promptly as energy in the visible light region because of the thin atmosphere.?’ Principally for this reason, such highaltitude detonations do not present a serious hazard for eye damage. Detonations occurring at lesser altitudes encounter more atmosphere, where there are greater opportunities for inter- action of the bomb debris with the air, resulting in a greater fraction of the total energy appearing as promptvisible light. Detonations below about 60 miles can produce sufficient energy. in the visible light region to be a potential eye hazard if they occur above the horizon and are viewed directly. Ex- perience at Hiroshima and Nagasaki suggest that permanent eye injury would be expected only if one were looking directly at the fireball. This applies only to the instant of burst. If the detonation occurs below the horizon, the instant of high thermal energy release is past before the fireball rises into view. Under these conditions human reflexes of blinking or turning away should further insure safety. The Data visual acuity recovered to 20/30 in one eye and 20/40 in the other about one month later, and to 20/25 in both eyes about a year afterwards in the area of primary retinal damage. The A FIGURE 8.—Special high density goggles are worn by observers on-site at the Nevada Test Site. Note man at right of center without goggles, but who has turned away from the direction of burst. This procedure is equally safe providing there is no reflecting surface directly in view. other man’s visual acuity followed a similar pattern starting at 20/400 in both eyes in the area of retinal damage and 20/60 in the adjacent areas. These recovered to 20/50 and 20/80 in a month, and at one year later to 20/40 on one eye and 20/60 in the other in the areas of primary retinal damage.” Experimental rabbits were exposed under nighttime conditions to the high altitude shot on August 1, 1958—a detonation in the megaton rangeat a:, altitude of about 48 miles. Lesions with diameters of about 500 microns were observed out to 345 miles —the farthest distance at which rabbits were exposed. Evaluation es There have been no recorded permanent eye injuries to persons off-site, although a few individuals near the Nevada Test Site have complained of temporary eye impairment. The burst from a 1.4 million tons detonation that took place over Johnston Island in the Pacific on July 9, 1962 at an altitude of about 250 miles was viewed directly under nighttime conditions by thousands in the Hawaiian Islands without any reported eye injury. Six military personnel participating in nuclear weapons tests have received eye injury—only one of which resulted in a severe visual handicap.” 2° The latter individual “sneaked” a view over his left shoulder at the time of the detonation resulting in a reduction of 20/20 vision to 20/100 in his left eye. It did not improve with time. His right eye apparently was shielded by his nose and retained its 20/20 visual acuity.” (Values such as 20/100 represent the ability of the eye to read standard letters and characters at 20 feet that a normal eye could read at 100 feet. 20/400 is generally interpreted as legal blindness.) Two military personnel at Johnston Island participating in the high altitude tests in 1962 also received eye injury. Immediately after the exposure, the visual acuity of both eyes of one man dropped to 20/400 for the area of primary retinal injury and 20/100 for adjacent areas of the retina. This man’s Nuclear detonations in the yield range tested offer no serious hazards to the eye when they are at very high altitudes, say above 150 miles, or below the horizon at the instant of burst. Detonations in the lower atmosphere should not be viewed directly without the aid of special high density goggles (Figure 8). Past precautionary procedures of closing highways and air lanes nearthe testing sites at the times of bursts have added to the safety in respect to potential eye damage. The procedures also were useful in preventing a driver or pilot being startled while in motion. OF