Complications of Cyclodestructive Procedures

Introduction

Cyclodestructive procedures aim to reduce aqueous production through ablation of ciliary body tissue. This treatment modality has traditionally been utilized for patients with advanced glaucoma whose intraocular pressure (IOP) is insufficiently controlled on maximal medical treatment. In the past, many patients undergoing cyclodestruction had failed filtering surgery or were considered to be at high risk for surgical complications, including patients with aphakic glaucoma, neovascular glaucoma, and secondary glaucoma after penetrating keratoplasty. Cyclodestructive procedures are also appropriate for patients with poor visual potential and high IOP, enabling them to avoid invasive surgery. Newer endoscopic cyclodestructive techniques are frequently used even earlier in the treatment regimen, often prior to filtering surgery in specialized circumstances.

Early forms of cyclodestruction included diathermy and cryotherapy, both of which were associated with high complication rates and low success rates. Therapeutic ultrasound and cyclectomy have also been used in the past with some degree of success. The first form of cyclopho­tocoagulation was performed with the xenon arc photocoagulator followed by the introduction of laser in 1971. Transpupillary and transcleral xenon arc and laser cycloablation were found to have better success rates than other forms of cyclodestruction, with comparatively fewer side effects. The transpupillary cyclophotocoagulation approach treated only a small portion of the ciliary process, constituting less than 20% of the entire process, and thus resulted in only limited short-term IOP lowering. The transscleral route soon became the preferred method, starting with the continuous-wave Nd:YAG laser, and then the solid-state diode laser using a G-probe. Endoscopic cyclophotocoagulation using a diode laser has become gradually more popular due to increased precision in tissue targeting, less collateral damage, and promising IOP-lowering capabilities. This chapter will detail the complications associated with the most popular methods of cycloablation currently utilized, namely transscleral diode cyclophotocoagulation and endoscopic cyclophotocoagulation.

Complications of Transscleral Diode Laser Cyclophotocoagulation

Since FDA approval in 1994, multiple studies have proved the relative safety and efficacy of contact diode laser cyclophotocoagulation (CDC) in various forms of glaucoma. Despite improved control and therapeutic effects compared to previous transscleral cycloablative methods, postoperative complications still exist with CDC, including pain, hyphema, persistent inflammation, and fluctuation of IOP.

Early postoperative complications arising from CDC include pain, hyphema, conjunctival burns, anterior chamber inflammation, high or low pressure, and cataracts ( Box 124-1 ). Pain associated with CDC is usually transient and controlled with mild over-the-counter analgesics. A minority of patients require more potent pain medications for a short period to control discomfort. Hyphema appears to occur more frequently in patients with neovascular glaucoma than others and is treated with topical steroids and cycloplegia, as is standard post CDC. Destruction of ciliary body tissue, and in some cases surrounding structures, may lead to an acute iridocyclitis with accompanying photophobia and discomfort. This can usually be treated with topical steroids until resolution. It is important to note that a subset of patients experience a chronic low-grade anterior chamber cell and flare reaction with few symptoms as a result of breaching the blood–aqueous barrier. These patients do not require long-term topical steroid therapy as this represents a breakdown of tissue barriers within the anterior chamber and not a true iridocyclitis.

Conjunctival burns are an infrequent complication of CDC if cautionary measures are taken and appropriate technique is utilized. Common reasons for conjunctival burns include failure to wet the conjunctival surface between laser applications, improper settings in cases of darkly pigmented conjunctiva, and use of defective, damaged, or soiled contact laser probes. It is important to examine the end of the G-probe to ensure that the quartz tip is free of surface irregularities and debris, and that the aiming beam is clearly visible prior to performing the procedure. Albeit long-lasting, G-probes do have a limited shelf life and should be discarded after approximately five treatment sessions or when defects are noted. Injury to the conjunctiva is usually mild and successfully treated with observation, topical steroids, and/or lubricating ointments, although treatment with a damaged or dirty probe may result in not only conjunctival burns, but also scleral burns or outright penetration of the globe.

IOP fluctuations after CDC can be frustrating and difficult to manage. A small percentage of patients experience a short-lasting spike in IOP typically controlled with medical therapy. Contreras and colleagues evaluated the incidence of IOP spikes after CDC in a retrospective study of 116 eyes (110 patients) with refractory glaucoma. IOP measurement was obtained immediately before and 1 hour after treatment with an IOP spike defined as an increase of >5 mmHg. They reported a mean IOP decrease of 6.96 mmHg after 1 hour (p < 0.001). However, 10.8% of eyes treated experienced an IOP spike noted to be more frequent in eyes with neovascular glaucoma. The authors do not typically check IOP immediately after CDC, but rather instruct patients to follow up the next day for evaluation.

Postoperative hypotony after CDC remains a major risk in a certain subset of patients. Specifically, neovascular glaucoma (NVG) patients appear to be predisposed to this complication. A study by Nabili and Kirkness identified previous pars plana vitrectomy as an added risk factor for hypotony in NVG patients undergoing CDC. Treating hypotony usually involves long-term topical steroids, cycloplegia, and eliminating other causes of chronic hypotony such as retinal detachment and/or choroidal detachment. Despite treatment, very rarely eyes progress to phthisis and may require enucleation.

The most worrisome complication of CDC is loss of vision, either early or late. Incidence of vision loss following CDC depends on the study population, aggressiveness of laser application, and length of follow-up. Although the incidence of decreased vision appears to be lower with CDC than with previous transscleral cycloablation methods, there are no prospective studies adequately addressing this issue to allow for an evidence-based medicine approach to guide physician practice. Kosoko and colleagues investigated the utility of CDC in eyes with severe glaucoma. Out of 27 treated eyes, one eye with light perception vision declined to no light perception. Three eyes lost two lines of vision and five (19%) lost three or more lines. Most patients maintained visual acuity within one line of baseline levels. Egbert and colleagues prospectively evaluated the efficacy of CDC as primary therapy for patients with primary open-angle glaucoma. They reported visual acuity decreases in 18 (23%) of 79 eyes treated by CDC versus 10 (23%) of 47 fellow eyes treated only with glaucoma medications.

Ansari and Gandhewar evaluated the long-term efficacy and safety of CDC for a range of glaucoma conditions in a retrospective analysis of 74 treated eyes conducted over a period of 4–30 months. A subanalysis of patients with ‘ambulatory vision’ of 6/36 or better was then performed. Within this subgroup, 3/23 (13%) patients with primary open-angle glaucoma (POAG) lost vision due to cataract (2 patients) and glaucoma progression (1 patient). Eight patients with ambulatory vision diagnosed with chronic angle-closure glaucoma did not show any significant deterioration in vision. There were no cases of hypotony (IOP <5 mmHg) or phthisis, and only one eye required retreatment. Reasons for decreased vision after CDC range from advancing cataracts to improper intraocular pressure control and chronic hypotony. Inflammation from the procedure may also result in cystoid macular edema with associated visual disturbances. As a general rule, the physician must investigate the reason for a decline in vision and address it appropriately. It is unknown whether chronic postoperative treatment with nonsteroidal anti-inflammatory drugs (NSAIDs), as is the case in post cataract extraction, may lead to a lower incidence of macular edema. More studies are needed to prospectively evaluate the effect of CDC on vision and whether subtype of glaucoma or laser settings are predictive of future vision loss.

Other infrequent complications following CDC include necrotizing scleritis, malignant glaucoma, and sympathetic ophthalmia. Albeit rare, the treating physician must be aware of their possible existence and follow patients closely for prompt and effective intervention.