Micropulse probe transforms transscleral cyclophotocoagulation

Micropulse transscleral cyclophotocoagulation (TSCPC) with a diode laser (Cyclo G6 Glaucoma Laser System, Iridex) is demonstrating promising efficacy with better safety and tolerability than traditional TSCPC.

The early experience with this approach suggests the potential for broadening the role of cyclophotocoagulation in the glaucoma treatment paradigm, said E. Randy Craven, MD, at the Glaucoma Symposium during the 2017 Glaucoma 360 meeting.

“The micropulse procedure can be done using only a limited peribulbar or retrobulbar block to achieve comfort,” said Dr. Craven, associate professor, Wilmer Eye Institute, Johns Hopkins University, Baltimore, MD, and chief of glaucoma, King Khaled Eye Specialist Hospital (KKESH), Riyadh, Saudi Arabia. “Because it is less painful than standard TSCPC, we have been able to prepare to transition these cases to a minor procedure room.”

Dr. Craven said this procedure will be beneficial for decreasing operating room utilization at KKESH, considering 10 to 15 standard TSCPC procedures are performed there weekly.

“Furthermore, we are not seeing hypotony and phthisis after micropulse TSCPC, which are significant risks with continuous wave TSCPC,” he added. “Because of its favorable safety, the micropulse procedure is not only an option for treating end-stage glaucoma and in pseudophakic eyes, but that it may be used in phakic eyes, as a supplemental procedure in eyes with a prior tube, and for patients on anticoagulant therapy who are at risk for intraocular hemorrhage with a filtration procedure.”

How it performs

The micropulse procedure is performed with a novel contact probe (MicroPulse P3 Glaucoma Device, Iridex) that delivers the laser energy with a 31.3% duty cycle (0.5 ms on time, 1.1 ms off time) using a continuous motion or “sweep” over the treatment site. By delivering energy in bursts, the micropulse technique allows tissue to cool between pulses, thereby minimizing damage.

The tip design of the probe used to perform micropulse TSCPC supports a sweeping motion and the treatment is applied in two arcs from the 9:30 to 2:30 and 3:30 to 8:30 clock positions. Dr. Craven noted that exact algorithms for micropulse TSCPC are being developed and should be available soon.

“Currently, most (physicians) doing this procedure are setting the energy at 2000 mW and then varying the total sweep time duration between 100 and 320 seconds, depending on such parameters as iris pigmentation and the disease characteristics,” Dr. Craven said. “Unlike continuous wave TSCPC, there is no ‘pop’ that indicates the treatment endpoint.”

Published data

Published data

There are few published reports of outcomes with micropulse TSCPC, but the limited data available are encouraging. Investigators at the National University of Singapore initially published their experience treating 40 eyes with refractory glaucoma [Tan et al. Clin Exp Ophthalmol. 2010;38(3):266-272.]

Mean IOP averaged 39.3 mm Hg at baseline and decreased to 26.6 mm Hg at 1 year. There were no cases of hypotony or phthisis.

Subsequently, they reported results from a study randomizing 48 eyes with refractory glaucoma to micropulse or continuous wave TSCPC [Aquino et al. Clin Exp Ophthalmol. 2015;43(1):40-46]. Success, defined as IOP between 6 mm Hg and 21 mm Hg with at least a 30% reduction in IOP with or without medications at 18 months, was achieved by 52% of eyes treated with micropulse CPC and by only 30% of those treated with continuous wave TSCPC.

Dr. Craven also presented data collected in a prospective observational study by Shan Lin, MD, University of California, San Francisco. The series included 57 eyes treated from June 2015 to August 2016. The majority of eyes (75%) had primary open angle glaucoma, but the entire spectrum of glaucoma diagnoses was represented in the remaining eyes, and 30% had had prior filtration surgery.

In an analysis of outcomes from follow-up at 6 or 12 months post-treatment and excluding 7 eyes that needed retreatment, mean IOP was reduced by 28%, from 23.89 mm Hg at baseline to 17 mm Hg. Mean daily medication use was reduced from 3.5 to 3.3. Success, defined as IOP lowering ≥20% with or without medications, was achieved in 68% of eyes.

Randy Craven, MD

E: ecraven1@jhmi.edu

Dr. Craven has no relevant financial interests to disclose.