Chapter 7. Vision: From Eye to Brain
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By Angus Chen Jumping spiders are the disco dancers of the arachnid world. The males thump and throb their brightly patterned legs and abdomens at the ladies like in the video above. Yet most of these bright colors should be impossible for the arachnids to see. That’s because their eyes have only two types of color-sensitive cone cells, which are designed to detect just ultraviolet and green light. Now, researchers report today in Current Biology that the North American genus of jumping spiders sees extra colors via a small, thin layer of red-pigmented cells partially covering the center of their retinas. The layer acts as a filter, allowing only red light to pass through and activate retinal cells just below the layer. This essentially converts a few of their green-sensitive cells into red-sensitive cells, allowing the spiders to build palates from three colors much the same way humans do—we have blue, green, and red cone cells. These jumping spiders have some limitations, though. Because their red filter is a small dot over the center of their retinas, they can see red only if they look directly at it. And because the filter blocks out any light that’s not red, anything that they look at has to be pretty bright before they can see any redness on it. Luckily for them, they like to spend time dancing in the sun. © 2015 American Association for the Advancement of Science
Link ID: 20947 - Posted: 05.19.2015
By Tina Hesman Saey A man who had been blind for 50 years allowed scientists to insert a tiny electrical probe into his eye. The man’s eyesight had been destroyed and the photoreceptors, or light-gathering cells, at the back of his eye no longer worked. Those cells, known as rods and cones, are the basis of human vision. Without them, the world becomes gray and formless, though not completely black. The probe aimed for a different set of cells in the retina, the ganglion cells, which, along with the nearby bipolar cells, ferry visual information from the rods and cones to the brain. No one knew whether those information-relaying cells still functioned when the rods and cones were out of service. As the scientists sent pulses of electricity to the ganglion cells, the man described seeing a small, faint candle flickering in the distance. That dim beacon was a sign that the ganglion cells could still send messages to the brain for translation into images. That 1990s experiment and others like it sparked a new vision for researcher Zhuo-Hua Pan of Wayne State University in Detroit. He and his colleague Alexander Dizhoor wondered if, instead of tickling the cells with electricity, scientists could transform them to sense light and do what rods and cones no longer could. The approach is part of a revolutionary new field called optogenetics. Optogeneticists use molecules from algae or other microorganisms that respond to light or create new molecules to do the same, and insert them into nerve cells that are normally impervious to light. By shining light of certain wavelengths on the molecules, researchers can control the activity of the nerve cells. © Society for Science & the Public 2000 - 2015
Link ID: 20938 - Posted: 05.16.2015
by Rachel Ehrenberg It was the dress that launched a million tweets. In February, a mother-in-law-to-be sent a picture of a dress she was considering wearing to her daughter’s Grace’s wedding to Grace and her fiancé. The couple couldn’t agree on the dress’s color: was it blue and black or white and gold? (White and gold, obviously.) The disagreement prompted the daughter to post the picture on social media, recruiting other opinions. That post caused such a stir that BuzzFeed picked it up, asking the masses to weigh in. And then the Internet went haywire. Within a few days, the original BuzzFeed article had more than 37 million hits. Serious news outlets interviewed neuroscientists and psychologists about color perception and optical illusions. Bevil Conway, a neuroscientist at Wellesley College, was one of those scientists. At the time, he thought the hullabaloo was interesting mostly because it showed how passionately people feel about color (as in, insanely riled-up and deeply offended by alternative views). He joked with NPR’s Robert Siegel, off air, that the story was “fluff,” Conway told me. Well, there’s nothing like a little research to turn fluff into gold (or blue or black). Conway, coauthor of a study appearing online May 14 in Current Biology that explores people’s perceptions of the dress, now calls the phenomenon “profound.” “I think it will go down as one of the most important discoveries in color vision in the last 10 years,” Conway says. “And all because of a crazy photograph.” In those February interviews, Conway (and some other scientists) explained the disparity of opinions on the dress in terms of “color constancy,” a feature of perception that allows us to identify colors under different lighting conditions. If we see a red poisonous snake or a red delicious apple, we need to be able to identify it as red (and dangerous or delicious), whether in bright sunlight or the gloom of clouds. © Society for Science & the Public 2000 - 2015
Link ID: 20937 - Posted: 05.16.2015
By C. CLAIBORNE RAY Q. I heard that people can’t look at a color in one room and then pick it out of a set of similar colors in the next room. But there are people with perfect pitch, so are there people with “perfect hue”? A. “The short answer is no,” said Mark D. Fairchild, director of the program of color science at the Munsell Color Science Laboratory of Rochester Institute of Technology. “Color is almost always judged relative to other colors,” Dr. Fairchild said, and the human ability to remember colors over any period of time, or even from room to room, is extremely poor. “Based on memory alone, we can probably reliably identify tens of colors, with some people perhaps able to study hard and get up to a hundred or so,” he said. “If we were to learn a systematic way to scale colors, we might be able to get up to several hundred.” If colors are compared side by side, however, “then we can easily distinguish several thousand colors, and some estimate more than a million,” Dr. Fairchild said. Such ability is somewhat analogous to differentiating tones in hearing, he said. Almost everyone can distinguish tones when they are compared in close succession, he said, but only a very small percentage of people have what is called perfect pitch or absolute pitch: the ability to recall and identify tones after a considerable period of time, without a reference tone for comparison. “Unfortunately, color appearance seems to be even more difficult to remember,” Dr. Fairchild said, “to the point that we don’t speak of anyone as having perfect hue.” © 2015 The New York Times Company
Link ID: 20916 - Posted: 05.13.2015
by Bethany Brookshire Certain images conjure up intense emotion: crying children, a bloody face, a snake rearing for a strike. When people take in pictures that hold deep meaning for them, they actually see the images more vividly. For them, emotion gives the world an extra burst of Technicolor and increases the odds that they will remember the scene. But the amount of visual boost — called emotionally enhanced vividness — varies from person to person. Some of this variability is in our genes, a new study finds, suggesting that people really do see the world in different ways. Many of us are familiar with the chemical messenger norepinephrine as a stress chemical. But it doesn’t just dictate whether we fight or flee, says Rebecca Todd, a cognitive neuroscientist at the University of British Columbia in Vancouver. Norepinephrine is also very important for emotional memory. “It’s important in the initial perception of emotional stimuli,” she explains. “It weighs down emotional memories so they burn brighter.” Norepinephrine is produced in an area of the brain called the locus coeruleus. In an ideal system, the cells in this area produce norepinephrine in response to a signal such as stress. The norepinephrine signals pass to other areas of the brain, but some chemical messenger remains, binding to receptors called alpha2b adrenoreceptors on cells in the locus coeruleus. These adrenoreceptors act as a brake, stopping the production of norepinephrine before things get out of hand. The receptors are produced by the gene ADRA2b. But a substantial proportion of Europeans and Africans have a variation on ADRA2b that deletes the alpha2b adrenoreceptor, possibly cutting some of the wires on the norepinephrine brakes. People with this deletion had stronger memories of emotionally charged events, a 2007 study found. Todd and graduate student Mana Ehlers wanted to see if this deletion might affect how people perceived emotional images. © Society for Science & the Public 2000 - 2015.
by Laura Sanders On a test of visual perception, children with autism perceive moving dots with more clarity than children without the disorder. The results, published in the May 6 Journal of Neuroscience, reveal a way in which children with autism see the world differently. When asked to determine the overall direction of a mess of dots moving in slightly different directions, children with autism outperformed children without the disorder. Other tests of motion detection didn’t turn up any differences. The results suggest that children with autism may be taking in and combining more motion information than children without autism, says study coauthor Catherine Manning of the University of Oxford. This heightened ability may contribute to feelings of sensory overload, the researchers suggest. © Society for Science & the Public 2000 - 2015
By Jocelyn Kaiser One of the most heralded successes of gene therapy may not be the permanent fix that many had hoped. Leaders of two clinical trials report this week that a treatment that restored some vision to blind patients begins to fade within a few years. A third group, however, says their patients, who received a different version of the therapy, are retaining their improved vision, and a company is moving ahead with efforts to gain regulatory approval for their treatment. It is not a huge surprise that the treatment effects may not last, says eye disease researcher Mark Pennesi of Oregon Health & Science University in Portland, who is running a similar trial. “These are complex diseases and everything that’s been done is sort of first generation,” he says. “The fact that there was biological activity at all is a milestone.” At issue is gene therapy for a rare form of inherited blindness known as Leber’s congenital amaurosis (LCA) that results in complete vision loss by about age 40. About 10% of cases are due to a mutation in retinal pigment epithelium 65 (RPE65), a gene that codes for an enzyme that helps retinal cells make rhodopsin. The pigment is needed by photoreceptor cells—the retina’s light-sending rods and cones—and when RPE65 is mutated, the photoreceptor cells gradually die. In 2007, in the first-ever effort to use gene therapy to treat people with blindness, three separate teams in the United States and the United Kingdom launched clinical trials for the RPE65 type of LCA. A surgeon injected one eye of each patient with a solution containing a harmless virus that ferried a good copy of RPE65 into retinal cells. © 2015 American Association for the Advancement of Science
Link ID: 20892 - Posted: 05.05.2015
By Gretchen Vogel BERLIN—A German neuroscientist who has been the target of animal rights activists says he is giving up on primate research. Nikos Logothetis, a director at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, says he will conclude his current experiments on macaques “as quickly as possible” and then shift his research to rodent neural networks. In a letter last week to fellow primate researchers, Logothetis cites a lack of support from colleagues and the wider scientific community as key factors in his decision. In particular, he says the Max Planck Society—and other organizations—should pursue criminal charges against the activists who target researchers. Logothetis’s research on the neural mechanisms of perception and object recognition has used rhesus macaques with electrode probes implanted in their brains. The work was the subject of a broadcast on German national television in September that showed footage filmed by an undercover animal rights activist working at the institute. The video purported to show animals being mistreated. Logothetis has said the footage is inaccurate, presenting a rare emergency situation following surgery as typical and showing stress behaviors deliberately prompted by the undercover caregiver. (His written rebuttal is here.) The broadcast triggered protests, however, and it prompted several investigations of animal care practices at the institute. Investigations by the Max Planck Society and animal protection authorities in the state of Baden-Württemberg found no serious violations of animal care rules. A third investigation by local Tübingen authorities that led to a police raid at the institute in late January is still ongoing. © 2015 American Association for the Advancement of Science.
by Andy Coghlan These neon cells may be blinding, but targeting them could also help preserve sight. In this close-up image of blood vessels – shown in blue – that supply blood to the retina of a one-week-old mouse, the nuclei of cells lining their walls appear in fluorescent colours. The bright-yellow cells are the ones of interest: they could be targeted to help prevent blindness in ageing eyes. Age-related macular degeneration, or AMD, often strikes in middle age, causing a person's vision to deteriorate. A key driver of the disease is excessive growth of obtrusive blood vessels in the retina. A team led by Alain Chédotal of the Institute of Vision in Paris has now discovered that a protein called Slit2 contributes to the rapid increase in offending blood vessels. The yellow cells in the picture are the ones that are dividing. When this activity occurs in middle age, it triggers the excessive increase in blood vessels that results in AMD. By blocking Slit2, it might be possible to reduce this effect, says Chédotal. When the team genetically altered mice so that they couldn't produce Slit2, the animals no longer overproduced the blood vessels that lead to blindness. The researchers think that drugs targeting Slit2 could generate new treatments for AMD. © Copyright Reed Business Information Ltd
Link ID: 20839 - Posted: 04.23.2015
By LISA FELDMAN BARRETT and JOLIE WORMWOOD THE Justice Department recently analyzed eight years of shootings by Philadelphia police officers. Its report contained two sobering statistics: Fifteen percent of those shot were unarmed; and in half of these cases, an officer reportedly misidentified a “nonthreatening object (e.g., a cellphone) or movement (e.g., tugging at the waistband)” as a weapon. Many factors presumably contribute to such shootings, ranging from carelessness to unconscious bias to explicit racism, all of which have received considerable attention of late, and deservedly so. But there is a lesser-known psychological phenomenon that might also explain some of these shootings. It’s called “affective realism”: the tendency of your feelings to influence what you see — not what you think you see, but the actual content of your perceptual experience. Affective realism illustrates a common misconception about the working of the human brain. In everyday life, your brain seems to be a reactive organ. You stroll past a round red object in the produce section of a supermarket and react by reaching for an apple. A police officer sees a weapon and reacts by raising his gun. Stimulus is followed by response. But the brain doesn’t really work this way. The brain is a predictive organ. A majority of your brain activity consists of predictions about the world — thousands of them at a time — based on your past experience. These predictions are not deliberate prognostications like “the Red Sox will win the World Series,” but unconscious anticipations of every sight, sound and other sensation you might encounter in every instant. These neural “guesses” largely shape what you see, hear and otherwise perceive. © 2015 The New York Times Company
By Chris Cesare The beautiful color of a sunset might be more than just a pretty picture. It could be a signal to our bodies that it’s time to reset our internal clock, the biological ticktock that governs everything from sleep patterns to digestion. That’s the implication of a new study in mice that shows these small rodents use light’s changing color to set their own clocks, a finding that researchers expect will hold for humans, too. “I think this work opens up how we're just starting to scratch the surface and look at the environmental adaptations of clocks,” says Carrie Partch, a biochemist at the University of California, Santa Cruz, who was not involved in the new study. Scientists have long known about the role light plays in governing circadian rhythms, which synchronize life’s ebb and flow with the 24-hour day. But they weren’t sure how different properties of light, such as color and brightness, contributed to winding up that clock. “As a sort of common sense notion people have assumed that the clock somehow measures the amount of light in the outside world,” says Tim Brown, a neuroscientist at the University of Manchester in the United Kingdom and an author of the new study. “Our idea was that it might be doing something more sophisticated than that.” To find out, Brown and his colleagues targeted an area in the brain called the suprachiasmatic nucleus, or SCN, a region common to all vertebrates. It’s where the body keeps time using chemical and electrical rhythms that last, on average, 24 hours. The team wanted to know if color signals sent from the eyes reached the SCN and whether that information affected the timing of the clock. © 2015 American Association for the Advancement of Science
By Jonathan Webb Science reporter, BBC News Living in total darkness, the animals' eyes have disappeared over millions of years A study of blind crustaceans living in deep, dark caves has revealed that evolution is rapidly withering the visual parts of their brain. The findings catch evolution in the act of making this adjustment - as none of the critters have eyes, but some of them still have stumpy eye-stalks. Three different species were studied, each representing a different subgroup within the same class of crustaceans. The research is published in the journal BMC Neuroscience. The class of "malocostracans" also includes much better-known animals like lobsters, shrimps and wood lice, but this study focussed on three tiny and obscure examples that were only discovered in the 20th Century. It is the first investigation of these mysterious animals' brains. "We studied three species. All of them live in caves, and all of them are very rare or hardly accessible," said lead author Dr Martin Stegner, from the University of Rostock in Germany. Specifically, his colleagues retrieved the specimens from the coast of Bermuda, from Table Mountain in South Africa, and from Monte Argentario in Italy. One of the species was retrieved from caves on the coast of Bermuda The animals were preserved rather than living, so the team could not observe their tiny brains in action. But by looking at the physical shape of the brain, and making comparisons with what we know about how the brain works in their evolutionary relatives, the researchers were able to assign jobs to the various lobes, lumps and spindly structures they could see under the microscope. © 2015 BBC.
By Kate Galbraith Most evenings, before watching late-night comedy or reading emails on his phone, Matt Nicoletti puts on a pair of orange-colored glasses that he bought for $8 off the Internet. “My girlfriend thinks I look ridiculous in them,” he said. But Mr. Nicoletti, a 30-year-old hospitality consultant in Denver, insists that the glasses, which can block certain wavelengths of light emitted by electronic screens, make it easier to sleep. Studies have shown that such light, especially from the blue part of the spectrum, inhibits the body’s production of melatonin, a hormone that helps people fall asleep. Options are growing for blocking blue light, though experts caution that few have been adequately tested for effectiveness and the best solution remains avoiding brightly lit electronics at night. A Swiss study of 13 teenage boys, published in August in The Journal of Adolescent Health, showed that when the boys donned orange-tinted glasses, also known as blue blockers and shown to prevent melatonin suppression, in the evening for a week, they felt “significantly more sleepy” than when they wore clear glasses. The boys looked at their screens, as teenagers tend to do, for at least a few hours on average before going to bed, and were monitored in the lab. Older adults may be less affected by blue light, experts say, since the yellowing of the lens and other changes in the aging eye filter out increasing amounts of blue light. But blue light remains a problem for most people, and an earlier study of 20 adults ages 18 to 68 found that those who wore amber-tinted glasses for three hours before bed improved their sleep quality considerably relative to a control group that wore yellow-tinted lenses, which blocked only ultraviolet light. Devices such as smartphones and tablets are often illuminated by light-emitting diodes, or LEDs, that tend to emit more blue light than incandescent products. Televisions with LED backlighting are another source of blue light, though because they are typically viewed from much farther away than small screens like phones, they may have less of an effect, said Debra Skene, a professor of neuroendocrinology at the University of Surrey in England. © 2015 The New York Times Company
By Jan Hoffman As adults age, vision deteriorates. One common type of decline is in contrast sensitivity, the ability to distinguish gradations of light to dark, making it possible to discern where one object ends and another begins. When an older adult descends a flight of stairs, for example, she may not tell the edge of one step from the next, so she stumbles. At night, an older driver may squint to see the edge of white road stripes on blacktop. Caught in the glare of headlights, he swerves. But new research suggests that contrast sensitivity can be improved with brain-training exercises. In a study published last month in Psychological Science, researchers at the University of California, Riverside, and Brown University showed that after just five sessions of behavioral exercises, the vision of 16 people in their 60s and 70s significantly improved. After the training, the adults could make out edges far better. And when given a standard eye chart, a task that differed from the one they were trained on, they could correctly identify more letters. “There’s an idea out there that everything falls apart as we get older, but even older brains are growing new cells,” said Allison B. Sekuler, a professor of psychology, neuroscience and behavior at McMaster University in Ontario, who was not involved in the new study. “You can teach an older brain new tricks.” The training improved contrast sensitivity in 16 young adults in the study as well, although the older subjects showed greater gains. That is partly because the younger ones, college students, already had reasonably healthy vision and there was not as much room for improvement. Before the training, the vision of each adult, young and older, was assessed. The exercises were fine-tuned at the beginning for each individual so researchers could measure improvements, said Dr.G. John Andersen, the project’s senior adviser and a psychology professor at the University of California, Riverside. © 2015 The New York Times Company
by Andy Coghlan Who needs sight to get around when you've got a digital compass in your head? A neuroprosthesis that feeds geomagnetic signals into the brains of blind rats has enabled them to navigate around a maze. The results demonstrate that the rats could rapidly learn to deploy a completely unnatural "sense". It raises the possibility that humans could do the same, potentially opening up new ways to treat blindness, or even to provide healthy people with extra senses. "I'm dreaming that humans can expand their senses through artificial sensors for geomagnetism, ultraviolet, radio waves, ultrasonic waves and so on," says Yuji Ikegaya of the University of Tokyo in Japan, head of the team that installed and tested the 2.5-gram implant. "Ultrasonic and radio-wave sensors may enable the next generation of human-to-human communicationMovie Camera," he says. The neuroprosthesis consists of a geomagnetic compass – a version of the microchip found in smartphones – and two electrodes that fit into the animals' visual cortices, the areas of the brain that process visual information. Whenever the rat positioned its head within 20 degrees either side of north, the electrodes sent pulses of electricity into its right visual cortex. When the rat aligned its head in a southerly direction, the left visual cortex was stimulated. The stimulation allowed blind rats to build up a mental map of their surroundings without any visual cues. During training, blind rats equipped with digital compasses improved at finding food rewards in a five-pronged maze, despite being released from one of three different arms of the maze at random each time. © Copyright Reed Business Information Ltd
Jon Hamilton A biotech company and two scientists hope to change that. On Wednesday, Avalanche Biotechnologies in Menlo Park and the University of Washington in Seattle announced a licensing agreement to develop the first treatment for colorblindness. The deal brings together a gene therapy technique developed by Avalanche with the expertise of vision researchers at the University of Washington. "Our goal is to be treating colorblindness in clinical trials in patients in the next one to two years," says Thomas Chalberg, the founder and CEO of Avalanche. Dalton the squirrel monkey during the color vision test. i Dalton the squirrel monkey during the color vision test. Courtesy of Neitz Laboratory The agreement has its roots in a scientific breakthrough that occurred six years ago. That's when two vision researchers at the University of Washington used gene therapy to cure a common form of colorblindness in squirrel monkeys. "This opened the possibility of ultimately getting this to cure colorblindness in humans," says Jay Neitz, who runs the Color Vision Lab at UW along with his wife, Maureen Neitz. The couple knew that transferring their success from monkey to man would be a challenge. But they were determined, says Maureen Neitz. "We've spent our entire careers writing NIH grants where we say our goal is to improve human health." © 2015 NPR
Link ID: 20725 - Posted: 03.26.2015
By Rachel Feltman I'm not usually one for heartstring-tugging ads, but this collaboration between Valspar Paint and EnChroma, a company that makes color-boosting sunglasses for the color-blind, is pretty cool. And the coolest thing about the glasses in the above video is that they weren't designed to help the color-blind at all. Smithsonian Magazine reports that EnChroma Labs founder Don McPherson (a materials scientist) had originally engineered the glasses with surgeons in mind. The lenses contained rare earth iron and absorbed a ton of light to protect surgeons performing laser eye surgery. The boosted absorption also made colors pop more vibrantly, allowing them to more easily distinguish among different tissues during surgery. But the stellar eye protection and vibrant colors meant that many surgeons wanted to wear them outside the operating room. McPherson himself started using them as regular sunglasses. And when a color-blind friend tried them on, he was amazed: He could distinguish orange traffic cones from the grass and pavement around them. He was perceiving color in a way he never had before. Now EnChroma sells the glasses (which have been specifically tailored for color blindness since the accidental discovery) for a few hundred bucks a pop. McPherson explains that all people have three photopigments in the eye, also known as cones, which are sensitive to blue, green and red. Blue operates fairly independently, while the red and green cones, in most humans, overlap, affecting the perception of certain colors. For example, if 10 photons landed on the red cone and 100 landed on the green cone, the object viewed would appear more green. Whereas if an equal number of photons landed on the red and green cones, the color perceived would be yellow.
Link ID: 20720 - Posted: 03.25.2015
|By Susana Martinez-Conde and Stephen L. Macknik All visual art is illusory in that it involves a departure from reality, a filtering through the mind of the artist. This subjectivity applies not only to abstract works but also to representational art, in which the artist translates his or her perception into a physical object capable of inducing a similar perception in the viewer. Painters render the three-dimensional world on a flat surface. These representations are enough to suspend our visual system's disbelief and trigger barrages of neuronal firing that become visions of bathers, bridges and water lilies. It is never about reality but about how the artist sees and wants to portray it. This artistic vision is a mishmash of expectations, memories, assumptions, imagination and intent. It is also, in a sense, a reflection of neural shortcuts and basic visual processes. The picture becomes even more complicated when painters suffer from pathologies of the eyes or brain that force them to see their surroundings in ways that diverge from standard experience. The artwork produced by such artists allows us to participate in their perception—and misperception—of the world. For example, failing vision can translate into an eerie loss of precision and detail in paintings. The pictures of American artist Georgia O'Keeffe became flatter and less intricate as she developed bilateral age-related macular degeneration, a retinal disease that affects central, high-resolution vision. The later works of American painter Mary Cassatt similarly show an uncharacteristic absence of delicacy in faces as she developed cataracts. French impressionist Claude Monet also had cataracts, which rendered his paintings imprecise and muted in color. After he underwent successful cataract surgery, his paintings regained definition and vibrancy. As the examples in this column attest, the effects of vision or brain diseases can sometimes be traced in great works of art. © 2015 Scientific American
Link ID: 20710 - Posted: 03.24.2015
Elie Dolgin The southern city of Guangzhou has long held the largest eye hospital in China. But about five years ago, it became clear that the Zhongshan Ophthalmic Center needed to expand. More and more children were arriving with the blurry distance vision caused by myopia, and with so many needing eye tests and glasses, the hospital was bursting at the seams. So the centre began adding new testing rooms — and to make space, it relocated some of its doctors and researchers to a local shopping mall. Now during the summer and winter school holidays, when most diagnoses are made, “thousands and thousands of children” pour in every day, says ophthalmologist Nathan Congdon, who was one of those uprooted. “You literally can't walk through the halls because of all the children.” East Asia has been gripped by an unprecedented rise in myopia, also known as short-sightedness. Sixty years ago, 10–20% of the Chinese population was short-sighted. Today, up to 90% of teenagers and young adults are. In Seoul, a whopping 96.5% of 19-year-old men are short-sighted. Other parts of the world have also seen a dramatic increase in the condition, which now affects around half of young adults in the United States and Europe — double the prevalence of half a century ago. By some estimates, one-third of the world's population — 2.5 billion people — could be affected by short-sightedness by the end of this decade. “We are going down the path of having a myopia epidemic,” says Padmaja Sankaridurg, head of the myopia programme at the Brien Holden Vision Institute in Sydney, Australia. The condition is more than an inconvenience. Glasses, contact lenses and surgery can help to correct it, but they do not address the underlying defect: a slightly elongated eyeball, which means that the lens focuses light from far objects slightly in front of the retina, rather than directly on it. © 2015 Nature Publishing Group
|By Erez Ribak and The Conversation UK The human eye is optimised to have good colour vision at day and high sensitivity at night. But until recently it seemed as if the cells in the retina were wired the wrong way round, with light travelling through a mass of neurons before it reaches the light-detecting rod and cone cells. New research presented at a meeting of the American Physical Society has uncovered a remarkable vision-enhancing function for this puzzling structure. About a century ago, the fine structure of the retina was discovered. The retina is the light-sensitive part of the eye, lining the inside of the eyeball. The back of the retina contains cones to sense the colours red, green and blue. Spread among the cones are rods, which are much more light-sensitive than cones, but which are colour-blind. Before arriving at the cones and rods, light must traverse the full thickness of the retina, with its layers of neurons and cell nuclei. These neurons process the image information and transmit it to the brain, but until recently it has not been clear why these cells lie in front of the cones and rods, not behind them. This is a long-standing puzzle, even more so since the same structure, of neurons before light detectors, exists in all vertebrates, showing evolutionary stability. Researchers in Leipzig found that glial cells, which also span the retinal depth and connect to the cones, have an interesting attribute. These cells are essential for metabolism, but they are also denser than other cells in the retina. In the transparent retina, this higher density (and corresponding refractive index) means that glial cells can guide light, just like fibre-optic cables. © 2015 Scientific American