MicroPulse transscleral cyclophotocoagulation an option for range of glaucoma patients

Issue: October 10, 2016

ByNathan M. Radcliffe, MD

ByShan C. Lin, MD

Cyclophotocoagulation is a form of cycloablation used to treat glaucoma through the destruction of the ciliary body epithelium and stroma. While this results in a reduction of aqueous secretion and IOP, it is associated with numerous risks. Traditionally performed using cyclocryotherapy, the treatment has proven safer when delivered by contact transscleral methods using an 810 nm continuous wave diode laser. Using this modality, the treatment is generally effective for all forms of glaucoma, but effects can be unpredictable. Notable complications can include morbidity from hypotony, visual deterioration and phthisis bulbi. A new paradigm, MicroPulse P3 from Iridex, offers equivalent or superior efficacy results with significantly reduced risk factors.

While traditional continuous wave lasers can be destructive to ancillary tissue, MicroPulse delivers the laser in short bursts to allow the surgeon to target specific areas while giving the tissue time to cool down between bursts, minimizing damage. MicroPulse has been used successfully in retinal diseases, and now MicroPulse transscleral cyclophotocoagulation (mTSCPC) using the MicroPulse P3 probe and the new Cyclo G6 glaucoma laser system (Iridex) has been shown to have excellent safety and efficacy rates. Studies have reported greater IOP reduction rates and lower incidence of complications than continuous-wave procedures, with most reporting no cases of macular edema, phthisis or visually significant hypotony.

Recovery from mTSCPC is a wholly different scenario from past surgeries. Inflammation does occur but at a significantly lower severity than with previous procedures. To combat inflammation, patients can be given an injection in the subconjunctival or sub-Tenon’s space of the eye the day of treatment. Afterward, patients can be given a topical medication such as prednisolone. However, instead of needing this medication for a month or longer, patients will only need it four times a day, tapered over approximately a week. Most of the inflammation seen with this treatment fades within a week.

Serving a variety of patient profiles

A wider range of patients can be treated with the mTSCPC procedure, including those with primary open-angle glaucoma, congenital glaucoma, pigmentary glaucoma and steroid-induced glaucoma. This is used for patients who are often on maximum medical therapy or for whom other treatments have failed. It can be used in place of traditional surgery and even together with cataract surgery and other microincisional glaucoma surgeries. Those who are not good surgical candidates for one reason or another may do well with this procedure. Patients who may have bleeding problems or who would have a difficult time with care after traditional glaucoma surgery are also good candidates (Figure 1).

Figure 1. Anterior segment photograph of an aphakic highly myopic eye with uncontrolled glaucoma and a history of retinal detachment with surgical repair. Vitreous is seen in the anterior segment, and the eye was considered to be high risk for both surgical complications and surgical failure after traditional filtration surgery with trabeculectomy or tube shunt, which both would have required vitrectomy. Non-incisional mTSCPC was performed with excellent IOP lowering and no complications.

Duration of efficacy

While a single mTSCPC treatment may not adequately treat every patient, the procedure is repeatable. This procedure is particularly efficacious in eyes that start out with very high pressures, between 30 mm Hg and 50 mm Hg. Several patients in our experience have had reductions from the 20s and 30s down to the teens. Typically, the higher the baseline pressure, the more significant the reduction rate. Those patients who respond well generally maintain that response for a significant period of time, many lasting a year or longer.

Clinical results

In a study conducted by Radcliffe and colleagues, mTSCPC was performed on 48 eyes of 45 patients. Patients received retrobulbar anesthesia followed by two 50- to 90-second mTSCPC treatments over the superior and inferior hemispheres, sparing the temporal most clock hour. The duty cycle was 31.3% with a power setting between 2,000 mW and 2,250 mW. Topical steroids were prescribed postoperatively, and IOP was monitored. The procedures produced a low rate of postoperative inflammation. There was a mean IOP reduction of 29.8% after 3 months. The procedures also resulted in a significant reduction in the number of ocular hypotensive medications used to control IOP, from a mean of 3.3 medications at baseline to a mean of 2.4 medications at month 3. No cases of visually significant hypotony, macular edema or phthisis bulbi were observed.

Pearls

Unlike a tube shunt in which if the pressure drops too low the tube can be tied off to bring the pressure back up, laser treatment is irreversible. Therefore, it is a good idea to treat lightly at first and repeat as necessary. With this procedure, the surgeon is in control of how much laser to apply.

Figure 2. The MicroPulse P3 probe is held flush against the eye during treatment.

It is important to pay attention to a patient’s pigment. People who are in general more pigmented absorb laser energy better, and it is necessary to use lower laser settings on these patients to avoid overtreatment and inflammation. Someone with less pigment, such as a patient with blue eyes, can be treated with higher settings.

When the probe is moved back and forth sparing the 3 and 9 o’clock hours, it should be maintained flush with the eye. If it is lifted, the focus of the probe could be in a different area from where it is needed and could cause complications. Also, keep the probe perpendicular to the eye as it is moved between the positions. This allows the focus of the laser to be in the appropriate area of the eye (Figure 2).

Physicians may be concerned about the anesthesia that is required for this procedure. Because the probe contacts the surface of the eye and can be uncomfortable, it is recommended that the patient be given either a retrobulbar or peribulbar anesthesia. Using lidocaine gel for the eye can also reduce patient discomfort.

It always takes time for new techniques to be fully accepted, and mTSCPC is no exception. Most physicians were trained with the knowledge that cyclophotocoagulation is a last resort treatment only done in blind, painful eyes with high pressure. However, with MicroPulse technology, this no longer appears to be the case.

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For more information:

Shan C. Lin, MD, is director of the Glaucoma Service at the University of California, San Francisco Medical School. He can be reached at Glaucoma Clinic, 8 Koret Way, Suite U519, San Francisco, CA 94143-0644; email: lins@vision.ucsf.edu.
Nathan Radcliffe, MD, is director of glaucoma service at New York University and operates at New York Eye Surgery Center. He can be reached at email: drradcliffe@gmail.com.

Disclosures: Lin and Radcliffe report they are paid consultants for Iridex.