Selective Laser Trabeculoplasty

Selective laser trabeculoplasty (SLT) is a relatively recent modality for treating patients with open-angle glaucoma and ocular hypertension. Similarly to argon laser trabeculoplasty, SLT uses laser energy to target the trabecular meshwork and lower intraocular pressure by increasing aqueous outflow. However, although argon laser trabeculoplasty has been used successfully for several years to treat open-angle glaucoma, it has been shown to cause collateral thermal damage to the trabecular meshwork (Kramer & Noecker, 2001). This often results in scarring and synechiae formation, which compromise the possibility of further retreatment. SLT uses a low-energy pulse (0.8 mJ to 1.2 mJ) and short pulse duration (approximately 3 nsec) in order to selectively target trabecular pigmented cells and reduce energy dissipation to the surrounding tissue. It was first reported in 1995 when Latina and Park irradiated a culture of pigmented and non-pigmented trabecular meshwork cells with different types of laser sources and analyzed their effect by electron microscopy (Latina & Park, 1995). They showed that selective cytotoxicity on pigmented trabecular meshwork cells could be achieved with pulse durations of 10 nsec and irradiance between 20 mJ/cm2 and 1000 mJ/cm2 for the 532 nm, frequency-doubled Q-switched Nd:YAG laser. Fracture of melanin granules and rupture of lysosomal membranes in the pigmented trabecular meshwork cells and absence of ultrastructural damage in neighboring non-pigmented cells were revealed.