Two Trabeculotomy Approaches Have Similar IOP-Lowering Capabilities

Checking for glaucoma
Axial length could affect the IOP reduction achievable with the procedure.

Success rates and postoperative complications between 2 types of glaucoma surgeries are similar, according to a study published in Clinical Ophthalmology.1 The research also shows that axial length could affect the ability of either procedure to lower intraocular pressure (IOP).

Researchers reviewed outcomes of a single surgeon who used 2 different approaches to trabeculotomy — ab interno suture trabeculotomy (AbI-TLO) and ab externo metal trabeculotomy (AbE-TLO) — in patients with glaucoma older than 40 years. The AbE-TLO approach includes a pair of metal trabeculotomy probes inserted into the canal of Schlemm and rotated by approximately 120 degrees, cutting the inner wall of the trabecular meshwork, according to the surgeon. The AbI-TLO involves a high-molecular-weight viscoelastic material injected into the anterior chamber through a temporal side port and rounded tip 5-0 nylon sutures, as described in a 2014 report in Ophthalmology.2

Researchers of the current study included 49 patients who underwent AbI-TLO between February 2017 and June 2019 and 32 patients who underwent AbE-TLO between January 2015 and February 2017. The study defined surgical success as a postoperative IOP of 18 mm Hg or lower and at least a 20% reduction from the preoperative IOP, without the need for additional surgery. Prior to the procedure, the AbI-TLO group had a mean IOP 27.9±7.3 mm Hg. Patients who received AbE-TLO had a mean IOP of 25.6±8.1 mm Hg. In addition to changes in IOP, the researchers monitored each set of patients for changes in central corneal thicknesses, best-corrected visual acuity (BCVA), and axial lengths.

Following either approach to trabeculectomy, patients’ IOPs reduced significantly. Surgical success rates at 12 months postoperatively were 77.6% and 62.5% in the AbI-TLO and AbE-TLO groups, respectively. The IOPs lowered by 39.7±20.3% in the AbI-TLO group and 33.6±17.8% in the AbE-TLO group (P =.067). The postoperative glaucoma drug score at the final visit was 3.4±1.5 in the AbI-TLO group and 2.9±1.4 in the AbE-TLO group (P =.223).

Some differences were noted between groups. For instance, the AbI-TLO group experienced significant improvements in postoperative logMAR visual acuities (P =.007), whereas the AbE-TLO group saw no significant acuity changes (P =.175).

Additionally, “AbI-TLO requires a clear corneal incision, which is beneficial for future filtering surgery; however, AbE-TLO requires a conjunctival incision and scleral flap. Thus, the duration of AbI-TLO is significantly shorter than that of AbE-TLO,” the research says.

Researchers noted some complications, particularly postoperative hyphema with level formation in both groups — 22.4% in the AbI-TLO group and 18.8% in the AbE-TLO group. They also noted transient ocular hypertension higher than 30 mm Hg in 26.5% of the AbI-TLO group and 12.5% of the AbE-TLO group. The researchers believe that patients with longer preoperative axial lengths were at greater risk for surgical failure, noting that eyes with axial lengths smaller than 24.0 mm exhibited significantly better outcomes than those with axial lengths of 24.0 mm or larger.

The study’s retrospective nature, the possibility of selection bias, relatively short-term follow-up, and limited sample size are all potential limitations.

Although the research shows no significant differences in postoperative outcomes between the groups, it indicates that axial lengths longer than 24.0 mm are associated with insufficient IOP reduction for both approaches to trabeculotomy.


1. Otori Y, Matsuoka T, Kumoi M. Comparison of surgical outcomes between ab interno suture trabeculotomy and ab externo metal trabeculotomy in adult patients with glaucoma. Clin Ophthalmol. Published online July 20, 2021. doi:10.2147/OPTH.S322166

2. Grover D, Godfrey D, Smith O, et al. Gonioscopy-assisted transluminal trabeculotomy, ab interno trabeculotomy. Ophthalmol. 2014;121(4):855-861. doi:10.1016/j.ophtha.2013.11.001