 November 2014

streptococcus pneumoniaeScientists from Massachusetts Eye and Ear/Harvard Medical School Department of Ophthalmology have used the power of new genomic technology to discover that microbes that commonly infect the eye have special, previously unknown properties. These properties are predicted to allow the bacterium ― Streptococcus pneumoniae ― to specifically stick to the surface of the eye, grow, and cause damage and inflammation. Researchers are now using this information to develop new ways to treat and prevent this bacterium, which is becoming increasingly resistant to antibiotics. Their findings are published in the the paper, entitled "Unencapsulated Streptococcus pneumoniae from conjunctivitis encode variant traits and belong to a distinct phylogenetic cluster," and appeared in the Nov. 13 issue of issue of the prestigious international science journal, Nature Communications.

S. pneumoniae is a leading cause of infection and is responsible for diseases ranging from infection of the lungs, pneumonia, to infection of the brain, to infection of the surface of the eye known as conjunctivitis. Although infection of the eye can usually be safely treated, S. pneumoniae infection is a leading cause of illness and death worldwide.

According to Mass. Eye and Ear researcher Michael S. Gilmore, Ph.D., Sir William Osler Professor of Ophthalmology, Harvard Medical School, an effective vaccine is available that helps prevent many of the most severe types of infection. "I believe it is especially important for children and the elderly to be vaccinated. The vaccine causes the body to react to a slimy coating on the bacterial surface called a 'capsule.' The capsule allows S. pneumoniae to escape from white blood cells that try to eliminate it, and S. pneumoniae goes on to cause lung and other infections."

However, the strains of S. pneumoniae that cause eye infection have been known to lack this capsule, yet they still cause infection. "Because they lack the capsule, they are not affected by the vaccine either," he continued.

To design a better vaccine, and to understand how these 'unencapsulated' strains of S. pneumoniae are still able to cause infection of the ocular surface, the research team, spearheaded by postdoctoral researcher Michael Valentino and including Mass. Eye and Ear scientists Wolfgang Haas and Paulo Bispo, as well as a collaborative team from the Broad Institute of Harvard University and Massachusetts Institute of Technology, the U.S. Centers for Disease Control and Prevention, and elsewhere, examined the genomes of a large collection of S. pneumoniae strains collected from across the United States.  

 
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