When weighing options for surgical intervention to control glaucoma, we need to consider the "cyclodestructive" procedures, particularly when coexisting conditions, such as cataract, compromised ocular tissue or prior failed filtering surgery come into play. We have several procedures for decreasing aqueous production at our disposal; however, each presents its own challenges, efficacy rates and potential complications.

Let's look at these options and why endoscopic cyclophotocoagulation (ECP) may be the technique of choice for your glaucoma patients.

Traditional surgery options

Cyclodestructive techniques (ultrasound, cyclocryo-therapy and laser cyclophotocoagulation) are designed to lower aqueous production and intraocular pressure (IOP). As you know, cyclocryotherapy essentially freezes the ciliary processes. Unfortunately, it also freezes much of the peripheral cornea, the ciliary muscle and the sclera.

Laser options include:

► Transscleral cyclophotocoagulation (TCP). This procedure, which can be contact or non-contact, uses either an Nd:YAG laser or a semiconductor diode laser. The Nd:YAG laser produces somewhat better results than cryotherapy. It uses a 1,064-nm wavelength for ciliary body ablation. Basically, it causes an acoustic shock wave that damages the targeted structures.

►Transvitreal endocyclophotocoagulation (TVECP). This procedure is performed during vitrectomy using an argon laser and scleral depression to rotate the ciliary processes into view of the pupil. The argon laser, with a wavelength of about 500 nm, causes thermal damage to the target tissues.

► Endoscopic cyclophotocoagulation (ECP). This procedure uses an 810-nm diode laser. This wavelength is optimal for treating the ciliary body because the pigmented cells absorb the majority of laser energy.

Another advantage of ECP is that the laser energy is applied directly to the target tissue using an internal approach, making the treatment titratable. Working in an illuminated area and being able to monitor the exact location being lasered gives the surgeon an extra level of control and precision for a more accurate treatment with few side effects. In comparison, TCP uses an indirect approach so you can't see what you're treating.

Complication Rates

Glaucoma surgeries can carry considerable risks of side effects and complications. Caprioli and colleagues¹ reported some 24% of patients treated with cyclocryotherapy experienced complications including phthisis, hypotony and corneal decompensation.

Laser treatments have similar drawbacks. Shields and Shields² reported noncontact TCP with an Nd:YAG laser produced a significant amount of hypotony and phthisis, 8% and 1.2%, respectively. Thirty-nine percent of the patients in this study experienced two lines or more of vision loss, most likely secondary to macular edema. About 21% of patients needed retreatment.

In TCP, the laser is applied indirectly, so the treatment is not well-centered over the ciliary process and may even stray onto the ciliary body muscle. Several problems result, including a coagulative necrosis of all ciliary process layers, potential vascular damage in the stroma and disruption of the ciliary epithelium architecture.

A noncontact transscleral approach with a diode laser also produces complications, such as reduced vision. In a 1993 study, Hawkins and Stewart³ reported no incidences of hypotony and phthisis; however, almost 30% of patients required other procedures.

Additional studies by Schuman and Brancato analyzed outcomes of contact TCP using Nd:YAG lasers. A 1992 study by Schuman and colleagues⁴ found a 41% incidence of decreased vision with this technique, most likely due to cystoid macular edema. In a 1989 study, Brancato and colleagues⁵ noted 57% of patients needed retreatment.

Studies of TVECP reveal drawbacks with this procedure, as well. In separate studies, Patel and Zarbin showed a 6% and a 10% incidence of hypotony, respectively. In 1986, Patel and colleagues⁶ found that 11% of patients experienced vitreous hemorrhage and 11% experienced choroidal detachment following TVECP with the argon blue-green laser.

Compared to these findings, the safety profile of ECP is impressive. A clinical study⁷ at the University of California in San Francisco found no hypotony or phthisis in cases done with the ECP diode probe. This is a key benefit of this surgical approach. What's more, the study found only a 6% incidence of vision decrease of two or more lines and no serious complications in ECP patients.

With ECP, most of the vascular architecture remains very well preserved. Jorge A. Alvarado, M.D., UCSF, 2002.13

Histopathology of ECP

Endoscopic cyclophotocoagulation has shown promising outcomes in monkey, rabbit and human trials. The histopathology of a gross specimen from a patient who had ECP shows that the ciliary process and the stroma remain intact post-procedure. We can find some disruption of the small capillaries, but most of the vascular architecture remains very well preserved. When we analyze the epithelial bi-layer, we see that the ciliary epithelium retains normal architecture, with a relative absence of pigment encircling the treated zone.

Another key to ECP success is the 360° treatment. It's important to note that, even with 360° application, you won't treat the entire ciliary epithelium. The valleys between each crest of the ciliary process remain untreated. A typical procedure leaves about 30% of the ciliary process intact. Therefore, we don't see a total shutdown of aqueous production. This means no hypotony and no phthisis.

Because the treated ciliary processes shrink post-treatment, that 30% untreated surface becomes available if we need to retreat later. In these cases, it's easy to identify where to focus the laser because of a clear demarcation line between treated and untreated ciliary process. We simply look to where pigment remains versus where pigment has been lost.

In patients who are fairly well-controlled with medications and who have normal architecture and anatomy, I've found the retreatment rate with ECP is less than 10%.

Practical Considerations

When deciding on the best treatment of the ciliary processes, you need to consider certain factors. Is the wavelength of the laser absorbed well by the target tissue? Are you approaching the target tissue directly or indirectly?

ECP compares very favorably to other treatments. It's well-tolerated and preserves the normal architecture of the ciliary processes. When considering treatment, it makes sense to move away from a cyclodestructive approach and toward a more directed treatment of the ciliary epithelium.

Dr. Francis practices at the Doheny Eye Institute of the University of Southern California in Los Angeles.

References

1. Caprioli JC, Strang SL, Spaeth GL et al. Cyclocryotherapy in the treatment of advanced glaucoma. Ophthalmology. 1985;92:947-954.

2. Shields MB, Shields SE. Noncontact transscleral Nd:YAG cyclophotocoagulation: a long-term follow-up of 500 patients. Trans Am Ophthalmol Soc. 1994;XCII:271-287.

3. Hawkins TA, Stewart WC. One-year results of semiconductor transscleral cyclophotocoagulation in patients with glaucoma. Arch Ophthalmol. 1993;111:488-491.

4. Schuman JS, Bellows AR, Shingleton BJ, et al. Contact transscleral Nd:YAG laser cyclophotocoagulation. Midterm results. Ophthalmology. 1992;99:1089-94; discussion 1095.

5. Brancato R, Leoni G, Trabucchi G, et al. Contact transscleral irradiation of the human chorioretina with continuous-wave Nd:YAG laser. Ophthalmic Res. 1989; 21:1-7.

6. Patel A, Thompson JT, Michels RG, Quigley HA. Endolaser treatment of the ciliary body for uncontrolled glaucoma. Ophthalmology. 1986;93:825-830.

7. Chen J, Cohn RA, Lin SC, et al. Endoscopic photocoagulation of the ciliary body for treatment of refractory glaucomas. Am J Ophthalmol. 1997;124:787-796.