SLT: A new standard in glaucoma treatment

Long-term control of IOP is key to minimizing the ocular damage that eventually occurs in glaucoma patients. The effects of traditional anti-glaucoma eye drops are short-lived and therefore require diligent, long-term use. Even argon laser trabeculoplasty, which is known to deliver effective results, starts to lose efficacy within several years. In contrast, selective laser trabeculoplasty (SLT) delivers effective IOP reduction that lasts far longer than any other treatment. In this video interview, SLT expert Lawrence F. Jindra, MD, shares his long-term results for SLT when used as a primary, secondary, and replacement therapy. (Video courtesy of Ellex)

Floral Park, NY-Medication has long been the mainstay of glaucoma treatment. Until 20 years ago, laser trabeculoplasty had traditionally been considered a final-stage treatment for patients hoping to avoid surgery.

However, over the past two decades, research into the capabilities of laser technology has brought attention to laser trabeculoplasty as an effective first- and second-line treatment for open-angle glaucoma (OAG).

The 1989 Glaucoma Laser Trial was one of the first major studies to confirm that argon laser trabeculoplasty (ALT) effectively lowers IOP and is effective as a primary treatment of glaucoma.¹

However, as a procedure that involves the use of a hot, high-energy laser, ALT carries a notable risk of causing collateral damage to surrounding ocular tissue. A more novel procedure called selective laser trabeculoplasty (SLT), approved by the FDA in 2001, offers a safe, effective alternative to ALT.

SLT involves the use of cool, low-energy, nanosecond laser pulses, which works by selectively targeting pigmented cells only (selective photothermolysis) and bypasses the thermal or coagulative damage seen with ALT.²

Clinical studies, such as that by McIlraith et al. and Bovell et al., have shown that SLT is not only as effective in lowering IOP as prostaglandin drugs, but also produces the same 5-year IOP-lowering results as ALT.^3,4

Questions remain about SLT and its place in the glaucoma-treatment algorithm-questions that have arisen from misunderstandings about the mechanism that underlies SLT.

Setting the record straight: SLT is not ‘ALT-Lite’

It is a commonly held belief that SLT is simply a weaker version of ALT. This is not the case. Unlike ALT, SLT does not work by damaging the trabeculum to create an opening for outflow. Instead it uses a Q-switched frequency-doubled (532 nm) Nd:YAG laser, such as the Tango SLT/YAG laser from Ellex, to trigger a biologic response that reduces IOP. The low-energy laser used in SLT selectively targets melanocytes in the pigmented trabecular meshwork with 1/6,000 flux density of ALT.^2,5

In contrast to ALT, which tends to lose efficacy over time, among the 4,300-plus eyes from patients with glaucoma I have treated with SLT since 2001, the 5-year efficacy rate achieved is significantly higher than that achieved with ALT.

Specifically, when my colleagues and I used a Kaplan Meier analysis to measure the cumulative probability of success with SLT, we found a cumulative probability of success of more than 90% at 10 years post-treatment when SLT was used as a primary treatment. A considerable number of patients who I treated with SLT in 2001/2002 are still within their target IOP, medication-free, and have not needed surgery or repeat treatment with SLT.

As with any scenario, there are exceptions to the rule. Some patients will require subsequent SLT treatment(s) to keep IOP within required levels.

Such eyes are typically heavily or weakly pigmented (where surgeons are often overly cautious with SLT application and/or give insufficient treatment on the first application).

However, even when repeat treatment with SLT is required, there is almost no risk of collateral damage.⁴

Results achieved with primary, secondary or repeat therapy

Though primary SLT has been shown to lower IOP significantly, it has also been shown to stabilize diurnal IOP variation in these patients.^6,7

With this in mind, unless a patient specifically requests eye drops, I exclusively use SLT as a primary treatment in patients who are medication-naïve with OAG.

The results show that this strategy works. Among 1,983 eyes treated with SLT in my New York-based practice, mean IOP fell by 29% (from a mean of 18.1 to 12.8 mm Hg) over an average follow-up of 917 days, with a cumulative probability of success at 10 years of 90%.

Although I prefer to use SLT as a primary treatment, in many cases, it is patients who remain uncontrolled despite taking multiple medications, or those who are in IOP control but suffer from the significant side effects seen with such topical hypotensive agents, who either seek out SLT or are referred to me by their ophthalmologists, optometrists, or primary care physicians.

While studies have shown that SLT increases the IOP-lowering effect of pharmacological agents, such as prostaglandins, beta-blockers and carbonic anhydrase inhibitors, when performed prior to the use of ocular hypertensive medications, SLT also performs well as a secondary treatment in an adjunctive fashion after the use of ocular hypotensive medications. Among 1,130 eyes treated with secondary SLT at my practice, mean IOP fell by 22% (from mean of 19.6 to 15.2 mm Hg) over a follow-up period of 610 days and mean medication use fell by 86% from a mean of 2.2 to 0.3 medication types, with a cumulative probability of success at 10 years of 88%.

In short, if a patient taking one medication presents, I have an almost 80% chance of resolving the raised IOP and getting that patient off the medication with SLT. Those on two medications have a probability of almost 60%, which falls to abouty 40% for those taking three and four medications. I have found that secondary SLT is so effective that slightly less than two out of every three patients that I have treated with secondary SLT so far, end up completely medication-free.

Repeat treatment carried out at an interval of several weeks or months or years has also yielded promising results among patients. When a retrospective chart review was performed, I found that only 706 of 3113 (23%) eyes uniquely treated with SLT over 10 years required repeat treatment.

For primary repeat SLT, the mean follow-up period was 986 days, mean IOP drop was 22%, with a cumulative probability of success at 7 years of 78% and a prevalence of repeat treatment over 7 years of 9%.  For secondary repeat SLT, the mean follow-up period was 730 days, mean IOP drop was 23%, mean medication change was +0.1 medications, with a cumulative probability of success at 9 years of 95% and a prevalence of repeat at 9 years of 10%.  Among these eyes-while some eyes ultimately required surgical intervention to control IOP-there were no adverse effects observed with repeat SLT treatment for both the primary and secondary groups.

The gift of variety

The efficacy, repeatability, and safety of SLT are standout benefits of the procedure. However, from a day-to-day clinical perspective, the huge variety of patients benefiting from SLT treatment is of immense importance. I have performed SLT with successful outcomes in patients with primary open-angle, pigmentary, and exfoliative glaucoma.

The only patients that I avoid treating with SLT include those with uveitic, inflammatory, or neovascular glaucoma. The inflammation-triggering mechanism of SLT is ineffective in these types of glaucoma, as they already feature a large degree of inflammation and/or scarring of the trabecular meshwork.

It is also important to bear in mind that slight procedural changes should be made when treating various types of glaucoma. For example, patients with exfoliative glaucoma and those with low-pigment eyes (e.g., blue eyes) require higher energy levels than those with highly pigmented eyes (e.g., pigmentary glaucoma or brown eyes).

A notable strength of SLT is its suitability and efficacy in multiple scenarios. I have had success when using SLT with patients of different ethnicities and ocular conditions. Patients of Asian origin are often highlighted as a group unsuitable for laser trabeculoplasty owing to their narrow drainage angles. When the argon laser of ALT is used in such eyes with narrow angles, there is a significant risk of creating peripheral anterior synechia, which can trigger a severe/chronic pressure spike.

However, as SLT is based on the process of selective photothermolysis, the energy required to produce the peripheral synechia that give rise to pressure spikes has simply not been observed with this approach. When my colleagues and I analyzed our 4,000-plus eye database to identify the effect of race on SLT efficacy, we found almost no difference in outcomes in patients of European, African, Asian, Indian, or Hispanic origin.

SLT and the future

Patients with OAG are often placed in a confusing management situation. They are told to use a complicated medication routine with great diligence, but they usually cannot feel or see if their efforts are paying off.

Furthermore, they are expected to spend around $100 per month, many times on a fixed income, for each small bottle of eye drops, which is a figure that quickly adds up over the course of several years, especially if multiple eyedrops are prescribed.

To that end, it is unsurprising that patient compliance or adherence to medical therapy often falters and frustration sets in when the desired IOP reduction is not acutely or chronically achieved.

With SLT, patients are freed from this frustration, this need to comply, and from this expense, as IOP typically falls within a couple of weeks after treatment with SLT and, more importantly, this reduction in IOP usually lasts for many years.

As society continues to become more technologically advanced and patient expectations grow alongside, there is no better time for physicians to rework the antiquated eyedrop-centered glaucoma treatment regime. SLT offers the treatment efficacy and convenience patients today need and stands to give the 1970s-based management of glaucoma a long-awaited shake-up in the 2010s.

References

The GLT Research Group. Glaucoma Laser Trial. Ophthalmology. 1990;97:1403-1413.

Latina MA, et al. Q-switched 532-nm Nd:YAG laser trabeculoplasty (selective laser trabeculoplasty): a multicenter, pilot, clinical study. Ophthalmology. 1998;105:2082-2090.

McIlraith I, Strasfeld M, Colev G, Hutnik CM. Selective laser trabeculoplasty as initial and adjunctive treatment for open-angle glaucoma. J Glaucoma. 2006;15:124-130.

Bovell, A.M., Damji, K.F., Hodge, W.G., et al. Long-term IOP lowering effect of Selective Laser Trabeculoplasty vs. Argon Laser Trabeculoplasty: Follow-up results from a randomized clinical trial. Canadian Journal of Ophthalmology (2011), doi:10.1016/j.jcjo.2011.07.016.

Latina MA, et al. Selective targeting of trabecular meshwork cells: in vitro studies of pulsed and CW laser interactions. Exp Eye Res. 1995;60:359-372.

Weinreb RN, Tsai CS. Laser Trabeculoplasty. In Ritch R, Shields MB, Krupin T, eds. The glaucomas: glaucoma therapy. 2nd ed. Missouri: Mosby-Year Book, 1996;III:1575-1590.

Donnelly JA, Miglino EM, Jindra LF. Selective Laser Trabeculoplasty as Primary Therapy in Patients with Glaucoma: Ten-Year Experience. Poster presented at: American Society of Cataract and Refractive Surgery; 2013, San Francisco.

Matthews RM, Miglino EM, Jindra LF. Selective Laser Trabeculoplasty as Secondary Therapy in Patients with Glaucoma: Ten-Year Experience. Poster presented at: American Society of Cataract and Refractive Surgery; 2013, San Francisco.

Whitney TL, Miglino EM, Jindra LF. Selective Laser Trabeculoplasty as Repeat Therapy in Patients with Glaucoma: Ten-Year Experience. Poster presented at: American Society of Cataract and Refractive Surgery; 2013, San Francisco.