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R. Brinkmann, J. Kandulla, H. Elsner, M. Hilmes, C. Hartert, R. Birngruber; Non–Invasive Real–Time Retinal Temperature Determination During TTT . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1406.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In almost all retina laser treatments, except PDT, a temperature increase is induced and desired at and around the RPE, which initiates the therapeutic effect. We investigated a non–invasive optoacoustic method enabling to determine non–invasively the temperature increase during laser treatments at the fundus. Especially in TTT the laser induced temperature increase is crucial. However, calculations show that differences in pigmentation, light scattering and choroidal perfusion can lead to a temperature increase varying by a factor of 5 under same treatment conditions. Therefore we demonstrated this technique first of all on TTT. Methods: If a specimen is irradiated with a short laser pulse, a thermoelastic wave is emitted due to its thermal expansion. Since the thermal expansion coefficient depends on the temperature of the target, the amplitude of the pressure wave allows to determine the temperature. We performed TTT in vitro on porcine eye globes and in vivo on rabbits with a 810 nm diode laser. Additionally, short (1ns) low energy (< 10 µJ) probe laser pulses of a frequency doubled Nd:YAG–laser (532 nm) were repetitively applied for optoacoustic exitation. In order to detect the pressure waves, we modified a standard contact lens with an ultrasonic transducer. Results: The temperature dependent relative thermal expansion coefficient for porcine RPE/choroid samples was found to raise by 10 % between 37 °C and 50 °C. Using this relation we optoacoustically determined the temperature increase during TTT under different treatment parameters. In vitro, a maximum central spot temperature increase of 8.5 °C/100mW for a TTT irradiation spot size of 2 mm in diameter was observed. The results are in high agreement with simultaneously performed measurements by means of thermocouples positioned in the choroid. The in–vivo results of TTT–induced retinal temperatures will be presented. Conclusions: The opto–acoustic on–line temperature determination seems to be an appropriate method for real–time temperature monitoring during TTT. It might serve as a dosimetry control and temperature regulation in TTT and other retinal treatments like photocoagulation.
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