Ab interno trabeculectomy safely lowers IOP to mid-teens

Study finds minimally invasive procedure provides greater IOP reduction for exfoliation glaucoma than primary open-angle glaucoma.

Issue: August 10, 2012

Anecdotal experience that patients with exfoliation glaucoma fare better than those with primary open-angle glaucoma after ab interno trabeculectomy has gained support from a prospective cohort study.

Ab interno trabeculectomy is a relatively new incisional procedure that removes an arc of trabecular meshwork and inner wall of Schlemm’s canal. Further, combination with cataract surgery and IOL implantation showed improved results, according to the study.

“Compared to standard trabeculectomy, ab interno trabeculectomy is less invasive and more elegant procedure,” study co-author Jessica L.M. Ting, MD, said. “Rather than creating a subconjunctival filtering bleb, which can be associated with severe complications, the ab interno trabeculectomy uses electrode surgical ablation to excise a segment of the meshwork and inner wall of Schlemm’s canal. Studies to date have revealed a low rate of complications.”

The study was published in the Journal of Cataract and Refractive Surgery.

Protocol, outcomes

The study compared 12-month postoperative outcomes for two treatment modalities, each with two arms: ab interno trabeculectomy performed alone for exfoliation (67 patients) or primary open-angle glaucoma (450 patients); and ab interno trabeculectomy performed in combination with cataract surgery and IOL implantation for exfoliation (45 patients) or for primary open-angle glaucoma (263 patients).

“There was significantly greater IOP lowering in exfoliation glaucoma vs. primary open-angle glaucoma patients in both ab interno trabeculectomy alone and when combined with cataract surgery,” Ting said.

For treatment with ab interno trabeculectomy alone, exfoliation patients achieved a mean IOP decrease of –12.3 mm Hg at 12 months postop, while patients with primary open-angle glaucoma (POAG) attained a mean IOP reduction of –7.5 mm Hg. For combined ab interno trabeculectomy, the mean IOP decreases were –7.2 mm Hg and –4.1 mm Hg, respectively.

“We feel exfoliation glaucoma patients may do better because the underlying mechanism appears to be accumulation of exfoliative material at the level of the trabecular meshwork,” Ting said. “Ab interno trabeculectomy specifically creates a cleft in the trabecular meshwork and the inner wall of Schlemm’s canal, removing this mechanical blockage. In contrast to POAG, which is a heterogenous disease, the level of obstruction appears to be the trabecular meshwork but may also involve more distal obstruction in the aqueous drainage pathway.”

The number of glaucoma medications needed decreased the most among exfoliation patients, from 3.09 to 2.21 after ab interno trabeculectomy alone and from 1.8 to 1.57 after the combined procedure with cataract surgery. Patients with POAG experienced a reduction from 2.73 to 2.16 medications daily for those undergoing ab interno trabeculectomy alone, while those undergoing the combined procedure experienced a decrease from 2.4 to 1.65.

Complications, secondary surgery

The most common complication was intraoperative blood reflux from the episcleral venous system, but most cases resolved within the first few days.

“We did not see the significant complications associated with standard trabeculectomy, such as sustained hypotony, wound leaks from the bleb, infections like endophthalmitis or blebitis, choroidal effusion and hemorrhage,” Ting said.

The rate of secondary surgery, mostly standard trabeculectomy, for ab interno trabeculectomy alone was significantly higher for POAG than for exfoliation: 34.9% vs. 20.9%. But for ab interno trabeculectomy combined with cataract surgery, there was no significant difference: 6.1% for POAG vs. 6.7% for exfoliation.

Overall, in ab interno trabeculectomy alone, the cumulative probability of success (no secondary surgery, IOP less than 21 mm Hg and greater than 20% reduction from baseline) was significantly higher in patients with exfoliation glaucoma (79.1%) vs. POAG (62.9%). In contrast, in the combined procedure, there was no significant difference between the exfoliation (86.7%) and POAG (91%) groups.

For patients with mild to moderate glaucoma, particularly exfoliation glaucoma, ab interno trabeculectomy may be an initial alternative to standard trabeculectomy to lower IOP to the mid-teens. However, for patients with advanced glaucoma and significantly elevated IOP, standard trabeculectomy may still be more appropriate to obtain greater IOP lowering, Ting said.

More prospective studies are needed, and Karim F. Damji, MD, and Ting are currently involved in a randomized control trial of ab interno trabeculectomy vs. standard trabeculectomy. – by Bob Kronemyer

Reference:

Ting JLM, Damji KF, Stiles MC. Ab interno trabeculectomy: outcomes in exfoliation versus primary open-angle glaucoma. J Cataract Refract Surg. 2012;38(2):315-323.

For more information:

Jessica L.M. Ting, MD, can be reached at Department of Ophthalmology, University of Alberta, 10240 Kingsway Ave., Royal Alexandra Hospital, Edmonton, Alberta, T5H 3V9, Canada; email: jting@ualberta.ca.
Disclosure: Ting has no relevant financial disclosures.