Ten Years of Selective Laser Trabeculoplasty
Brian A. Francis, M.D., M.S.
Tuesday, October 04, 2011
This is a condensed version of the full article which can be seen here.
Ten Key Points Regarding SLT
In the ten years since the FDA approval of selective laser trabeculoplasty for the treatment of open-angle glaucomas, the 10 unique features that have emerged are: 1) selectivity and minimal tissue damage of target tissue, 2) mechanism of action of increasing trabecular aqueous outflow facility, 3) efficacy equal to that of the most potent class of glaucoma medications, 4) excellent safety and side effect profile, 5) ability to improve patient compliance, 6) ability to decrease patient cost of treatment as well as societal economic burden of glaucoma treatment, 7) success as an adjunctive treatment in patients who have failed medical or prior laser therapy, 8) reduction of glaucoma medications in patients with medically controlled IOP (replacement therapy), 9) reduction in diurnal IOP fluctuation, and 10) repeatability of SLT in previously treated patients.
1. Selectivity and Minimal Damage of Target Tissue
"The pulse duration is very short, so it’s below the thermal relaxation time and there is really no appreciable heating occurring in the cells that are targeted" says Dr. Robert Noecker who published some of the original histological comparisons of ALT and SLT,
2. Mechanism of Action: Trabecular Outflow
Laser trabeculoplasty is one of the few glaucoma treatments that address the key problem in open-angle glaucomas: decreased trabecular outflow facility. There are several theories of how it exerts this effect, but it is agreed that this is a biologic response.
3. Clinical Efficacy of SLT
SLT is quite effective as primary or adjunctive treatment to lower IOP. Many clinical trials have shown an IOP reduction of approximately 30%, and demonstrate equality to the most potent class of glaucoma medical therapy: prostaglandin analogues.
4. Minimal Side Effects and Excellent Risk Profile
One key aspect of SLT is a favorable side-effect profile, even when compared with glaucoma medications. Most experts agree that a lower power level (barely enough to elicit cavitation bubbles 50% of the time or less) with more treatment spots (up to 200) gives the best ratio of efficacy to side effects. In patients with excessive angle pigmentation such as pigment dispersion glaucoma and pseudoexfoliation glaucoma, much lower powers are used and the treatment can be performed segmentally.
Dr. Frank Howes had several comments related to side effects of medications compared to SLT. “As ophthalmologists I think we tend to forget the rare but potentially serious systemic risks of some glaucoma medications such as reduced cardiac and pulmonary function. In addition, ocular surface disease is a real issue with topical therapy. I think with SLT there is a diminishment of conjunctival scarring by the regular use of this modality as opposed to a treatment (medications) that you’re putting a toxin onto the surface of the eye. From the moment patients use it, you are beginning a scarring crisis. With SLT, then, we’re increasing the chance of surgical success. The patients see better and they get less corneal disease: It’s a positive benefit cycle.”
5. Eliminate Compliance Issues
While medical therapy for glaucoma is quite effective, it still relies on the regular and proper administration of the drug to achieve its effect. The use of SLT gives 100% compliance: The physician performs the treatment and knows whether it is effective or not without wondering if glaucoma therapy is being applied correctly.
Dr. Jay Katz notes, “I think you can make a strong argument in favor of primary therapy with SLT because we know what a huge problem there is with adherence to medical therapy. The best assumption we have out there is that 50% of our patients are truly compliant with medical therapy.”
6. Favorable Individual and Societal Cost Profile
"If you’re picking up a treatment that is cost effective to roll out in a supervised fashion at a triage level to a much larger volume of patients, and if you’re going to prevent those patients from entering into the dependency sector for their needs with blindness at an earlier stage, that’s worth billions to the economy"
says Dr. Kate Coleman, Head of the African Multicenter Glaucoma Study and African Glaucoma SLT Trial.
7. Effectiveness of SLT as Adjunctive Treatment
SLT is also useful as an adjunct to medical therapy and prior failed argon laser trabeculoplasty. Those groups of patients who are uncontrolled despite medical and possibly prior laser therapy are the most challenging, and are often being considered for glaucoma filtration surgery.
Dr. Mark Latina, the inventor of SLT and primary investigator in the pivotal trial, discussed the patients treated in this initial clinical study.7 “We enrolled two groups of patients: both with uncontrolled IOP on maximally tolerated medical therapy, but the second also with prior failed ALT. Even in these patients with glaucoma refractory to medical and laser therapy, the results did show that there was about a 65 percent success rate in both groups. Based on those results, we feel that SLT is a viable alternative in patients who have had prior argon laser trabeculoplasty and those that have failed medical therapy.”
8. Replacing Medical Treatment
The typical glaucoma practice consists of treatment naïve patients, those uncontrolled with medical therapy, and the majority group of those controlled with medical therapy. SLT can be used in this latter group as a replacement therapy to reduce dependence on medications.
According to Dr. Rob Noecker, “Even glaucoma patients who have good IOP on medications are candidates for SLT. The concept of medical substitution was explored in an early paper by Francis and colleagues.11 The laser may be useful in getting patients off of drops. Even if the IOP is controlled, you’re trying to improve quality of life both economically or with regards to side effects.”
9. Reducing IOP Fluctuation
As shown in sleep studies by Weinreb, selective laser trabeculoplasty may help to limit the IOP fluctuation that can lead to progressive optic nerve damage and vision loss.
10. Repeatability of SLT
The ability to repeat the laser sets SLT apart from ALT and increases its usefulness in the lifetime treatment of a glaucoma patient.
The Lumenis SLT Laser is available to ophthalmologists as a laser rental by the day.
Marketing Manager, Option3 LLC
Westchester County, NY