Integrating SLT into your practice

Switching to SLT can be a boon, but be sure you know what you’re getting into.

By Linda Huang, MD, and Albert S Khouri, MD

About the Authors
	Linda Y. Huang, MD, is an ophthalmology resident at New Jersey Medical School in Newark.
	Albert S. Khouri, MD, is director of the ophthalmology residency program and associate director of the glaucoma division at New Jersey Medical School. Disclosures: The authors have no relevant relationships to disclose.

The technology and techniques ophthalmologists use to treat glaucoma are constantly evolving, and while new innovations spring up frequently, few have had the long-term impact and growth of selective laser trabeculoplasty (SLT). Medicare reports that laser trabeculoplasty has been performed about six times as often as trabeculectomy in 2008. From 2001 to 2009 the number of SLT procedures almost doubled, totaling 150,000 procedures a year.

As with any other technology, a physician must be properly informed of the equipment’s method of action, capabilities, variations and limitations. This article will review that necessary information as well as detail adjunctive treatments for glaucoma patients.

HOW SLT WORKS

Mode of action

SLT uses a Q-switched frequency-doubled (532 nm), low-energy density Nd:YAG laser that targets melanocytes in the pigmented trabecular meshwork.^1,2 All available SLT lasers have a range of energy outputs that allows a surgeon to adjust in increments of 0.1 millijoule (mJ). The surgeon can also accurately adjust the intensity of the aiming beam.

Comparison with ALT

Unlike argon laser trabeculoplasty (ALT), SLT does not cause apparent thermal or coagulative changes. Instead SLT induces an inflammatory response that, through cytokine release, monocyte recruitment and possibly other cellular changes, leads to an increase in the aqueous outflow facility, lowering IOP. The IOP-lowering effect usually takes about one to two months to manifest, and most eyes maintain it for up to two years. However, some eyes have shown efficacy of SLT that may last three to five years after treatment.³

Figure 1: This line graph depicts mean IOP at baseline and up to 36 months of follow-up after first and repeat SLT treatments in open angle glaucoma patients in a study we conducted at our center.

PERFORMING SLT

Preoperative prophylaxis and IOP spikes

Prior to treatment, most patients receive a prophylactic topical glaucoma medication, usually either apraclonidine or brimonidine, to prevent a postoperative IOP spike. This is particularly important if you will be treating eyes with higher IOP or patients with a documented previous IOP spike after SLT treatment.

Prophylactic alpha-adrenergic agonists can reduce postoperative IOP spikes by two-thirds.⁴ Postoperative IOP rise is more severe and frequent with higher energy levels, 360° treatments, posterior placement, heavy angle pigmentation and a low preoperative outflow facility.

Applying the laser pulses

The procedure may be performed to 90°, 180° or 360° of the trabecular meshwork. With 360° applications, approximately 100 pulses are applied. To begin the procedure, the patient is placed in front of the laser and a 400-μm laser spot is focused at the trabecular meshwork using a specialized gonioscopy lens.

The ALT laser spot (much smaller at 50 μm) requires precise focusing on the trabecular meshwork to effectively lower IOP and avoid the adverse effects of misplaced laser spots. The majority of treatments in clinical practice are performed with energy levels ranging between 0.6-1.2 mJ.

The physician chooses the energy level by titrating it to a visual response during the treatment. The energy can be increased by 0.1 mJ increments until small bubbles (known as “champagne bubbles”) appear at the trabecular meshwork with each laser application. Then the energy is dialed back 0.1 mJ and that setting is used for the rest of the treatment.

Postoperative risks

IOP spike is a rather serious complication after SLT. Although transient, IOP elevation can lead to serious visual consequences in glaucoma patients. To detect spikes, patients are monitored after SLT. IOP is typically checked an hour after treatment.

In SLT patients treated prophylactically for IOP spike, the reported rate of an IOP rise greater than 5 mm Hg is around 10%; and the rate of an IOP rise greater than 10 mm Hg is around 3%.⁵ These spikes are usually controlled with topical glaucoma medications and are typically short lived, lasting for a few days.⁴

Other reported but rare complications include corneal clouding and reactivation of herpetic disease. Barring any complications, patients are usually followed up in 4-8 weeks to assess the effect on IOP.

ADVANTAGES OF SLT

Efficacy

SLT has been studied as a first-line, adjunctive and repeat therapy.^5–8 Several studies have shown SLT’s ability to further lower IOP with retreatment. In a study we conducted at our center, repeat SLT significantly reduced IOP (more than 20%) when performed up to 28 months after the initial SLT treatment. This reduction was significant up to 36 months of follow-up.⁹ (Figure 1).

SLT is not meant for patients with high IOP and advanced disease requiring low targets for disease control. However, SLT offers a large portion of glaucoma patients an effective treatment for IOP control. Its efficacy is equivalent to a prostaglandin analog,¹⁰ and the treatment is repeatable if needed.

Figure 2: A patient receives SLT treatment delivered with the laser mounted onto a slit lamp.

Adherence

Another well-recognized advantage of SLT treatment is its ability to circumvent non-compliance. In a chronic disease such as glaucoma, adherence to a daily regimen of eye drops remains a constant struggle for patients. Even with a simplified regimen of a single medication, adherence is by no means optimal.

In a study monitoring patients on a single prostaglandin, mean compliance was only 71%.¹¹ Meanwhile patient persistence with initial topical therapy drops to 33% to 39% in one year.¹² SLT provides a stable form of IOP reduction and minimizes risks for patients who are non-adherent or only occasionally adherent. SLT may also benefit patients on multiple topical medications who cannot afford all their medicines, or have intolerable side effects.

In a prospective trial, adjunctive SLT therapy allowed a reduction in topical medication use while maintaining target IOP.¹³ Because many clinicians agree SLT provides reductions equivalent to a prostaglandin, SLT may provide cost-effective benefits in certain settings as a primary therapy.¹⁴

INTEGRATION

Specifications among SLT models

Specifications among brands tend to be similar. For example, Ellex (Adelaide, Australia) and Lumenis (Santa Clara, Calif.) both use a Q-switched frequency doubled Nd:YAG laser at wavelength of 532 nanometers and spot size of 400 μm with duration of 3 nanoseconds. The energy output of the Lumenis varies from 0.3 mJ to 2.0 mJ, while the output of the Ellex SLT is 0.3 mJ to 2.6 mJ. Most treatments are done in the 0.6 to 1.2-mJ range. Patent expiration will allow other manufacturers to enter the market this year. Quantel Medical (Bozeman, Montana) offers a portable SLT that can be adopted to a slit lamp or to their YAG laser making it a combination laser.

The Ellex dedicated SLT offers 10x, 16x and 28x magnification with ability to upgrade to five-position magnification changer. The Lumenis dedicated SLT comes with six-position magnification changer.

Investment

A typical initial investment in an SLT laser varies between ranges from $50,000 to $80,000. Most companies offer financial options for purchase or lease. Currently, Medicare covers SLT and repeat SLT treatments as minor surgical procedures with a 10 day global period with eligibility for a facility fee.

REFERENCES

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14. Seider MI, Keenan JD, Han Y. Cost of Selective Laser Trabeculoplasty vs Topical Medications for Glaucoma. Arch Ophthalmol. 2012;130:529-530.