Selective laser trabeculoplasty: physiology and effects of SLT

For more than a century and a half, primary therapy for intraocular pressure (IOP) reduction in eyes with open-angle glaucoma (OAG) and ocular hypertension (OHT) has consisted of topical medications, but primary medical therapy for glaucoma has many important limitations. It is well established that nonadherence with glaucoma medical therapy is common, and nonadherence increases the risk of disease progression. Another limitation is that topical drops have side effects both local and systemic. The most common of these is chronic ocular surface disease, estimated to occur in 30%–70% of patients. Selective laser trabeculoplasty (SLT) is a treatment option that overcomes these limitations of medical therapy with no need for concordance/compliance with regular drug administration, no systemic side effects, and minimal risk of local (ocular) side effects. The mechanism by which SLT lowers IOP is incompletely characterized. Three theories have been proposed: a mechanical effect, a biochemical effect, and a cellular effect. At the organ level, SLT’s effect on aqueous humor dynamics is to increase trabecular outflow. The Laser in Glaucoma and Ocular Hypertension Trial was a robustly designed and appropriately powered randomized trial in newly diagnosed and treatment-naïve patients with mild–moderate OAG or high-risk OHT. In all, 718 patients were enrolled, assigned to primary SLT or primary medical therapy, and followed for 3 years. At 36 months, mean IOP was similar between groups (16.6 mmHg in the SLT group and 16.3 mmHg in the medication group). Of SLT-treated eyes, 76.6% required only a single SLT during the 3-year period, and 78.2% remained medication-free at 3 years. Most ophthalmologists acknowledge that they would prefer SLT to medical therapy if diagnosed with OAG or OHT. And yet the widespread adoption of an SLT-first practice pattern has remained elusive. Common reasons for not adopting an SLT-first practice pattern include lack of time for the requisite patient education and lack of patient enthusiasm. We believe that these are in fact the same issue, and if educated properly, most patients—just as most ophthalmologists—would choose primary SLT over medical therapy. The tantalizing possibility is that regenerating tissues and restoring function by laser-stimulated stem cell repopulation of the trabecular meshwork could control IOP for many years without need for regular hypotensive medication. To achieve this by SLT, early in the disease and repeated regularly, would be a paradigm shift indeed.