Selective damage of pigmented cells by means of a rapidly scanned cw laser beam

Selective targeting the retinal pigment epithelium (RPE) while sparing adjacent tissue such as the photoreceptors has been demonstrated by repetitively irradiating the fundus with a train of green μs-laser pulses. The aim of this study was to investigate selective RPE effects alternatively by means of rapidly scanning a cw-laser beam across the RPE to obtain the required μ s-illumination times. The radiation of an Ar⁺ laser (514 nm) was transmitted through a 25 μm core diameter fiber to a scanner unit. The fiber tip was imaged onto the object plane with a magnification of 0.75. The beam was repetitively scanned across porcine RPE samples in vitro providing an irradiation time of 1.6 μ s. Cell damage was investigated with a fluorescence viability assay. The ED₅₀ cell damage power was determined to 580 mW when applying 10 exposures with a repetition rate of 500 Hz. It decreases to 250 mW for 500 exposures and more. The threshold keeps constant for an axial focus displacement of about 250 μ m. In conclusion, selective cell targeting has been proved with a laser scanning device. The technique can be adapted for clinical RPE treatment to a slit-lamp or by modifying a retina angiograph.