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TJ Desmettre, C-A Maurage, S Mordon; Transpupillary Thermotherapy (ttt) With Short Duration Laser Pulses Induce Heat Shock Protein (hsp) Hyperexpression On Choroido-retinal Layers . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4408.
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Purpose: To assess a choroidal heat shock protein hyperexpression after transpupillary thermotherapy performed with laser pulses shorter than 60s. Methods: Six male pigmented rabbits were anesthetized and TTT was performed on their right eye with a 810nm diode laser (Iridis, Quantel-Medical (France)) (spot size : 1,3 mm). Various pulse duration (60 seconds, 30seconds or 15 seconds) were used with 3 ranges of power for each duration (low, mild or high, ranging from 70 to 250mW). Series of 9 to 12 laser impacts were delivered to the posterior pole of the retina. Left eyes were used as control. 24 hours after laser irradiation, the animals were killed and histological study was performed on retina. The histology technique as been recently described (1). Results: During the experiments, the laser spots were not visible except for the strongest powers for each pulse duration, were a faint whitening was discernable at the end of the laser pulses. On histology, no photocoagulation nor modification of chorioretinal architecture was observed. No HSP-70 immunoreactivity was detected on control eyes. HSP-70 immunoreactivity was detected in choroidal, non pigmented cells for pulses lasting 60, 30 and 15 seconds with high and mild power. On the contrary no HSP hyperexpression was detected for the lowest powers. Conclusion: Since TTT is a subthreshold procedure the power and duration of the laser pulse cannot be modulated during treatment. For long exposures such as 60 seconds, heat convection through choroidal blood flow moderates the temperature rise and impedes a reliable modelization of the temperature elevation throughout the duration of the laser pulse. The use of shorter laser pulses could help to control the temperature elevation by reducing the role of convection during the laser pulse. (1) Desmettre et al IOVS 2001;42(12):2976-2980.
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