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Gopal Swamy Jayabalan, Nooshin Salehi, Xiao Wen Mao, Howard Gimbel, Michael Rauser, Josef Bille, Joseph T Fan; Retinal toxicity evaluation of femtosecond two-photon laser scanning ophthalmoscope in live rats. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5844.
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The safety power limit for the near-infrared two-photon imaging according to ANSI standard is approximately 13 mW. However, our preliminary data suggested that the lowest power threshold required for two-photon autofluorescence imaging was 80mW. The purpose of the study is to investigate the laser power and exposure time required to cause the retinal toxicity by near-infrared two-photon laser system in rats.
A femtosecond laser with 780 nm, 270 fs, 50 MHz was used as a light source for two-photon imaging. Brown Norway rats (N=8) and Albino rats (N=8) were used in this study. The retina was exposed to the scanning and stationary laser beam at 13 mW, 80 mW and 160 mW for 100 seconds, 5 minutes and 10 minutes. Fluorescein angiography (FA) was performed after the laser exposure to investigate the microvasculature damages on the retina. Furthermore, the immunohistology study the fluorometric TUNEL assay was performed to detect the apoptotic cells.
No retinal toxicity were identified by fundus photography, FA and TUNEL study with scanning laser beam in brown Norway and albino rats at 13 mW, 80 mW and 160 mW with 100 seconds, 5 minutes and 10 minutes exposure time.The stationary laser beam at 13 mW and 80 mW with 100 seconds exposure time did not cause any retinal toxicity. However, the stationary laser beam at 13 mW and 80 mW with exposure time of 5 or 10 minutes did cause some minor retinal toxicity. Also, the retinal toxicity was found at 160 mW stationary laser beam with all three exposure time.Although, the retinal toxicity was identified by fundus photography at 13mW and 80 mW with exposure time of 5 or 10 minutes, no TUNEL positive cell was found. And at 160 mW, with all three exposure time the apoptosis was primarily seen at the outer nuclear layer and retinal ganglion cell layer. The number of TUNEL positive cells was significantly increased in brown Norway rats as compared to albino rats.
This study suggested that the two-photon laser scanning for retinal imaging is safe in rats, and less likely to cause the retinal toxicity compared to the stationary laser.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Fundus photography of brown Norway rat after exposure (yellow box) to a stationary laser beam at 80 mW for 5mins.
Fluorescence images of the control (left) and treated (right) eyes at 80 mW for 5 mins. No apoptosis was noticed in the treated eyes. Retinal sections stained with DAPI to reveal the cell nuclei.
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