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Stefan O. Koinzer, Marco Bever, Kerstin Schlott, Lars Ptaszynski, Alex Baade, Susanne Luft, Yoko Miura, Reginald Birngruber, Ralf Brinkmann, Johann B. Roider; Real Time Temperature Measurement During Laser Photocoagulation Of Human Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):551.
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In retinal photocoagulation, dosimetry relies on retrospective evaluation of fundus whitening. This carries the risk of focal overtreatment, because effects of identical laser powers are variable. Retinal temperature measurement is expected to predict these effects more precisely. Retinal temperatures during photocoagulation will be presented and correlated with retinal morphology.
Fifty-seven laser lesions from four patients have been studied so far (300 µm, 200 ms, 110-200 mW). They were applied with a modified 532 nm photocoagulator (Zeiss 532s AutoPhoN) that emitted additional trigger signals during laser exposure. Optoacoustic echo recording allowed retinal temperature assessment as published elsewhere. Two values of retinal peak temperatures were assessed for each lesion, i. e. mean over area and maximum at center. Fundus photographs, autofluorescence and spectral domain optical coherence tomography (OCT) images were recorded at baseline, after one hour, one week and three months. Vertical retinal damage extent after one hour was correlated to laser powers and retinal temperatures.
Retinal peak temperatures ranged from 52 to 90°C (mean) and 58 to 120°C (center), respectively. All but one spots were in the clinical therapeutic range. Spots with signal changes in part of the outer nuclear layer (ONL) after one hour displayed a lower mean temperature than those with signal changes of the entire ONL, and spots with affection of all retinal layers had an even higher mean temperature. Mean laser powers of the first subgroup were not lower than those of the second. The inner retinal layers were intact after one week and three months in all but one lesions, while photoreceptor layers were interrupted. Autofluorescence lacked in the lesions after one hour but showed hyperfluorescence of an increased area with hypofluorescent dots after three months.
Optoacoustic data allowed temperature calculation for all study lesions. This is the first report of human in vivo retinal temperature measurement during laser photocoagulation. Mean temperatures of subgroups of laser spots correlated with the early retinal damage. Additional lesions will be examined in this ongoing study. Temperature assessment is expected to allow temperature-feedback automatic laser shut off, as has already been realized on rabbits in vivo.
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