Advancements in cyclophotocoagulation: The good, the better and the best

Reviewed by Dr Shan C. Lin.

Ophthalmologists have seen a progression in cyclophotocoagulation (CPC), with each generation becoming more doctor- and patient-friendly. Dr Shan C. Lin, a glaucoma specialist at the Glaucoma Center of San Francisco, California, United States, recently described some of the recent advancements in the technology.

Trans-scleral cyclophotocoagulation

The first attempt at CPC was trans-scleral cyclophotocoagulation (TCPC), which has its limitations. In some cases, the treatment did not reach the targeted tissue because the tissue was not visualised, and the pars plana was often treated instead.

In addition, there was the potential for the surrounding structures to be damaged. Excessive treatment using TCPC can occur and cause an audible popping and explosion of the ciliary processes and pars plana, which can result in inflammatory conditions such as cystoid macular oedema (CMO).

Introduction of the G-Probe Illuminate Delivery Device (Iridex Corporation) helped to address these problems. This technology uses a diode laser to treat the ciliary processes through the sclera and reduces the intraocular pressure (IOP) by decreasing aqueous production. “This latest generation of the technology allows identification of the ciliary process locations either before or at the time of treatment,” Dr Lin said.

He explained that the locations of the ciliary processes can vary among the different ocular quadrants and among different patients with glaucoma, and cited a study¹ reporting that the ciliary processes can range from 2 to 5 mm behind the limbus.

Endoscopic CPC

Endoscopic CPC is a newer technology that facilitates direct visualisation of the ciliary processes as they are being treated. Probes with different gauge sizes (18-, 19-, 20- and 23-gauge) are available for this intraoperative procedure. In addition, the availability of curved probes allows a greater area to be treated within the same incision, according to Dr Lin.

A typical procedure, as he described, is one performed in a patient with pseudophakia through a limbal approach. “The goal is to cause shrinkage and whitening of the ciliary processes,” he said.

A study² of endoscopic CPC, involving 68 patients with a range of glaucoma types, found that the IOP decreased from approximately 27 mm Hg preoperatively to approximately 17 mm Hg postoperatively. In addition, the numbers of medications decreased from approximately three to two.

The complications associated with endoscopic CPC included fibrin exudate (24%), hyphaema (12%), CMO (10%), vision loss (6%; because of CMO in most cases) and choroidal detachment (4%).

Micropulse technology

Micropulse is the newest of the technologies. The Cyclo G6 Glaucoma Laser with the MicroPulse P3 probe (Iridex) is a trans-scleral procedure designed to deliver laser energy in a pulse pattern to avoid excessive damage to the tissues. This procedure also differs from the G-Probe in that the treatment is aimed at the pars plana rather than the ciliary processes, and it involves a slow sweeping motion along the superior and inferior limbuses rather than the discrete spot placement of the G-Probe.

An advantage of this new technology is that it can be performed either in a clinic or in the operating theatre, but Dr Lin prefers performing the procedure in the operating theatre for increased control and patient comfort. In addition, there are no pops involved with the treatment.

Dr Lin cautioned that the sweeping motion should avoid the 3 and 9 o’clock positions. “Having slower sweeps with the MicroPulse facilitates better uptake of the laser and efficacy,” he said.

One study³ with follow-up of almost 7 years detailed the long-term efficacy and durability of this treatment. The authors reported a 43% reduction of IOP at 78 months in 14 patients and a concomitant reduction in medications from 1.8 to 1.1. However, numerous treatments were needed, with an average of approximately 4.5, to achieve IOP lowering.

Dr Lin also reported results of MicroPulse technology in a retrospective analysis of 54 patients with a baseline IOP of 24 mm Hg, three-quarters of whom had primary open-angle glaucoma. Postoperatively, the average IOP was 17 mm Hg (P = 0.0002). Success in this study was defined as IOP lowering of 20% or more with or without medications, which was met in 68% of patients. Seven of the eyes required re-treatment.

The potential complications of the technology include rare unexplained visual loss, hypotony, ocular inflammation and CMO. In anatomical assessments using ultrasound biomicroscopy, there were no observable changes comparing before and after treatment.

MicroPulse controls the thermal effect by chopping a continuous wave of the energy beam into repetitive short pulses interrupted by relaxation times, which makes for less thermal damage to the targeted area. Dr Lin said the technology is also thought to stimulate biological factors, such as cytokines and growth factors, at the treatment area.

Iridex recently introduced a revised MicroPulse P3 (REV-2) probe with a footplate that helps with limbal alignment, improves tissue coupling for better laser delivery, makes the technique easier to perform and potentially has fewer complications. “Diode TCPC with the G-Probe is typically reserved for blind, painful eyes, and now is available with transillumination,” Dr Lin said.

“Endoscopic CPC can be useful in some cases. However, there are risks associated with penetrating surgery,” he said. “Micropulse TCPC is useful for patients with refractory glaucoma, with less inflammation and, possibly, less risk than with [the] diode laser.”

Shan C. Lin, MD

E: sl@glaucomasf.com

This article is adapted from Dr Lin’s presentation at the Glaucoma Research Foundation 25th Annual Glaucoma Symposium that took place in 2021. Dr Lin is a consultant to Iridex Corporation.

References

1. Agrawal P, Martin KR. Ciliary body position variability in glaucoma patients assessed by scleral transillumination. Eye (Lond). 2008;22:1499-1503.

2. Chen J, Cohn RA, Lin SC, et al. Endoscopic photocoagulation of the ciliary body for treatment of refractory glaucomas. Am J Ophthalmol. 1997;124:787-796.

3. Chew P, Aquino MC. Long-term efficacy of micropulse diode transscleral cyclophotocoagulation in the treatment of refractory glaucoma. Abstract presented at: 12th European Glaucoma Society Congress; 19–22 June 2016; Prague, Czech Republic.