Morphologic Changes in Trabecular Meshwork after Patterned and Argon Laser Trabeculoplasty in Cats

Abstract

Purpose: Patterned laser trabeculoplasty (PLT) was introduced as it claimed to cause less thermal damage and provide more uniform coverage of the trabecular meshwork than argon laser trabeculoplasty (ALT). The objective of this study was to investigate morphologic changes in the trabecular meshwork after PLT or ALT in cats. Materials and Methods: We performed ALT in the right eyes and PLT in the left eyes of 6 domestic cats. A seventh cat was assigned as a control. Two ranges of laser energy were used for PLT: supra-threshold energy of 400-450 mW in 3 cats and sub-threshold energy of 250 to 350 mW in 3 cats. Specimens were obtained at 1, 4 and 9 weeks after treatment. Structural changes in the trabecular meshwork were evaluated by light microscopy and scanning electron microscopy. Results: The trabecular meshwork after supra-threshold PLT revealed coagulative damage such as a crater-like lesion with disruption of trabecular beams in early period and extensive membranous obliteration in the late period (at 4 and 9 weeks after treatment), which were comparable to tissue changes after ALT. Sub-threshold PLT resulted in thinning of the uveal meshwork and denudation of trabecular endothelial cells whereas it did not disrupt trabecular beams. Nevertheless, following sub-threshold PLT, partial membranous coverages were observed in the trabecular meshwork in the late period. Conclusions: When used at sub-threshold power, PLT caused less thermal damage to the trabecular meshwork than ALT. However, it did not effectively prevent late scarring of the trabecular meshwork in cats.