• A Goldmann, Latina, or Ritch gonioscopic lens is placed on the anesthetized cornea with a viscous coupling solution. Lens placement is facilitated by asking the patient to look upward and gently inserting the inferior rim of the lens in the lower fornix. Once the lens is in contact with the globe, the patient is asked to look forward (Fig. 22-1). If there is poor visibility of the trabecular meshwork, asking the patient to move his/her gaze toward the mirror may further improve visualization.

• Since the introduction of argon laser trabeculoplasty (ALT) in 1979 by Witter and Wise, there has been remarkably little alteration of the technique. A 50-µm spot size is applied to the trabecular meshwork with up to 1,000 mW of energy, enough to cause minimal blanching of the pigment. The least amount of energy is employed to attain the tissue end point (Fig. 22-2).

• The laser spot is aimed at the junction of the pigmented and nonpigmented
trabecular meshwork. Either a single treatment session of the entire 360 degrees with up to 100 applications or two sessions of 180 degrees each with 50 shots may be performed.

• A topical alpha-agonist (apraclonidine or brimonidine) is given pre- and postlaser treatment to minimize the possibility of a transient intraocular pressure spike (Fig. 22-3). A topical corticosteroid is prescribed four times daily for a week to prevent postlaser inflammation.

• After the treatment, the patient is examined 1 hour later to measure the eye pressure. If a pressure spike occurs, it is treated with glaucoma medications such as oral carbonic anhydrase inhibitors or oral hyperosmotic agents. The patient is reexamined at 1 week and again 1 month after the treatment. At the last visit, a determination is made as to whether the laser therapy was beneficial.

• Theories have been offered, but none verified, as to how laser therapy lowers the eye pressure. The extent of pigmentation of the trabecular meshwork seems to be critical for the success of laser trabeculoplasty. Heavier pigmentation is generally a positive predictor of success. The thermal burn with the argon laser has been shown histologically to result in crater formation with associated disruption of trabecular beams and fibrinous exudates and lysis of trabecular endothelial cells.

• The mechanical theory of argon trabeculoplasty states that laser burns to the trabecular meshwork causes tissue contraction and tightening of the trabecular ring, resulting in a mechanical stretch over the intervening tissue and the widening Schlemm canal.

• The cellular theory suggested that the laser stimulated the trabecular endothelial cells to duplicate, migrate, and repopulate the trabecular meshwork (Fig. 22-4). These cells are thought to be instrumental in maintaining the intratrabecular spaces free of excess extracellular matrix components and debris that have been implicated in the increased resistance to outflow seen in glaucomatous eyes.

• Intraocular pressure is typically reduced 20% to 30% below baseline levels with ALT. Not all eyes are responsive to laser trabeculoplasty. Positive predictors of a favorable response include heavy pigmentation of the trabecular meshwork, age (older patients), and diagnosis (pigmentary glaucoma, primary open-angle glaucoma, and exfoliation syndrome).

• There is an apparent waning of the effect of ALT over time. In long-term studies of 5 to 10 years, ALT failure ranged from 65% to 90%. Retreatment after a previous 360-degree application of ALT is at best a short-term benefit, with failure at 1 year up to 80%. Because there is structural alteration of the outflow system with ALT, repeat treatment may lead to a paradoxical persistent elevation of intraocular pressure. Repeat argon laser application to the angle structures in animals was used by Gaasterland to create an experimental open-angle glaucoma model. If a prompt reduction in intraocular pressure is needed, or a relatively large reduction in pressure is desired (e.g., more than a 30% lowering below baseline pretreatment intraocular pressure), then ALT may not be a good choice. Medication or filtering surgery is more likely to achieve those objectives.

• The current treatment paradigm for glaucoma in the United States is medication first, then ALT, and, finally, filtering surgery. This regimen is only a guideline, and treatment
needs to be individualized for each patient to provide optimum care.