Malik Y. Kahook,
Robert J. Noecker,
Joel S. Schuman
INTRODUCTION
Cyclodestructive surgery involves the ablation of the ciliary body to reduce intraocular pressure (IOP) by decreasing aqueous production. The first reports of IOP reduction by ciliary body destruction using diathermy were in 1933 and the procedure was quickly abandoned due to low success rates and significant hypotony.[1,2] Destruction of the ciliary body by freezing was proposed in 1950 and found to be less destructive and more predictable than cyclodiathermy.[3-8] Therapeutic ultrasound and partial cyclectomy are other modalities which have been used in the past with limited success.[9-14]
The first form of cyclophotocoagulation (CPC) was performed with the xenon arc photocoagulator.[15] It was not until 1971 that the use of the laser for CPC was introduced. A transpupillary CPC procedure produced limited success, due to the small amount of ciliary process that could be visualized and accessed through the pupil.[16,17] The transscleral route, while not permitting direct visualization of the target tissue, proved to be less invasive and has become a preferred method of cycloablation in cases of refractory glaucoma.[18-20] Over time, the preferred type of laser used has changed from the Nd:YAG equipped with a sapphire tipped contact probe to a solid state diode laser equipped with a disposable probe. Recently, endoscopic cyclophotocoagulation (ECP) using a diode laser equipped with an endoscope has become increasingly popular due to the promise of even more precise tissue targeting and less collateral damage.
INDICATIONS
CPC lowers IOP by destroying the ciliary epithelium, leading to decreased aqueous humor production. This treatment has been traditionally indicated in advanced glaucoma, in which the IOP is inadequately controlled despite maximal treatment. CPC is useful in eyes that have failed filtering surgery, are at high risk for complications of filtering surgery or expected to fail further filtering surgery. This includes patients with aphakic glaucoma, neovascular glaucoma, glaucoma after penetrating keratoplasty, or eyes with low visual potential. Treatment that is too aggressive may lead to hypotony and/or chronic inflammation, while inadequate treatment will not lower the IOP to a satisfactory level.
The use of proper technique and proper patient selection is very important to fall within the narrow therapeutic window. The risks of cyclodestructive surgery include inflammation, pain, chronic hypotony, macular edema, vitreous hemorrhage, and phthisis. These risks tend to make this procedure a treatment of last resort in the management of advanced glaucoma. Better understanding of treatment endpoints with transscleral techniques has led to fewer complications and more controlled inflammation postoperatively. With the recent introduction of ECP, cycloablation has become increasingly titratable with a dramatic decrease in risks and side effects. While still used in cases of refractory glaucoma, ECP has found a role in treating glaucoma when combined with cataract extraction (CE) and in cases not amenable to other forms of IOP lowering surgery.
TRANSSCLERAL LASER CPC
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Key Features |
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Transscleral Nd:YAG and diode laser cycloablation results in destruction of the ciliary body structures that absorb these wavelengths of light, including the ciliary epithelium and associated vessels. There are two transscleral approaches that have been used in cycloablation: noncontact and contact. Both approaches have been performed with the Nd:YAG and diode lasers. The use of Nd:YAG laser for cycloablation has largely been replaced with the diode laser due to the diode laser's size, convenience, and availability.
Noncontact and Contact Transscleral Nd:YAG CPC
Noncontact Nd:YAG laser cyclophotocoagulation (NCYC), primarily of historical interest, may be performed with a slit-lamp delivery system using the LASAG Microruptor laser (LASAG, Thun, Switzerland). Contact Nd:YAG laser cyclophotocoagulation (CYC) is performed with a continuous-wave Nd:YAG laser (Surgical Laser Technologies, Inc., Malvern, PA) which is connected to a fiber-optic probe with a 2.2 mm diameter convex synthetic sapphire tip.
Complications of both techniques include severe inflammation, ocular pain, a transient increase in IOP, loss of vision, severe hypotony, flat anterior chamber, serous choriodal detachment, and phthisis bulbi.
Success following NCYC has been reported to be 45-86% with an average follow-up of 6-22 months.[21-24] Success rates following CYC have been reported to be 56-72% with a mean follow-up of 12-36 months.[25] A study by Lin and colleagues looked at the long-term follow-up of CYC.[26] Mean follow-up was 5.85 ± 4.0 years, mean preoperative IOP was 36.3 ± 10.1 mmHg and mean postoperative IOP was 18.9 ± 12.2 mmHg at 10 years of follow-up. Five of eight eyes with pretreatment visual acuity better than 20/200 lost two or more Snellen lines by the end of follow-up. Overall, 44.1% of eyes required re-treatment and overall failure rate was 51.5%.
Transscleral Semiconductor Diode Laser CPC
The US Food and Drug Administration approved a diode laser (Iridex, Mountain View, CA) for contact transscleral CPC in 1994. CDC has results nearly identical to those of CYC,[26] but because of the delivery system and the balance between transmission and absorption at the diode laser's ?810 nm wavelength, CDC requires less energy per spot and fewer applications (Figs 224.1 and 224.2). In a multicenter study of CDC in 27 eyes, Kosoko and co-workers found a 44% reduction in the IOP at 19 months follow-up.[27] Using 1.5-2.0 watts for 2 s and treating 16-18 spots over 270° with the fiber-optic probe centered 1.2 mm posterior to the limbus, the authors noted a success rate of 72-84% after 1 year and 52-62% after 2 years. There was mild transient inflammation, but no hypotony was reported. Seventy percent of eyes were either unchanged or remained within one line of preoperative visual acuity, while 30% lost two or more lines. Carassa and colleagues reported a 50% IOP reduction in 12 of 12 eyes treated with 16 spots over 360° and 2.5 watts for 1.5 s.[28] Results from these clinical studies suggest that CDC aids in the surgical management of refractory glaucoma.
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FIGURE 224.1 Placement of probe on eye for diode laser transscleral CPC. The G-Probe (Iridex Corporation, Mountain View, CA) has a fixed offset and is applied to flush to the limbus. |
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FIGURE 224.2 Tip of specially designed diode laser contact probe for transscleral CPC (G-probe, Iridex Corporation, Mountain View, CA). |
ENDOSCOPIC DIODE LASER CPC
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Key Features |
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ECP is performed with an 810 nm diode laser, a 175 W Xenon light source and a helium-neon laser aiming beam (Endo Optiks, Little Silver, New Jersey). A fiber-optic imaging system allows for direct visualization of ciliary processes during treatment to allow for precise and titratable treatment (Figs 224.3 and 224.4). Maximum power is limited to 1.2 W and exposure time is adjustable up to continuous mode. Typically, the power is set at 0.25 W with continuous exposure, controlled by foot pedal, and increased to achieve tissue whitening and shrinkage.
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FIGURE 224.3 ECP with entry through a clear cornea incision using a curved probe. |
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FIGURE 224.4 Ciliary body processes are visualized using diode laser ECP for more precise treatment. In this endoscopic view, the white arrow points at the posterior untreated portion of a ciliary process; the black arrows show freshly coagulated ciliary processes. |
In a study that evaluated ECP for treatment of refractory glaucoma, Chen and co-workers used 500-900 mW for 0.5-2.0 s over a mean 245° of the ciliary body on 68 eyes of 68 patients.[29] They reported a mean decrease in IOP of 34% with an average follow-up of 12.9 months. The success rate for IOP less than 21 mmHg at 1 and 2 years were 94% and 82%, respectively. Visual acuity improved or remained stable in 94% of eyes, while 6% lost two or more lines of acuity. Postoperative complications included anterior chamber fibrin, hyphema, cystoid macular edema, and choroidal effusion. No hypotony or phthisis was observed.
A study by Lima and colleagues compared the use of Ahmed shunts versus ECP in cases of refractory glaucoma.[30] Success was defined as postoperative IOP between 6 and 21 mmHg with or without medications and mean follow-up was 19.82 ±8.35 months and 21.29 ± 6.42 months for the Ahmed and ECP groups, respectively. Preoperative IOP was 41.32 +/?°±? 3.03 mmHg decreasing to 14.73 ± 6.44 mmHg, and 41.61 ± 3.42 mmHg decreasing to 14.02 ± 7.21 mmHg in the Ahmed and ECP groups respectively. While the results were similar, the ECP group was less likely to have serious postoperative complication including choroidal effusions and shallow anterior chambers.
ECP has also found a role in treating pediatric glaucoma. Neely and Plager reported on 51 ECP procedures, treating 260°(±58°), performed on 36 eyes of 29 patients.[31] Posttreatment IOP was 23.63 (+/?°±?11.07) mmHg after a baseline IOP was 35.06 (± 8.55) mmHg and follow-up of 19.25 (±19.36) months. This was a 30% decrease in IOP after 1.42 ±0.87 laser treatments. Overall success rate was 43% after final follow-up with complications including two retinal detachments, hypotony in one patient, and one patient's vision decreasing from hand motion to no light perception vision. The coexistence of aphakia with glaucoma was a poor prognostic indicator.
The concomitant use of ECP with phacoemulsification is increasing in patients with coexisting cataracts and glaucoma. Gayton and colleagues compared the combined procedures of CE and trabeculectomy with CE and ECP.[32] They found that 30% of combined CE-ECP patients achieved an IOP below 19 mmHg with 2 years of follow-up. With use of postoperative ocular hypotensive agents, 65% of combined CE-ECP procedures resulted in IOP below 19 mmHg. This compared to rates of 40% and 52% for the combined CE-trabeculectomy patients without and with medication use respectively. They concluded that combined CE-ECP was an effective and safe alternative to combined CE-trabeculectomy surgery.
ECP may be a viable option for treating cases of refractory glaucoma with or without combined CE. The efficacy and increased safety profile compared to transscleral CPC and traditional trabeculectomy makes it a practical alternative when used properly. Further studies with long-term follow-up will be needed to define the role of ECP as a primary intervention for glaucoma failing maximal medical treatment.
CONCLUSION
Cycloablation provides the opportunity to reduce IOP in eyes with advanced glaucoma refractory to medical and other surgical treatment. Cyclocryotherapy has largely been replaced by laser destruction of the ciliary body. Over time, transscleral Nd:YAG laser CPC has been largely replaced by the use of the diode laser. CDC is successful in reducing IOP using less energy and fewer spots than NCYC and CYC.
The transscleral route for treatment has two main disadvantages: the inability to precisely quantitate the amount of ciliary process damage, and unwanted damage to ocular structures adjacent to the ciliary processes, both related in part to lack of visualization of the target tissue. As a result, unwanted inflammation due to overtreatment may occur. Because of the effect of transscleral CPC on visual acuity and its attendant risk of hypotony, it is usually reserved for patients with poor visual potential. ECP permits direct visualization of the ciliary processes and allows more precise CPC, resulting in more focal damage to the ciliary processes and relative sparing of adjacent tissues. The trade-offs for the greater control offered by ECP compared to transscleral CPC, however, are the need for incisional surgery with ECP and potentially less long-term efficacy.
Finally, cyclodestructive procedures are traditionally an option of last resort. The risk-benefit ratio is such that medical therapies and other conventional surgical techniques typically are more attractive than CPC. ECP has become an increasingly frequently used technique for the treatment of refractory glaucoma or in cases in which traditional incisional glaucoma surgery is a less desirable option. The increased safety profile of this technique has led to its use earlier in the treatment algorithm of caring for glaucoma patients. Authors have begun to suggest the use of CPC prior to filtering surgery in developing countries.[33] In this setting, the risk-benefit ratio may be altered such that CPC becomes a more reasonable treatment option. In the majority of the developed world, however, cyclodestructive surgery is still reserved until after more traditional surgical options have been explored.
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