Latest CPC Laser Technologies & Glaucoma

Latest CPC Laser Technologies & Glaucoma

December 13, 2021
1155 read

Cyclophotocoagulation is a laser treatment that targets the ciliary processes of the eye. The ciliary processes are the part of the eye that produce the fluid, or aqueous humor, that bathes the tissues in the front of the eye.

Although the part of the eye that does not function well in glaucoma is the “outflow” or drainage system, including the trabecular meshwork, many treatments target the “inflow” system, such as the ciliary processes which form a ring 360 degrees around the circumference of the eye.

For example, timolol, a commonly used glaucoma medication, actually lowers eye pressure by targeting the ciliary processes and reducing the amount of aqueous humor that is produced.

Utilizing the same concept, cyclophotocoagulation is a laser treatment that targets the ciliary processes to reduce aqueous humor production.

The cyclophotocoagulation laser treatment causes the ciliary processes to shrink, resulting in less aqueous humor production and lower eye pressure. However, the ciliary processes can regenerate, so sometimes the procedure needs to be repeated.

In addition, because this procedure causes destruction of the ciliary processes, it was generally reserved after other surgeries, such as trabeculectomy or tube shunt surgery, had been attempted.

These surgeries bypass the diseased outflow system by creating a new path for fluid to escape the eye.

However, in more recent years, cyclophotocoagulation has been used earlier in the treatment algorithm, particularly with the development of different laser techniques that cause more targeted tissue treatment and/or less inflammation.

Dr Shan Lin, a glaucoma specialist at the Glaucoma Center of San Francisco in California, United States, recently described some of the latest 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. 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%).

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 latter location, 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 the results of MicroPulse technology in a retrospective analysis of 54 patients with a baseline IOP of 24 mm Hg, 75% of whom had primary openangle 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 also 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.

“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.”