Trabeculectomy After Failed Glaucoma Drainage Device Surgery

Trabeculectomy Outcomes After Glaucoma Drainage Device Surgery

Alizadeh R, Akil H, Tan J, Law SK, Caprioli J
J Glaucoma. 2017 Dec 12. [Epub ahead of print]

Study Summary

Trabeculectomy after failed glaucoma drainage device (GDD) is often thought of as a poor choice due to the possibility of violated conjunctiva leading to failure of the trabeculectomy. Thus, no large studies on the success rate of trabeculectomy after GDD have been performed.

This study is one of the first retrospective chart reviews evaluating the outcomes of trabeculectomy with adjunctive mitomycin-C (MMC) in patients with uncontrolled intraocular pressure (IOP) after GDD.

Twenty eyes from 19 patients were included for analysis. Mean IOP (±SD) decreased, from 19.3 ± 4.2 mm Hg prior to surgery to 9.8 ± 2.2 mm Hg at 1 year, 8.8 ± 3.2 mm Hg at 3 years, and 8.4 ± 1.5 mm Hg at 5 years (all P < .001).

The primary outcome was surgical success with stratified IOP targets based on the following criteria: (A) IOP < 18 mm Hg and IOP reduction of 20%; (B) IOP < 15 mm Hg and IOP reduction of 25%; (C) IOP < 12 mm Hg and IOP reduction of 30%. The cumulative success rate between the first to fifth year of follow-up (± SD) for criterion A was 73.2% (± 10.0%) and for criterion B was 68.2% (± 9.5%). Cumulative success for criterion C was 49.1% (± 10.8%) at the first year of follow-up and 32.7% (± 12%) between the second and fifth years of follow-up.

The complication and reoperation rates were 10%. The two patients with complications had uveitic glaucoma and developed hypotony maculopathy, which resolved after bleb revision. No cases of shallow anterior chamber, blebitis, bleb-related leak, infection, or endophthalmitis were recorded. Additional glaucoma surgery for IOP control was required in two other eyes (10%).

Viewpoint

GDDs are more frequently becoming the primary glaucoma surgery for many patients.

Studies such as the Tube Versus Trabeculectomy study^[1] have supported this approach, demonstrating that the success rate of GDD in reducing IOP is similar to that of a trabeculectomy while potentially reducing vision-threatening complications. When failure of GDD to control IOP occurs, it is often related to fibrous encapsulation of the plate, which causes increased outflow resistance and elevated IOP.^[2] Traditional teaching has been that after a failed GDD, trabeculectomy is usually not an option because the conjunctiva is considered violated, possibly increasing the risk for trabeculectomy failure. Therefore, usually either a second GDD or cyclophotocoagulation (CPC) is the first choice in circumstances of increased IOP with a GDD implant. One study^[3] demonstrating the success of these secondary procedures reported rates of 60% for a second GDD and 70% for transcleral CPC. Depending on the definition of success, these rates will vary; overall, however, the success rates in this study are comparable to those of these other procedures. Similarly, the success rate of a second trabeculectomy after a failed previous trabeculectomy is lower than the success rate of initial trabeculectomy, and lower than when a trabeculectomy is performed after a failed GDD.^[4]

The results of this study introduce another option for patients who have increased IOP following a GDD implant, and in some patients, a trabeculectomy may provide good IOP control. Care must be taken, however, to not generalize these results. This was a retrospective study, and only patients who were already determined to be good candidates for trabeculectomy were included. Despite the stringent selection, it was noted in the study that patients with uveitic glaucoma were the ones who were more likely to have complications and thus may be less optimal candidates. Thus, patient selection is key. Ophthalmologists must evaluate the conjunctival health and mobility to assess whether the patient is a potential candidate for a trabeculectomy. An assessment of all options and risks for failure of trabeculectomy may lead to even higher success rates than those reported.

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