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Selective Cell Targeting by Means of a Rapidly Scanned Laser beam
1Özdemir M., 1Koop N., 1Brinkmann R., 1Alt C., 1Birngruber R., 2Lin C. P.,
1Medizinisches Laserzentrum Lübeck GmbH (Lübeck)
2Wellmann Laboratories of Photomedicine, Massachuetts General Hospital (Massachusetts)
Purpose: Selective treatment of the retinal pigment epithelium (RPE) by repetitively applying green µs-laser pulses is a new method for retinal diseases associated with a degradation of the RPE, which spares the retina. We investigated an alternative approach to induce selective RPE effects by rapidly scanning a cw-laser beam across the RPE.
Methods: Two different kinds of irradiation with an Ar+ laser beam (514 nm) are treated. A tophat profil with a diameter of 18.75 µm and a gaussian profil with 16 µm were repetitively scanned across porcine RPE samples in vitro providing an irradiation time of 1.6 µs 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/cm2 (tophat profil) and approximately 200mJ/cm2 (gaussian) when applying 10 exposures with a repetition rate of 500 Hz. The threshold decreases with the number of exposures, a saturation was found at 135 mJ/cm2 (tophat) and 118mJ/cm2 (gaussian) with more than 500 scans applied.
Conclusions: Selective cell targeting has been proved with a laser scanning device. For clinical selective RPE-treatment, an application at a slit-lamp or with a modified retina angiograph seem to be attractive alternatives to the pulsed µs laser device.