Clinical application of optoacoustic on–line dosimetry in Selective–RPE–Laser–Treatment (SRT)

Abstract

Abstract: : Purpose: Selective–RPE–laser–treatment (SRT) is currently investigated in a multicenter clinical trial for patients with diabetic maculopathy (DMP). In comparison to conventional argon laser treatment SRT uses a train of µs laser pulses. Due to intracellular microbubble formation around the strongly absorbing melanosomes the irradiated RPE cells are selectively damaged sparing retinal structures. The RPE lesions are biomicroscopically invisible and therefore conventional dosimetry of laser energy is impossible. In this study optoacoustic value (OA) measurements recorded during SRT are evaluated in order to establish a reliable on–line dosimetry means. Methods: 17 patients with focal DMP have been treated in Luebeck with SRT using a frequency doubled Q–switched Nd:YLF laser (527 nm) by applying a train of 30 pulses, each 1,7 µs, at a repetition rate of 100 Hz. Prior of treating the central pathology test expositions are placed close to the vascular arcades using defined energy levels (100–400 µJ). For each SRT exposition an OA value is recorded by a modified contact glass with an integrated microphone. 1 hour post SRT Fluorescein (FLA) and Indocyanin Green (ICG) angiography is performed to visualize RPE lesions caused by SRT expositions. OA values and angiography results are correlated to determine an OA value threshold causing visible SRT lesions on ICG. Results: ICG delineated much more precisely RPE lesions caused by SRT expositions than FLA does. The recorded OA values showed a range between 0,10 and 4,00. At an OA value of 0,3 we have been able to determine a threshold for the used contact glas. At laser energy levels producing OA values of 0,3 and above we have seen visible RPE lesions on ICG in > 96%. At energy levels producing OA–values below 0,3 we have seen visible RPE lesions on ICG in < 21%. Conclusions:Having determined the OA–value threshold for the used contact glas, optoacoustics on–line dosimetry is a reliable means in order to perform save and efficient SRT.

Keywords: laser • retinal pigment epithelium • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials