nt leekee ce eeHk ee eeete om ee mn Ls eeeea - promptly as energy in the visible light region because of the thin atmosphere. ?? Principally for this reason, such high altitude detonations do not present a serious hazard for eye damage. Detonations occurring at lesser altitudes encounter more atmosphere, where there are greater opportunities for interaction of the bomb debris with the air, resulting in a greater fraction of the total energy appearing as prompt visible 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. Experience at Hiroshima and Nagasaki suggest that perma- nent 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 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 S90b9 19 eeet: ret 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 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. 24 The