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R. Brinkmann, H. Stoehr, L. Ptaszinsky, M. Saeger, E. Pörksen, A. Fritz, J. Roider, R. Birngruber; Optic Interferometric Realtime Dosimetry for Selective Retina Therapy (SRT). Invest. Ophthalmol. Vis. Sci. 2008;49(13):2767. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Selective retina therapy (SRT) is a new method to treat retinal diseases associated with a decreased metabolism at the chorio-retinal junction. By applying a train of µs laser pulses, irradiated RPE cells are selectively damaged by microbubbles nucleating around the strongly absorbing intracellular melanosomes. The adjacent photoreceptors and the neural retina are completely spared. In the healing period of 1-2 weeks, the RPE is rejuvenated. Due to the optical invisibility of the RPE defects, we developed and investigated an optic-interferometric on-line dosimetry system to monitor microvaporization. In vitro, in vivo and first clinical results in comparison to standard fluorescein angiography (FLA) are presented.
An optical fiber based interferometer was adapted to a laser slit lamp to probe the irradiated retinal spots simultaneously during treatment. A frequency doubled Q-switched Nd:YLF laser (527 nm, 350 ns) served to irradiate freshly harvested porcine RPE-samples in vitro an few rabbits in vivo. The interferometric transients were correlated to cell damage observed with a vitality stain and leakage visibility using FLA, respectively. Clinically, transients were recorded during standard SRT (SRT laser: 527nm, 100 Hz, 30 pulses a 1.7 µs) on patients with chronic serous chorioretinopathy (CSCR).
High frequencies in the MHz range were only detected in vitro in case of cell damage, which can be attributed to microbubble nucleation and dynamics. Due to the eye’s small numerical aperture of NA=0.1 the signal to noise ratio is worse in vivo, however, microbubble formation could be detected approximately 30% above angiographically determined threshold radiant exposure. First data on CSCR-patients will be reported and correlated to the angiographic visibility after treatment as well as to optoacoustic dosimetry as the current method to determine bubble formation.
Optic interferometery can detect laser induced microbubble formation in SRT, non-invasively in realtime for every single laser pulse. Thus the method has the potential to serve as a basis to realize an automatic feedback-controlled SRT, unburden the clinician from any dosimetry.
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