Word: retinas
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Dates: during 1990-1999
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...still remembers the day in the mid-1980s when her heart broke. She was sitting across the dining-room table from Dorothy Coppens, her vibrant 85-year-old mother, who had just been found to be suffering from macular degeneration, an incurable deterioration of the central portion of the retina that is the leading cause of blindness in people 60 and older. "Your face is just a brown smear," Coppens told her daughter. "I guess I'll never see your face again...
...knows what causes macular degeneration. In 90% of the cases involving older people, the retina wears thin and abnormal deposits called drusen start to appear. This is the so-called dry form of the disease, in which vision deteriorates slowly, if at all. Still, it should be checked periodically since complications can occur...
...smaller facets. Each focuses on a handful of photo receptors and produces only a single point in the insect's visual field. But the researchers, reporting last week in the journal Science, found that each of X. peckii's 100 eyelets is really a complete eye with its own retina, consisting of some 100 receptors, that samples a "chunk" of the visual field. These neighboring chunks, when combined in the insect's brain, produce an image with exceptionally high resolution...
...bright the incoming light is, the pupil grows wider or narrower, much like the adjustable aperture of a camera. The light then passes through the lens, which lies directly behind the iris and changes shape as needed--curving or flattening--to help focus the image onto the retina, the light-sensitive tissue at the back of the eyeball that converts the light into electrical signals. From there, the optic nerve sends these impulses to the brain's optic centers, which create the picture in your mind...
...happens, the eye's lens provides just a third of the eye's focusing power. The rest comes from the cornea, which acts like a second lens to help focus light onto the retina. If you're nearsighted, or myopic, your eye produces clear images of nearby objects or people. But light from distant sources is focused on a point somewhere in front of your retina--either because the curve of your cornea is too steep relative to the length of your eyeball, or the eyeball is too long relative to the corneal curve. If you're farsighted, or hyperopic...