First Author: M.Kim SOUTH KOREA
Co Author(s): Y. Park Y. Roh
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Selective retina therapy (SRT) damages the retinal pigment epithelium (RPE) with sparing the adjacent photoreceptors. Our purpose is to evaluate the retinal tissue response by using SRT in the presence or absence of real-time feedback-controlled dosimetry(RFD) in rabbits.
Basic animal experiment
Eighteen eyes of Chinchilla Bastard rabbits were treated by SRT with or with RFD (Q-switched Nd:YLF, wavelength: 527nm, pulse duration: 1.7µs, repetition rate: 100Hz, pulse energy: max. number of micropulses in a burst: 15, retinal spot diameter: 140 µm). RFD operated by optoacoustic (OA) and reflectometric(RM) methods detects RPE damage in real time and stops the following micropulse irradiation among 15 micropulses. For obtaining the margin of safety, the predetermined threshold of RFD va1.1 (OA; 100000 A.U., RM; 120000 A.U.) was set to detect RPE damage. The endpoints of SRT treatment were confirmed by colour fundus photography and fluorescein angiography. After SRT treatment, light microscopy(LM) and scanning electron microscopy(SEM) were performed at 1 hour, 3 days, 7 days and 1 month. The damaged area on RPE monolayer was measured by Image J
A total of 180 SRT spots in the absence of RFD were tested (range 5~25µJ). The damaged area by SRT without RFD showed a positive correlation with a ramping pulse energy (Pearson’s correlation coefficient: 0.797 P <0.001). With RFD, automatic-stop occurred in 212 of 220(96.3%) fluorescein angiography-positive SRT spots which did not show any discolouration like burns. There was no correlation between the damaged area of RPE by SRT with RFD and a ramping pulse energy (Pearson’s correlation coefficient: 0.211, P=0.044). LM revealed that SRT with RFD produced selectively disrupted RPE monolayer with sparing innersegment of photoreceptor layer at different timeline during 1 month. The proliferation and division of RPE cells were observed 3 days after treatment. The damaged RPE lesions were covered by 1 week. RPE rejuvenation was almost completed by 1 month.
RFD showed a safe and effective performance to produce selective RPE damages without damaging photoreceptor in this study. Therefore, RFD can be useful to titer the pulse energy without performing pretreatment fluorescein angiography