Trabeculotomy by Internal Approach: Dual Blade

24 Trabeculotomy by Internal Approach: Dual Blade

Handan Akil and Brian A. Francis

Intraocular pressure (IOP) is the most important modifiable risk factor for glaucoma.1 The dysregulation of IOP is thought to be caused by the obstruction of aqueous outflow at the juxtacanalicular trabecular meshwork (TM) and distal outflow structures.^2,3 Performing a goniotomy or trabeculotomy in adults with glaucoma has not been as successful as in cases with congenital glaucoma for lowering IOP.⁴ Inferior long-term outcomes in adults might be related to incomplete removal of TM and membrane formation or scarring across the remaining TM leaflets, with subsequent elevation in IOP.⁵ More recently, a novel dual-blade ab interno trabeculectomy procedure has been reported to remove TM more completely than traditional trabeculotomy in adult patients.^6,7

The Kahook Dual Blade (KDB, New World Medical, Inc., Rancho Cucamonga, CA) is a single-use ophthalmic knife designed to make parallel incisions in the trabecular meshwork, creating a free strip of tissue. The device has a micro-engineered profile that enables it to be inserted into the eye through a small clear corneal incision. The stainless steel body is composed of a long thin shaft that facilitates access across the anterior chamber, a pointed tip used to pierce the TM under gonioscopic view, a ramp that lifts and stretches the tissue as the device is advanced, and two blades for tissue cutting (Figs. 24.1, 24.2, 24.3). The angle of the distal cutting surface and the size of the device shaft are engineered to facilitate a maximum arc of treatment through a single clear corneal incision.

In a preclinical study of human donor corneoscleral rims, the KDB device was used to perform parallel incisions in the TM, and results were compared with the results of treatment with a microvitreoretinal (MVR) blade and the Trabectome (NeoMedix, Tustin, CA).⁶ Specimens were collected and examined histologically under light microscopy. The authors also completed human eye perfusion studies to assess the IOP-lowering efficacy of each approach. Use of the MVR blade resulted in a full-thickness incision through the TM with minimal tissue removal and large residual leaflets. Use of the MVR blade was also associated with damage to the adjacent sclera. The Trabectome produced an opening in the TM with residual tissue and thermal damage to the edges of the residual TM leaflets. Histological analysis of specimens treated with the KDB ophthalmic knife revealed more complete TM tissue removal without damage to adjacent tissues. In this study, all surgeries with the dual-blade, MVR blade, and Trabectome resulted in a statistically significant reduction of IOP. The dual-blade and Trabectome had a greater percentage decrease in IOP compared with the MVR blade, although this did not reach statistical significance. The size of the arc treated did not correlate with IOP lowering for any of the three devices.

Abdullah et al⁷ discussed their initial clinical experience with a novel dual-blade device in a meeting abstract (results not yet published). They designed a multicenter study of 122 eyes that underwent (1) combined cataract and KDB (60%); (2) combined cataract, endoscopic cyclophotocoagulation (ECP), and KDB (14%); (3) combined KDB and ECP (16%); (4) KDB alone (7%); or (5) KDB plus other surgery (4%; percents sum to more than 100% because of rounding). The glaucoma type was mostly primary open-angle glaucoma (70%), with exfoliation, pigmentary dispersion, angle closure, and normal tension glaucoma comprising the rest.

The results for all eyes was a preoperative IOP of 18.9 ± 6.8 mm Hg (mean ± standard deviation), and after 3 months the IOP was reduced to 13.3 ± 4.1 mm Hg. For the 73 eyes that underwent combined cataract and dual-blade surgery, the IOP was reduced from 17.5 ± 5.3 mm Hg to 11.8 ± 2.5 mm Hg. The authors found that 83% of the eyes showed a reduction of at least one IOP lowering medication compared with preoperative values for all surgeries. The percentage of eyes with medication reduction was 69% for the combined cataract and dual-blade surgery cases. The complications noted were hyphema in 10% of patients at 1 day, and one case of additional glaucoma surgery.

Early results of dual-blade ab interno trabeculectomy are encouraging as a combined procedure with cataract extraction and/or ECP, and as a stand-alone surgery. Longer term results are awaited to demonstrate the long-term efficacy.