Word: sclera
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...then there are Balaam's eyes. Rembrandt's eyes. Lastman has followed the van Mander prescription. The prophet is amazed to hear his donkey speak. Follow the stage direction. Make his eyes pop out with astonishment. Give the customers dilated pupils, white sclera, and lots of it. With a stroke of perverse genius (excuse the term), Rembrandt has done the opposite, painting Balaam's eyes as dark crevices. For this is, after all, the moment _before_ God opens those eyes to the angel and the light of truth...
...eyes are surrounded by a tough, protective layer called the sclera. Only at the front of the eyeball does the sclera give way to the cornea, which is transparent. Light passes through the cornea to the pupil, the hole in the middle of the iris, or colored part of your eye. Depending on how 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...
...study has conclusively settled the origins of myopia, nor how much heredity or eye-strain is to blame. "Myopia has been associated with everthing from pregnancy to tooth decay," Greene says. Researchers agree only that myopia is the abnormal bulging of the back of the eye or "posterior sclera," usually around the gap for the optic nerve. But no one is sure what causes the swelling, whether myopics are born with bulge or have brought it on themselves by reading in dark corners...
...McMahon and Greene set to work building a mechanical eye. The model immediately provided two insights. First, strain occurs when the two oblique muscles--the muscles in the back of the eye which control its rotation--are tensed greatly, as in reading. The tension stretches and strains the sclera. Though such stretching is normally elastic, if it is both frequent and extreme enough the sclera does not return to its normal position and myopia develops. Second, the eye is least able to reduce strain near the point where the optic nerve enters the eye--Greene draws an analogy with...
...Boom. Foreshadowed by Leonardo da Vinci in 1508, contact lenses were first made in Europe in the 1880s. They were big, covering most of the sclera (the white of the eye), heavy (made of glass), hard to fit and forbiddingly expensive. Early plastic lenses were also of the big scleral type, had to float on a bath of special wetting fluid, and could be worn only four to five hours at a stretch. Then came the methyl-methacrylate plastics (of the Plexiglas family), the discovery that fluid was unnecessary if lenses had a hole to permit tears to pass beneath...