Device earns praise as option for minimally invasive glaucoma surgery based on outcomes from clinical update

Key Points

"The experience with this procedure suggests it has application to adults with open angles, clear gonioscopic views, and appropriate anatomy, and may be expected to result in an IOP of 14 to 18 mm Hg. In addition, we presume it will be a better alternative for pediatric glaucoma surgery in eyes where the cornea is clear enough to allow visualization of the angle," said Dr. Minckler, professor of ophthalmology and pathology, University of California, Irvine.

Other advantages

"Skill transfer for performing the surgery has been easy for glaucoma specialists. Furthermore, the procedure involves much simpler follow-up than after trabeculectomy, and it appears to be safer, especially with regard to avoiding long-term risks, such as discomfort and late infections, since there is no external bleb formation," Dr. Minckler said. "Therefore, we believe it fits into the spectrum of surgical therapies before trabeculectomy and other filtering procedures and may be considered an alternative to laser trabeculoplasty or medication in some patients. Importantly, because the procedure using the novel device spares the conjunctiva, it does not preclude subsequent standard surgery if it is deemed necessary in the future."

The device is used in an ab interno approach to unroof Schlemm's canal by ablating its inner wall and the adjacent trabecular meshwork along an arc of 60° to 90°. Sometimes referred to as a "micro spark plug," the handpiece includes a microelectrocautery unit at its tip that ablates tissue with continual infusion and aspiration of liquid. The unit includes a 19-gauge infusion sleeve and a 25-gauge aspiration port to allow simultaneous removal of tissue debris.

Insulation coating on a protective footplate near the electrodes at the surgical end of the device, as well as continuous irrigation, prevents thermal damage to the posterior wall of Schlemm's canal and adjacent tissues during the ablation.

"Previously, we demonstrated the safety of this device for tissue removal in an in vitro model using corneoscleral rims. Histologic evaluation confirmed that there was less damage to collateral tissue than after use of a goniotomy knife," Dr. Minckler said. "Findings in autopsy specimens also provide evidence that there is no detectable injury."

Initial procedures

The 201 initial procedures were performed in patients aged 2 to 98 years; only two patients were aged fewer than 18 years, and the cohort had a mean age of 68 years. The patients were about equally divided by gender and comprised a slight majority of Caucasians (52%) and a high proportion of Hispanics (34%).

Almost all eyes (86%) had chronic OAG. In eyes with known visual field status, the majority had moderate (36%) or advanced (35%) damage. Nearly 80% of eyes were phakic, and 41 (20%) eyes underwent a combined procedure including cataract surgery.

Follow-up to date is still of limited duration for most eyes. Ninety eyes were followed out 3 months, whereas data from visits at 12, 24, and 36 months were available for only 43, 23, and five eyes, respectively. Interestingly, analyses of IOP changes show progressive reductions in both the mean IOP and standard deviation of the mean IOP with increasing duration of follow-up, said Dr. Minckler.

Preoperatively, the group had a mean ± SD IOP of 25.2 ± 7.4 mm Hg. The mean decreased to 17.5 ± 4.2 mm Hg at 3 months (–38%) and was 16.7 ± 2.6 mm Hg (–47%) at 12 months, 15.5 ± 2.4 mm Hg (–48%) at 24 months, and 14.6 ± 2.4 mm Hg (–42%) at 36 months.