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Sharpening up

发布时间:2019-03-07 06:16:14来源:未知点击:

By Jonathan Knight PEOPLE with razor-sharp vision may have a special protein to thank for their keen sight. The protein can compensate for blurred images, and scientists say this may lead to drugs to prevent short-sightedness. Like film in a camera, the retina of the eye must be a precise distance from the lens. Images become blurred if the distance is not correct. As a developing eye grows and changes shape, it must somehow keep the world in focus. Researchers know that when chicks or monkeys wear fogged goggles, their eyes elongate. This extra distance from the lens to the retina means that when the goggles are removed, the animals are short-sighted because their lenses bring light to a focus before it hits the retina. Andy Fischer and his colleagues at the University of Calgary in Canada suspected that the protein ZENK, which regulates genes in the retina, might be involved in this response to blurred vision. So they fitted chicks with fogged lenses and checked the amount of ZENK in retinal cells after the lenses were removed. The team reports in this month’s Nature Neuroscience (vol 2, p 706) that the blurred vision after the lenses were removed caused a sixfold jump in the number of cells containing ZENK within two hours. Fischer thinks that the protein helps to correct vision, perhaps by shutting down genes for growth factors that make cells in the eyeball divide. If ZENK’s role is to ensure the retina ends up in the plane of focus, its levels should increase only when images come into focus in front of it. Sure enough, when Fischer gave the chicks glasses that focused images behind the retina, ZENK levels plummeted. “There is some type of retinal circuitry that is hard-wired to detect image focus,” Fischer concludes. No one knows how this might work, but Fischer speculates that part of the answer may be “rings of defocus” similar to the faint lines that appear around objects on a movie screen as a projectionist focuses in and out to get a sharp picture. These are different for “positive” and “negative” defocus, and the retina might somehow distinguish between the two. Neurons in the retina are known to signal to each other, and some of this information may help determine the focus of the image. Debora Nickla, a myopia researcher at the New England College of Optometry in Boston, says her lab will look for the same signals in primates. “In terms of eye growth, there are a lot of similarities,” she says. If scientists can find the molecular signals that elongate the eye, Nickla says,