Noninvasive Monitoring Technique of Choroioretinal Temperature During Transpupillary Thermotherapy with Thermosensitive Liposome

Abstract

Abstract: : Purpose:To develop a noninvasive and real-time monitoring technique of chorioretinal temperature in transpupillary thermotherapy (TTT). Methods:A modified slit lamp, which was installed with two laser wavelenghs (490 nm for illumination and fluorescein excitation and 810 nm for hyperthermia), was developed for TTT and temperature monitoring. Five types of liposomes were prepared; their phase-transition temperatures were 40°C, 46°C, 47°C, 48°C, and 52°C, respectively. Carboxyfluorescein was encapsulated in each liposome. Following intravenous injections of each liposome, TTT with the modified slit lamp was performed on normal rat choroid or choroidal neovascularization (CNV). During TTT, chorioretinal temperature was monitored by observing release of fluorescein from circulating liposomes. Results:Fluorescence from liposomes was initially observed around the heated lesion immediately after TTT began, and disappeared rapidly when irradiation stopped. Choroidal and retinal temperatures were monitored separately. Chorioretinal temperature rise correlated with the power setting of TTT when TTT was performed on the normal fundus. Retinal whitening appeared on the overlying retina with TTT power above 15mW, when the choroidal temperature was expected to be about 47°C. When TTT was performed on CNV, temperature rise varied among vessels. In addition, TTT for CNV required higher laser power than that for the normal choroid. Conclusions:Our results showed the potential use of a noninvasive monitoring technique of chorioretinal temperature during TTT. The method sould be useful to establish the TTT setting to achieve the optimal temperature increase in CNV.

Keywords: age-related macular degeneration • retinal pigment epithelium • choroid: neovascularization