A Proposal for the Use of a Fixed Low-Energy Selective Laser Trabeculoplasty for Open Angle Glaucoma

Abstract

Selective laser trabeculoplasty (SLT) has been in routine clinical use for over 20 years with millions of patients successfully treated and a low rate of clinically significant complications. The procedure requires the clinician to manually position the laser beam on the trabecular meshwork using a gonioscopy lens and to titrate the SLT laser energy based on the amount of pigmentation in the angle, as well as the observation of small bubbles produced by the laser effect. We propose that SLT energy titration is unnecessary either to achieve intraocular pressure (IOP) reduction or to minimize potential side effects. Ample evidence to support our proposal includes multiple clinical reports demonstrating comparable levels of IOP reduction resulting from different laser energies, a large variety of energy and other laser parameters used in commercially available SLT lasers, and the nature of the laser-induced changes in the trabecular meshwork tissue with respect to energy. Despite these variations in laser parameters, SLT consistently reduces IOP with a low complication rate. We propose that using low fixed energy for all patients will effectively and safely lower patients' IOP while reducing the complexity of the SLT procedure, potentially making SLT accessible to more patients.

FIGURE 1

OCT image of anterior chamber superimposed with SLT beam to scale. The convergence angle of the SLT beam is shown as a typical 3-degree full angle. The 400 µm spot diameter is effectively elongated at the TM by the high angle of incidence. The energy loss from the “overfilled” spot by irradiation of tissue beyond the TM is indicated graphically. OCT indicates optical coherence tomography; SLT, selective laser trabeculoplasty; TM, trabecular meshwork.

FIGURE 2

False color Intensity maps and intensity plots of beam profiles measured along orthogonal planes (dotted lines) of SLT spots imaged at the visible aiming beam focus locations. Colors denote intensity. Beam lineouts along the axis of the spot are shown on the left and bottom of each plot. The Gaussian beam profile of a laboratory laser (left) and the so-called “super-Gaussian” beam profile of a commercial SLT laser measured in the target plane (right). SLT indicates selective laser trabeculoplasty.

FIGURE 3

Beam profiles for different laser shots emitted by the same laser operating with the same nominal settings.