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Selective laser trabeculoplasty
Last reviewed: 04.07.2025
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Selective laser trabeculoplasty technique
The pulsed dual neodymium:yttrium-aluminum-garnet (YAG) laser was used by Latina in 1998 for trabeculoplasty. It was developed for selective action on pigmented tissue and for minimization of side effects. Unlike the continuous-wave argon laser, the selective laser does not damage the trabecular zone thermally. Due to the fixed size of the dots of 400 μm, the dots of 50 μm used in SLT seem very small. Thus, the distances between the laser action points in selective laser trabeculoplasty (SLT) are much more compact, practically merging. The size of the dots in selective laser trabeculoplasty is so large that one beam covers the entire angle. When using a laser, the number of pulses (50-60), the size of the angle of action (180-360°) and the power (up to 0.8 J) can be varied.
The final power level is determined by the tissue response to the initial laser application. Bleaching of the pigmented trabecular meshwork with minor bubble formation due to evaporation is ideal. With significant bubble formation, the power is reduced. The use of low power is strongly recommended for operations on heavily pigmented angles, as occurs in pigment glaucoma.
Mechanism of action of selective laser trabeculoplasty
Scanning electron microscopy reveals a difference between the application of an argon laser with "melting" of the trabecular bundles and a selective laser with minimal, if any, structural damage to the trabecular meshwork. Thus, the theory of mechanical stretching does not apply to the effect of a selective laser on intraocular pressure. In vitro cultures of trabecular meshwork cells were treated with an argon and a selective laser. The argon laser application damaged both pigmented and nonpigmented cells. In contrast to the argon laser, the selective laser affected only pigmented cells.
The involvement of macrophages in the outflow system has been demonstrated in animal models and in human eyes. Macrophages can release chemical mediators that regulate the rate of outflow. It is claimed that increasing the concentration of interleukins after laser exposure improves the outflow of moisture.
Efficiency of selective laser trabeculoplasty
Comparative studies have confirmed that neodymium:yttrium-aluminum-garnet laser and selective laser trabeculoplasty are equally effective in reducing intraocular pressure in eyes refractory to medical therapy. Preliminary data suggest that initial use of selective laser trabeculoplasty before medical therapy reduces intraocular pressureintraocular pressure by 24-30% of the initial level. Because of the lack of structural damage with selective laser trabeculoplasty, repeated attempts at laser therapy should theoretically be safe and could potentially reduce intraocular pressure. Successful reduction of intraocular pressure has been reported after selective laser trabeculoplasty in patients who had previously undergone unsuccessful ALT.