Comparison of Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty

1. Essentials of Glaucoma Therapy
2. Lasers
3. Comparison of Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty

←Selective Laser Trabeculoplasty

Laser Peripheral Iridotomy →

Primary authors	Fiorella Saponara, MD Joshua D. Stein, MD, MS

Although previous chapters in this book describe in detail the indications, safety profile, effectiveness, risks, and complications of argon laser trabeculoplasty (ALT; Chapter 20) and selective laser trabeculoplasty (SLT; Chapter 21), in this chapter we compare and contrast these surgical procedures with one another.

Efficacy of Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty

A few studies have compared the efficacy of ALT and SLT at lowering intraocular pressure (IOP). With sample sizes ranging from 36 to 60 patients, and follow-up times ranging from 3 months to 5 years, these studies have demonstrated that ALT and SLT achieve a relatively similar level of IOP reduction. The series with the longest length of follow-up, by Juzych et al, found a 24% reduction of IOP among patients with primary open-angle glaucoma who underwent ALT, and a 27% reduction in IOP among those who received SLT—a difference in pressure lowering that was not statistically significant. Table 22-1 shows the findings from the studies in the literature comparing the efficacy of these 2 lasers.

Table 22-1. Summary of Selected Studies That Compare Argon Laser Trabeculoplasty With Selective Laser Trabeculoplasty

Author	Glaucoma	# of Eyes	Follow- Up	ALT Preop IOP (mm Hg)	ALT Postop IOP (mm Hg)	ALT Reduction (%)	SLT Preop IOP (mm Hg)	SLT Postop IOP (mm Hg)	SLT Reduction (%)	P Value
Damji et al2	POAG	18 ALT 18 SLT	6 months	22.5 ± 3.6	17.7 ± 3.3	21.3	22.8 ± 3.0	17.8 ± 4.8	21.9	.97
Popiela et al3	Mixed	27 ALT SLT	3 months	20.3 ± 4.0	17.6 ± 3.6	13.0	21.3 ± 4.8	18.4 ± 4.6	13.4	.84
Martinez-de-la-casa et al4	POAG	20 ALT SLT	6 months	23.6 ± 3.8	19 ± 3.2	19.5	24.0 ± 4.7	18.6 ± 4.2	22.2	.74
Juzych et al1	POAG	40 ALT SLT	5 years	24.3 ± 4.1		23.5 ± 25.2	23.9 ± 2.6		27.1 ± 21.4	.58
ALT indicates argon laser trabeculoplasty; SLT, selective laser trabeculoplasty; IOP, intraocular pressure; POAG, primary open angle glaucoma; SD, standard deviation; preop, preoperative; postop, postoperative.

ALT indicates argon laser trabeculoplasty; SLT, selective laser trabeculoplasty; IOP, intraocular pressure; POAG, primary open angle glaucoma; SD, standard deviation; preop, preoperative; postop, postoperative.

Repeatability of Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty

Several studies have assessed the repeatability of ALT and SLT. Most studies of patients undergoing repeat ALT have found that only approximately one-third of those who underwent retreatment experienced additional pressure lowering at 6 to 12 months following the repeat procedure. Not only was retreatment with ALT ineffective in the majority of patients in these studies, one study also found that nearly one-fifth of those who received a second ALT experienced an acute rise in IOP of 10 mm Hg or higher following the repeat procedure. Because one of the proposed mechanisms of action of ALT is that the laser creates scar tissue at the site of application, with contraction and opening of the adjacent trabecular meshwork tissue to improve outflow, repeat treatment may result in further scarring of the trabecular meshwork, resulting in a reduced ability for aqueous to exit through the trabecular meshwork and a subsequent increase in IOP. Thus, it is generally not recommended to perform repeat ALT.

Little is known about the success of repeating SLT. Unlike with ALT, because SLT does not induce significant scarring of the trabecular mesh-work, retreatment offers a greater potential for achieving an additional IOP-lowering effect relative to ALT without as great a risk for complications. A study by Shah et al of patients who underwent repeat SLT demonstrated a 70% and 53% success rate at 1 and 2 years, respectively. Although more studies are underway that will further elucidate the efficacy and risks of repeat SLT, we feel that it is reasonable to consider retreating patients who had achieved a good response to their first treatment with SLT. However, if the patient had a limited response the first time SLT was performed, it is unlikely he or she will achieve a better response with additional treatment, and, often, one should look for other options for lowering the IOP, such as filtering surgery.

Various studies have reported success with SLT in patients who had previously undergone ALT. Given that the mechanism of action of ALT and SLT differ from one another, it is not surprising that a subset of patients who do not respond to ALT achieve a pressure-lowering effect from SLT. In patients who have undergone previous ALT, if the IOP is close to target, it is reasonable to try SLT to further reduce the IOP before proceeding with more invasive incisional surgical procedures.

Complications of Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty

Few reports are in the literature comparing the rates of complications associated with ALT and SLT. The 2 most common adverse events associated with both of these lasers are an acute postoperative rise in IOP following the procedure and postoperative inflammation. Marked elevations in IOP have been reported in patients with heavily pigmented trabecular mesh-work following both lasers, some eventually requiring trabeculectomy. Martinez-de-la-casa et al reported greater rates of transient anterior chamber reaction at 1 hour post-treatment and pain with ALT as compared with SLT. By contrast, Damji et al found that overall there was no significant difference between these 2 lasers in terms of frequency of postoperative IOP spikes, pain, and peripheral anterior synechiae formation. Overall, the complications associated with both of these lasers are usually mild, transient, and self-limiting.

Costs of the Lasers Used to Perform Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty

Purchasing a laser to perform trabeculoplasty can be expensive. ALT is performed using an argon laser, which costs approximately $30,000 to $50,000. By comparison, the cost of a laser to perform SLT is approximately $80,000. When comparing the costs of these lasers, one should also consider the capability of using these lasers to perform other procedures besides trabeculoplasty. In addition to performing ALT with the argon laser, this laser can be used to perform panretinal photocoagulation, focal laser to treat macular edema, retinopexy for retinal tears, as well as peripheral iridotomy and iridoplasty procedures. Some lasers that can be used for SLT are also capable of being used for YAG iridotomy and capsulotomy procedures. Thus, if a practice can afford to purchase only one laser, the argon laser may be a better option given its cheaper price and its ability to be used for multiple purposes in addition to simply trabeculoplasty.

Teaching Trainees How to Perform Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty

When comparing and contrasting these 2 lasers, it is worth noting that it is easier to teach trainees and clinicians who have a limited knowledge of angle anatomy how to perform SLT because the 400- µm spot size of this laser fills up the entire angle. By comparison, with ALT, the spot size is considerably smaller and it is necessary to apply the laser in a precise location to achieve the desired effect.

Key Points

1. Current evidence suggests that ALT remains a safe and effective treatment for ocular hypertension and open-angle glaucoma.
2. Most studies show similar efficacy at lowering IOP with ALT and SLT.
3. Risk of complications is relatively low with both procedures.
4. Although most agree that the potential risks outweigh the potential benefits when it comes to retreatment with ALT, it is possible to per-form retreatment with SLT.