Production of Cataracts in Animals by X-Rays and Fast Neutrons

Abstract

Our particular interest in ionizing radiation of various types stems from the relationship between exposure to such sources of energy and the subsequent occurrence of cataract. In the initial work with x-rays, instances of cataract in both the operator and the patient were observed, but as technics improved, the hazard became more and more limited to the patient. Continued experience demonstrated that additional shielding of the patient's eye could often be effectively used, and that fractionation of the total dose into repeated smaller doses would further reduce the incidence of radiation cataract. When large eye doses are necessary, cataract production usually becomes relatively unimportant, since the eye may be more seriously damaged by the secondary glaucoma that may follow irradiation. Although the cataractogenic dosage is of interest to all who work with x-rays, it is not possible to say exactly what it is in all conditions of exposure. Cataract may be partial, interfering little or not at all with vision, or it may become dense (or complete), so that no useful vision is possible. The extent of opacification depends primarily upon the quality and quantity of irradiation received, but the effect is lessened when the total dosage is divided into smaller units given over a longer period of time. Perhaps the average young adult would get a complete cataract from 2,500 to 4,000 r of 250-kv radiation (filtered with copper and aluminum), while only 500 to 1,000 r at 125 kv (aluminum filter) might result in at least partial opacity. Young persons would be injured by smaller dosages, while old people would be resistant to such exposures. Cataract following roentgen irradiation need no longer be a hazard to the x-ray worker, as the potential danger has been recognized and adequate shielding can be provided. During research in development of nuclear energy, some workers were accidentally exposed to neutron radiation, with later cataract formation (1). The nature of the exposure was known with sufficient precision to indicate that the cataracts were the result of irradiation of the eye region. The number of these accidents was small, but it alerted scientists to the danger to the lens entailed by such irradiation. As the result of atom bomb explosions in Japan, more information concerning the effects of neutrons on the lens has been accumulated (2, 3). From these data it is possible to conclude that the cyclotron worker, for example, is in danger of cataract formation unless he uses the protective measures available. Although the usual results of both acute and chronic whole-body exposures to radiation are serious general disturbances, it is possible that the only manifestation of radiation injury may be the development of lens changes. This is particularly true when there is repeated exposure of the head to low dosages over a long period of time.