It is well known that eyes with a history of glaucoma drainage device (GDD) implantation have an increased risk of corneal edema secondary to endothelial cell loss. Potential causes of corneal decompensation include mechanical trauma involving the tube touching the endothelium, foreign body reaction to the tube, disruption of the blood-aqueous barrier, and changes in aqueous circulation and composition with increased inflammatory mediators. Descemet stripping endothelial keratoplasty (DSEK) has become the standard surgical approach for treating endothelial failure. Performing a DSEK in an eye with a GDD can be challenging. The tube can interfere with surgical placement of the graft and may allow intracameral air to escape, especially when the tube is in the anterior chamber (AC). Placement of the tube in the pars plana (PP) may ameliorate these intraoperative challenges, and positions the tube further away from the corneal graft.
Kang and associates retrospectively compared the outcomes of DSEK in eyes with GDD placement in the AC and PP. The study evaluated 85 eyes that underwent DSEK and had previous or concurrent GDD implantation, including 37 eyes with AC tubes and 48 eyes with PP tubes. Graft dislocation occurred in 35.1% and 29.2% in the AC and PP groups, respectively (p = 0.56). Secondary graft failure developed in 18.9% in the AC group and 41.7% in the PP group (p = 0.51). The higher rate of graft failure in the PP group was most likely attributable to the longer follow-up (median 41.9 months) relative to the AC group (median 16.4 months), and significant differences between groups were not apparent in Kaplan-Meier survival analysis. Tube location, age, sex, concurrent tube revision, and new tube insertion were not significantly associated with secondary graft failure in multivariable analysis.
Differing patient characteristics may have directed the surgeon toward insertion of the tube into the AC or PP, and this is a potential source of selection bias
This is the first study to evaluate the outcomes of DSEK in eyes with AC versus PP GDD tube placement. The presumed benefit of improving DSEK outcomes with PP positioning of the tube was not supported by data from this study. However, results should be interpreted in the context of study limitations. Differing patient characteristics may have directed the surgeon toward insertion of the tube into the AC or PP, and this is a potential source of selection bias. Postoperative endothelial cell counts, corneal thickness measurements, and type of GDD implanted would have been valuable additional data. Some of the patients in the AC group had repositioning of the tube into the ciliary sulcus, which is distinctly different from AC tube placement. The relatively small number of patients in the study reduced its power to detect significant differences, especially in identifying predictors of graft failure. Despite these limitations, the authors are to be congratulated for contributing important new information on the outcomes of DSEK in patients with a GDD.