December 2013

 

GLAUCOMA

 

Device focus

Diode lasers not just for end-stage treatments


by Michelle Dalton EyeWorld Contributing Writer
   

Endoscopic cyclophotocoagulation showing treated and untreated ciliary body on the monitor and the laser unit Source: Marty Uram, MD

Some glaucoma specialists believe lasers have a place much earlier in the treatment paradigm

Transscleral cyclophotocoagulation (TCP) applies laser treatment to the ciliary body with an aim of lowering the pressure by decreasing aqueous production. Surgeons have used the 810-nm wavelength in both transscleral and endo- cyclophotocoagulation (ECP), the latter of which is typically used in combination with cataract surgery to lower IOP and reduce dependence on glaucoma medications. Earlier cyclodestruction methods included cyclectomy, diathermy, ultrasonic energy, and cryotherapy, but the potential side effects—including relatively high rates of hypotony and vision loss—offset the gains in IOP reduction. Although TCP and ECP use the same wavelength laser, and both lower IOP by decreasing ciliary endothelium function, they differ widely in their approach and, to some extent, the types of patients who are best served by each. Some clinicians believe all uses of ciliary ablation are for end stage cases, said Steven R. Sarkisian Jr., MD, glaucoma fellowship director, Dean McGee Eye Institute, and clinical associate professor, University of Oklahoma, Oklahoma City. "However, ECP is best performed in early to moderate glaucoma, and TCP is best after other procedures have failed," such as trabeculectomy filtering surgery or tube surgery.

In TCP, the surgeon uses a contact G-probe (Iridex Corp., Mountain View, Calif.), which Dr. Sarkisian deemed a "game changer" over cyclo-cryoablation because it helped surgeons better target the end-organ tissue.

"In terms of effectiveness, a trabeculectomy, a tube shunt, and TCP typically achieve more IOP lowering than ECP, but they also have higher complication rates," said Parag Parekh, MD, in private practice, Laurel Eye Clinic, Brookville, Pa. "With ECP, I usually get a moderate effect—somewhere between 0 and 10 mm Hg; I average around 5-7 mm Hg. ECP is very convenient and safe to do in conjunction with cataract surgery, so phaco-ECP has become my go-to surgery for phakic patients with glaucoma."

Comparing transscleral to ECP

Dr. Parekh said with the advent of ECP and other MIGS procedures such as the iStent, he will rarely perform a trabeculectomy as a first line surgical procedure for primary open angle glaucoma, at least not before giving phaco-ECP and/or iStent a chance to be effective. "If it was my own eye, I'd want to give the least invasive procedures a try first," Dr. Parekh said. ECP is "totally different from transscleral," Dr. Sarkisian said. "TCP treats the entire ciliary body, and also affects any nerves that happen to be in the way." Because the laser emits the energy onto the sclera the procedure is "far more inflammatory" than ECP and, therefore, comes with higher potential complications and risks. Dr. Parekh recommended surgeons "go gingerly" when using TCP. "Titrate it to where you need the pressure to be. If you overdose on the laser, you could end up with hypotony; it's better to have to do a 'light diode' twice than overdoing it on the first round. It's a quick procedure—20 shots at 2 seconds each after a retrobulbar block; it's low-risk overall and with no real risk of infection. Furthermore, follow-up is simple for the patient," he said. Dr. Parekh has begun using TCP more in earlier stage patients—particularly those in whom he believes are too frail or who have exhibited poor compliance or are unlikely to have a successful trab. "I have a fair number of 90-year-olds who have excellent acuity but IOP that was elevating out of control. I didn't think they could handle a tube or a trab, so I performed a 'light diode TCP'. Afterward, their vision remained excellent, IOP came under control, and they even came off a few of their drops, and were very grateful for their outcome," Dr. Parekh said. Dr. Sarkisian said he's performed "gentle" or "limited" TCP on patients with vision better than 20/80 and "none havelost vision." If, however, patients are overtreated, vision loss after TCP is a risk. With TCP, the high risk of macular edema and inflammation need to be weighed against the improvement in pressure.

ECP, on the other hand, produces little risk of macular edema beyond what cataract surgery can produce, Dr. Sarkisian said. Dr. Parekh added, "Let's not forget that the data shows that trabeculectomy and tube shunt patients often have decreased vision after those procedures as well. All of our 'heavy duty' glaucoma procedures risk at least some vision loss."

Optimizing use

Some highly informed patients who truly understand the pros and cons of trab and tubes may request TCP earlier than most glaucoma specialists would recommend it. "ECP is less effective than TCP, but it has an outstanding safety profile," Dr. Parekh said. "The biggest downside is if there's not enough pressure lowering. There are very few true adverse events or complications.

"TCP may be more effective, and I think it has fewer side effects than most people think," Dr. Parekh said.

Dr. Sarkisian said phaco-ECP is a reasonable first-line procedure but continues to reserve TCP after patients have failed other treatments. "When you've run out of conjunctiva, TCP is the way to go," he said. "Or when patients have very poor visual prognosis. To put them through the rigors of conjunctival filtration surgery and all the postop required is unrealistic for someone who has light perception or hand movement visual acuity," as the visual prognosis is typically more limited. With TCP and ECP, Dr. Parekh always uses subconjunctival steroids to minimize postoperative inflammation. In addition, he'll then keep patients on topical steroids four times daily for a month. Usually, patients will come off at least some of their medications. The advantage to TCP is that it is repeatable, and to avoid giving too much of the laser, Dr. Sarkisian recommends avoiding the 3 o'clock and 9 o'clock positions. Being overaggressive in treating those areas can lead to patients ending up with neurotrophic corneal ulcers. Dr. Sarkisian will make exceptions—he'll opt to use TCP in eyes with silicone oil rather than use a tube shunt. "Those are often single chamber eyes and the oil gets into the tube, so it's likely you won't get satisfactory results," he said.

Editors' note: The physicians have no financial interests related to this article.

Contact information

Parekh:
parag2020@gmail.com
Sarkisian: steven-sarkisian@dmei.org

Diode lasers not just for end-stage treatments Diode lasers not just for end-stage treatments
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