Micropulse Laser Trabeculoplasty as Replacement for Supplementary Topical Glaucoma Therapies

The procedure may avoid adherence issues with multiple drop regimens.

By Edward Meier, MD

Despite the availability of a variety of glaucoma treatments, patients’ lack of adherence to the traditional topical antiglaucoma therapy paradigm continues to be a problem.1 I deal with this compliance quandary in my own practice on a regular basis. Adherence issues are exacerbated with the addition of every supplementary medication, and thus it stands to reason that keeping patients on a one-drop therapy can greatly improve outcomes.2

Conversely, finding an effective therapy regimen for patients whose intraocular pressure (IOP) is not adequately controlled on one drop is problematic. Adding a drop will increase the possibility of poor adherence, and without proper compliance, the condition could worsen. Therefore, moving to a treatment option that can decrease dependence on a second drop makes a great deal of sense.

MLT AS EFFECTIVE AS DROPS

Over the past several years, selective laser trabeculoplasty (SLT) has gained popularity and has been found equally efficacious to drops in lowering IOP.3 SLT targets intracellular melanin, however, and it can activate macrophages and damage cells in the trabecular meshwork.4 SLT may also cause IOP spikes and mild pain or inflammation.4

Micropulse laser trabeculoplasty (MLT) using the IQ 577 laser with MicroPulse technology (Iridex), on the other hand, incites a biological response in the trabecular meshwork and has been shown to effectively treat IOP without the tissue damage caused by other laser treatments.5-10 MLT has been shown to reduce the need for medication in some patients,11 and the possibility of lowering IOP without the need for additional topical therapies can be a significant benefit.

MLT uses a tissue-sparing, concentrated laser modality in which a continuous wave laser beam is chopped into a series of short pulses. For instance, with a 15% duty cycle, the laser is on 15% of the time and off 85% of the time.

This modality gives tissue time to cool between pulses, preventing thermal buildup, while stimulating the trabecular cells without destroying them. The MLT mode is also multifunctional, facilitating treatment of other glaucoma and retinal disorders. By contrast, the laser used for SLT (Selecta II; Lumenis) is a single-purpose system. A further benefit of MLT is that it is potentially more titratable than SLT, permitting additional treatments in the future if necessary (Figures 1 and 2).

PEARLS FOR TREATMENT

Some patients may be hesitant to undergo laser therapy due to either adverse past experiences, misconceptions, or lack of education on the subject. However, in my experience, most are willing to try it once they understand the mechanics of this relatively painless procedure.

Figure 1. Trabecular meshwork after SLT. Continuous wave laser exposures can cause high thermal rise, resulting in tissue damage.

Figure 2. MLT allows the meshwork to stay intact without the signs of tissue damage.

As the MLT procedure causes no tissue damage, there is no visible reaction in the trabecular meshwork during the procedure. Traditional argon laser trabeculoplasty creates a blanching in the tissues, and small bubbles can form during SLT. In contrast, there are no visible consequences with MLT. This can make it difficult to determine which areas have been treated. Therefore, the clinician may initially have a tendency to retreat some areas and skip others.

To ensure that I am treating the entire area without repeating, I use a special lens designed for MLT (Ocular MicroPulse Laser Trabeculoplasty Lens with Flange; Ocular Instruments) that acts as a guide. It has an indexed rotation system that can be turned, enabling me to keep track of the laser spots applied at each clock hour. This lens has made a vast difference in my ability to place the treatment spots efficiently.

CASE SERIES

The results of the small series of six patients I have treated in my practice have been excellent to date. I used the Iridex IQ 577 yellow laser, and the procedures were conducted in the office. The patients do not receive systemic anesthesia. A numbing drop and the special marked contact lens are placed on the eye prior to treatment. I treat for 0.3 seconds with 1,000 mW at a 15% duty cycle applied around 360°. I apply approximately 120 spots with a size of 300 μm, as opposed to the 400-μm spots produced by SLT.

The mean preoperative IOP in these patients was 18.83 mm Hg (range 16.5-20.5 mm Hg). At 1 month after laser, the mean was 16.50 mm Hg (range 14.0-21.0 mm Hg), an average decrease of 2.33 mm Hg.

I typically see patients for follow-up 1 week after the procedure and again at 1 month. The effect of MLT takes slightly longer than with SLT, so IOP does not drop as quickly. However, patients’ pressure will continue to drop through 3 months after the procedure. I have seen no postoperative inflammation in these patients.

Long-term results have been excellent. I have been performing MLT procedures for 2 years, and the patients I have been following for 18 months to 2 years have retained excellent IOPs. Before implementing MLT in my practice, between 5% and 10% of my SLT patients would have cell and flare 1 week after the procedure. I have not seen that occur in any MLT patient.

CONCLUSION

MLT has definite potential as an option for patients who face the addition of supplementary drops to their medication regimen. Reducing IOP without the need for further drops may eliminate cost and compliance issues for many patients, and it also provides a beneficial solution with minimal, if any, adverse consequences. n

1. Ung C, Zhang E, Alfaro T, et al. Glaucoma severity and medication adherence in a county hospital population. Ophthalmology. 2013;120(6):1150-1157.

2. Chang DS, et al. Development and validation of a predictive model for nonadherence with once-daily glaucoma medications. Ophthalmology. 2013 Jul;120(7):1396-1402.

3. Katz LJ, Steinmann WC, Kabir A, et al. Selective laser trabeculoplasty versus medical therapy as initial treatment of glaucoma: a prospective, randomized trial. J Glaucoma. 2012;21:460-468.

4. Kagan DB, Gorfinkel NS, Hutnik CM. Mechanisms of selective laser trabeculoplasty: a review. Clin Experiment Ophthalmol. 2014;42(7):675-681.

5. Detry-Morel M, Muschart F, Pourjavan S. Micropulse diode laser (810 nm) versus argon laser trabeculoplasty in the treatment of open-angle glaucoma: comparative short-term safety and efficacy profile. Bull Soc Belge Ophthalmol. 2008;308:21-28.

6. Ogata N, Tombran-Tink J, Jo N, et al. Upregulation of pigment epithelium-derived factor after laser photocoagulation. Am J Ophthalmol. 2001;132(3):427-429.

7. Binz N, Graham CE, Simpson K, et al. Long-term effect of therapeutic laser photocoagulation on gene expression in the eye. FASEB J. 2006;20(2):383-385.

9. Vujosevic S, Bottega E, Casciano M, et al. Microperimetry and fundus autofluorescence in diabetic macular edema: subthreshold micropulse diode laser versus modified early treatment diabetic retinopathy study laser photocoagulation. Retina. 2010;30(6):908-916.

10. Lavinsky D, Cardillo JA, Melo LA Jr., et al. Randomized clinical trial evaluating mETDRS versus normal or high-density micropulse photocoagulation for diabetic macular edema. Invest Ophthalmol Vis Sci. 2011;52(7):4314-4323.

11. Fudemberg SJ, Myers JS, Katz LJ, et al. Trabecular meshwork tissue examination with scanning electron microscopy: a comparison of micropulse diode laser (MLT), selective laser (SLT), and argon laser (ALT) trabeculoplasty in human cadaver tissue. Invest Ophthalmol Vis Sci. 2008;49(5):1236.

Edward Meier, MD
• Comprehensive ophthalmologist, ApexEye Center, Mason, Ohio
• Edward.meier@apexeye.com; (513) 770-4020
• Financial interest: none acknowledged