The Changing Role of Laser in Glaucoma

Historically, laser trabeculoplasty was second-line therapy for primary open-angle glaucoma (POAG). Topical medications were the unquestioned first line. If maximum tolerated medications failed to yield adequate IOP reduction, argon laser trabeculoplasty (ALT) was a useful middle step before the more drastic decision to proceed to incisional surgery.

This landscape has changed over the past 20 years. What does the latest literature tell us about the current role of selective laser trabeculoplasty (SLT) in the management of POAG? And how should we be incorporating this management option in optometric practice? Let us explore the answers to these questions.

THE PROBLEM WITH MEDICATIONS

We practice in a golden age of topical glaucoma therapy. Today’s antiglaucoma medications are wonderfully effective with tolerable side effects. There is no shortage of options for first-line or adjunctive drops. However, topical glaucoma medications are not without problems.

First, we all know from personal experience that patient compliance is not optimal. The literature tells us that it is likely even worse than we suspect. Studies using health insurance claims data suggest that compliance decreases as dose frequency increases.¹ Compliance also suffers as time passes from the initiation of therapy.² Even our most compliant patients inevitably miss an occasional drop. Actual or perceived side effects complicate the compliance issue.

Second, diurnal control of IOP is another classic concern in the management of glaucoma. Although today’s glaucoma medications yield relatively good 24-hour control, a flat diurnal curve remains an elusive target for the glaucoma clinician. The literature demonstrates that SLT can blunt nocturnal spikes in IOP, even for patients who are on multiple medications.³

Finally, we find ourselves spending increasing time and resources jumping through formulary hoops. A given patient may be restricted to relatively few choices of topical medications on his or her formulary. If a physician’s preferred medication is excluded, acquiring it may be cost-prohibitive for the patient. Further, going through the process of step therapy can be burdensome for the practice from a clinical and logistical perspective. And when step therapy limits us to prescribing generic medications, we may have concerns about variable results in IOP control and tolerability.

ENTER SLT

Modern ALT was born at the end of the 1970s.⁴ SLT was introduced by Latina and Park in 1995; the first device for this procedure received FDA approval in 2001.⁵

The mechanism of action of SLT remains controversial, but it is thought to depend on a biological response to targeted inflammation.⁵ Laser energy targets intracellular melanin in the trabecular meshwork. The targeted cells activate cytokines, which activate macrophages. These inflammatory cells clean the area of cellular debris, decreasing outflow resistance. Unlike ALT, SLT causes no mechanical damage to the trabecular meshwork.

A number of recent publications have challenged the traditional glaucoma paradigm of medications first, followed by laser therapy as second-line treatment.

In the SLT/Med study in 2012, patients newly diagnosed with POAG or ocular hypertension patients were randomly assigned to either SLT or a topical prostaglandin analogue.⁶ The authors found no statistically significant differences in IOP reduction or need for additional treatment between the two groups. They concluded that SLT is a viable first-line treatment for patients with newly diagnosed POAG.⁶

The American Academy of Ophthalmology’s Preferred Practice Pattern for management of POAG states that laser trabeculoplasty can be considered as initial therapy in selected POAG patients.⁷ This is significant, as these guidelines are generally conservative and avoid adopting controversial therapies. (The American Optometric Association’s Clinical Practice Guideline for Primary Open Angle Glaucoma was in the review process at the time of this article’s writing.)

UpToDate is an online clinical service that catalogues studies and rates the strength of evidence. This service provides its strongest level of recommendation for the option of laser trabeculoplasty for first-line treatment of open-angle glaucoma.

A 2015 meta-analysis by Oi Man Wong et al concluded that there is robust evidence to support the use of SLT as primary treatment for POAG.⁸

In 2019, the LiGHT study evaluated SLT versus eye drops for first-line treatment of ocular hypertension and glaucoma.⁹ LiGHT was a randomized clinical trial in which more than 700 patients were followed for 3 years. Primary endpoints included quality of life, efficacy, cost, and safety. The authors found strong evidence to support the use of SLT. They found that SLT provided IOP stability superior to that achieved with drops and at a lower cost. Further, 74% of participants receiving SLT were successfully controlled without drops for at least 3 years after starting treatment. The authors also found a slightly higher rate of rapid visual field progression and more need for incisional surgery in the medication treatment group than in the SLT group.

The net result of these important publications is that trabeculoplasty is gaining widespread acceptance as first-line therapy for ocular hypertension and POAG.

REPEATABILITY

Questions have lingered regarding the repeatability of SLT. The procedure has generally been considered repeatable, but this has been based mostly on anecdote and small studies. Recently, new entries in the literature have thrown more light on this question.

A 2019 review by Guo et al catalogued several previous studies that addressed the repeatability of SLT. The authors concluded that the efficacy and complication rates of repeat SLT are comparable with those of primary SLT.¹⁰

The LiGHT authors also conducted a post hoc analysis of their study data to shed light on this issue.¹¹ The authors looked at patients requiring retreatment within 18 months of primary SLT. Retreatment was triggered either by failure to reach individualized target IOP and/or disease progression. In 115 eyes that met these criteria, Kaplan-Meier survival estimates illustrated a 67% success rate for repeat SLT at 18 months after retreatment. These data were striking, given that the eyes included in this post hoc analysis had demonstrated a 0% success rate 18 months after their primary SLT. The LiGHT authors concluded that repeat SLT may have a cumulative treatment effect that can provide a longer duration of clinical benefit than primary SLT alone.

THE ROLE OF OPTOMETRY

In states with expanded optometric scope that includes laser therapy, the implications of the findings reviewed above are clear. We should be discussing SLT with patients at our initial diagnosis and offering it when appropriate as a primary treatment option. Many patients, given the choice of instilling daily medication or undergoing an infrequent, noninvasive laser procedure, will prefer the convenience of the latter.

In my practice, initial treatment discussions with patients include SLT when clinically appropriate (ie, in most cases of POAG). Many patients opt to start with topical medications. However, we often return to the conversation about SLT with these patients months or years later. Sometimes patients find that side effects of their medication become problematic. Other times they realize that compliance is more difficult than they expected. Or perhaps insurance formulary changes make SLT a more cost-effective option.

SLT should also be discussed when we change drops or add adjunctive medications. Commonly, a medication problem prompts this conversation. Perhaps we are not achieving adequate IOP reduction or we need to change medications for some other reason. As noted above, compliance decreases with increasing medication burden, creating an opportune time to discuss SLT.

If you practice in a state where optometric scope does not include laser, it is advisable to partner with a glaucoma surgeon who is willing to comanage trabeculoplasty. Expect to re-refer patients for repeat procedures when necessary, generally every 1 to 3 years.

SLT plays a prominent role in the modern management of POAG. If it does not currently have a prominent role in your glaucoma treatment paradigm, consider rethinking the utility of SLT early in the management of patients with this disease.