Trabeculectomy combined with MMC and AMT not better than with MMC alone: Study
Trabeculectomy is the gold standard procedure in glaucoma surgery worldwide. It creates a drainage pathway between the anterior chamber and the subconjunctival space leading to a subconjunctival reservoir for the aqueous humor, referred to as the filtering bleb.
MSS Trab includes modifications such as a fornix-based conjunctival dissection, the use of an anterior chamber stabilizer, the use of adjustable/removable sutures and a wider surface area for antifibrotics application. Thereby, current procedures aim to achieve larger and more diffuse filtering blebs, less prone to long-term failure, leakage and infectious complications. Nevertheless, the wound healing process that occurs after surgery still leads to an excessive fibrosis at the subconjunctival space. This represents the ultimate reason for bleb failure and uncontrolled IOP after surgery.
Therefore, glaucoma surgeons use antifibrotic agents such as Mitomycin C (MMC) and 5-Fluorouracil (5-FU) in a great proportion of the eyes undergoing trabeculectomy, according to the individuals' risk of bleb failure. None of these antifibrotic agents has, however, completely superseded conjunctival scarring. On the other hand, these agents are associated with several short- and long-term complications, such as bleb avascularity, thinning of the conjunctiva, hypotony, and increased risk of endophthalmitis, hence the need for more specific modulators of the wound-healing pathway.
Newer adjunctive agents have been investigated in order to increase bleb survival. These include antivascular endothelial growth factor (VEGF) agents, space occupying components such as the Ologen® implant, and also amniotic membrane transplantation (AMT). Although none of these has clearly supplanted MMC-augmented trabeculectomy, amniotic membrane has been increasingly investigated in glaucoma surgery.
Human amniotic membrane is widely known for its anti-inflammatory, antifibrotic and antiangiogenic properties, distinctly acting at different levels of the wound healing process. It has shown promising results as a physiological bleb modulator in glaucoma filtering surgeries.
There are some data suggesting a favorable effect of the combination of AMT with MMC-augmented trabeculectomy but it is still unclear if this should be a routine procedure. This study by Roque et al evaluated the results of glaucoma patients submitted to trabeculectomy with MMC compared to patients submitted to trabeculectomy with simultaneous use of MMC and amniotic membrane.
This retrospective study analyzed the results of the first 12 postoperative months of glaucomatous eyes submitted to Moorfields Safer Surgery Trabeculectomy with MMC alone (non-AMT group) compared to MMC and AMT (AMT group). Both groups were compared in terms of intraocular pressure (IOP), number of antihypertensive medications and need for surgical reinterventions. Absolute and relative success rates 12 months after surgery were defined as IOP < 18 mmHg, without and with the use of antihypertensive medications, respectively.
The analysis included 51 eyes of 45 glaucoma patients (29 eyes in the non-AMT group and 22 in the AMT group). Mean IOP decreased from 24.72±5.11 mmHg and 26.86 ±10.62 mmHg preoperatively in non-AMT and AMT groups to 12.86±4.22 mmHg and 12.60 ±4.43 mmHg, respectively, at 12 months (p = 0.84).
Postoperative number of medications decreased significantly in both groups. Absolute success was seen in 71% of non-AMT eyes and 55% of AMT eyes (p = 0.46), whereas relative success was obtained in 14% and 30%, respectively (p = 0.55). Reinterventions were needed in 28% of the eyes (11 bleb injection/ needling and 4 Ahmed tube implantation) in the non-AMT group and in 27% of the AMT group (10 bleb injection/needling and 1 Ahmed tube implantation) (p = 0.89).
The healing process at the filtration bleb is the main reason for trabeculectomy failure, thus wound healing modulation has been thoroughly investigated as the key element to improve trabeculectomy outcomes.
The results did not prove a favorable effect of simultaneous use of MMC and AMT. Authors did not find significantly different postoperative IOP values, and surprisingly there was a higher need for antihypertensive medications in the AMT group. The need for surgical reinterventions reflected the existence of nonfunctioning blebs, whether they were flat or cystic. In the twelve month period, the percentage of eyes that required surgical reinterventions was similar in both groups, as well as the timing of those procedures.
Despite the known antifibrotic properties of amniotic membrane, in this study its addition to MMC-augmented trabeculectomy did not improve surgical outcomes in terms of IOP and need for medications or surgical reinterventions. Further investigations with prospective clinical trials are needed to better understand the role of amniotic membrane in glaucoma surgery. On the other hand, the search for new alternatives to antimitotic drugs is still imperative.
Source: Roque et al; Clinical Ophthalmology 2021:15 4527–4533
