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E. Poerksen, H. Elsner, D. Theisen–Kunde, G. Schuele, P. Hamilton, H. Laqua, R. Birngruber, R. Brinkmann, J. Roider; Selective Retina Treatment (SRT): Clinical Investigation of an Optoacoustic On–Line Dosimetry Control . Invest. Ophthalmol. Vis. Sci. 2005;46(13):294.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Selective Retina Treatment (SRT) is currently investigated in a prospective multicenter clinical trial for patients with focal diabetic maculopathy (DMP). In comparison to conventional Argon laser treatment, SRT uses a train of short laser pulses in order to selectively damage the RPE while sparing retinal structures. The main problem is that the laser lesions are ophthalmoscopically invisible. As a dosimetry control, we investigated an on–line dosimetry control system. It detects the microbubble formation in the RPE, which accounts for the cell damage. Methods: So far 32 patients have been treated in Luebeck with an SRT–Laser (frequency doubled Q–switched Nd:YLF at 527nm, pulsed at 100Hz, 30 pulses with 1,7µs). Test expositions are placed close to the vascular arcades using defined energy levels (100–400 µJ). Thermoeleastic and microbubble induced pressure waves are recorded with an ultrasonic transducer embedded in a contact lens. A mathematical algorithms reduces the transients to a single OA–value (0.07–4.9). Post SRT Fluorescein (FA) and Indocyanin Green (ICG) angiography is performed to visualize RPE lesions caused by SRT. OA values and ICG/FA results are correlated. Results: SRT–lesions are sharply demarked in ICG. FA shows more diffuse lesions because of leakage. Automated evaluation of the angiographic visibility against OA demonstrated that by raising above the individual OA–noise level lesions in angiography were observed. A sensitive threshold could be reached. By setting the appropriate angiographic visibility–probility to 95% resp. 100%, OA thresholds can be derived to 0.137 resp. 0.15. Above these levels visible effects are always observed in angiography. OA above 3.0 can lead to biomicroscopically visible lesions (damage threshold). Comparing the therapeutic and damage energy range shows interindividual overlap. This fact makes an individual precise on–line dosimetry compulsory. Conclusions: The OA value is highly sensitive to determine RPE–SRT–Effects and therefore sufficient for on–line dosimetry control in SRT. It is necessary to optimize the interindividual therapeutic energy during treatment. OA could be the first step in automated on–line dosimetry in selective RPE laser treatments.
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