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Editors Selection IGR 16-3

Surgical treatment: Trabeculectomy ab interno

Comment by Julian Garcia Feijoo on:

59017 Outcomes of ab interno trabeculectomy with the trabectome after failed trabeculectomy, Bussel II; Kaplowitz K; Schuman JS et al., British Journal of Ophthalmology, 2015; 99: 258-262

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Filtering surgery is still the 'gold standard' as it is very effective, but is linked to complications. In the past years new surgical techniques aiming to minimize the ocular trauma and the impact on the quality of life have been developed. Some of these, known as MIGS, aim to increase the outflow enhancing the physiological drainage pathways.¹ Trabectome is one of these blebless procedures and its mechanism of action is the ablation of the trabecular meshwork,² so to succeed the downstream conventional drainage system should be intact. However there is controversy regarding the theoretical efficacy of these procedures after failed conventional filtering surgery.

The objective of the paper is to address the role of trabectome after failed trabeculectomy. ³ These are challenging patients for a technique like this, as it has been reported that after a functional trabeculectomy the flow is directed to the bleb, inducing/causing the atrophy of the conventional outflow system.^4,5 The authors hypothesized that, by removing the diseased meshwork and subendothelial plaques, conventional outflow might be restored, if not completely to a certain level. Moreover they think that, as the TM could be more damaged in more advanced cases, the IOP reduction could even be greater than in patients with early disease.

A prospective study analyzing a homogeneous population (glaucoma diagnosis, stage..) and considering factors that may influence the results is needed to help identify the type of patients who could benefit the most from this surgery

So the study addresses a relevant question and of interest that challenges some of our believes. They have analyzed two subgroups of patients, one underwent Trabectome alone (AIT. N: 58) and the other trabectome plus cataract (Phaco-AIT. n: 15). In the AIT group mean IOP was reduced from 23.7 ± 5.5 to 16.2 ± 3.9 mmHg (28% mean reduction, p < 0.01) and the number of medications was reduced from 2.8 ± 1.2 to 2.0 ± 1.3 (p < 0.01) at one year. In the phaco-AIT group, the mean IOP was reduced from 20.0 ± 5.9 to 15.6 ± 5.1 mmHg (19% mean reduction, p = 0.11). More interestingly, the authors provide the success rate according to different criteria, by using the criteria of IOP < 18 mmHg and 20% IOP reduction the one-year success rate is of 53% in the AIT group and 54% in the Phaco-AIT group.

They have stratified the patients according to the VF Include patients with early, moderate, advanced glaucoma stage, and when VFs could not be categorized, due to non-glaucomatous VF changes, or unreliable test performance by software assessment, exams were categorized as 'other'. But a significant proportion of patients were included in this group: 47% of the Phaco-AIT patients and 24% of the AIT alone patients.

The study has some limitations, is retrospective and the study group not only includes POAG patients, but patients with other glaucoma diagnose. As there are many factors that could have an impact on the success rate more information baseline characteristic of the population, on the follow-up of the trabeculectomy (time to failure, re-introduction of adjunctive therapy..) and a clear definition of the glaucoma stage is missed.

A prospective study analyzing a homogeneous population (glaucoma diagnosis, stage..) and considering factors that may influence the results is needed to help identify the type of patients who could benefit the most from this surgery. Some of these factors could be the survival time of the previous trabeculectomy, time of complete or qualified success, total period of time from the trabeculectomy to the trabectome surgery.

But the conclusion of the author is fair and so it seems that this technique could be a viable option for patients after a failed trabeculectomy. If these results will be confirmed, we could raise the question of if other MIGS procedures aiming to bypass the trabecular meshwork could also be beneficial. There are obvious and marked differences between trabectome and these techniques, so even though the conclusion of this study does not apply directly to them, this study might open a window that for many was closed.

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