Laser iridectomy was one of the first laser techniques to achieve widespread application in glaucoma. It was initially performed using argon lasers. Creation of iridectomies with these continuous-wave, low-energy (500 to 1000 mW), long-duration (0.1 to 0.2 seconds) lasers was difficult and required precise technique. The introduction of high-energy, short-duration (nanosecond), pulsed Nd:YAG lasers converted this procedure into one that most trained ophthalmologists could easily perform. As a result, laser iridectomy has become the standard technique for treating papillary block angle-closure glaucoma except in those situations where lack of corneal clarity precludes delivery of the laser energy to the iris.¹

Creation of a through-and-through hole in the iris is made easier by administration of a drop of 1% pilocarpine 15 to 20 minutes prior to the treatment. The resulting miosis will place the iris on stretch and enhance pupillary block causing more fluid to collect between the iris and the lens in the posterior chamber. Use of a high plus contact lens such as a Wise or Abraham Lens focuses and concentrates the laser energy at the point of treatment, and then more rapidly defocuses the energy so that if any of it gets through the iridectomy, it will not be sufficiently intense enough to cause any retinal burns. If bleeding occurs, placing pressure on the globe with the contact lens for 30 to 60 seconds usually will be sufficient to stop it.

Recently, a second indication for laser iridectomy has been suggested. It has been hypothesized that in pigmentary glaucoma reverse pupillary block leads to abrasion of pigmented epithelial cells on the back of the iris releasing pigment granules that then plug the trabecular meshwork and may cause elevated intraocular pressure (IOP).² It has been demonstrated with ultrasonic high-resolution biomicroscopy (UBM) that laser iridectomy eliminates this reverse pupillary block and reduces concavity of the peripheral iris.³ It is believed that this will halt the release of additional pigment granules and as the existing pigment is cleared from the trabecular meshwork the IOP may decline. There have not yet been any long-term, controlled, prospective studies to validate the value of this treatment so its use is still the subject of much debate. If it is to be used, it probably should be reserved for eyes where there is noticeable posterior concavity of the peripheral iris.

Laser trabeculoplasty is probably the most widely used laser technique for the treatment of glaucoma. In spite of its very extensive use since its introduction by Wise and Witter⁴ in 1979, there are still many unanswered questions regarding the mechanism(s) by which it lowers IOP. While a number of different types of lasers (e.g., pulsed, continuous wave) and different wavelength laser energies have been shown to be effective in lowering IOP, the large majority of experience with this technique has been with continuous-wave argon lasers.⁵

Laser trabeculoplasty is effective in approximately two-thirds to three-quarters of patients with primary open-angle glaucoma. In these eyes, it lowers the IOP approximately 25%. It also is beneficial in some secondary open-angle glaucomas such as exfoliation syndrome glaucoma and pigmentary glaucoma, in eyes that have had previous filtering surgery, and in eyes that have had surgical or laser iridectomies because of acute angle-closure glaucoma and have residual elevated IOP with open angles. There is still some question as to whether it is as effective in pseudophakic eyes as in phakic ones, but is generally effective in these eyes as well. It has been well documented that it is more effective in older patients than younger ones with the notable exception of pigmentary glaucoma, where it is effective in young individuals. There have been some reported cases of glaucoma made worse by laser trabeculoplasty in patients with juvenile glaucoma and there have been mixed results in angle-recession glaucoma.

There have been two major multicenter collaborative studies that have been conducted to help define the role of laser trabeculoplasty in glaucoma therapy. The first of these studies was the Glaucoma Laser Trabeculoplasty Trial (GLT) in which laser trabeculoplasty was compared to medical therapy as the initial treatment for primary open-angle glaucoma. The results of this study showed that laser trabeculoplasty as initial therapy was both safe and effective in the treatment of open-angle glaucoma, but in a large majority of patients it was not sufficient by itself to lower the intraocular pressure sufficiently to control the disease, and additional medical therapy was required.⁶ There was a trend to suggest that the laser-first eyes might have done slightly better than the medicine-first eyes but these differences were not statistically significant.

The second study was the Advanced Glaucoma Intervention Study (AGIS). In this study, patients with medically uncontrolled open-angle glaucoma were randomly assigned to either laser trabeculoplasty or surgical trabeculectomy for the treatment of their glaucoma. There was stratification within the study population based on race, and there was some evidence that there was a racial difference in the response to treatment with the black patients initially showing a slightly better visual field response to the trabeculoplasty first, while the white patients responded better to trabeculectomy first. In both racial groups, however, lower IOP levels were achieved by filtering surgery and fewer patients required additional surgical treatment in the trabeculectomy-first eyes.⁷

The use of laser trabeculoplasty has declined somewhat in recent years, probably as a result of several factors. One has been the introduction of more potent topical ocular hypotensive eyedrops, namely the prostaglandin-type agents. These have a greater pressure-lowering effect than laser trabeculoplasty and have a better side effect profile than the β-blockers that had been the mainstay of topical glaucoma therapy previously. A second factor was the recognition of the fact that the effect of laser trabeculoplasty seemed to decrease over time, such that approximately half of the patients treated have returned their IOP to pretreatment levels after an average of approximately 5 years.

In 2001, a new technique for laser trabeculoplasty was introduced and has been named selective laser trabeculoplasty (SLT). It utilizes a frequency doubled, pulsed Nd:YAG laser.⁸ In this technique, there is much less thermal damage to the trabecular meshwork than there is with argon laser trabeculoplasty. The initial IOP response to SLT appears to be approximately the same as that of argon laser trabeculoplasty (ALT). The proponents of this technique claim that because of the lack of thermal damage to the trabecular meshwork, it can be repeated over time with renewed effectiveness and without damage to the trabecular meshwork. There are several reports of case series where patients with previous ALT whose pressure had come back up were treated successfully with SLT. Long-term follow-up studies will be needed to define what the role of SLT will be in the future.

When performing laser trabeculoplasty, a mirrored Goldmann gonioscopy lens is used to focus the laser energy in the angle. The laser spot is aimed at the junction of the pigmented and nonpigmented trabecular meshwork. With ALT, a 50-μm spot is used and the duration of the burn is 0.1 second. Many adjust the laser energy to a level where they see a blanching of the trabecular meshwork but without bubble formation (usually 500 to 1000 mW). The author routinely uses 800 mW on all eyes whether there is blanching or not. With SLT and with diode laser trabeculoplasty, there is less visual response to the laser treatment so one cannot treat to a reaction point. Some initially treat 180 degrees of the meshwork with 50 laser applications and then treat the remaining 180 degrees with an additional 50 laser applications approximately a month later if there has not been a sufficient reduction in IOP. Others treat the entire 360 degrees of the angle with 100 applications in a single session.

Approximately 10% to 20% of eyes will have an acute rise in IOP 1 to 3 hours after the trabeculoplasty so the IOP needs to be monitored immediately posttreatment. The risk of such IOP spikes can be reduced by pretreating the eye with an α₂-adrenergic agent such as apraclonidine or brimonidine prior to the laser treatment. Most ophthalmologists prescribe a topical anti-inflammatory agent such as a corticosteroid agent to their patients for several days after the treatment. The majority of the IOP reduction will be seen by 1 week but some additional effect may be noted over the following several weeks.

Lasers play a major role in the treatment of neovascular glaucoma; however, the treatment here is used more by retina specialists than by general ophthalmologists or glaucoma specialists. The main treatment technique in this area is panretinal photocoagulation (PRP) therapy. The high risk of developing rubeosis iridis and neovascular glaucoma after an ischemic central retinal vein occlusion has been well documented. Some individuals still recommend prophylactic PRP when extensive retinal ischemia has been documented by fluorescein angiography, however, most specialists delay the PRP until evidence of rubeosis becomes manifest. In the rubeosis that is seen with diabetes mellitus, there is fairly wide agreement that PRP should be reserved until there is evidence of neovascularization in the angle, because many people with diabetes with just rubeosis on the iris elsewhere, do not progress to angle closure. When PRP is performed, there is usually regression of rubeosis and more definitive forms of glaucoma therapy, such as trabeculectomy or shunt procedures can more safely and effectively be used if needed.

In the past, an additional form of laser therapy for rubeosis iridis was utilized. Abnormal vessels on the iris, particularly vessels bridging the angle were ablated with focal photocoagulation. This technique has been largely abandoned today because it does not work.

Numerous attempts have been made to use laser energy to create openings through the scleral wall from the anterior chamber to the subconjunctival space. Many of these have attempted to use noninvasive techniques so as to reduce the risk of endophthalmitis or other operative complications. Others have been designed with the idea that the opening created using a selected laser energy may have some advantages over those created with other surgical techniques.