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Selective Laser Trabeculoplasty

Eye (Lond). 2018 May;32(5):863-876. PMID: 29303146

Glaucoma is a progressive multifactorial disease characterised by damage to the optic nerve. It is strongly associated with elevated intraocular pressure (IOP) but may also occur with IOP in the normal range. The mainstay of glaucoma treatment is lowering of IOP to slow or prevent further progression and visual loss. applied radiation energy could be selectively absorbed by a pigmented cell population within a tissue to cause localised damage; a process known as selective photothermolysis (SP) ALT (Argon Laser Trabeculoplasty) ALT fulfilled the first requirement of SP, as melanin within the pigmented TM acted as the chromophore. However, the laser duration of ALT (~0.1 s) was longer than the thermal relaxation time of melanin (1 μs) allowing heat generated within pigmented cells to dissipate and damage surrounding TM IOP reduction in ALT was mediated by an increase in aqueous outflow,  postulated by mechanical changes as well as biologic signaling changes ALT induced an initial 30% reduction in IOP; however, the effect of ALT diminished over time The main adverse events related to ALT were transient acute IOP spikes following laser, development of peripheral anterior synechiae (PAS), corneal endothelial changes, and acute anterior uveitis The Glaucoma Laser Trial Research Group found better IOP control with ALT alone compared to a single medication at 6 months, 1 year, and 2 years but inferior control at 5 years or if two medications were used SLT (Selective Laser Trabeculoplasty) Introduced by Latina and Park in 1995, SLT uses a 532 nm Q-switched, frequency-doubled Nd:YAG laser that delivers a shorter pulse duration (3 ns). It satisfies the dual criteria of SP, preventing heat dissipation outside of pigmented TM cells and causing less collateral damage SLT increases aqueous outflow through the TM TM damage could be energy dose-dependent SLT has been demonstrated to induce biological changes that modulate increased aqueous outflow through the TM, including changes in gene expression, cytokine secretion, matrix metalloproteinase induction, and TM remodelling In vitro studies demonstrate that SLT and prostaglandin (PGA) analogues may share a common pathway of action by inducing intercellular junction disassembly in Schlemm’s canal and TM cells thus increasing aqueous permeability Using ocular hypotensive agents before or immediately after surgery lowered the risk of IOP spikes Topical anti-inflammatory drops are commonly prescribed post trabeculoplasty to mitigate early inflammation. anti-inflammatory drops after SLT do not cause a significant reduction in inflammation or altered IOP-lowering efficacy On the basis of the commonly adopted success criteria of IOP reduction >20% from baseline IOP success rates vary from  66.7 to 75% eyes at 6 months 58 to 94% at 12months 40 to 85% at 2years 38 to74% at 3years 38 to 68% at 4 years 11.1 to 31% at 5 years SLT demonstrated comparable efficacy with ALT in patients on maximally tolerated medical treatment 360 SLT had similar outcomes to latanoprost (worse for 90 or 180 SLT) SLT is as effective as medication (either PGA monotherapy or dif- ferent topical medications used in combination) for IOP control SLT is effective as an adjunct in patients who have previously undergone ALT SLT is effective as an adjunct in OAG patients on medical treatment SLT and PGAs are successful at reducing IOP variation (a potential risk factor for glaucoma progression) in POAG patients over the whole follow-up period, but PGAs are more effective repeat SLT can be applied to any TM area with similar efficacy and supports the theory that SLT retreatment is similarly effective to primary treatment. repeat SLT appears to be comparable to initial SLT. It achieves a similar absolute level of IOP control but mean IOP reductions following repeat SLT appear to be smaller SLT is not commonly performed in primary angle-closure glaucoma (PACG) patients. Visualisation of the TM within the angle is required, which can be limited in these patients mean IOP reduction for PXF eyes of ~31.5% at 12 months and 31.4% at 18 months. Sixty-four per cent of patients maintained ≥20% IOP reduction at 18 months and 47% at 36 months Increased frequency of post-procedure pain, inflammation and IOP spikes were noted in the Pigmentary Glaucoma (PG) group TM pigmentation in PG could cause more energy absorption following SLT resulting in increased pain. This has led to suggestions that lower  energy settings be used in PG patients topical medications particularly topical carbonic anhydrase inhibitors was associated with SLT treatment success Safety profile of SLT SLT is a safe procedure, which is well-tolerated with low complication rates. Complications associated with SLT are usually transient and self-limiting. IOP spikes immediately post laser can occur, with reported rises of ≥5 mm Hg being reported in up to 28% of eyes Anterior chamber inflammation is also common post SLT with up to 83% of eyes demonstrating some degree of inflammation (usually transient) Unlike ALT, the development of PAS is uncommon post SLT. Only 2.86% of cases developed PAS with increased occurrence after repeat SLT Transient corneal endothelial changes are well described post SLT. These can occur acutely, within an hour of treat- ment and are mostly self-limiting with no lasting changes to visual acuity, central corneal thickness, or endothelial cell count Trans-scleral or direct SLT  allows 360° treatment around the perilimbal sclera overlying the TM without a gonioscopy lens This eliminates corneal and gonioscopy- related side effects

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