Purpose: Chorioretinal tissue is a mixture of macromolecules that either are rigidly fixed into a structural matrix or can move. Fluctuation of the scattered light is related not only to possible molecules motions induced by the blood flow and by the temperature but also to the absorption and scattering coefficients which are temperature depended. Analyzing the light scattering fluctuations the retinal tissue temperature can be recovered. Methods: We conducted two experiments using fresh enucleated bovine eyes. The first experiment was performed on an eye cut at the equator to include retinal tissue and placed into a semispherical holder designed to heat the tissue at a known temperature by using a Peltier cell. A focused Helium-Neon laser was used to illuminate the central retina close to the fovea. The collection of the diffused radiation was performed by a single-mode fiber connected to a single photon counting (SPCM). The electrical signal from the SPCM was processed by a digital correlator to acquire the intensity autocorrelation function (ACF) at different retina temperatures. The second experiment was performed using an intact eye and the excitation laser was a standard therapy laser diode. The laser settings were: power=500mW, diameter spot=1mm, duration=60sec. The collection of the diffused radiation was performed exploiting the same setup used in the first experiment; the intensity ACF was acquired each 10 seconds. Results: The average decay time of the autocorrelation functions acquired during the first experiment exhibited a linear trend as a function of the temperature in the range 20-50 {degrees}C. The Pearson's correlation coefficient of the linear fit was R=0.99. During 500mW laser irradiation the average decay time of the ACF increased for the first 50 minutes then the last acquisition showed a decreased value. The trend of the average decay time of the ACF during irradiation showed a fast increasing of the temperature in the first 10 seconds of irradiation, then we observed a linear slow increasing of the temperature in the time interval (10min,50min). The fall of the average decay time in the last 10 seconds could be due to a deterioration of tissue (whitening). Conclusions: Analysis of the temporal fluctuations of the scattered laser light intensity could be used to determine in-vivo the chorioretinal temperature during TTT. The preliminary data presented shows an excellent correlation between the retinal temperature and the average decay time of the intensity ACF.
Analysis of the Temporal Fluctuations of the Laser Light Intensity Diffused by the Chorioretinal Tissue During Transpupillary Thermotherapy (TTT) / G., Staurenghi; Rovati, Luigi. - In: INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE. - ISSN 0146-0404. - STAMPA. - 46:(2005), pp. 2588-2588. (Intervento presentato al convegno ARVO tenutosi a Florida nel 2005).
Analysis of the Temporal Fluctuations of the Laser Light Intensity Diffused by the Chorioretinal Tissue During Transpupillary Thermotherapy (TTT)
ROVATI, Luigi
2005
Abstract
Purpose: Chorioretinal tissue is a mixture of macromolecules that either are rigidly fixed into a structural matrix or can move. Fluctuation of the scattered light is related not only to possible molecules motions induced by the blood flow and by the temperature but also to the absorption and scattering coefficients which are temperature depended. Analyzing the light scattering fluctuations the retinal tissue temperature can be recovered. Methods: We conducted two experiments using fresh enucleated bovine eyes. The first experiment was performed on an eye cut at the equator to include retinal tissue and placed into a semispherical holder designed to heat the tissue at a known temperature by using a Peltier cell. A focused Helium-Neon laser was used to illuminate the central retina close to the fovea. The collection of the diffused radiation was performed by a single-mode fiber connected to a single photon counting (SPCM). The electrical signal from the SPCM was processed by a digital correlator to acquire the intensity autocorrelation function (ACF) at different retina temperatures. The second experiment was performed using an intact eye and the excitation laser was a standard therapy laser diode. The laser settings were: power=500mW, diameter spot=1mm, duration=60sec. The collection of the diffused radiation was performed exploiting the same setup used in the first experiment; the intensity ACF was acquired each 10 seconds. Results: The average decay time of the autocorrelation functions acquired during the first experiment exhibited a linear trend as a function of the temperature in the range 20-50 {degrees}C. The Pearson's correlation coefficient of the linear fit was R=0.99. During 500mW laser irradiation the average decay time of the ACF increased for the first 50 minutes then the last acquisition showed a decreased value. The trend of the average decay time of the ACF during irradiation showed a fast increasing of the temperature in the first 10 seconds of irradiation, then we observed a linear slow increasing of the temperature in the time interval (10min,50min). The fall of the average decay time in the last 10 seconds could be due to a deterioration of tissue (whitening). Conclusions: Analysis of the temporal fluctuations of the scattered laser light intensity could be used to determine in-vivo the chorioretinal temperature during TTT. The preliminary data presented shows an excellent correlation between the retinal temperature and the average decay time of the intensity ACF.
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