A discussion of treatment timing, treatment with pigmentation, and efficacy.

In the June 2018 issue of Glaucoma Physician, we addressed several myths about selective laser trabeculoplasty (SLT). Among those myths were that it must be repeated yearly, it isn’t as safe as drops, and that it just doesn’t work. We argue that this safe therapy is capable of significant pressure reductions, and it has been around for a long enough time to have accumulated a strong literature base demonstrating safety, efficacy, and versatility. In this issue, we aim to debunk several more myths about SLT.

Myth 1: You can’t do SLT post laser peripheral iridotomy (LPI).

Patients who’ve had prior narrow angles whose angles are now open post LPI respond exceptionally well to laser trabeculoplasty. This could be because the disease is still in the trabecular meshwork (TM). The chronic narrowing of the angles can decrease flow through the TM, which can collapse the trabecular beams, which then further decreases outflow. Sihota et al found only subtle differences in the pathologic composition of the TM between eyes with chronic primary-angle closure glaucoma (PACG) (nonsynechial areas) and primary open-angle glaucoma (POAG).¹ The findings were predominantly widening and fusion of adjacent trabecular beams and homogeneous deposit enmeshing the TM tissue, suggesting that the pathology of the TM in eyes with PACG is similar to that in eyes with POAG and thus SLT may be effective in eyes with PACG. There is good evidence for this therapy and it provides an excellent treatment option for eyes with chronic angle closure whose angles have opened after laser iridotomy.

A recent study assessed the intraocular pressure (IOP)-lowering efficacy of SLT in eyes with primary angle closure (PAC) and PACG compared to a prostaglandin analog (PGA). They found no differences between the SLT and PGA groups in the absolute mean reduction of IOP (4.0 mmHg vs 4.2 mmHg, respectively; P=.78) or in the percentage of reduction in IOP (16.9% vs 18.5%, respectively; P=.52)² for patients who have had subacute angle closure or in cases where peripheral anterior synechiae (PAS) are present. Surgeons can treat in between the PAS. As long as one can visualize the TM post LPI, SLT is a viable option.

Myth 2: You only can do SLT on more pigmented TM.

Studies have demonstrated good efficacy of SLT in patient with lightly pigmented meshwork. Haque et al compared the effect of SLT in reducing intraocular pressure (IOP) in patients with light, moderate, or heavy pigmentation of the TM. They concluded there was a significant IOP reduction in all 3 groups (P<.005) but there was no difference in magnitude between the 3 groups (P=.65), therefore lightly pigmented patients do respond to SLT.³

Myth 3: SLT doesn’t work as well as argon laser trabeculoplasty (ALT).

Since 2001, several studies have shown SLT to be as effective as ALT for lowering IOP. For example, Damji et al randomized 176 eyes (152 patients with a mean age of 70) that had open-angle glaucoma and uncontrolled IOP of 16 mmHg or greater on maximal medical therapy (or had previously unsuccessful ALT or SLT) to receive ALT or SLT.⁴ One year later, IOP decreased an average of 5.6 mmHg, to 17.97 mmHg (23.75%), in eyes that underwent SLT, and by a mean 6.04 mmHg to 17.88 mmHg (25.25%), in eyes that underwent ALT.

Patients with a 20% or greater reduction in IOP were nearly identical: 59.7% of the SLT eyes and 60.3% of the ALT eyes. And, 82% of eyes in the SLT group could remain on the same number of medications at 1 year vs. 69% of eyes in the ALT group; 18% in the SLT group required 1 additional drug vs. 29% in the ALT group. Wang et al conducted a meta-analysis of SLT vs ALT in patients with open-angle glaucoma. The author concluded that SLT has at least comparable efficacy to ALT with a similar constellation of side effects.⁵

Myth 4: SLT doesn’t last more than a year or two.

Jindra et al conducted a study with 853 eyes that were treated over 5 years with primary SLT for glaucoma, mean follow-up time was 509 days (range: 11-1,726). Two-tailed paired t tests were used to compare maximum pre- and post-therapy IOP. Sixty eyes were retrospectively followed at 6-month intervals, for 5 years post SLT. They found more than a 35% decrease in IOP sustained at 5 years. They also observed a 93% success rate at 5 years.⁶

Myth 5: SLT doesn’t work if you are already on medications.

Latina et al conducted a multicenter, prospective, clinical study measuring IOP reduction efficacy of SLT in patients with open-angle glaucoma previously treated with medication on maximum medical therapy (n=30) and/or ALT (n=23). Fifty-three eyes of 53 patients were observed for 4 weeks to 26 weeks. All patients remained on their antiglaucoma medication throughout the study. They found 70% of patients achieved at least a 3 mmHg IOP reduction.⁷

Myth 6: SLT has no diagnostic potential.

Currently, there are no preoperative noninvasive diagnostic tools to provide the location and dynamics of outflow resistance. With SLT, we might gain some information on the outflow resistance of each patient. SLT applies selective photothermolysis to pigmented cells in the trabecular meshwork, which releases inflammatory mediators, such as macrophages and cytokines. This increases aqueous outflow through the trabecular meshwork and the inner wall of Schlemm’s canal.

If SLT has a significant effect, we may infer the TM is the main area of resistance. If SLT is not effective, this might tell us that resistance is in the canal or in the distal collector channels. We are only now starting to understand the potential diagnostic benefit of SLT as a first-line therapy. It is interesting to explore the notion that SLT may not only help us better understand a patient’s pathology, we might be able to use that information to select the best MIGS intervention for a given patient. GP

References

1. Sihota R, Goyal A, Kaur J, Gupta V, Nag TC. Scanning electron microscopy of the trabecular meshwork: understanding the pathogenesis of primary angle closure glaucoma. Indian J Ophthalmol. 2012;60(3):183-188.
2. Narayanaswamy A, Leung CK, Istiantoro DV, et al. Efficacy of selective laser trabeculoplasty in primary angle-closure glaucoma: a randomized clinical trial. JAMA Opthalmol. 2015;133(2):206-212.
3. Haque M, Hughes BA, Juzych MS, et al. The effect of selective laser trabeculoplasty (SLT) with heavy versus light pigmentation of the trabecular meshwork (TM). Invest Ophthalmol Vis Sci. 2009;50:161.
4. Damji KF, Bovell AM, Hodge WG, et al. Selective laser trabeculoplasty versus argon laser trabeculoplasty: results from a 1-year randomised clinical trial. Br J Ophthalmol. 2006;90(12):1490-1494.
5. Wang W, He M, Zhou M, Zhang X. Selective laser trabeculoplasty versus argon laser trabeculoplasty in patients with open-angle glaucoma: a systematic review and meta-analysis. PLoS One. 2013;8(12):e84270.
6. Jindra LF, Gupta A, Miglino EM. Five year experience with selective laser trabeculoplasty as primary therapy in patients with glaucoma. Poster presented at: The AAO Annual Meeting; November 10-13, 2007; New Orleans, LA.
7. Latina MA, Sibayan SA, Shin DH, Noecker RJ, Marcellino G. Q-switched 532-nm Nd:YAG laser trabeculoplasty (selective laser trabeculoplasty): a multicenter, pilot, clinical study. Ophthalmology. 1998 Nov;105(11):2082-2088.

Inder Paul Singh, MD, is a glaucoma specialist at the Eye Centers of Racine and Kenosha, in Wisconsin. Dr. Singh reports financial relationships with Ellex, Alcon, Allergan, New World Medical, Bausch + Lomb, Shire, Aerie, and Sun Ophthalmics. Reach him at ipsingh@amazingeye.com.

Nate Radcliffe, MD, is a clinical assistant professor in the department of ophthalmology at the New York Eye and Ear Infirmary and a surgeon at the New York Eye Surgery Center. Dr. Radcliffe reports consultancy to Aerie Pharmaceuticals, Lumenis, Iridex, Ellex, and Bausch + Lomb. Reach him at drradcliffe@gmail.com.