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April 7, 2009, 5:26 AM CT

How the retina works: Like a multi-layered jigsaw puzzle

How the retina works: Like a multi-layered jigsaw puzzle
Each neuron in the retina views the world through a small, irregularly shaped window. These regions fit together like pieces of a puzzle, preventing "blind spot" and excessive overlap that could blur our perception of the world.

Credit: Image: Courtesy of Dr. Jeffrey Gauthier, Salk Institute for Biological Studies

About 1.25 million neurons in the retina -- each of which views the world only through a small jagged window called a receptive field -- collectively form the seamless picture we rely on to navigate our environment. Receptive fields fit together like pieces of a puzzle, preventing "blind spots" and excessive overlap that could blur our perception of the world, as per scientists at the Salk Institute for Biological Studies.

In the April 7 issue of the journal Public Library of Science, Biology, the researchers say their findings suggest that the nervous system operates with higher precision than previously appreciated and that apparent irregularities in individual cells may actually be coordinated and finely tuned to make the most of the world around us.

Previously, the observed irregularities of individual receptive fields suggested that the collective visual coverage might be uneven and irregular, potentially posing a problem for high-resolution vision. "The striking coordination we found when we examined a whole population indicated that neuronal circuits in the retina may sample the visual scene with high precision, perhaps in a manner that approaches the optimum for high-resolution vision," says senior author E.J. Chichilnisky, Ph.D., an associate professor in the Systems Neurobiology Laboratories.........

Posted by: Mike      Read more         Source


March 31, 2009, 3:15 PM CT

Vision therapy to combat vision problems

Vision therapy to combat vision problems
A young patient undergoes vision therapy at the University Eye Institute at the University of Houston.

Credit: University of Houston

You've probably been there. In a doctor's office, being advised to do what you dread exercise. You get that feeling in your gut, acknowledging that, indeed, you should exercise but probably won't. Now imagine that the doctor is your optometrist.

Don't clean your glasses. You read that right. Eye exercises are used to treat a variety of vision disorders, as per Dr. Janice Wensveen, clinical associate professor at the University of Houston's College of Optometry.

Patient reactions to this quite common prescription range between surprise and relief, she said, but doing the treatment can improve their performance at school and work.

"They're curious, particularly when we tell them, instead of putting a Band-Aid on it like we do with glasses or contact lenses, we're actually going to solve your problem. You're going to be cured, and that's something we don't very often do," she said.

The standard at-home prescription is known as "pencil push-up treatment," said Wensveen, who practices at the University Eye Institute's Vision Therapy Clinic in the Family Practice Service.

"Patients visually follow a small letter on a pencil as they moved the pencil closer to the nose. The goal is to be able to keep the letter clear and single until it touches your nose".........

Posted by: Mike      Read more         Source


March 30, 2009, 5:10 AM CT

Action video games improve vision

Action video games improve vision
This is a Pelli-Robson chart showing decreasing contrast from upper left to lower right. True contrast varies between monitors.
To learn whether high-action games could affect contrast sensitivity, Bavelier, in collaboration with graduate student Renjie Li and his colleagues Walt Makous, professor of brain and cognitive sciences at the University of Rochester, and Uri Polat, professor at the Eye Institute at Tel Aviv University, tested the contrast sensitivity function of 22 students, then divided them into two groups: One group played the action video games "Unreal Tournament 2004" and "Call of Duty 2." The second group played "The Sims 2," which is a richly visual game, but does not include the level of visual-motor coordination of the other group's games. The volunteers played 50 hours of their assigned games over the course of 9 weeks. At the end of the training, the students who played the action games showed an average 43% improvement in their ability to discern close shades of grayclose to the difference she had previously observed between game players and non-game playerswhereas the Sims players showed none.

"To the best of our knowledge, this is the first demonstration that contrast sensitivity can be improved by simple training," says Bavelier. "When people play action games, they're changing the brain's pathway responsible for visual processing. These games push the human visual system to the limits and the brain adapts to it, and we've seen the positive effect remains even two years after the training was over".........

Posted by: Mike      Read more         Source


February 26, 2009, 6:07 AM CT

Retinal "Dark Cells" Imagined

Retinal
A layer of "dark cells" in the retina that is responsible for maintaining the health of the light-sensing cells in our eyes has been imaged in a living retina for the first time.

The ability to see this nearly invisible layer could help doctors identify the onset of a number of diseases of the eye long before a patient notices symptoms. The findings are reported today's issue of Investigative Ophthalmology and Visual Science.

"Our goal is to figure out why macular degeneration, one of the most prevalent eye diseases, actually happens," says David Williams, director of the Center for Visual Science and professor in the Institute of Optics at the University of Rochester. "Macular degeneration affects one in 10 people over the age of 65, and as the average age of the U.S. population continues to increase, it is only going to get more and more common. We know these dark retinal cells are compromised by macular degeneration, and now that we can image them in the living eye, we might be able to detect the disease at a much earlier stage".

In 1997, Williams' team was the first to image individual photoreceptor cells in the living eye, using a technique called adaptive optics, which was borrowed from astronomers trying to get clearer images of stars. To image the dark cells behind the photoreceptors, however, Williams employed adaptive optics with a new method to make the dark cells glow brightly enough to be detected.........

Posted by: Mike      Read more         Source


January 30, 2009, 6:01 AM CT

How vision sends its message to the brain

How vision sends its message to the brain
Researchers have known for more than 200 years that vision begins with a series of chemical reactions when light strikes the retina, but the specific chemical processes have largely been a mystery. A team of scientists from the United States and Switzerland, have she new light on this process by "capturing" this chemical communication for future study. This research, reported in the February 2009 issue of The FASEB Journal (http://www.fasebj.org), may lead to the development of new therapys for some forms of blindness and vision disorders.

At the center of the discovery is the signaling of rhodopsin to transducin. Rhodopsin is a pigment in the eye that helps detect light. Transducin is a protein (sometimes called "GPCR") which ultimately signals the brain that light is present. The scientists were able to "freeze frame" the chemical communication between rhodopsin and transducin to study how this takes place and what goes wrong at the molecular level in certain disorders.

As per Krzysztof Palczewski, a senior scientist involved in the research, "The results may have important implications for discovery and development of more specific medicines to treat GPCR-linked dysfunction and disease." Examples of health problems involving GPCR dysfunction include blindness, diabetes, allergies, depression, cardiovascular defects and some forms of cancer.........

Posted by: Mike      Read more         Source


January 15, 2009, 7:08 PM CT

Eye injuries caused by paintballs

Eye injuries caused by paintballs
Paintballs can cause severe and 'visually devastating' eye injuries, particularly when used in unsupervised settings without proper eye protection, reports a study in the recent issue of the American Journal of Ophthalmology (www.AJO.com), published by Elsevier.

"Eye injuries secondary to high-velocity paintballs can cause tremendous damage to vital ocular structures often requiring extensive surgical intervention," comments Dr. Kyle J. Alliman of Bascom Palmer Eye Institute, University of Miami Miller School of Medicine. "Unfortunately, visual loss is often permanent".

Dr. Alliman and his colleagues analyzed the characteristics and outcomes of 36 patients treated for paintball injuries to the eye at Bascom Palmer Eye Institute between 1998 and 2005. The patients were mainly young men, average age 21 years.

The injuries were often quite severe, including rupture of the eyeball in 28 percent of patients and detached retina in 19 percent. Surgery was mandatory in 81 percent of patientsincluding eventual removal of the eye (enucleation) in 22 percent. Even when the eye was saved, a number of patients had permanent visual loss. Overall, near-normal vision (20/40 or better) was restored in only 36 percent of eyes.

All of the patients were injured when using paintballs in a "non-recreational, uncontrolled setting," as per Dr. Alliman. None of the injuries occurred in formal, sponsored event. In all but one of the 36 cases, the patient was not wearing any type of eye protection when the injury occurred.........

Posted by: Mike      Read more         Source


January 6, 2009, 7:32 PM CT

When do older drivers stop driving?

When do older drivers stop driving?
With 30 million drivers in the US aged 65 and over, we count on older Americans to recognize when they can no longer drive safely and decide that it's time to stay off the road. A newly released study finds that a decrease in vision function is a key factor in bringing about this decision.

The Salisbury Eye Evaluation and Driving Study (SEEDS), conducted by scientists affiliated with Johns Hopkins University, looked at changes in vision, cognition and the general health status of more than 1,200 licensed drivers aged 67-87 in Salisbury, MD, a community with limited public transportation. SEEDS is unique, in that the scientists performed comprehensive tests of both vision and cognitive function.

The results, recently published in Investigative Ophthalmology & Visual Science, reveal that after a year, 1.5 percent of the drivers had given up driving, and another 3.4 percent had restricted their driving. The most common predictors of stopping or decreasing driving were slow visual scanning, psychomotor speed and poor visuo-constructional skills, as well as reduced contrast sensitivity. (These skills are necessary to help drivers be aware of and respond to other cars, road conditions and road signs. Contrast sensitivity is the ability to detect detail in shades of gray; it is necessary for driving in poor weather and low lighting.)........

Posted by: Mike      Read more         Source


October 7, 2008, 10:50 PM CT

Atomic-resolution views suggest function of enzyme

Atomic-resolution views suggest function of enzyme
Iris of Eye with Model of GAF Domain

Image of the iris of researcher Clemens Heikaus' eye with a model of a GAF domain imbedded in the pupil. A messenger molecule binds to the GAF domain to regulate an enzyme, PDE6, that is central to the way light hitting the retina is converted to signals to the brain.

Credit: Brad Clifton
An atomic-resolution view of an enzyme found only in the eye has given scientists at the University of Washington (UW) clues about how this enzyme, essential to vision, is activated. The enzyme, phosphodiesterase 6 (PDE6), is central to the way light entering the retina is converted into a cascade of signals to the brain.

This particular form of the enzyme comes from the cone photoreceptors of the retina and has not been well-researched, in contrast to its rod form. Rods are involved in night vision and motion sensation; the cones are responsible for color sensitivity, visual acuity, daylight vision, and adjustment to bright light.

The section of the enzyme molecule that most interests the scientists is the so-called GAF A domain. A small messenger molecule, cGMP, binds to the GAF A domain to regulate the enzyme.

"The domain binds to this small molecule with extremely high sensitivity," said UW biochemist Clemens Heikaus, who along with Sergio E. Martinez, now a research associate at Rutgers, carried out the study. "From our structure, we can infer why it prefers cGMP over other messenger molecules." He added that the domain is quick in recognizing and responding to the messenger molecule to create an instantaneous flow of information to the brain.........

Posted by: Mike      Read more         Source


September 11, 2008, 9:25 PM CT

Rural HIV care has economic and health implications

Rural HIV care has economic and health implications
An Indiana University study observed that HIV care providers in rural Indiana report significant stigma and discrimination in the rural medical referral system surrounding issues of HIV and substance abuse. Providers felt that these factors impeded their ability to offer quality care to their patients.

"The findings of this study demonstrate inefficiencies in our public health care system and our inability to link people easily to a range of health care providers in rural areas," said Michael Reece, lead investigator of the study and director of The Center for Sexual Health Promotion in Indiana University Bloomington's School of Health, Physical Education and Recreation. "This also has an important economic impact given that our investments in the public health system may not be achieving the outcomes we need, such as improvements in health status."

While most studies involving HIV and stigma rely on patient perspectives, this study focused solely on the perspectives of providers serving rural Indiana residents. Providers reported that some rural physicians refused to provide care for their patients. They also reported widespread stigmatizing comments and behavior from the rural medical community.

The study, "HIV Provider Perspectives: The Impact of Stigma on Substance Abusers Living with HIV in a Rural Area of the United States," appears in the latest issue of the journal AIDS Patient CARE and STDs. For Reece, focusing research locally is important.........

Posted by: Mike      Read more         Source


September 11, 2008, 9:21 PM CT

Keeping nerve axons on target

Keeping nerve axons on target
When immature neurons are placed on a microscopic running track, where flanking lanes are carpeted with repellant factors, their growing axons remain in their lanes (top). Neurons from mice lacking p75 are unreceptive to repulsive cues: when placed on the track, their axons meander all over the field, crossing lanes and running down repellant-covered stripes (bottom).

Credit: Courtesy of Dr. Yoo-Shick Lim, Salk Institute for Biological Studies
Neurons constituting the optic nerve wire up to the brain in a highly dynamic way. Cell bodies in the developing retina sprout processes, called axons, which extend toward visual centers in the brain, lured by attractive cues and making U-turns when they take the wrong path. How they find targets so accurately is a central question of neuroscience today.

Using the mouse visual system, a team of Salk Institute for Biological Studies researchers led by Dennis O'Leary, Ph.D., identified an unanticipated factor that helps keep retinal axons from going astray. They report in the Sept. 11 issue of Neuron that p75, a protein previously known to regulate whether neurons live or die, leads a double life as an axon guidance protein.

"Historically, we thought that factors that mediate cell survival and those controlling axon guidance were part of two separate processes," says O'Leary, a professor in the Molecular Neurobiology Laboratory, "But in this study we show a direct interaction between these two systems".

Collaborating with Kuo-Fen Lee, Ph.D., professor in the Clayton Foundation Laboratories for Peptide Biology, the O'Leary team observed a defect in mice genetically engineered to lack p75. Through their synaptic connections, retinal axons develop a two-dimensional map of the retina in their targets in the brain. In the mice lacking p75, retinal axons stopped short of their final target and formed a map that was shifted forward to the superior colliculus, a major visual center in the brain.........

Posted by: Mike      Read more         Source



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