Word: retina
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Light enters the eye in parallel rays, which are gradually bent as they pass through the cornea and lens. In the normal eye, they converge, or focus, precisely on the retina at the back of the eyeball. Electrical impulses then transmit a sharp image to the brain. In the nearsighted, however, the eyeball is usually too long or the cornea too curved, so that the rays come to a focus in front of the retina. In the farsighted, the eyeball is too short or the cornea too flat and the light rays, if they could pass through it, would converge...
...correct these conditions would be to change the curvature of the cornea so the images fall directly on the retina. The pioneer of surgery that accomplishes that optical feat is Ophthalmologist José Barraquer of Bogotá, Colombia, who for the past two decades has been performing a variety of delicate and complex corneal operations that he calls refractive keratoplasty (an operation on the cornea for optical reasons). In one procedure known as keratomileusis (cornea carving), the front of the cornea is sliced off with a high-speed vibrating blade, quickly frozen, and then reshaped on its underside...
...itself, a pleasant little mountain town swamped by the world. The Games provided a kind of ritual relief during a troubled American moment, supplanting cold war fears with cheers for an ice hockey upset. Like all Olympics, the 13th Winter Games left a gallery of bright images on the retina...
...problem is that lasers produce beams of light so intense that if directed or even reflected into the human eye, they can blister and burn the retina, causing instant and permanent damage. To avoid that possibility, the FDA wants light-show operators to use low-powered lasers and to design the shows so that the beams of light are aimed far above the heads of spectators...
...that chance discovery 17 years ago has emerged a new and highly controversial treatment for helping flawed vision. It is called "orthokeratology." In myopia, images of the outside world do not focus precisely on the retina but rather in front of it, either because the eyeball is too long or because the cornea and lens bend light rays too much. Just as orthodontists use braces to correct the position of crooked teeth, orthokeratologists employ hard contact lenses to alter the curvature of the cornea to improve vision. At least 300 optometrists now specialize in "ortho-k," and tens of thousands...