In Which Glaucoma Patients Should I Consider Cyclodestruction?
Malik Y.
Kahook,
MD
Cycloablative procedures target the ciliary body epithelium, which produces aqueous humor, to reduce intraocular pressure (IOP). Various methods of cyclodestruction including diathermy, ultrasonic energy, and cryotherapy have existed for many years and have been traditionally reserved for end-stage glaucoma. Newer cyclodestructive procedures have replaced these earlier methods beginning with Xenon arc photocoagulation and later followed by Nd:YAG and diode lasers. Currently, the diode laser is most widely used for cyclophotocoagulation (CPC) and treatment can be delivered by either the transscleral route with a G-probe (Iris Medical Instruments, Mountain View, CA) (Figure 49-1) or by the endoscopic route.
Figure 49-1. The G-probe is used with transscleral cyclophotocoagulation (CPC). The quartz tip indents the conjunctiva and directs the laser energy through the sclera to the ciliary body.
I often use transscleral CPC for patients with advanced glaucoma and poor IOP control, despite maximal medical therapy, who have also failed one or two penetrating surgeries. Other potential candidates include patients with glaucoma in aphakia, neovascular glaucoma (NVG), and glaucoma after penetrating keratoplasty. These patients are at increased risk for complications or frank failure of penetrating surgery and may benefit from CPC as first-line surgical therapy when medications fail to control IOP. Nonseeing eyes with pain and high IOP also benefit from this noninvasive procedure. Recent reports indicate that transscleral CPC may be an appropriate first-line option in patients who experience difficulty with follow-up or in populations with limited resources for medical or surgical therapy.1
Posttreatment complications of transscleral CPC including pain, inflammation, hyphema, fluctuation of IOP, and, in some cases, loss of vision remain a major obstacle to the more prevalent use of CPC. Other complications of transscleral diode therapy include conjunctival burns, cataract formation, irregular/tonic pupil, and cystoid macular edema. Of these, fluctuations in IOP and changes in vision represent the major barriers to the more widespread use of this treatment modality.
IOP spikes after CPC can usually be controlled with topical medical therapy. Contreras and colleagues reported that 10.8% of eyes treated with CPC experienced an IOP spike.2 Although elevations in IOP may be seen with all forms of glaucoma, patients with NVG are more prone to this complication and should be watched closely. I see patients on the first postoperative day and institute topical and/or oral therapy to control IOP spikes if they occur. In most cases, the pressure is lowered and medical therapy may be slowly weaned.
Postoperative hypotony after CPC is a serious complication that often requires intense therapy and close follow-up to lessen the chance of long-term morbidity. My usual treatment regimen consists of both long-term topical steroids and cycloplegia after eliminating other possible causes of chronic hypotony, such as retinal and/or choroidal detachments. Despite close follow-up and treatment, eyes suffering from long-term hypotony will have decreased vision and may become phthisical and/or require enucleation. The best way to avoid complications from hypotony is to prevent its occurrence in the first place. The laser is initially set to 2000 mW and 2000 ms duration; the power is increased in increments of 250 mW until the first audible “pop” is heard. Following this sign of overtreatment, I decrease the power by 250 mW and proceed with treatment. I do not perform 360 degrees of CPC in any of my patients. I typically start by treating 270 degrees and observe closely. If IOP lowering is insufficient, the remaining 90 degrees can be treated in a second session. This method helps prevent a dramatic drop in pressure that may be irreversible, especially in patients with NVG who tend to experience hypotony after CPC more frequently than other diagnostic groups.
Vision loss is the most dreaded complication of cyclodestructive procedures. Although well known, there is little information as to the true incidence and etiology of vision loss after CPC. Some factors leading to vision loss include development of cataract, high or low IOP, chronic uveitis, and cystoid macular edema. Many of the complications linked to transscleral diode therapy result from the transmission of energy across the sclera to tissue adjacent to the ciliary body or from excessive energy application required to treat the targeted tissue.
Endocyclophotocoagulation
A major limitation of transscleral CPC is the indirect method of treating the ciliary body epithelium without visualization of the targeted tissue. Endoscopic cyclophotocoagulation (ECP) is a more recent method of cycloablation performed with an 810-nm diode laser, a 175-W Xenon light source, and a helium-neon laser aiming beam (Endo Optiks, Little Silver, NJ). The endoscopic imaging system affords direct visualization of ciliary processes during treatment, resulting in a more precise and titratable treatment (Figure 49-2). The power is set at 0.25 W on continuous mode, with tissue whitening and shrinkage of the ciliary processes as the goal of treatment. Surrounding tissue is spared in experienced hands thus decreasing postoperative complications.
Figure 49-2. Endoscopic view during endocyclophotocoagulation showing ciliary processes (black arrow), iris (yellow arrow), and anterior capsule (white arrow).
The efficacy of ECP for treatment of refractory glaucoma has been reported by Chen and coworkers in 68 eyes of 68 patients.3 They noted a mean decrease in IOP of 34% with average follow-up of 12.9 months. Treatment complications included anterior chamber fibrin, hyphema, cystoid macular edema, and choroidal effusion. No hypotony or phthisis was observed. Other studies have also shown successful and safe outcomes from ECP treatment comparable to both aqueous shunts and trabeculectomy.4,5
Appropriate patient selection is the key to successful outcomes with ECP. I reserve ECP for glaucoma patients in 3 categories. The first category includes patients undergoing phacoemulsification who use 2 or more topical glaucoma medications even in the setting of controlled IOP. The goal is to enable them to stop taking one or more of their medications postoperatively while preserving IOP control. Patients with poorly controlled glaucoma despite maximal medical therapy and IOP under 35 to 40 mm Hg make up the second group. The goal in this category is to achieve improved IOP control postoperatively with or without medical therapy. The third group is made up of patients who have failed previous penetrating surgery and are poor candidates for further filtration procedures. This has traditionally been the category for transscleral CPC treatment; however, the direct visualization made possible with ECP allows for effective and safe treatment while resulting in less tissue damage.6
Few prospective studies have been reported on the utility of ECP in decreasing IOP or affect on decreasing dependence on topical medications.7 I have found that treating 360 degrees through 2 clear cornea incisions results in improved IOP lowering that is long lasting without an increase in inflammation or hypotony. The second incision, constructed 100 degrees away from the first, allows treatment of the tissue underneath the initial clear cornea incision. I have observed an average IOP decrease of 30% to 40% when treating 360 degrees through a clear cornea incision approach. Sixty percent of patients are able to decrease the use of topical medications postoperatively. There have been no cases of chronic hypotony or phthisis in my clinic to date with 360-degree treatment.
Summary
Cycloablative procedures have played an important role in treating glaucomas often refractory to other methods of IOP control. While transscleral CPC has often been reserved for patients with poor vision, careful titration of laser spot application and energy used can allow for both safe and effective treatment in patients with functional vision. ECP is a relatively newer method of cycloablation that allows direct visualization of targeted tissue and has found a role in treating glaucoma earlier in the course of the disease. More prospective research is needed to better understand the differences between CPC and ECP, as well as their role in treating glaucoma in different patient populations.
References
1. Lai JS, Tham CC, Chan JC, Lam DS. Diode laser transscleral cyclophotocoagulation as primary surgical treatment for medically uncontrolled chronic angle closure glaucoma: long-term clinical outcomes. J Glaucoma. 2005;14:114-119.
2. Contreras I, Noval S, Gonzalez Martin-Moro J, Rebolleda G, Munoz-Negrete FJ. IOP spikes following contact transscleral diode laser cyclophotocoagulation. Arch Soc Esp Oftalmol. 2004;79:105-109.
3. 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.
4. Lima FE, Magacho L, Carvalho DM, Susanna R Jr, Avila MP. A prospective, comparative study between endoscopic cyclophotocoagulation and the Ahmed drainage implant in refractory glaucoma. J Glaucoma. 2004; 13:233-237.
5. Gayton JL, Van Der Karr M, Sanders V. Combined cataract and glaucoma surgery: trabeculectomy versus endoscopic laser cycloablation. J Cataract Refract Surg. 1999;25:1214-1219.
6. Pantcheva MB, Kahook MY, Schuman JS, Noecker RJ. Comparison of acute structural and histopathological changes in human autopsy eyes after endoscopic cyclophotocoagulation and trans-scleral cyclophotocoagulation. Br J Ophthalmol. 2007;91:248-252.
7. Berke SJ, Sturm RT, Caronia RM, et al. Phacoemulsification combined with endoscopic cyclophotocoagulation in the management of cataract and glaucoma. Paper presented at: The AAO Annual Meeting; November 14, 2006; Las Vegas, Nev.