The availability of new technologies that detect glaucoma early and allow for expedient treatment may provide ophthalmologists with an unprecedented opportunity to initiate effective therapy before the disease significantly affects patients' vision. Traditionally, first-line treatment consists of monotherapy with a prostaglandin analogue. If this approach fails to lower the IOP, ophthalmologists proceed to adjunctive therapy with as many as three additional drugs before they consider surgical intervention.
Studies suggest, however, that selective laser trabeculoplasty (SLT) is a viable alternative to first-line medical therapy. This article describes how I am using this in-office laser procedure to overcome obstacles to adherence,1-3 reduce patients' dependence on topical medications,4-7 and dampen diurnal fluctuations in IOP. 8-10
TECHNOLOGY
During SLT, surgeons use a frequency-doubled Q-switched laser (Lumenis Selecta Duet; Lumenis, Inc., Santa Clara, CA) (Figure 1). This laser has a longer wavelength (532 vs 488 to 514 nm) and emits a larger spot (400 vs 50 µm) than that used for argon laser trabeculoplasty (ALT) (Figure 2). In addition, SLT's pulse duration of 3 nanoseconds is shorter than the thermal relaxation time of melanin and thus does not cause any collateral thermal damage to the trabecular meshwork11 (Figure 3).
Because SLT does not damage the trabecular meshwork, it is not associated with the formation of peripheral anterior synechiae, and clinicians can perform the procedure on eyes that were previously treated with ALT.12 Furthermore, SLT can theoretically be repeated in the same eye,13 and the treatment does not preclude future surgery in or around Schlemm's canal.
REASONS FOR EARLY SLT
Simplification of the glaucoma treatment regimen is paramount to improving our patients' adherence and the overall success of treatment. I use SLT as first- and second-line therapy in my practice, because I believe it streamlines the treatment of glaucoma in several crucial ways.
PRIMARY THERAPY
Nordstrom et al showed that the percentage of patients who adhered to glaucoma therapy decreased from between 50% and 75% with monotherapy to 32% with multiple medications.1 These bleak statistics are supported by data from the National Community Pharmacists Association and Pharmacists for the Protection of Patient Care. In a telephone survey, 75% of the respondents admitted to behaviors that affected their adherence to therapy, 33% did not fill a prescription, and almost 25% took less than the recommended dosage.2 Even patients who initially adhere to therapy tend to lapse, with 50% of them discontinuing their eye drops after only 6 months.3
Studies have shown that first-line therapy with SLT lowers IOP as effectively as topical medications. In a prospective, randomized clinical trial, a similar percentage of eyes treated with daily latanoprost (n = 39) and SLT to 360° of the trabecular meshwork (n = 44) had a 20% to 30% decrease in IOP from baseline at 10.3 months' follow-up. The investigators did not observe a statistically significant difference in outcomes between the two groups.4 McIlraith et al found that, at 12 months, latanoprost and SLT provided a mean reduction in IOP of 30.6% and 31%, respectively.5 Perhaps the strongest multicenter randomized study was conducted by Katz et al, who found similar reductions in IOP with latanoprost (7.6 mm Hg) and SLT as primary therapy (6.7 mm Hg).6 Longer-term studies showed that the IOP-lowering effect of primary SLT persisted for as long as 5 years postoperatively.7,14,15
I believe that patients can benefit from primary SLT, because they can achieve lower IOPs without having to follow the strict dosing schedule required for successful medical therapy. First-line therapy with SLT is also associated with a lower mean cost of treatment over 5 years ($4,949) compared with medication alone ($6,553) and surgery ($6,386).16
SECONDARY THERAPY
In addition to using SLT as primary therapy, I offer this treatment to patients with well-controlled IOPs who are interested in using fewer medications. One study showed that approximately 50% of patients (760 eyes) who used one to three drugs preoperatively maintained low IOPs without any medication after SLT.14 This effect was most pronounced among patients who used one medication preoperatively (86%); it decreased according to the number of drugs used at baseline (62% for two, 42% for three, and 32% for four preoperative medicines).10 In a separate study, Francis et al found that 87% of eyes required one fewer medication than at baseline to maintain lower IOPs 12 months after secondary SLT.17
Because SLT is essentially an "outflow" treatment that does not depend on medication, I like to complement this procedure with drugs that use different mechanisms of action to decrease the IOP. My colleagues and I found that SLT was more likely to lower IOP by at least 3 mm Hg in patients who used aqueous suppressants versus prostaglandin analogues.18 These results suggest that prostaglandin analogues and SLT compete for the same therapeutic pathway. I therefore tend to discontinue or taper prostaglandin analogues and pilocarpine (both outflow enhancers) in patients who undergo SLT. On the other hand, I often treat patients who need to achieve a lower IOP after SLT with an aqueous suppressant (eg, a beta-blocker or a carbonic anyhdrase inhibitor).
FLUCTUATIONS IN IOP
Data from the Advanced Glaucoma Intervention Study (AGIS) showed that the risk of glaucomatous progression increased by 30% for each 1-mm Hg elevation from the mean IOP. In other words, eyes in which the IOP regularly deviated from the mean by more than 3 mm Hg experienced a higher rate of progression than those that maintained a steadier pressure.19 Asrani et al also noted that frequent deviations from the mean IOP was associated with a higher risk of progression,8 a finding supporting the identification of IOP fluctuation as an independent risk factor for glaucomatous visual loss in the AGIS.
Clinical studies by Lee et al9 and Prasad et al10 suggest that laser trabeculoplasty can decrease the range of IOP fluctuation in glaucoma patients. In the latter study, the investigators randomized 41 eyes to receive primary SLT over 180° (n = 19) or 360° (n = 22) of the trabecular meshwork. At 2 years' follow-up, 86% of eyes in the 360° group experienced fluctuations of less than 2 mm Hg. A similar reduction was observed in only 52% of eyes in the 180° group. These data support treating 360° of the angle with SLT, because it provides a greater overall reduction of IOP and dampens fluctuations in pressure.
CONCLUSION
In my experience, SLT is a safe first- and second-line therapy that is cost effective, successfully lowers IOP, reduces patients' dependence on topical medications, and modulates the effect of a major risk factor for glaucomatous progression.
