Needling revision beneficial after Xen implantation

Davinder S. Grover, MD, MPH<br> Ronald L. Fellman, MD

Midha and colleagues reviewed the clinical course of their initial cohort of 149 eyes that underwent Xen gel stent (Allergan) implantation and found that 51 eyes required needling by 2 years due to excessive IOP. Their current study concentrates on the fate of these 51 eyes, revealing 60.8% had a single needling, 25.5% had two needling procedures, and 13.7% had three needling procedures, with ultimately 27.5% of eyes requiring further glaucoma surgery. The exact method of application of mitomycin C (dose and method of application) are unclear from the study as well as initial application (dose and method) of MMC used during the original gel stent surgery. It is unclear if additional applications of MMC were applied for second and third revisions. It is assumed all the initial Xen procedures were performed ab interno but the success of bleb needling after ab externo technique is unknown. The needling procedures in this study were performed in the operating room, while most needling procedures in the U.S. are performed at the slit lamp.

It is important to note that the technique and expectations from typical slit lamp bleb needling after trabeculectomy are completely different than after Xen gel stent filtration surgery. A different set of skills is necessary when needling the tissues surrounding a failed gel stent compared with a failed bleb. These differences are obviously related to bleb morphology that develops after trabeculectomy vs. Xen gel stent as well as the fact that a trabeculectomy flap is a much larger needling “target” than the Xen45 gel stent. One major difference between Xen and trabeculectomy needling includes disruption of bands of fibrous tissue surrounding the gel stent compared with needling a bleb cavity after trabeculectomy. Bleb cavities may be absent after subconjunctival gel stent surgery, making the needling much more technically demanding and requiring multiple attempts. The application of MMC is also critical for failed Xen surgeries requiring needling.

Given the unique challenges associated with needling a microshunt at the slit lamp, we have designed a special spatula (the Grover-Fellman microshunt spatula, Epsilon Instruments) that has allowed for a more efficient and more effective needling technique at the slit lamp as well as in the operating room. This spatula is designed to separate fibrous bands surrounding the gel stent and allows for enhanced dissection around the Xen implant, enhanced posterior sweeping while minimizing the risk for conjunctival perforation.

Ophthalmologists should keep in mind that the methodology and expectations of bleb needling after Xen gel stent are different from the classic bleb needling after trabeculectomy. In fact, wound modification around the Xen45 implant postoperatively is a unique skill set that must be learned as the technique is distinctly different from needling a trabeculectomy bleb. This new learning curve creates a more challenging and vigilant environment in order to achieve long-lasting success with this minimally invasive filtration technique. While Xen needling is a unique skill set, one can master it with proper instruction, practice and use of appropriate wound-modulating medications.