Micropulse Transscleral Diode Laser Photocoagulation: What We Do and Don't Know

In the treatment of glaucoma, the ability of continuous-wave (CW) transscleral laser photocoagulation (TSCPC) to lower intraocular pressure (IOP) must be weighed against its established risks. Attempting to reap these benefits without the safety concerns has led to the development of micropulse (MP) TSCPC, which differs from CW-TSCPC in that the energy to the ciliary body is delivered in short pulses with an on and off cycle, in theory reducing the risk for inflammation and hypotony.

Although MP-TSCPC has shown clinical promise, most studies looked at patients who had received prior CW-TSCPC. Investigators behind a recently published study^[1] retrospectively reviewed a series of 37 consecutive patients who underwent MP-TSCPC as a first-line cyclodestruction procedure for refractory glaucoma.

Treatment was deemed a success if patients required no further addition of glaucoma medication, no need for further surgery, and no decrease in vision.

In addition, they needed to experience IOP lowering as follows: between 6 and 18 mm Hg and reduced by 20% from baseline (criterion A), between 6 and 15 mm Hg and reduced by 25% from baseline (criterion B), or between 6 and 12 mm Hg and reduced by 30% from baseline (criterion C).

The percentage of success was determined at months 3, 6, and 12. With each criterion, the percentage of success decreased from month 3 to 6 to 12. For example, the success rate for criterion A went from 76% at month 3 to 35% at month 12. For all eyes from baseline to month 12, the mean IOP decreased from 28.7 mm Hg to 18.5 mm Hg, respectively, and the mean number of medications decreased from 4.7 to 3.6, respectively. Overall, there was a 36% reduction in IOP and 35% success rate at 1 year.

Weighing the Benefits of MP-TSCPC

Previous MP-TSCPC publications have reported higher success rates, ranging from 52% to 74%^{[2,3,4,5,6,7,8]}; however, my own results with MP-TSCPC have been more consistent with those of this current study. I still reserve a diode treatment for refractory cases, a population for whom the goal IOP is often very low because the optic nerve damage is severe. Success in these patients entails a significant decrease in IOP, and thus the stricter success criterion in this paper seems more consistent with clinical application.

As in this study, I have found that more patients experience a decrease in pressure initially after the procedure, with the amount of reduction greatest from 1 to 3 months post procedure. Unfortunately, after that time, IOP increases and the success rate decreases, with many patients needing a second procedure.

Micropulse diode is a good temporizing measure, especially in situations where immediate reduction in IOP is critical. I perform micropulse diode in both the clinic and the operating room. In patients who are unable to tolerate a surgical procedure, micropulse diode plays a significant role in the options available.

In my experience, the absolute IOP lowering is less with MP-TSCPC than with CW-TSCPC, which is consistent with clinical studies that report an approximately 50% lower IOP at 1 year with CW-TSCPC.^[9,10,11,12] But with MP-TSCPC, there is significantly less inflammation, and I have not had any cases of hypotony.

As I am performing more MP-TSCPC, I am finding the right niche of patients who would benefit from this procedure versus standard CW-TSCPC. For patients who may already have poor vision, have very severe glaucoma, and are already pseudophakic, it may be more productive to proceed with CW-TSCPC. Like the authors of this latest study, I have used only the traditional power settings for MP-TSCPC; adjusting the power as well as the application time may possibly result in success rates similar to CW-TSCPC.

I have adopted MP-TSCPC into practice and find that this procedure is useful in selected patients. Some variation of the power and time application may make the procedure more broadly applicable to include more patients. On the other hand, given the low-risk profile, instead of reserving this procedure for refractory glaucoma only, it may have a more generalizable use in patients with mild to moderate glaucoma. Further studies on different subtypes of glaucoma will be helpful to broaden the use of this laser.

Shuchi B. Patel, MD, is director of glaucoma services in the department of ophthalmology at West Palm Beach VA Medical Center in Florida. She explores the ever-changing glaucoma space for Medscape, including advances in diagnostics and treatments.

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