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Editors Selection IGR 16-4
Surgical Treatment: XEN Implant II: Ab Interno or Ab Externo?
Comment by Kaweh Mansouri & Julien Torbey on:
104658 Clinical Outcomes of Ab Interno Placement versus Ab Externo Placement of XEN45 Gel Stents, Ruda RC; Yuan L; Lai GM et al., Ophthalmology. Glaucoma, 2023; 6: 4-10
This retrospective study compares the approved ab-interno surgical XEN45 Gel Stent technique to the off-label ab-externo approach, which is gaining popularity.1‐3 The rationale is that the ab-externo approach provides more precise positioning in the subconjunctival space, prevents the stent from getting entangled in the Tenon's capsule and does not require access to the anterior chamber (AC) with the use of ocular visco-elastic devices. On the other hand, the insertion into the AC gets more unpredictable with a higher risk of improper placement and adverse events such as hyphema and irido-dialysis.4
The study demonstrated that both techniques deliver a significant drop in IOP and treatment for up to two years, in line with previous studies.5 The authors stated that no significant difference in success rate was noted at any time. However, the criteria for success were not mentioned in the paper.
The study design censored the analysis's follow-up data for surgical failure cases (34.8%), which can skew the outcome positively. Such a number, albeit elevated, can be explained by the glaucoma severity of the included patients.
The discussion mentions similar revision rates while the data demonstrate fewer needling in the ab-externo group (16.7% vs 34.5%, P = 0.11). Despite not being significant, which can be attributed to the limited number of subjects, this is an interesting finding worth investigating further.
As the authors state clearly in the limitations, the analysis is underpowered to detect the superiority of any technique. Also, they divided each group with standard and pneumo-dissection of the conjunctiva subgroup, adding more confounding factors and an additional layer of complexity to interpreting the results.
This study strengthens previous observations that ab-externo implantation is non-inferior to the conventional ab-interno technique
Nevertheless, this study strengthens previous observations that ab-externo implantation is non-inferior to the conventional ab-interno technique, which provides added flexibility and confidence to the glaucoma surgeon while implanting XEN45 Gel Stent.
References
- Vera V, Gagne S, Myers JS, Ahmed IIK. Surgical approaches for implanting xen gel stent without conjunctival dissection. Clin Ophthalmol. 2020;14:2361-2371. doi:10.2147/OPTH.S265695
- Tan NE, Tracer N, Terraciano A, Parikh HA, Panarelli JF, Radcliffe NM. Comparison of safety and efficacy between ab interno and Ab externo approaches to xen gel stent placement. Clin Ophthalmol. 2021;15:299-305. doi:10.2147/OPTH.S292007
- Gallardo MJ, Vincent LR, Porter M. Comparison of Clinical Outcomes Following Gel Stent Implantation via Ab-Externo and Ab-Interno Approaches in Patients with Refractory Glaucoma. Clin Ophthalmol. 2022;16:2187-2197. doi:10.2147/OPTH. S354038
- Ruparelia S, Shoham-Hazon N. Iris-Occlusion of XEN Gel Stent following Ab Externo Transconjunctival Implantation Technique. Case Rep Ophthalmol Med. 2021;2021:1-3. doi:10.1155/2021/2936047
- Panarelli JF, Vera V, Sheybani A, et al. Intraocular Pressure and Medication Changes Associated with Xen Gel Stent: A Systematic Review of the Literature. Clin Ophthalmol. 2023;17:25-46. doi:10.2147/OPTH.S390955
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