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Masami Kojima, Cheng-Yu Tsai, Yukihisa Suzuki, Kensuke Sasaki, Kanako Wake, Soichi Watanabe, Yoshitsugu Kamimura, Masao Taki, Kazuyuki Sasaki, Hiroshi Sasaki; Investigation of crystalline lens injury threshold by 75 GHz band exposure in rabbit. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1211.
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© ARVO (1962-2015); The Authors (2016-present)
Millimeter waves (MMWs) are prevalent in high-speed wireless LAN, automobile collision prevention systems, and high-resolution radar imaging, such as airport full-body scanners. It is known that MMWs are mainly absorbed at the surface of the body. International MMWs safety guideline focuses on the surface of biological tissues or organs. The effects on ocular tissue, especially inside the eye, remain unclear. Here, we investigated the lens damage threshold of 75 GHz band MMW exposure in rabbit eye.
Pigmented rabbits (N=18, Dutch, 14-15 week-old) were exposed unilaterally to 200, 100, 50 mW/cm2 75 GHz band MMW for 30 min at the center of the pupillary area, with a lens antenna. Anterior damage was examined by slit lamp. Ocular temperatures were continuously recorded, using a fluoroptic thermometer, during 0 to 50 min MMW exposure. Lens epithelial cells were evaluated by lens flat mounting technique. Microencapsulated thermo-chromic liquid crystal (MTLC), which changes color with temperature change, was used for visualization of heat transport in the anterior chamber by 200 mW/cm2 exposure.
Exposure to 200 and 100 mW/cm2 for 30 min caused corneal damage. Exposure to 200 mW/cm2 caused lens epithelial cell damage in the pupillary area. The damage had 3 features; 1) areas of dense epithelial cells with mitotic cells, 2) low-cell density area, and 3) regular-cell density area. Exposure to 100 mW/cm2 did not induce prominent damage, but mitotic cells were observed in the exposed area. Exposure to 50 mW/cm2 resulted in no ocular change or mitotic cells in the exposed area. The average temperatures of cornea during exposure at 200, 100, 50 mW/cm2 were as follows; 49.4±0.9°C (200 mW/cm2), 42.2±0.4°C (100 mW/cm2), 38.2±0.2°C (50 mW/cm2), respectively. MTLC color change was observed to rise from the right under the cornea and the convection descended to the upper pupil area or the upper crystalline lens side (200 mW/cm2 data).
Exposure to 75 GHz MMW induced not only corneal damage but also lens epithelial cell damage in rabbit eye. It was absorbed by cornea and caused heat transport to the crystalline lens. The present data is evidence of a corneal and lens damage threshold between 100 to 50 mW/cm2.
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