Sclerothalamotomy ab interno shows promise for open-angle glaucoma

Sclerothalamotomy ab interno may be a safe and effective surgical procedure for lowering IOP in patients with open-angle or juvenile glaucoma, according to a study.

“Compared to trabeculectomy and perforating and non-perforating deep sclerectomy, [sclerothalamotomy] ab interno has a low rate of postoperative complications and a constant level of reduced IOP,” Bojan Pajic, MD, PhD, FEBO, one of the study authors, said in an email interview with Ocular Surgery News.

Comparatively, the procedure is simplistic, quick to perform and often does not result in hypotension, a frequent postoperative side effect of trabeculectomy and perforating and non-perforating deep sclerectomy, Dr. Pajic said.

Surgical indications include IOP that remains unregulated or too high following medicinal intervention with two or more drugs, according to Dr. Pajic.

The prospective study presented 6-year outcomes for sclerothalamotomy (STT) ab interno, following up on 2-year results that showed a 90.6% success rate and few postoperative complications.

Surgical mechanics

The STT ab interno procedure was performed in 58 eyes of 58 patients, including 53 with open-angle glaucoma and five with juvenile glaucoma, using a 19-gauge, high-frequency diathermic probe (Oertli) that applies a bipolar current of 500 kHz.

The probe penetrated approximately 1 mm into the nasal sclera, through the trabecular meshwork and Schlemm’s canal, creating four deep sclerotomies, or what the authors call “thalami,” of 0.3 mm height and 0.6 mm width in each eye.

The procedure creates an additional route for aqueous humor drainage into the scleral layer, potentially facilitating a bypass effect, according to Dr. Pajic.

“The access to the scleral space [differentiates this procedure from] other minimally invasive glaucoma surgeries and gives a higher potential to decrease the IOP during the first 6 months postop,” he said.

In addition to such bypassing mechanisms, scleral thinning at the base of the deep sclerotomy and drainage of the aqueous into the ciliary body may also reduce outflow resistance, the study authors said.

Dr. Pajic added that a four-mirror lens is needed to view the trabecular meshwork during STT ab interno, making the procedure unfit for cases in which the anterior chamber angle is too narrow.

Results

Baseline IOP was 25.6 ± 2.3 mm Hg for eyes with open-angle glaucoma and 39.6 ± 2.3 mm Hg for eyes with juvenile glaucoma. At 72 months, IOP for these groups improved to 14.7 ± 1.8 mm Hg and 13.2 ± 1.3 mm Hg, respectively.

Postoperative IOP was significantly lower than baseline IOP at all follow-up exams (P < .001), and the complete success rate, defined as an unmedicated IOP of less than 21 mm Hg at 72 months, was achieved in 79.2% of patients with open-angle glaucoma and four out of five patients with juvenile glaucoma. At the 6-year follow up, IOP-reducing agents were only necessary in 20.8% of eyes with open-angle glaucoma and one eye with juvenile glaucoma.

Following an early postoperative reduction, IOP continued to gradually decrease for 6 months and then remained stable; the study authors suggested that the continued decrease in IOP may have been caused by newly formed blood vessels and lymph vessels close to the surgical site.

While there were no serious postoperative complications, 11.4% of eyes in the open-angle glaucoma group developed a hyphema that resolved within 2 weeks, 22.6% experienced temporary postoperative ocular hypertension, 11.3% developed moderate cataract that did not affect visual acuity and 5.7% developed cataract with a coinciding decrease of one Snellen line. No complications were observed for patients with juvenile glaucoma.

It remains unknown whether the inner surface of the deep sclerotomy will eventually be covered by corneal or trabecular endothelial cells, potentially inhibiting its functioning, the study authors wrote. However, STT ab interno does avoid stimulating the episcleral and conjunctival tissues, which occurs in trabeculectomy and nonpenetrating surgery.

Dr. Pajic and colleagues are interested in investigating the possibility of further IOP reduction through the creation of six deep sclerotomies, as well as conducting a randomized, multicenter study to compare STT ab interno, trabeculectomy and deep sclerectomy. – by Michelle Pagnani

Reference:

• Pajic B, Pajic-Eggspuehler B, Haefliger I, et al. Minimally invasive, deep sclerotomy ab interno surgical procedure for glaucoma, six years of follow-up. J Glaucoma. 2011;20(2): 109-114.

• Bojan Pajic, MD, PhD, FEBO, can be reached at the Swiss Eye Research Foundation, Eye Clinic ORASIS, Titlisstrasse 44, 5734 Reinach, Switzerland; email: bpajic@datacomm.ch.
• Disclosure: Dr. Pajic has no relevant financial disclosures.

Deep sclerotomy ab interno involves creating several ablative fistulae at the junction of the trabecular meshwork along the sclera that appear to enhance uveoscleral outflow. Based on images in the study, these fistulae appear similar to cyclodialysis clefts. The procedure does not involve creating a full-thickness hole, guarded or unguarded, such as with trabeculectomy. The authors report good success rates and relatively low complication rates, and although sample attrition is not clearly displayed, the implication is that all patients completed the study.

Currently, developing filtration procedures that do not rely upon a bleb is a high priority for glaucoma specialists. The study authors report an excellent average IOP lowering and indicate that a multicenter, prospective, randomized, controlled study is planned. I was intrigued by the data presented and look forward to hearing future results.

– Douglas J. Rhee, MD
OSN Glaucoma Board Member
Disclosure: Dr. Rhee has no relevant financial disclosures.