Ex vivo investigation of different μs laser pulse durations for selective retina therapy

Selective retina therapy (SRT) is currently used in clinical studies to treat several chorioretinal diseases. For SRT a laser pulse duration of 1,7 μs is currently used. At this pulse duration the retinal pigment epithelium (RPE) cells are destroyed by transient microbubbles without damaging the neuronal retina. So far it is unclear whether slightly longer laser pulses are still acting thermomechanically or whether thermal effects show responsible for cell damage close above damage threshold. In order to investigate the damage threshold increase with pulse duration, a novel laser with adjustable pulse duration in the range of 2-20 μs was used to investigate RPE damage on ex-vivo porcine RPE explants. The specimen were fixed in an eye model and were exposed to laser pulse energies ranging from 15-150 μJ with a top hat square of 120×120μm², exhibiting a spatial intensity modulation factor of 1,3. Viability tests using binary evaluation result in threshold values with peak radiant exposures of 233 mJ/cm² and 389 mJ/cm² for 2 μs and 20 μs laser durations, respectively. An almost logarithmic increase of the threshold radiant exposure over pulse duration was found.