Newer CPC laser technologies are improving glaucoma outcomes
Benefits include better visualisation of ciliary processes and avoidance of tissue damage.
Reviewed by Dr Shan C. Lin.
Ophthalmologists have seen a progression in cyclophotocoagulation (CPC), with each generation of the technology becoming more doctor- and patient-friendly. Dr Shan Lin, a glaucoma specialist at the Glaucoma Center of San Francisco in California, United States, recently described some of the recent advancements in the treatment.
Transscleral cyclophotocoagulation (TCPC) was developed first, but it has its limitations. In some cases, the treatment is unable to reach the targeted tissue because the tissue is not visible.
In addition, the surrounding structures can potentially be damaged. Excessive treatment using TCPC can also occur and cause an audible popping and explosion of the ciliary processes and pars plana, which can result in inflammation such as cystoid macular oedema (CMO).
The G-Probe Illuminate Delivery Device (Iridex) has 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. He cited a study1 reporting that they can range from 2–5 mm behind the limbus.
Endoscopic visualisation
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 the treatment of a larger area within the same incision, according to Dr Lin.
A typical procedure, as he described, is one performed in a pseudophakic patient through a limbal approach. “The goal is to cause shrinkage and whitening of the ciliary processes,” he said.
A study of endoscopic CPC in 68 patients, which included a range of glaucoma types, found that the IOP decreased from approximately 27 mm Hg preoperatively to 17 mm Hg postoperatively. In addition, the numbers of medications needed decreased from approximately three to two.2 The complications associated with endoscopic CPC included fibrin exudate (24%), hyphaema (12%), CMO (10%), vision loss (6%)—due to CMO in most cases—and choroidal detachment (4%).2
Short pulse technology
MicroPulse is the newest of the technologies. It 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 explained that the technology is also thought to stimulate biological factors, such as cytokines and growth factors, at the treatment area.
The Cyclo G6 Glaucoma Laser with the MicroPulse P3 probe (Iridex) is a transscleral procedure designed to deliver laser energy in a pulse pattern to avoid excessive damage to the tissues. It also differs from the G-Probe in that the treatment is aimed at the pars plana rather than the ciliary processes and 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 an ophthalmologist’s surgery or in the operating theatre. Dr Lin said that he prefers performing the procedure in the operating theatre, for increased control and patient comfort.
In addition, there are no pops involved with the treatment. However, Dr Lin noted 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 explained.
A study with follow-up of almost 7 years reported 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. A number of treatments were needed, with an approximate average of 4.5, to achieve IOP lowering.3
Dr Lin also presented results of MicroPulse technology in a retrospective analysis of 54 patients with a baseline IOP of 24 mm Hg, 75% 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; this criterion 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. Iridex recently introduced a new 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.
Conclusion
“Diode TCPC with the G-Probe is usually reserved for blind, painful eyes and is now available with transillumination. Endoscopic CPC can be useful in some cases; however, there are risks associated with penetrating surgery,” Dr Lin concluded.
“Micropulse TCPC is useful for patients with refractory glaucoma, with less inflammation and possibly less risk than with diode laser. In addition, the new REV-2 probe is now available.”
Shan C. Lin, MD
E: sl@glaucomasf.com
This article is adapted from Dr Lin’s presentation at the Glaucoma Research Foundation’s 25th Annual Glaucoma Symposium. Dr Lin is a consultant to Iridex.
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References
1. Agarwal 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. Aquino MC, Chew P. Long-term efficacy of micropulse diode transscleral cyclophotocoagulation in the treatment of refractory glaucoma. Meeting abstract. Presented at the European Glaucoma Society (EGS) Meeting,Prague, Czech Republic, June 19-22, 2016.
