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Editors Selection IGR 24-1

Surgical Treatment: Post-op Hypotony after Microshunt and Trabeculectomy

Comment by Anastasios E Sepetis & Nishani Amerasinghe on:

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Recent advancements in glaucoma devices target bypass of the trabecular meshwork, either by augmenting flow through Schlemm's canal or by creating alternative pathways to the subconjunctival space. These devices have shown promise in reducing intraocular pressure (IOP), but challenges persist. The static dimensions of such devices and the inability to adjust them post-implantation raise concerns about achieving an optimal balance between IOP reduction and the risk of excessive filtration.

In this study, Bøhler et al. examined the safety and efficacy of the Preserflo MicroShunt versus trabeculectomy. The focus was primarily on the incidence of hypotony in the early postoperative phase. The Preserflo MicroShunt, measures 8.5 mm with a 70 µm lumen and is designed to maintain IOP above 5 mmHg, as dictated by the Hagen-Poiseuille equation.

In this registry study, 100 patients, who were among the first to receive the MicroShunt in the hospital, were compared to 100 patients on the register who had trabeculectomy surgery.

Both procedures used fornix based conjunctival incisions and Mitomycin C 0.04% for two minutes or 0.02% for three minutes. All surgeries were performed by five experienced trabeculectomy surgeons, following similar operation protocols. Patients were given the same postoperative regimen.

Mean preoperative IOP was 20.6 ± 7.1 mmHg in the MicroShunt group and 21.6 ± 7.1 mmHg in the trabeculectomy group. Patients used a mean of 3.0 ± 0.9 and 3.1 ± 0.9 glaucoma medications in each respective group.

Both procedures effectively lowered IOP. Overall, there was a 52% IOP reduction in the MicroShunt group and a 50% reduction in the trabeculectomy group. Complete success (≥ 20% IOP reduction and no glaucoma medications) after eight weeks was achieved by 83 patients in the MicroShunt group and 78 patients in the trabeculectomy group (p = 0.79).

After eight weeks, IOP was 10.4 ± 5.4 mmHg vs 11.3 mmHg ± 4.6 mmHg in the trabeculectomy group, the difference was not statistically significant (p = 0.23).

Hypotony (defined as an IOP < 6mmHg) occurred in 63 patients in the MicroShunt cohort, with 11 of those suffering from choroidal detachment. In contrast, 21 patient had hypotony in the trabeculectomy group, with only one case leading to choroidal detachment.

While a significant number of patients with the MicroShunt experienced hypotony this was well-tolerated and did not adversely affect visual acuity. Only one patient in the MicroShunt group required a re-operation. The MicroShunt group had fewer needling procedures (4 vs 15 p = 0.08), but required more surgical revisions (12 vs 2 p = 0.10).

While a significant number of patients with the MicroShunt experienced hypotony this was well-tolerated and did not adversely affect visual acuity

High IOP (> 21 mmHg or requiring intervention) occurred in 14% of the patients in the MicroShunt group versus 34% in the trabeculectomy group during the first eight weeks (p < 0.001).

It is important to note that the follow-up period was relatively short, and these figures may evolve over a longer time frame. Also, as a registry study, the patients were not randomized, though the baseline characteristics of the group were similar. The patients in the MicroShunt group were the first to receive the procedure in the hospital and there may have been an influence of a learning curve on these results.

The presence of hypotony without associated pathology appeared to have minimal clinical impact in the early postoperative period, suggesting that immediate intervention might not be necessary. The MicroShunt effectively reduced IOP after 8 weeks, showing comparable results to trabeculectomy.

It would be interesting to see the longer-term outcomes of the MicroShunt versus trabeculectomy in this study.

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