Article

SLT earns a place as first-line therapy

Selective laser trabeculoplasty may supersede drops in glaucoma treatment.

Glaucoma specialists have traditionally viewed topical therapy as first-line treatment for glaucoma. Recently, however, this paradigm has been challenged. Selective laser trabeculoplasty (SLT), though FDA approved since 2001, has gained acceptance as first-line treatment over the last 5 to 10 years. Furthermore, SLT’s role in the armamentarium of glaucoma therapy is expanding as it is used by some as a diagnostic tool to help determine where resistance to outflow may be present.1 This is of clinical significance when selecting tailored surgical options for patients.

LASER TRABECULOPLASTY REVIEW

SLT uses a 532-nm, Q-switched, frequency-doubled Nd:YAG laser, which delivers a shorter pulse of 3 ns that limits the conversion of energy to heat. Selective photothermolysis employed by SLT targets only pigmented trabecular cells and causes no structural or coagulative damage to the trabecular meshwork.2 This is in contrast to the previously available laser trabeculoplasty option: argon laser trabeculoplasty (ALT). In ALT, the pulses of laser energy are of longer duration than in SLT and cause coagulative tissue damage,3 which is thought to increase the risk of IOP spikes and peripheral anterior synechiae (PAS) formation.

When viewing SLT as first-line therapy in the management of glaucoma, it is important to understand the history of laser trabeculoplasty with respect to glaucoma therapy. As early as the 1990s, it was established that laser trabeculoplasty, in this case ALT, was as effective as topical therapy. The Glaucoma Laser Trial (GLT) showed that laser trabeculoplasty was at least as efficacious as medical therapy for the first-line treatment of patients with newly diagnosed primary open-angle glaucoma.4 Though the GLT’s study design drew criticism, it nevertheless was one of the first studies to demonstrate laser trabeculoplasty’s role as first-line treatment for glaucoma.

Since that time, multiple studies have looked at the benefits of using SLT as first-line therapy for glaucoma treatment. Finishing a glaucoma fellowship in 2015, I trained in an era when SLT was offered to patients as first-line therapy.

So, why should ophthalmologists consider SLT as first-line therapy?

EFFICACY

As early as 2003, the SLT/MED study, a prospective, multicenter randomized trial was underway to investigate the efficacy of SLT as initial treatment for open-angle glaucoma compared to medical treatment. This study showed similar efficacy between SLT and eyedrops as initial therapy, with an IOP reduction of about 27%.5

The more recent Laser in Glaucoma and ocular HyperTension (LiGHT) study suggests that SLT as primary treatment is just as effective, if not more so, at maintaining IOP than topical therapy.6 The LiGHT study is an observer-masked, randomized controlled trial conducted in the United Kingdom. Patients with newly diagnosed, untreated open-angle glaucoma or ocular hypertension were randomized with either SLT or topical therapy.

Patients in the SLT group were within target IOP range at more visits (93%) than in the eyedrop group (91.3%). Furthermore, 0 patients in the SLT group and 11 patients in the eyedrop group required glaucoma surgery, implying greater disease progression in the eyedrop group.

SAFETY

Topical therapy has side effects ranging from toxicity to the ocular surface, alterations in appearance of the periorbital area,7 systemic side effects such as exacerbations of airway pathology and bradyarrhythmias. SLT is an option that can curtail these side effects while providing IOP control. As such, SLT has a favorable side effect profile compared to topical therapy; its most common side effects are self-limiting post-laser inflammation8 and IOP spikes,9 occurring in approximately 5% of patients.10

Clinical pearl: To minimize post-SLT IOP spikes, I titrate my laser settings according to the pigmentation of the patient’s trabecular meshwork. For a patient with a lightly pigmented trabecular meshwork, I am comfortable starting with 0.8 mJ to 0.9 mJ of energy vs. 0.7 mJ of energy for a patient with a moderately pigmented trabecular meshwork. I take caution when treating patients with pigment dispersion glaucoma as they are more prone to persistent IOP spikes. As such, I usually start at 0.4-0.5 mJ and perform 180 degrees (as opposed to the usual 360-degree treatment). All patients obtain a pre-SLT IOP check with instillation of an alpha-agonist such as 0.2% brimonidine.

Immediately post-SLT, I instill another drop of an alpha-agonist. IOP is checked within 1 hour of the procedure to ensure any IOP spikes are caught and treated in office. With such a regimen, I have minimized post-laser IOP spikes.

Some patients do have light sensitivity and a “sore eye” for about 24 hours, so I typically prescribe a short course of a topical NSAID for patient comfort.

COMPLIANCE

Adherence to topical therapy can certainly be an issue for glaucoma patients.11 Actual compliance has been reported as being approximately 50%. Many factors contribute to this ongoing issue, such as cost of topical therapy, tolerance of side effects, difficulty physically administering such drops or simply forgetting to administer eyedrops.

Clinical pearl: In practice, patients have a multitude of reasons they are unable to consistently adhere to topical therapy. For patients who elect topical therapy as first-line management, if I sense any irregularity in their ability to consistently take eyedrops, I am quick to discuss, or rediscuss, SLT therapy with them. Also, I inform patients that SLT does not last forever but is repeatable and that close follow-up is still needed lifelong.

Selective laser trabeculoplasty improves circulation of aqueous humor through the trabecular meshwork.

DIURNAL IOP CONTROL

Large IOP fluctuations are an independent risk factor for the progression of glaucoma, as reported by Asrani et al in 2000.12 SLT reduces mean IOP and IOP variation between office visits as found in normal tension glaucoma (NTG) patients.13 More recently, it was found that IOP fluctuations in patients with NTG had a statistically significant decrease in the range of nocturnal IOP fluctuation 1 to 2 months after SLT.14 This may result in a lower risk for continued glaucoma progression.

Clinical pearl: I may not see such a robust drop in IOP in my NTG patients, but every point of IOP reduction does indeed matter in the long term. It is known that NTG patients have fluctuations in IOP, including nocturnally, when IOP is not checked.12-14

Curtailing such IOP fluctuations is beneficial for patients with respect to their long-term prognosis.

COST-EFFECTIVENESS

With respect to cost, laser trabeculoplasty was found to be most cost-effective in the comparison of medication, SLT and filtering surgery. A 2008 study demonstrated that the costs over the course of 5 years, respectively, were $6,571, $4,838 and $6,363.80 in the United States.15

Practically speaking, out-of-pocket expenses for eyedrops can range from $4/month to $200/month — which certainly can get costly over a lifetime. SLT therapy is cost-effective for patients and is well covered by insurance, minimizing the financial burden on patients.

MORE EFFECTIVE WHEN USED FIRST LINE

SLT may be more effective when used as first-line therapy, as opposed to following topical treatment.16 In McIlraith et al’s study, patients on topical therapy underwent a “washout” period of 4 weeks before SLT. IOP reduction was greater in the treatment-naïve group (8.1 mm Hg vs 6.4 mm Hg, P<0.001).

Clinical pearl: Anecdotally, I have seen impressive IOP reductions in treatment naïve ocular hypertensive patients. According to one theory, aqueous suppressants may cause the trabecular meshwork to atrophy and not functions at its full capacity because aqueous flow has been decreased, whereas SLT may enhance outflow or “rejuvenate” the meshwork. This theory certainly needs further investigation but brings up some interesting points.

SLT is an excellent first-line option for the management of glaucoma. This effective and economical option helps mitigate some of the difficulties with glaucoma care such as eyedrop compliance and side effects. It is reasonable to envision SLT’s value as a diagnostic tool to help narrow down the location of a patient’s resistance to outflow. This information is of value, as it may be used to better asses a patient’s response to potential future treatments.

SLT IN PRACTICE

I currently offer SLT as primary therapy for patients with primary open-angle glaucoma and ocular hypertension. I also discuss with them all medical therapy options and let patients decide which option suits them best. By far, most patients elect prostaglandin therapy initially.

On follow-up, once patients have experienced the ins and outs of using an eyedrop consistently, I re-evaluate their experience and needs. At this point, some patients elect SLT therapy in lieu of topical therapy. This dialogue is dynamic and continuous over the lifetime of our patients. OM

REFERENCES

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