Vegetarian Diet Linked to Lower Cataract Risk

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Posted on 20th April 2011 by Pacific ClearVision Institute in Cataracts |General

NEW YORK (Reuters Health) Apr 08 – Eating less meat and more vegetables is tied to a lower risk of cataracts, a British study says.

In a large dietary survey that followed people for as long as 15 years, researchers found that about three in 50 meat eaters had cataracts, compared to about two in 50 vegans and vegetarians.

The results translated to a 30% to 40% lower cataract risk among vegetarians and vegans compared with the biggest meat eaters.

“People who don’t eat meat have a significantly lower risk of developing cataracts,” said Naomi Allen, an epidemiologist at the UK’s University of Oxford who coauthored the study.

The study does not prove that eating meat promotes cataracts. Instead, eating a lot of vegetables might be protective. Some past research has linked certain nutrients in plant foods to a lowered risk of cataracts. Or a vegetarian diet may simply be a sign of other healthy behaviors that contribute to the lowered risk.

The new findings actually contradict a study done in India, where a vegetarian diet was associated with high numbers of cataracts, said Dr. Jack Dodick, who chairs the department of ophthalmology at New York University Langone Medical Center.

“It means that still to this day we don’t know what influences cataracts. It may be more lifestyle. There may be other factors in causing cataract other than diet,” Dr. Dodick, who did not work on the current study, told Reuters Health.

The British researchers asked more than 27,600 people older than 40 to fill out dietary surveys between 1993 and 1999, then monitored the participants’ medical records between 2008 and 2009 to see if they developed cataracts. Almost 1,500 had cataracts during the follow-up period.

The highest risk was seen among the heaviest meat-eaters – those who consumed more than 100 g (3.5 ounces) of meat daily. Moderate meat eaters were only slightly less likely to develop cataracts. Fish eaters’ risk was 15% lower than that of the heavy meat eaters, vegetarians’ 30% lower and vegans’ 40% lower.

This study, published online March 23rd in the American Journal of Clinical Nutrition, was well done, Dr. Dodick said, but there are “still a lot of questions that need to be answered.”

Whether nutrition really plays a role in cataract risk is still not clear cut, he said.

It’s generally accepted that if you live long enough everyone will develop a cataract, Dr. Dodick added.

“It’s the most performed operation in the U.S.,” he said. “Approximately 3.5 million cataract surgeries are performed a year.”

To decrease the probability of early onset cataracts, “the top of my list would be always protect eyes against ultraviolet rays when outdoors” Dr. Dodick said.

“The moral of the story is, live life in moderation,” Dr. Dodick added. “A healthy active lifestyle with exercise might decrease the risk of cataracts.”

Vitamin D may protect against early AMD in women

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Posted on 18th April 2011 by Pacific ClearVision Institute in General |Retina

High concentrations of serum 25-hydroxyvitamin D may protect against early age-related macular degeneration in women younger than 75 years, according to a large observational study.

“Inflammation is thought to be involved in the pathogenesis of AMD. Vitamin D, because of its anti-inflammatory, immune-modulating properties, may suppress the cascade of destructive inflammation that occurs at the level of the retinal pigment epithelium-choroid interface in early stages of AMD,” the authors said.

The Carotenoids in Age-Related Eye Disease Study (CAREDS) included 1,313 women aged 50 to 79 years who were enrolled in the multicenter Women’s Health Initiative Observational Study (WHIOS).

Researchers evaluated samples from serum 25(OH)D assays, which reflect vitamin D exposure from food, supplements and sunlight. Stereoscopic fundus photographs determined early AMD status in 241 subjects.

Although multivariate models did not reveal a significant relationship between early AMD and 25(OH)D, there was a significant age interaction (P =.002) that suggested a selective mortality bias in older women, the study found.

Serum 25(OH)D decreased the odds of early AMD in 968 women younger than 75 years (P = .02) and increased the odds in 319 women older than 74 years (P = .05). Adjusting for body mass index and physical activity, which are predictors of 25(OH)D, attenuated the association in the younger age group.

Multivariate models also revealed that oral intake of vitamin D decreased the odds of AMD in subjects younger than 75 years, but direct sunlight exposure did not.

According to the authors, a prospective study is needed to confirm the association between vitamin D and AMD, and to understand how vitamin D and genetic and lifestyle factors could affect early AMD risk.

How Do Neurons in the Retina Encode What We ‘See’?

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Posted on 18th April 2011 by Pacific ClearVision Institute in General |Retina

The moment we open our eyes, we perceive the world with apparent ease. But the question of how neurons in the retina encode what we “see” has been a tricky one. A key obstacle to understanding how our brain functions is that its components — neurons — respond in highly nonlinear ways to complex stimuli, making stimulus-response relationships extremely difficult to discern.

Now a team of physicists at the Salk Institute for Biological Studies has developed a general mathematical framework that makes optimal use of limited measurements, bringing them a step closer to deciphering the “language of the brain.” The approach, described in the current issue of the Public Library of Science, Computational Biology, reveals for the first time that only information about pairs of temporal stimulus patterns is relayed to the brain.

“We were surprised to find that higher-order stimulus combinations were not encoded, because they are so prevalent in our natural environment,” says the study’s leader Tatyana Sharpee, Ph.D., an assistant professor in the Computational Neurobiology Laboratory and holder of the Helen McLorraine Developmental Chair in Neurobiology. “Humans are quite sensitive to changes in higher-order combinations of spatial patterns. We found it not to be the case for temporal patterns. This highlights a fundamental difference in the spatial and temporal aspects of visual encoding.”

The human face is a perfect example of a higher-order combination of spatial patterns. All components — eyes, nose, mouth — have very specific spatial relationships with each other, and not even Picasso, in his Cubist period, could throw the rules completely overboard.

Our eyes take in the visual environment and transmit information about individual components, such as color, position, shape, motion and brightness to the brain. Individual neurons in the retina get excited by certain features and respond with an electrical signal, or spike, that is passed on to visual centers in the brain, where information sent by neurons with different preferences is assembled and processed.

For simple sensory events — like turning on a light, for example — the brightness correlates well with the spike probability in a luminance-sensitive cell in the retina. “However, over the last decade or so, it has become apparent that neurons actually encode information about several features at the same time,” says graduate student and first author Jeffrey D. Fitzgerald.

“Up to this point, most of the work has been focused on identifying the features the cell responds to,” he says. “The question of what kind of information about these features the cell is encoding had been ignored. The direct measurements of stimulus-response relationships often yielded weird shapes, and people didn’t have a mathematical framework for analyzing it.”

To overcome those limitations, Fitzgerald and colleagues developed a so-called minimal model of the nonlinear relationships of information processing systems by maximizing a quantity that is referred to as noise entropy. The latter describes the uncertainty about a neuron’s probability to spike in response to a stimulus.

When Fitzgerald applied this approach to recordings of visual neurons probed with flickering movies, which co-author Lawrence Sincich and Jonathan Horton at the University of California, San Francisco, had made, he discovered that on average, first-order correlations accounted for 78 percent of the encoded information, while second-order correlations accounted for more than 92 percent. Thus, the brain received very little information about correlations that were higher than second order.

“Biological systems across all scales, from molecules to ecosystems, can all be considered information processors that detect important events in their environment and transform them into actionable information,” says Sharpee. “We therefore hope that this way of ‘focusing’ the data by identifying maximally informative, critical stimulus-response relationships will be useful in other areas of systems biology.”

The work was funded in part by the National Institutes of Health, the Searle Scholar Program, The Alfred P. Sloan Fellowship, the W.M. Keck Research Excellence Award and the Ray Thomas Edwards Career Development Award in Biomedical Sciences.

Vision Loss in Eye Disease Slowed Using Novel Encapsulated Cell Therapy

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Posted on 18th April 2011 by Pacific ClearVision Institute in General |Retina

A phase 2 clinical trial for the treatment of a severe form of age-related macular degeneration called geographic atrophy (GA) has become the first study to show the benefit of a therapy to slow the progression of vision loss for this disease. The results highlight the benefit of the use of a neurotrophic factor to treat GA and provide hope to nearly one million Americans suffering from GA.

The multi-center research team, including Kang Zhang, MD, PhD, of the University of California, San Diego, Shiley Eye Center, the lead author of the paper and one of the leading investigators in the study, found that long-term delivery of ciliary neurotrophic factor (CNTF) served to re-nourish the retina and stop or slow the loss of visual acuity caused by the disorder. The results were recently published online in the Proceedings of National Academy of Sciences (PNAS).

According to Zhang — professor of ophthalmology and human genetics at the UCSD School of Medicine and director of UCSD’s Institute of Genomic Medicine — there is currently no effective treatment for dry AMD or GA, though there is a very big need. “This could open the door to long-term treatment of dry AMD, using a simple surgical procedure.”

Age-related macular degeneration, or AMD, is a leading cause of vision loss in Americans age 60 and older. It is a disease that causes cells in the macula — the part of the eye that allows us to see in fine detail — to die. There are two forms of the disorder, wet and dry AMD. GA is considered the end stage of dry AMD, where central vision is lost.

According to the National Eye Institute, wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula. These new blood vessels tend to be very fragile and often leak blood and fluid. The blood and fluid raise the macula from its normal place at the back of the eye, resulting in rapid loss of central version. There is currently a very effective therapy for wet AMD. Dry AMD occurs when the light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye.

In the trial, high-dose CNTF was delivered to 27 GA patients using encapsulated cell therapy (ECT). Another 24 patients received either a sham surgery (12) or a low-dose of CNTF (12). CNTF affects survival and differentiation of cells in the nervous system, including retinal cells. CNTF has been shown to retard the loss of photoreceptor cells in many animal models of retinal degeneration.

The ECT utilized a capsule that contains genetically engineered cells to continuously produce CNTF over a 12-month period. The CNTF-secreting capsule was implanted in the back of the study subject’s eye. The implant allows the CNTF molecules to diffuse into the eye tissue, while keeping out antibodies and immune cells that would attack and destroy the CNTF-producing cells.

There was a statistically significant difference in the change of the total macular volume in the eyes of study participants at the 12-month point, versus baseline in the high-dose group, according to Zhang. “In addition, all but one of the patients in the high dose group, or 96.3 percent, maintained stabilized vision, compared to only 75% of the patients in the sham-treatment group.”

The patients treated with a high dose of CNTF also showed an increase in retinal thickness as early as four months after implant, an increase that correlated to the stabilization of vision.

Additional contributors to the study included Jill J. Hopkins, Retina-Vitreous Associates Medical Group, Los Angeles; Jeffrey S. Heier, Ophthalmic Consultants of Boston; David G. Birch, Retina Foundation of the Southwest, Dallas; Lawrence S. Halperin, Retina Group of Florida, Ft. Lauderdale; Thomas A. Albini, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine; David M. Brown, Retina Consultants of Houston, Houston; Glenn J. Jaffe, Duke University Eye Center; Weng Tao, Neurotech USA, Lincoln, RI; and George A. Williams, Beaumont Eye Institute, Royale Oak, MI.

Zhang’s research is supported by the National Eye Institute, National Institutes of Health; the Macula Vision Research Foundation; Burroughs Wellcome Fund; Research to Prevent Blindness, Lew Wasserman Merit Award and Senior Investigator Award; and the Chinese National 985 Project to Sichuan University and West China Hospital.