Controlling Glaucoma With SLT
Advanced laser technology can help you increase fluid outflow without damaging the trabecular meshwork.
Before the introduction of selective laser trabeculoplasty (SLT), the most effective treatment for medicine-resistant open-angle glaucoma was argon laser trabeculoplasty (ALT). Research1 has shown that this procedure, which uses a thermal laser to ablate trabecular tissue, lowers IOP as effectively as initial treatment with topical IOP-lowering agents.
Unfortunately, ALT can damage the trabecular meshwork (TM); repeat treatment can create scars, increase IOP and lead to open-angle glaucoma.
SLT offers the proven advantages of ALT without causing coagulative damage and irreversible scarring. The Lumenis Selecta II Glaucoma Laser System's Q-switch produces a 3-nanosecond high-energy light beam that selectively targets melanin-rich TM cells while avoiding thermal damage and scarring to adjacent non-melanin cells.
SLT addresses the nagging issues of patient compliance and the costs and discomforts of using medications. But is SLT safe enough to replace medicine as the preferred first-line therapy for glaucoma? Several recent roundtable participants say it is.
SLT selectively targets melanin-rich cells that block fluid outflow through the trabecular meshwork.
Clinicians are studying SLT's utility for treating patients with ocular hypertension. "I've treated ocular hypertensive patients with SLT, aiming to achieve the 20% IOP reduction outlined in the Ocular Hyper-tension Treatment Study guidelines," says Robert J. Noecker, M.D., vice-chair of the department of ophthalmology and director of the glaucoma service at the University of Pittsburgh. "It's nice to offer these patients a surgical option instead of drug therapy, because often they've never been on a drug."
SLT's ability to preserve TM architecture and lower IOP effectively make this procedure a safer alternative to ALT, says Mark A. Latina, M.D., associate clinical professor at Tufts University School of Medicine in Boston. "The laser has great utility, even for patients who use only one medication, because we want patients to use as few medications as possible," says Dr. Latina.
James B. Wise, M.D., of Glaucoma and Laser Surgery Associates in Oklahoma City, recommends SLT for patients who have drug compliance or tolerance problems. "SLT is an extremely safe procedure, which, in my hands, usually produces about a 6-mm Hg -- or a 30% -- reduction in IOP, which is usually enough for most people," he says.
"Drops don't treat trabecular meshwork impairment, which is often the primary cause of open-angle glaucoma. ALT and SLT can treat this condition, so it's rational to improve trabecular function in early glaucoma treatment," says Dr. Wise.
Additional studies are investigating whether surgeons can use SLT as replacement therapy. In one unpublished study, Brian A. Francis, M.D., and his colleagues from Doheny Eye Institute in Los Angeles performed SLT on open-angle glaucoma patients who were maintaining their target IOPs with one or more medications. One month after undergoing conservative 180° SLT treatment, the patients followed a stepped protocol for reducing their medication use.
"If IOP was at or below target at 1 month, 3 months and 6 months we discontinued one medication," Dr. Francis explains. "On the next visit, if IOP still was at or below target, we'd try to discontinue another medication. At 6 months, our patients averaged two fewer medications per person, which averaged out to about 1.5 fewer medications per patient at 12 months. Although the patients were using fewer medications, they still maintained their target IOPs," says Dr. Francis.
Another physician who's had positive experiences with SLT is Ronald L. Gross, M.D., professor of ophthalmology at Baylor College of Medicine Cullen Eye Institute in Houston.
"SLT is a reasonable option anywhere along the therapeutic decision-making tree," he says. Although Dr. Gross isn't using SLT to treat secondary glaucomas, he is using this procedure more than he ever used ALT. "I've been pleasantly surprised by SLT's efficacy, which has been at least as good as advertised," he says.
Glaucoma specialist Monte Dirks, M.D., of Blackhills Regional Eye Institute in Rapid City, S.D., says he's relying on SLT more and more in his practice. "The underlying principle of causing less or even no damage to the trabecular meshwork is very appealing," explains Dr. Dirks. "In my experience, SLT hasn't caused the same amount of post-op inflammation as ALT. And I feel I'm getting better results. The happiest patients I have are those who didn't like using even one medication, and now use none," he says.
Dr. Dirks also is performing more SLTs in response to increasing patient demand. "Our market is fairly small, with a draw of about half a million in a city of 70,000 people, but we're already benefiting from word-of-mouth recommendations. Patients are specifically seeking me out to perform SLT because they want to eliminate their medications," says Dr. Dirks.
Specifically asking for SLT is one matter, but how are patients responding to the results? Dr. Wise's patients have responded well to SLT whether he's reduced their medications before the procedure or after it.
"In cases where I reduced a patient's medication, I was sometimes pleasantly surprised to see that his IOPs were as well-controlled on less medicine, so there was no need to proceed with SLT," he says. "But if his IOPs weren't satisfactorily controlled after I reduced his medicine use, I'd treat him with the laser without changing his post-op medicine routine. This approach gave me a better idea of the laser's role in controlling glaucoma."
Dr. Wise believes, "The most important aspect of SLT is that this procedure is additive to all currently available medications. SLT is a very strong and very useful kind of 'medication' that can benefit almost any glaucoma patient," he says.
Evolving First-line Treatment
Glaucoma is a lifetime condition controlled by daily medications, a strategy that is only minimally satisfactory under the best of circumstances. Non-destructive SLT may be a better option for glaucoma patients, particularly those who are noncompliant with or who, for various reasons, can't tolerate glaucoma medications.
|Glaucoma medications reduce IOP by one of two mechanisms: Decreasing the production of aqueous humor or increasing aqueous outflow.
"SLT essentially is an outflow medication," says Mark A. Latina, M.D. "We don't know the exact mechanism behind it, but we do know it can potentially improve outflow.
"I've been particularly interested in comparing patients using SLT in conjunction with aqueous suppressants with those using outflow drugs, such as prostaglandins," Dr. Latina says. "Of patients who routinely used at least one IOP-lowering agent and achieved at least a 3-mm Hg drop in IOP after SLT, more were on aqueous suppressants than on prostaglandins."2,3 Monte Dirks, M.D., has found that as many as half of his patients who are on prostaglandins or other outflow drugs don't have a significant IOP drop following SLT; however, their IOPs do remain constant when he discontinues prostaglandin use following SLT.
Ninety-nine percent of Robert J. Noecker, M.D.'s patients use outflow medications, and he notes that they do very well with the addition of SLT. "I get a very high success rate -- as high as is reported in the literature on any medication," he says.
1. GLT Research Group. Glaucoma Laser Trial: Results of argon laser trabeculoplasty versus topical medicines. Ophthalmology. 1990;97:1140311412.
2. Latina MA, Sibayan SA, Shin DH, et al. Q-switched 532-nm Nd:YAG laser trabeculoplasty (selective laser trabeculoplasty): A multicenter, pilot, clinical study. Ophthalmology. 1998;105:20822088.
3. Melamed S, Ben Simon GJ, Levkovitch-Verbin H. Selective laser trabeculoplasty as primary treatment for open-angle glaucoma: A prospective, nonrandomized pilot study. Arch Ophthalmol. 2003;121:957960.