Dosimetry for microsecond selective laser trabeculoplasty

Abstract

Selective Laser Trabeculoplasty (SLT) is a treatment option for open-angle glaucoma, however, it lacks an instant evidence for successful irradiation. So far ophthalmologists use the visible appearance of permanent champagne like bubbles as an indicator for appropriate pulse energy. We hypothesize that micro bubbles, which take place far below the appearance of macro bubbles already trigger the therapeutic benefit. Here we present two techniques for real-time detection of the onset of micro bubbles. The trabecular meshwork of freshly enucleated porcine eye globes was irradiated, in contrast to conventional SLT, with a series of 15 pulses with a pulse duration of 1.7 µs and with increasing energy at a repetition rate of 100 Hz per each spot of 200 µm in diameter. Both observation methods, an optoacoustic and an optical, are equally capable of detecting micro bubble nucleation, with sensitivities over 0.83 and specificities over 0.89. We demonstrated an accurate method for detection of micro bubble formation in SLT. In case that the therapeutically demanded pressure reduction is already achieved with these micro bubbles, which needs to be proved clinically, then the methods presented here can be used in a feedback loop controlling the laser irradiation. This will unburden the clinicians from any dosing during SLT.