Selective occlusion of vessels using repeated short laser pulses

The occlusion of arterioles and venules (30 μm in diameter) by means of repeated dye laser pulses (577 nm, 160 μs, 0.5 Hz) was studied in the hamster cheek pouch model. Microscopically visible changes during and after irradiation were recorded and monitored by a video system. The energy necessary per pulse for vessel occlusion with a single pulse (arterioles 5 J/cm², venules 3.5 J/cm²) can be lowered more than 50% with 100 pulses (1.8 J/cm², 1.2 J/cm²). Rupture of vessels, which regularly occurs with a single pulse, can be totally avoided with 100 repetitive laser pulses. Investigations of the temperature dependence of the occlusion rate of arterioles showed different interaction mechanisms with one pulse and 100 pulses (mechanical and thermal respectively). Light and electron microscopic investigations supported this concept of selective occlusion using repeated short laser pulses. Possible clinical applications are portwine stains of the eyelid, neovascularisation on the cornea and subretinal neovascularisation.