The Future of SLT
Will selective laser trabeculoplasty become a first-line treatment?
BY FRANK CELIA, CONTRIBUTING WRITER

Selective laser trabeculoplasty (SLT) presents ophthalmologists with a tantalizing prospect. Here is a procedure that is easy to learn and perform, lowers IOP as effectively as drug therapy, is relatively non-invasive and safe, and above all, can obviate, or at least reduce, a large patient populations' need for years of treatment with expensive glaucoma medications. Additional features include reduced worries over adverse side effects, compliance problems and patients' financial woes.

This scenario could come to pass if SLT succeeds in differentiating itself from its less accomplished predecessor, argon laser trabeculoplasty (ALT), which never caught on as a primary therapy, due to its lack of repeatability. Theoretically, because SLT laser induces far less inflammation and tissue damage, it should offer more repeat potential — and while preliminary data suggests it does — the jury is still out on this question.

Many surgeons are finding SLT a big favorite with patients, and are moving this "kinder, gentler" version of laser trabeculoplasty closer to the front of the glaucoma algorithm. However, below are some of the issues that could affect its final fit in the glaucoma treatment regimen.

SLT vs. ALT

Selective laser trabeculoplasty employs a Q-switched, frequency-doubled (532 nm) Nd:YAG laser that targets melanocytes in the pigmented trabecular meshwork. Like ALT, its mechanism of action is not completely clear, but it involves the release of cytokines that trigger macrophage recruitment, with an eventual result of enhanced aqueous outflow. Unlike ALT, it treats the meshwork without causing thermal or coagulative damage to surrounding tissue and employs short pulses of energy, rather than ALT's continuous wave laser. Overall, the amount of laser energy applied to the trabecular meshwork by SLT is less than 1% of that applied by ALT.

Despite these and other significant power and function differences, SLT and ALT are inextricably linked due to their assumed shared mechanism of action. This is both a strength and a weakness for SLT. It is a strength because it allows SLT to benefit from the Glaucoma Laser Trial results, which in the early- and mid-1990s showed that primary ALT controlled IOP and protected visual fields at least as well as primary drug therapy, and in some cases better. On the other hand, it is a weakness because surgeons assume SLT possesses the faults that made ALT unpopular, e.g., postoperative IOP spikes, long-term attrition, lack of repeatability and difficulty in future filtration surgery.

Nonetheless, studies suggest SLT is more beneficial than ALT. A 1999 study published in the British Journal of Ophthalmology found that patients with previous ALT treatments showed a greater decrease in IOP when treated with SLT than those compared to eyes treated with a second ALT procedure. This data, while not viewed as conclusive, is often cited to suggest SLT might offer more repeatability than ALT. Overall, the study concluded that SLT was equal to ALT in lowering IOP for the first six months after treatment.1 The U.S. trials for the SLT laser, which received FDA approval in 2001, found a mean pressure reduction of 3 mm Hg at 26 weeks among three groups: patients who had received maximum medical therapy, patients who had previously failed laser trabeculoplasty and a combined group.2 These results have encouraged the belief that SLT might be effective on patients who had previously failed laser trabeculoplasty.

Primary Therapy

A few years ago, many of the glaucoma patients who were treated at the practice of Lawrence F. Jindra, M.D., of Floral Park, N.Y., were unhappy with the cosmetic side effects of their drug therapy, which included intolerance to eye makeup and hyperemia. He has since begun using SLT as a primary treatment for glaucoma, and has seen a great jump in patient satisfaction. Dr. Jindra estimates that he has
performed 1,500 SLT procedures, about 700 of which were primary therapy for newly diagnosed patients. Retrospective analysis of his procedures, which he presented at an international ophthalmology meeting, showed that his practice achieved a 95% success rate on initial therapy, which means about 650 patients avoided many years of daily drug therapy. The other 800 SLT procedures were secondary, performed on patients who were already undergoing glaucoma therapy, usually drops. Those patients were able to reduce their medications by a mean of two medications each.

"Glaucoma patients now have hope," concludes Dr. Jindra. "They used to think it was a lifetime disease like diabetes that would never be cured, only treated. We can't cure glaucoma, but if patients can have a laser treatment and avoid using drops for five years, and only need a second laser procedure at that time — in their mind, they've beaten the disease." Patients as far away as Delaware travel to his practice for SLT, simply because they want to eliminate or reduce their need for daily medications, he says.

Few ophthalmologists are as sanguine as Dr. Jindra, but many now offer patients SLT as a first- or second-line alternative to drug therapy, whereas in the past, ALT was usually relegated to a last-ditch effort before incisional surgery. "There are people who prefer it after discussing the options," says L. Jay Katz, M.D., of Philadelphia, Pa. These include patients who cannot afford medications, arthritic patients unable to open bottle tops, patients with dementia or other problems that might hinder compliance and patients who have tried and failed at medical therapy.

Pressure Spikes

By far the most significant adverse side effect associated with SLT is a spike in IOL in the days immediately following the procedure. Most surgeons use a prophylactic topical alpha-agonist pre- and postoperatively. Pressure spikes are more likely in patients with pigmentary glaucoma. In such cases, surgeons suggest treating less of the angle than they normally would.

Anecdotal evidence suggests risk of pressure spikes with SLT is far less than what is encountered with ALT. In 1,500 procedures, Dr. Jindra has encountered spikes in pressure only twice, and those were patients who had been referred to him for filtration surgery, which he had hoped to avoid by a last-minute SLT. As a glaucoma fellow, Dr. Jindra recalls being taught to be cautious about performing ALT on a Friday because there was a 5% chance of the patient ending up in the OR on Saturday with a dangerously spiking pressure that needed to be addressed surgically. SLT could put an end to that. "I think there is a whole generation being trained right now that are just not going to have to worry about trabeculitis," he says.

How Much Angle?

An unresolved question in SLT is how much angle should be treated. Some surgeons treat half, some treat two-thirds and some treat the whole thing. Most doctors believe it is perfectly safe to treat the whole angle in those not at risk for pressure spikes, especially since full treatment is associated with better pressure control. But it does no harm to hedge your bets because the remaining angle can be treated at any time. "Both approaches are reasonable," says Andrew Iwach, M.D., of San Francisco, Calif. "The earlier the patient is in the treatment process, the more response you'll see with 180Þ, evidence shows. But if the patient has had previous ALT, he or she may benefit more from the 360Þ." A reluctance to treat the whole angle is a holdover from ALT days, ophthalmologists say, when such treatment had more potential to affect future surgeries.

The Role of Inflammation

Another ongoing debate in SLT circles is whether postoperative inflammation should be treated. The theory is that inflammation plays some role in the mechanism of the procedure and therefore should not be overly suppressed. However, because patients will feel this procedure the next day (mild redness, photosensitivity and irritation is normal) most physicians prescribe a mild anti-inflammatory or non-steroidal with a consideration toward patient comfort. Dr. Iwach is an exception, pointing out that postoperative inflammation resolves very quickly on its own, and regardless of what role inflammation plays in SLT's mechanism, if you can avoid prescribing a drug, you should probably do so.

Industry Perception

Despite positive evidence, SLT has yet to prove itself among mainstream physicians as substantially better than ALT. "I'm willing to believe SLT causes less damage to the trabecular meshwork," says Henry D. Jampel, M.D., of Baltimore, Md., who uses both ALT and SLT at his practice, often as a primary therapy if patients request it. "Theoretically, that should be an advantage, but whether that will play out in real-world, clinical experience is still totally up in the air." The current evidence is promising, but far from conclusive, he notes.

Other factors come into play as well — price, for example. the Selecta II laser from Lumenis, Inc. (Santa Clara, Calif.) is $70,000 and can only be used for SLT. However, the company does offer the Selecta Duet, which combines SLT and YAG laser capability.

Reimbursement for laser trabeculoplasty (LT) is not what it once was. Dr. Jampel notes that in his memory Medicare reimbursement for LT has dropped from $1,200 to $290, a slide that could take away from the procedure's attractiveness.

Finally, there is a decades old mindset in glaucoma that clings stubbornly to the notion medication must always come before surgery, no matter how mild or noninvasive the surgery claims to be. Many believe this was a factor in ALT failing to become a more popular primary surgery in the 1990s. Medications are reversible, laser surgery is perceived as less so. If a drug fails to perform, blame is laid on the drug or the noncompliant patient. If a surgery fails, it is the surgeon's fault.

Many in the industry will be watching for the results of the SLT/MED study, a large, prospective, randomized and controlled study that will evaluate SLT as an initial treatment for glaucoma compared to drug therapy. Results could be available in the next year or so. This study plans to evaluate pressure reduction, cost analysis, quality of life and other factors, including long-term repeatability, which is viewed as a key to SLT's future. As the surgery's inventor Mark Latina, M.D., of Boston, Mass. notes: "This does not last forever. There is going to be a need to retreat these patients." OM

References:

1. Damji KF, et al. Selective laser trabeculoplasty vs. argon laser trabeculoplasty: a prospective randomized clinical trial. Br J Ophthalmol. 1999;83:718-722.

2. Latina MA, et al. Q-switched 532nm Nd:YAG laser trabeculoplasty (Selective Laser Trabeculoplasty). Ophthalmology. 1998;105:2082-2090.

Frank Celia is a freelance medical writer who frequently reports on eye care. He can be reached at frankcelia@aol.com.