Abstract
Purpose. To compare morphologic changes in human trabecular meshwork (TM) after selective laser trabeculoplasty (SLT) and argon laser trabeculoplasty (ALT). Design. Laboratory evaluation of ex vivo human eye TM after laser trabeculoplasty. Methods. Corneoscleral rims from human cadaver eyes were sectioned and treated with varying powers of either SLT or ALT. Specimens were examined using light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results. TEM of SLT at all powers resulted in disrupted TM cells with cracked and extracellular pigment granules. SEM of SLT samples treated at high power revealed tissue destruction with scrolling of trabecular beams. SEM of ALT-treated tissue showed increasing destruction with exposure to higher power. The presence or absence of “champagne” bubbles during SLT did not alter the histologic findings. Conclusions. SLT-treated human TM revealed disruption of TM cells with cracked, extracellular pigment granules, particularly at higher treatment powers. Tissue scrolling was noted at very high SLT energy levels. ALT-treated tissue showed significant damage to both the superficial and deeper TM tissues in a dose-dependent fashion. Further studies are needed to guide titration of treatment power to maximize the IOP-lowering effect while minimizing both energy delivered and damage to target tissues.
Highlights
The use of laser surgery in the treatment of glaucoma has been an option for decades, providing an alternative to topical glaucoma medications and more invasive incisional surgeries [1]
Laser trabeculoplasty is a well-established treatment for glaucoma, the exact mechanism of action and changes that occur in targeted tissues remains unclear
We confirmed these findings for argon laser trabeculoplasty (ALT) across a wider range of treatment powers and noted a dose-dependent response, with larger craters and more tissue destruction seen with higherpowered treatments
Summary
The use of laser surgery in the treatment of glaucoma has been an option for decades, providing an alternative to topical glaucoma medications and more invasive incisional surgeries [1]. Initial efforts employed a Q-switched ruby laser to perform direct goniopuncture, the intraocular pressure (IOP) lowering effect was short-lived [2]. Wise and Witter shifted the focus away from the concept of direct tissue puncture towards what they termed “laser trabecular tightening” with the development of argon laser trabeculoplasty (ALT) [3,4,5]. The Glaucoma Laser Trial (GLT) showed that initial use of ALT was at least as efficacious as treatment with the topical medications available at that time [6, 7]. Termed selective laser trabeculoplasty (SLT), it was postulated to offer the advantage of selective treatment of pigmented trabecular meshwork (TM) cells without collateral thermal or structural damage
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