Targeting of the retinal pigment epithelium (RPE) by means of a rapidly scanned continuous wave (CW) laser beam

Background and Objectives: Selective treatment of the retinal pigment epithelium (RPE) by repetitively applying green is-laser pulses is a new method for retinal diseases associated with a degradation of the RPE, which spares the neural retina. We investigated an alternative approach to realize repetitive mus-laser exposure by rapidly scanning a continuous wave (CW)-laser-beam across the RPE. Study Design/Materials and Methods: An Ar+ laser beam (514 nm) with a diameter of 18.75 mum was repetitively scanned across porcine RPE samples in vitro providing an irradiation time of 1.6 mus per point on the central scan axis. RPE cell damage was investigated by means of the fluorescence viability assay Calcein-AM. Results: The ED50 cell damage is 305 mJ/cm(2) when applying 10 scans with a repetition rate of 500 Hz. The threshold decreases with the number of scans, a saturation was found at 135 mJ/cm(2) with more than 500 exposures applied. The depth of focus in beam direction is 350 mum, defined by an increase of the threshold radiant exposure by 20%. Conclusions: Targeting of pigmented cells with high local resolution has been proved with a laser-scanning device. Looking ahead selective RPE-treatment, the adaptation of a laser-scanning device on a slit-lamp or into a modified retina angiograph seems to be an attractive alternative to the pulsed mus laser device. (C) 2003 Wiley-Liss, Inc.