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The Power of Light |
The story now jumps to the period after World War II. In the wake of the explosion of the first atomic bomb, many researchers began investigating the retinal burns suffered by people who had seen the atomic flash from as far as 50 miles away and later went blind. A similar phenomenon, eclipse blindness, had been known at least since Plato's time. In the spring of 1946, German ophthalmologist Gerd Meyer-Schwickerath became interested in the problem after examining a number of patients who had sustained retinal damage in association with the solar eclipse of July 10, 1945. He noticed that the retinal scars caused by their exposure to intense sunlight "resembled the sort of scar resulting from surface diathermy," that is, the kind of scar that doctors were trying to induce by applying heat to the eye to seal retinal holes or treat areas of diabetic retinopathy.
Over the next several years, Meyer-Schwickerath carried out extensive experiments in an effort to perfect a technique of therapeutic photocoagulation--using light to coagulate retinal tissue. It was not a simple proposition. On the one hand, sealing a retinal hole could prevent the retina from detaching. On the other hand, the area of the retina subjected to coagulation would be ruined. The trick was to coagulate as small a spot as possible and preserve as much vision as possible.
Meyer-Schwickerath's research showed that some wavelengths of light--namely, between 400 and 900 nanometers--could pass through to the retina without losing energy through absorption or scattering by proteins in the cornea and lens. He also learned that, as the heat produced by the absorption of light energy in adjacent layers of pigmented cells raised the temperature of the retina, the normally transparent retina would turn white. The area would begin reflecting rather than absorbing the light, and coagulation would stop.
He needed an instrument that could produce precise localized coagulation burns at retinal tears and do so in a short time so as to minimize thermal damage to other parts of the eye. In the mid-1950s the American Optical Corporation in Southbridge, Massachusetts, developed high-pressure xenon arc lamps for a movie producer. These gas lamps produced light so bright that people who looked at it directly ran the danger of unintentionally coagulating their retinas.
Here was the artificial source Meyer-Schwickerath was seeking. Soon Zeiss Laboratories in Oberlochen, Germany, had incorporated the xenon lamp into a photocoagulator that Meyer-Schwickerath praised as being "of the greatest technical perfection" and easier for physicians to use. In 1959 Zeiss sent three of these machines to the United States.
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