Abstract-Dielectric property measurements of corneal tissues for computational dosimetry of the eye in terahertz band in vivo and in vitro

 

Maya Mizuno, Hideaki Kitahara, Kensuke Sasaki, Masahiko Tani, Masami Kojima, Yukihisa Suzuki, Takafumi Tasaki, Yoshinori Tatematsu, Masafumi Fukunari, and Kanako Wake

 Schematic diagram of the setups of specimens for (a) ATR and (b) T-type dielectric constant measurement, and reflectance measurement systems for (c) vertical and (d) oblique incidences. The white arrow in the left x-y image of (c) indicates the position with the largest reflection signal.

https://www.osapublishing.org/boe/fulltext.cfm?uri=boe-12-3-1295&id=447535

The dielectric constant of the normal corneal tissue of a rabbit eye was obtained in vitro in the range from approximately 0.1 to 1 THz, and the drying process on the eye surface exposed to high-power terahertz waves was investigated by in vivo reflectance measurement using terahertz time-domain spectroscopy. When the rabbit eye was exposed to terahertz waves at 162 GHz for 6 min with an irradiation power of 360 or 480 mW/cm2, the reflectance temporally increased and then decreased with a temperature increase. Based on multiple-reflection calculation using the dielectric constant and anterior segment optical coherence tomography images, those changes in reflectance were attributed to drying of the tear and epithelium of the cornea, respectively. Furthermore, the drying progressed over a temperature increase of around 5°C under our exposure conditions. These findings suggest that the possibility of eye damage increases with the progress of drying and that the setting of the eye surface conditions can be a cause of disagreement between computational and experimental data of absorbed energy under high-level irradiation because reflectance is related to terahertz wave penetration in the eye tissue. The time-domain spectroscopic measurements were useful for the acquisition of the dielectric constant as well as for the real-time monitoring of the eye conditions during exposure measurement.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Ocular Effects of Exposure to 40, 75, and 95 GHz Millimeter Waves

Masami Kojima, Yukihisa Suzuki, Kensuke Sasaki,  Masao Taki,  Kanako Wake,  Soichi  Watanabe, Maya Mizuno,  Takafumi Tasaki, Hiroshi Sasaki

https://link.springer.com/article/10.1007/s10762-018-0497-z

The objective of this study was to develop a model of ocular damage induced by 40, 75, and 95 GHz continuous millimeter waves (MMW), thereby allowing assessment of the clinical course of ocular damage resulting from exposure to thermal damage-inducing MMW. This study also examined the dependence of ocular damage on incident power density. Pigmented rabbit eyes were exposed to 40, 75, and 95 GHz MMW from a spot-focus-type lens antenna. Slight ocular damage was observed 10 min after MMW exposure, including reduced cornea thickness and reduced transparency. Diffuse fluorescein staining around the pupillary area indicated corneal epithelial injury. Slit-lamp examination 1 day after MMW exposure revealed a round area of opacity, accompanied by fluorescence staining, in the central pupillary zone. Corneal edema, indicative of corneal stromal damage, peaked 1 day after MMW exposure, with thickness gradually subsiding to normal. Three days after exposure, ocular conditions had almost normalized, though corneal thickness was slightly greater than that before exposure. The 50% probability of ocular damage (DD50) was in the order 40 > 95 ≈ 75 GHz at the same incident power densities.