The use of endoscopic cyclophotocoagulation in the treatment of glaucoma - a literature review

Glaucoma remains one of the most severe eye conditions, contributing to vision loss and blindness in patients, despite major advances in medical, laser, and surgical treatment [1]. In difficult cases of glaucoma, target intraocular pressure can most often only be achieved after a procedure involving the destruction of the ciliary body, which is responsible for the production of nearly 80–90% of the aqueous humor, directly contributing to increased intraocular pressure [2,3].

Until recently, cyclo-destructive procedures were used only in advanced cases as a therapy of last resort where other methods had failed [4]. Thanks to technological advances, this method is increasingly offered to patients in earlier stages of glaucoma and those with good visual acuity.

ECP, or endoscopic cyclophotocoagulation, is performed using an ophthalmic endoscope developed by Martin Uram in 1992 [5,6], which allows observation of the structures of the anterior segment of the eyeball, including the drainage angle, the ciliary body with its processes, the ciliary sulcus and the anterior part of the retina with simultaneous cyclophotocoagulation [5].

Currently, almost all types of open and closed-angle glaucoma are indications for ECP surgery, except for neovascular glaucoma, which is a relative indication. Advances in medicine and recent studies confirming the efficacy of cyclo-destructive procedures are increasingly changing the approach to ECP [7,8,9].

Several clinical trials have proven the efficacy and safety of ECP. These trials show better therapeutic results than minimally invasive glaucoma surgery and laser trabeculoplasty and a lower risk of complications than with trabeculectomy or glaucoma seton drainage surgery. Among ECP's most common side effects are ocular inflammatory reactions and tissue destruction associated with photocoagulation, hemorrhage, retinal detachments, and cataracts [9].

Access to the ciliary body processes can be gained via two routes: through the cornea or the pars plana. Surgery through the pars plana requires a vitrectomy for sufficient working space, which increases the risk of complications such as retinal detachment, hemorrhage, or cataracts. Access through the cornea is more common and less risky regarding bleeding. In addition, the continuity of the conjunctiva and sclera is preserved, facilitating possible future anti-glaucoma procedures [10].

The E2 Ophthalmic Laser Endoscopy System consists of a laser endoscope and the console to which it is attached. The laser endoscopy console combines a 175- or 300-watt xenon light source, an 810-nm diode laser for photocoagulation, and a video system for intraocular imaging. All these components are contained in an 18-, 19-, 20-, or 23-gauge endoscopic probe. The laser emits a power of up to 1.2 W, while the recommended starting power is 0.25 W, allowing for gradual energy adjustment during the procedure. Endoscopic probes are available in both straight and curved versions. During surgery, the surgeon observes the operation on a monitor, instead of looking through the operating microscope [11].

A key advantage of ECP over other cyclophotocoagulation techniques is its ability to precisely deliver laser energy to the ciliary processes, ensuring controlled treatment. The desired tissue response involves whitening and visible shrinkage of the ciliary processes, achieved using an endoscope 1.0–3.0 mm away. Kahook et al. suggest maintaining approximately 2 mm, typically allowing visualization of six ciliary processes in the endoscope's field. This distance optimizes energy delivery while reducing the risk of overtreatment [12]. The 810 nm diode laser power increases incrementally until the ciliary processes exhibit the intended bleaching and shrinking effects. To achieve significant intraocular pressure (IOP) reduction, treatment covering at least 270° of the ciliary body is often necessary. When using a single incision, the curved endoscope probe facilitates extending the treatment area beyond the capabilities of a straight endoscope [13].

Vitrectomy through the pars plana part of the ciliary body, also known as pars plana vitrectomy (PPV), is an intraocular microsurgical procedure used to remove the vitreous body - the gelatinous substance that fills the largest space in the eye, the vitreous chamber [25].

Gorovoy et al., in a retrospective study, evaluated the effectiveness of ECP in patients undergoing PPV with medically uncontrolled glaucoma. The mean intraocular pressure before surgery was 26.3 mmHg with 2.7 medications and was reduced to 17.9 mmHg after 1 month and 16.9 mmHg after 3 months with an average of 1.3 medications. One patient with neovascular glaucoma developed hypotonia [26]. In a study by Boyd et al, PPV combined with ECP also achieved statistically significant reductions in IOP from 20.3 mmHg before treatment to 14.6 mmHg after a mean follow-up of 12.2 months [27].

He et al. reported a 49.4% reduction in intraocular pressure compared to preoperative values in an analysis of 28 patients (30 eyes) with refractory glaucoma who underwent PPV combined with ECP. The mean IOP before surgery was 46.3 mmHg, and after 15.2 (12–20) months of follow-up, there was a reduction to a mean value of 18.5 mmHg. The effect of the surgery on patients' average medication intake was also evaluated, which decreased from 4 to 1 [28].

Multiple retrospective studies suggest combining ECP with PPV can significantly lower IOP, particularly in refractory cases. However, the absence of control groups, small sample sizes, and variability in follow-up durations limit the strength of these findings. While outcomes appear promising, especially in severe glaucoma, higher-quality evidence is needed to confirm long-term efficacy and safety.

Chen et al. demonstrated that ECP can be effective for refractory glaucoma, particularly in cases where prior trabeculectomy and transscleral cyclophotocoagulation had failed. They observed a reduction in intraocular pressure (IOP) from 27.7 mmHg ± 10.3 before surgery to 17.0 ± 6.7 mmHg at the final follow-up, reflecting a 34% decrease. The success rate, defined as achieving an IOP of ≤21 mmHg, was 90%. Additionally, anti-glaucoma medications decreased from 3.0 ± 1.3 before surgery to 2.0 ± 1.3 afterward. Visual acuity loss of two or more lines occurred in only 6% of patients. Reported complications included fibrin exudation (24%), anterior chamber hemorrhage (12%), cystoid macular edema (10%), and choroidal detachment (4%). Importantly, no severe complications such as ocular hypotony or phthisis bulbi were noted [29].

ECP has been compared favorably to other glaucoma surgeries. Lima et al. conducted a prospective study on 68 pseudophakic eyes with previous failed trabeculectomy, finding that ECP achieved a success rate comparable to the Ahmed Glaucoma Valve drainage system while associated with fewer complications [30].

Studies have found highly effective outcomes of ECP for refractory glaucoma, with a 90% success rate, significant IOP reduction, and favorable results compared to the Ahmed Glaucoma Valve. However, both studies' retrospective designs and small sample sizes highlight the need for larger, randomized trials to confirm long-term efficacy and safety.

Endoscopic cyclophotocoagulation is a modern method of glaucoma treatment gaining popularity due to its better safety profile and comparable efficacy to traditional cyclo-destructive techniques.

ECP combined with phacoemulsification has shown promising efficacy and safety for treating cataracts with concurrent glaucoma. However, most retrospective studies lack control groups and have limited evidence on their pressure-lowering effects. While some studies suggest ECP improves IOP outcomes when combined with KDB or iStent, the evidence is still preliminary and dependent on patient selection and disease severity. In pediatric patients, the long-term success of ECP remains mixed, with varying study quality and outcomes often influenced by patient-specific factors.

Additionally, while some studies report high success rates for combining ECP with PPV or ECP in refractory glaucoma cases, especially compared to devices like the Ahmed Glaucoma Valve, the retrospective nature and small sample sizes of these studies hinder the ability to draw definitive conclusions about long-term efficacy.

Although most of the available studies are retrospective, and large prospective studies with control groups are lacking, the results of the analyses to date suggest that ECP may be a valuable alternative to more invasive anti-glaucoma surgery. Further studies are needed to evaluate the long-term efficacy and safety of this method fully.