Pathophysiology of Selective Laser Trabeculoplasty

摘要

Laser photocoagulation of the human trabecular meshwork (TM) to reduce the intraocular pressure (IOP) has been performed since the early 1970s. However, it was not until 1979 that Wise and Witter described a modified technique to perform argon laser trabeculoplasty (ALT) that ALT became an established treatment modality for primary open angle glaucoma. Although the precise mechanism by which ALT lowers the IOP is not known, histologic studies show that coagulative thermal damage to the TM is associated with ALT. Similar changes are seen after laser trabeculoplasty with Nd:YAG laser (1064 nm) in a free-running, thermal mode, and the diode lasers. With all these lasers, laser energy is absorbed primarily by the melanin contained within the pigmented TM cells present in the irradiation zone. However, these are continuous wave lasers with pulse duration in the milliseconds range or greater. These pulse durations result in dissipation of the heat from pigmented cells to surrounding tissues, which can denature the proteins and cause coagulative damage to the nonpigmented cells and tissues within the zone of laser irradiation.