In vitro studies of microwave-induced cataract: reciprocity between exposure duration and dose rate for pulsed microwaves.

Rat ocular lenses exposed to pulsed microwave irradiation were maintained at constant temperature by circulating phosphate buffered saline in a thermostatically-controlled chamber. Irradiations with pulsed radiation (10 musec, 24 kW pulses) of 918 MHz were done at several different specific absorption rates (SAR) for durations up to 1 hr in order to explore a possible reciprocal relationship. The extent of damage was measured by the maximum depth of granular degeneration in the equatorial region of lenses fixed immediately after irradiation. The parameters of the pulses were increased to 20 musec and 48 kW to explore the variation in the biological effects and threshold with respect to average power, as well as pulse parameters (pulse width, peak power and energy per pulse). A total of 47 lenses were used in 3 X 4 factorial experimental design to explore effects observed at different average powers and durations (6, 20 and 60 min). The results were statistically analyzed by ANOVA and multiple regression analysis with logarithmic transformation. The results are summarized as follows. This data showed clear trends towards increasing depth of granular degeneration with increasing duration of exposure and dose rate. There was considerable evidence to confirm such reciprocity suggesting that total dose is an important parameter. A model postulating reciprocity was shown to explain observed variation in depth of damage as well as one allowing for separate effects of duration and dose rate. Lens fibre cell effects were detected by scanning electron microscopy after 6 min irradiation at the SAR values of 40 and 20 mW g-1. Light microscopic evidence of lens fiber cell damage can be detected at an SAR of 10 mW g-1 after a 1 hr exposure.