INVESTIGATION OF SINGLE‐EXPOSURE MICROWAVE OCULAR EFFECTS AT 3000 MHz

Microwave cataracts, their morphology, and their mechanism of production have received much attention since the early 1950s, when the first suspected clinical case of microwave-induced cataracts was reported by Hirsch and Parker.' Before 1950, Duke-Elder2 suggested that the long wavelengths of the electromagnetic spectrum might be cataractogenic and proposed a mechanism of action. It was not until the widespread use of high-powered multiple-frequency radar and communication equipment that this intense interest was channeled into the Tri-Service Ad Hoc Committee of the late 1950s and early 1960s. Since that time, other clinical case reports of cataracts occurring in persons with the potential for occupational exposure t o microwaves3 and ocular effects surveys of similar group^^-^^ have been published. These reports have often incited controversy and precipitated much speculation as to the potential hazards of nonionizing radiation at levels found within the environment. As a result of the increased utilization of microwaves for communication and the predicted rise in domestic use of microwave ovens, a renewal of interest in the biologic effects of this energy has occurred. In addition, frequent publications in lay magazine^'^.^^ have generated public concern. A brief history of microwave ocular effects research is in order to help understand the development of our approach to this subject. In 1948, the cataractogenic properties of microwave radiation were demonstrated by Daily and colleagues14 and by Richardson and ass~cia tes . '~ Daily and colleagues reported cataract production and an associated 3°C rise in the eye in dogs and albino rabbits after repeated exposure to 12-cm (2450 MHz) diathermy with an output of 100 W. The lens changes were initially anterior cortical opacifications that appeared within 24 hr of exposure in those animals that were to show the development of posterior cortical opacities within 9 weeks. Richardson and associates reported their results from rabbits exposed to 3000-MHz microwave radiation produced by a 100-W Raytheon generator. The rabbits were positioned 5 cm from the source, and temperature increases of as much as 17°C were noted in the eye. Thirty-two of 54 irradiated eyes had lenticular opacities, which ranged from small posterior polar defects to complete opacification. There was no mention in these papers of what are now described as the critical exposure parameters: duration and number of exposures, free field, or other estimates of dosimetry. It is unfair to criticize the lack of good exposure parameters, however, because the state of the art was then quite limited. Although this situation is somewhat better today, the precise measurement of absorbed power