Superior vs Inferior Glaucoma Drainage Device Implantation
Superior vs Inferior Glaucoma Drainage Device Implantation
Many surgeons prefer to place the initial GDD at the superior limbus. Advantages include greater intraoperative exposure, greater postoperative coverage of the patch graft by the upper eyelid, and relatively increased orbital volume in that area to accommodate a bleb over the plate. The superotemporal quadrant is often selected to avoid the superior oblique muscle in the superonasal quadrant, as this may lead to a higher incidence of induced persistent diplopia due to pseudo-Brown syndrome.
GDD surgery has been demonstrated to be safe and effective when performed at the inferior limbus. Placement of the initial GDD at the inferior limbus offers advantages to the eyes with significant conjunctival scarring, intraocular silicone oil, or anatomic abnormalities at the superior limbus. However, limited data exist comparing the relationship between the implant location and surgical success. To our knowledge, 1 study has examined this relationship in the eyes following the AGV surgery. Rachmiel et al reported similar success rates among the 83 eyes following superiorly and inferiorly placed AGVs (72% vs. 65%, respectively) using a similar criterion as our study but observed a significantly higher rate of postoperative complications in the inferior group. Outcomes often differ using the AGV and BGI. A recent prospective randomized controlled trial comparing the treatment outcomes with the AGV and the BGI demonstrated higher IOP following the AGV, yet fewer serious postoperative complications occurred after 1 year of follow-up. The present study was conducted to compare the midterm outcomes following initial BGI surgery performed at the inferior and superior limbus.
In the present study, we found that the mean IOP and the number of required antiglaucoma medications were similar in both the inferior and superior GDD groups during the first 2 years of postoperative follow-up. There was no difference in cumulative proportions of the eyes failing between the groups. Both groups had a mean IOP of approximately 15 mm Hg and required 2 medications, which was consistent with the previous reports. However, during the third year of follow-up, there was a significantly greater mean IOP in the inferior GDD group with respect to the superior GDD group. In addition, the reoperation rate for uncontrolled IOP was significantly greater in the inferior GDD group. The number of eyes available for the follow-up during year 3 was significantly low in both the groups, which may represent a confounding factor. A larger, prospective, randomized study size with longer follow-up would be useful to further explore this observation. The failure rates in our study were high when compared with the 5-year outcomes in the tube versus trabeculectomy study; however, both cohorts in this study included a substantial number of eyes with low baseline pressures. Twenty-four percent of eyes in the superior GDD group and 35% of eyes in the inferior GDD group had baseline IOPs<18, which was the lower limit for eligibility in the tube versus trabeculectomy study. This causes a low threshold for elevated IOP using the lowering by ≥20% criterion.
The types of adverse events and incidence of complications among both the groups were similar. The only difference in complications between the 2 groups was a greater incidence of vitreous hemorrhage (P=0.04) in the inferior group. In contrast, Rachmiel et al reported a significantly greater incidence of postoperative wound dehiscence and transient diplopia in eyes with AGV performed at the inferior limbus when compared with the superior limbus. The overall complication rate in the present study (47% to 52%) is consistent with prior reports.
Our study has potential limitations. The number of inferior GDD eyes enrolled was relatively small owing to the infrequent nature by which initial GDD surgery is performed at the inferior limbus. Differences in the baseline IOP between the treatment groups may influence the efficacy of IOP lowering. As a retrospective, nonrandomized design, it is possible that inadvertent selection bias contributed to the observed higher reoperation rate for uncontrolled IOP or complications among the inferior group. In addition, many of the eyes in this study had significant surgery previously including scleral buckle, penetrating keratoplasty, and pars plana vitrectomy that may have influenced the outcome. Although there was no significant difference (P>0.05) in previous intraocular surgery between the 2 groups, it is possible that the inferior GDD group had other mitigating factors that could have influenced the higher reoperation rate. The most common indication for performing primary inferior GDD in our study was superior conjunctival scarring (n=10). Other indications consisted of orbital phimosis (n=2), presence of a superior bleb (n=2), desire to spare the superior conjunctiva for possible future surgery (n=2), and superior vitreous prolapse (n=1). Finally, although equally distributed among the inferior and superior GDD groups, variable implant size plates were incorporated in the present analysis.
In summary, no overall differences were observed in the success rates of initial GDD implantation performed at the superior and inferior limbus in this cohort. However, inferior GDD implantation was associated with a greater incidence of reoperation for IOP control and complications. A prospective randomized trial is warranted to further explore the safety and efficacy of initial GDD surgery when performed at the inferior limbus.
Discussion
Many surgeons prefer to place the initial GDD at the superior limbus. Advantages include greater intraoperative exposure, greater postoperative coverage of the patch graft by the upper eyelid, and relatively increased orbital volume in that area to accommodate a bleb over the plate. The superotemporal quadrant is often selected to avoid the superior oblique muscle in the superonasal quadrant, as this may lead to a higher incidence of induced persistent diplopia due to pseudo-Brown syndrome.
GDD surgery has been demonstrated to be safe and effective when performed at the inferior limbus. Placement of the initial GDD at the inferior limbus offers advantages to the eyes with significant conjunctival scarring, intraocular silicone oil, or anatomic abnormalities at the superior limbus. However, limited data exist comparing the relationship between the implant location and surgical success. To our knowledge, 1 study has examined this relationship in the eyes following the AGV surgery. Rachmiel et al reported similar success rates among the 83 eyes following superiorly and inferiorly placed AGVs (72% vs. 65%, respectively) using a similar criterion as our study but observed a significantly higher rate of postoperative complications in the inferior group. Outcomes often differ using the AGV and BGI. A recent prospective randomized controlled trial comparing the treatment outcomes with the AGV and the BGI demonstrated higher IOP following the AGV, yet fewer serious postoperative complications occurred after 1 year of follow-up. The present study was conducted to compare the midterm outcomes following initial BGI surgery performed at the inferior and superior limbus.
In the present study, we found that the mean IOP and the number of required antiglaucoma medications were similar in both the inferior and superior GDD groups during the first 2 years of postoperative follow-up. There was no difference in cumulative proportions of the eyes failing between the groups. Both groups had a mean IOP of approximately 15 mm Hg and required 2 medications, which was consistent with the previous reports. However, during the third year of follow-up, there was a significantly greater mean IOP in the inferior GDD group with respect to the superior GDD group. In addition, the reoperation rate for uncontrolled IOP was significantly greater in the inferior GDD group. The number of eyes available for the follow-up during year 3 was significantly low in both the groups, which may represent a confounding factor. A larger, prospective, randomized study size with longer follow-up would be useful to further explore this observation. The failure rates in our study were high when compared with the 5-year outcomes in the tube versus trabeculectomy study; however, both cohorts in this study included a substantial number of eyes with low baseline pressures. Twenty-four percent of eyes in the superior GDD group and 35% of eyes in the inferior GDD group had baseline IOPs<18, which was the lower limit for eligibility in the tube versus trabeculectomy study. This causes a low threshold for elevated IOP using the lowering by ≥20% criterion.
The types of adverse events and incidence of complications among both the groups were similar. The only difference in complications between the 2 groups was a greater incidence of vitreous hemorrhage (P=0.04) in the inferior group. In contrast, Rachmiel et al reported a significantly greater incidence of postoperative wound dehiscence and transient diplopia in eyes with AGV performed at the inferior limbus when compared with the superior limbus. The overall complication rate in the present study (47% to 52%) is consistent with prior reports.
Our study has potential limitations. The number of inferior GDD eyes enrolled was relatively small owing to the infrequent nature by which initial GDD surgery is performed at the inferior limbus. Differences in the baseline IOP between the treatment groups may influence the efficacy of IOP lowering. As a retrospective, nonrandomized design, it is possible that inadvertent selection bias contributed to the observed higher reoperation rate for uncontrolled IOP or complications among the inferior group. In addition, many of the eyes in this study had significant surgery previously including scleral buckle, penetrating keratoplasty, and pars plana vitrectomy that may have influenced the outcome. Although there was no significant difference (P>0.05) in previous intraocular surgery between the 2 groups, it is possible that the inferior GDD group had other mitigating factors that could have influenced the higher reoperation rate. The most common indication for performing primary inferior GDD in our study was superior conjunctival scarring (n=10). Other indications consisted of orbital phimosis (n=2), presence of a superior bleb (n=2), desire to spare the superior conjunctiva for possible future surgery (n=2), and superior vitreous prolapse (n=1). Finally, although equally distributed among the inferior and superior GDD groups, variable implant size plates were incorporated in the present analysis.
In summary, no overall differences were observed in the success rates of initial GDD implantation performed at the superior and inferior limbus in this cohort. However, inferior GDD implantation was associated with a greater incidence of reoperation for IOP control and complications. A prospective randomized trial is warranted to further explore the safety and efficacy of initial GDD surgery when performed at the inferior limbus.