Millimeter waves (MMW) are pervasive in society; however, studies on the biological effects of MMW exposure are usually performed in laboratory settings not reflecting global environmental diversity. We investigated the effects of a 6-min exposure to 60 GHz MMW (wavelength, 5.0 mm) at incident power densities of 200 and 300 mW cm-2 in eyes (exposed right eyes vs. unexposed left eyes) under various ambient temperature/relative humidity environments (24 °C/50%, 45 °C/20%, and 45 °C/80%) using an in vivo rabbit model. Correlations were examined with adverse ocular events, including corneal epithelial damage (assessed using fluorescein staining), corneal opacity (evaluated by slit-lamp microscopy), and corneal thickness (measured via optical coherence tomography). Our findings indicate that higher temperatures and humidity tend to exacerbate MMW-induced ocular damage, albeit not significantly in the present study. Further research with a larger sample size is warranted. Incident power density emerged as a factor that was directly linked to the ocular damage threshold. High ambient temperature and humidity tended to exacerbate ocular damage from MMW exposure, although the effect was secondary. Ocular damage in a high-temperature (45 °C), high-humidity (80%) environment was increased to the same extent as that by incident power density increased by approximately 100 mW cm-2 in an ocular damage model in a standard environment (24 °C, 50%). In a high-humidity environment, the internal ocular tissue temperature increased at a high ambient temperature of 45 °C, suggesting that the eyeball may respond differently compared to other tissues.
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