Comparison of Argon Laser Trabeculoplasty and Selective Laser Trabeculoplasty
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.
|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
||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
||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
||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.
- Current evidence suggests that ALT remains a safe and effective treatment for ocular hypertension and open-angle glaucoma.
- Most studies show similar efficacy at lowering IOP with ALT and SLT.
- Risk of complications is relatively low with both procedures.
- 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.
- Juzych MS, Chopra V, Banitt MR, et al. Comparison of longterm outcomes of selective laser trabeculoplasty versus argon laser trabeculoplasty in open-angle glaucoma. Ophthalmology. 2004;111(10):1853-1859.
- Damji KF, Shah KC, Rock WJ. Selective laser trabeculoplasty v argon laser trabeculo-plasty: a prospective randomised clinical trial. Br J Ophthalmol. 1999;83(6):718-722.
- Popiela G, Muzyka M, Szelepin L, et al. Use of YAG-Selecta laser and argon laser in the treatment of open angle glaucoma [Polish]. Klinika Oczna. 2000;102(2):129-133.
- Martinez-de-la-Casa JM, Garcia-Feijoo J, Castillo A, et al. Selective vs argon laser trabeculoplasty: hypotensive efficacy, anterior chamber inflammation, and postoperative pain. Eye. 2004;18(5):498-502.
- Stein JD, Challa P. Mechanisms of action and efficacy of argon laser trabeculoplasty and selective laser trabeculoplasty. Curr Opin Ophthalmol. 2007;18(2):140-145.
- Damji KF, Shah KC, Rock WJ et al. Selective laser trabeculoplasty versus argon laser trabeculoplasty: results from a 1-year randomized clinical trial. Br J Ophthalmol. 2006;90(12):1490-1494.
- Feldman RM, Katz LJ, Spaeth GL, et al. Long-term efficacy of repeat argon laser trabeculoplasty. Ophthalmology. 1991;98(7):1061-1065.
- Richter CU, Shingleton BJ, Bellows AR, et al. Retreatment with argon laser trabeculo-plasty. Ophthalmology. 1987;94(9):1085-1089.
- Weber PA, Burton GD, Epitropoulos AT. Laser trabeculoplasty retreatment. Ophthalmic Surg. 1989;20(10):702-706.
- Grayson DK, Camras CB, Podos SM, Lustgarten JS. Long-term reduction of intraocular pressure after repeat argon laser trabeculoplasty. Am J Ophthalmol. 1988;106(3):312-321.
- Starita RJ, Fellman RL, Spaeth GL, et al. The effect of repeating full-circumference argon laser trabeculoplasty. Ophthalmic Surg. 1984;15(1):41-43.
- Shah N, Yadav R, Nagar M. Selective laser trabeculoplasty: the effect of enhancement and retreatment on IOP control. Paper presented at: XXIV Congress of the European Cataract and Refractive Surgeons (ESCRS); 2006; London, UK
- Latina MA, Sibayan SA, Shin DH, et al. Q-switched 532-nm Nd :YAG laser trabeculo-plasty (selective laser trabeculoplasty): a multicenter, pilot, clinical study. Ophthalmology. 1998;105(11):2082-2088.
- Kano K, Kuwayama Y, Mizoue S, Ito N. Clinical results of selective laser trabeculoplasty [Japanese]. Nippon Ganka Gakkai Zasshi. 1999;103(8):612-616.
- Harasymowycz PJ, Papamatheakis DG, Latina M. et al. Selective laser trabeculoplasty (SLT) complicated by intraocular pressure elevation in eyes with heavily pigmented trabecular meshworks. Am J Ophthalmol. 2005;139(6):1110-1113.