Superior vs Inferior Glaucoma Drainage Device Implantation
Superior vs Inferior Glaucoma Drainage Device Implantation
A total of 459 eyes were identified to have undergone GDD surgery between September 11, 2006 and April 5, 2011 using billing records (CPT code 66180 aqueous humor shunt implant). Sixty-two eyes were identified as having BGI implantation at the inferior limbus. Forty-five eyes were excluded from the analysis that did not satisfy the enrollment criteria (24 eyes had <6 mo of follow-up, 21 eyes had undergone prior GDD implant surgery). Fifty eyes (17 inferior, 33 superior) of the 43 patients (mean age 68.4 and 72.8 y, respectively) were enrolled (Table 1). Indications for performing inferior GDD surgery in these patients consisted of extensive superior limbal conjunctival scarring (n=10), poor exposure (n=2), superior bleb location (n=2), superior vitreous prolapse associated with inferior intraocular lens dislocation (n=1), and desire to preserve superior conjunctiva for future surgery (n=2).
Baseline clinical characteristics are presented in Table 1. All patient characteristics were similar between the superior and inferior groups expect for the mean preoperative IOP, which showed a significant difference (P=0.02) between the inferior GDD group (21±7 mm Hg) and the superior GDD group (26±11 mm Hg). One eye (6%) in the inferior group and 2 eyes (6%) in the superior group received a 250 mm BGI and there was no statistical difference between the groups (P=1.00).
Figure 1 illustrates the Kaplan-Meier survival plot of the cumulative probability of failure defining inadequate IOP reduction as IOP>21 mm Hg or not reduced by 20% below baseline, IOP≤5 mm Hg on 2 consecutive follow-up visits after 3 months, reoperation for glaucoma, or loss of light perception vision. There was no difference in the cumulative proportions of eyes failing between the groups (P=0.20, log-rank test). Success rates were similar (P>0.05) between the inferior and superior GDD groups during the study period, with 64.7% and 75.8% classified as successful at 1-year of follow-up and 43.1% and 65.7% at 2 years of follow-up, respectively.
(Enlarge Image)
Figure 1.
Kaplan-Meier plot of the cumulative probability of the failure defining inadequate intraocular pressure (IOP) reduction as IOP > 21mm Hg or not reduced by 20% below baseline, IOP≤5mm Hg on 2 consecutive follow-up visits after 3 months, reoperation for glaucoma, or loss of light perception vision (P = 0.20, using log-rank test).
The mean postoperative IOP (mm Hg) at 6, 12, 18, and 24 months (Table 2) was similar (all P>0.05) in the inferior GDD group (16±5, 15±5, 15±6, 15±5) and the superior GDD group (14±4, 13±4, 17±6, and 16±7) at 2 years. Mean postoperative IOP was significantly higher (P=0.046) in the inferior GDD group at the 3-year follow-up time point. Mean number of postoperative medications was similar in both the groups (P=0.5), averaging 2.4±1.6 in the inferior GDD group and 2.7±1.5 in the superior GDD group. All 10 (100%) of the failures in the superior GDD group were initially because of consecutive high IOPs, whereas in the inferior GDD group the reasons were: 8 (80%) high IOP, 1 (10%) reoperation to control pressure, and 1 (10%) hypotony. These differences between the groups were not statistically significant (P=1.00, exact χ test). When the groups were compared with respect to the incident reoperations for failure to control pressure, the inferior GDD group had a significantly higher rate (P=0.040, log-rank test). At 36-month follow-up, the cumulative proportion of reoperations to control pressure were 9.9% (SE=0.09) and 33.8% (SE=0.15) in the superior and inferior groups, respectively. The single eye reoperated in the superior GDD group received a second GDD, which was placed inferiorly. Of the 5 eyes reoperated in the inferior GDD group, 3 received a superior trabeculectomy and 2 eyes received a second GDD, both of which were implanted superiorly.
The overall incidence of postoperative complications was similar (Table 3), with 8 of the 17 inferior GDD eyes (47%) and 17 of the 33 superior GDD eyes (52%) experiencing either early-onset (≤1 mo after GDD implantation) or late-onset (>1 mo after GDD implantation) complications. Early complications consisted of choroidal effusion, hyphema, suprachoroidal hemorrhage, vitreous hemorrhage, shallow or flat anterior chamber, and cystoid macular edema. Late complications included persistent corneal edema, choroidal effusion, cystoid macular edema, chronic or recurrent iritis, and tube obstruction or malposition. The frequency and types of postoperative complications in both the groups were similar (all P>0.05) except for vitreous hemorrhage (P=0.04), which occurred in 2 patients from the inferior GDD group.
There were 2 reoperations for complications in the inferior GDD group. One patient underwent drainage of a suprachoroidal hemorrhage and 1 patient with a tube malposition required revision of the drainage tube. There were 4 reoperations for complications in the superior GDD group. Two of the eyes required tube revision (1 for malposition, 1 for obstruction) and 2 eyes underwent subsequent corneal transplantation. There was no difference in time to reoperation for complications between the 2 groups (P=0.99, log-rank test).
When reoperations for both pressure control and complications were combined into 1 incidence of "return to the operating room" outcome, there were no significant differences between the groups (P=0.18, log-rank test). At 36 months, the cumulative proportions requiring any reoperation were 24.6% (SE=0.12%) and 45.5% (SE=0.16%) in the superior and inferior groups, respectively (Fig. 2).
(Enlarge Image)
Figure 2.
Kaplan-Meier plot of the cumulative probability of the reoperation for inadequate intraocular pressure control or complications. There was no significant difference between the superior and inferior glaucoma drainage device groups with respect to total reoperations (P = 0.18, log-rank test).
Results
A total of 459 eyes were identified to have undergone GDD surgery between September 11, 2006 and April 5, 2011 using billing records (CPT code 66180 aqueous humor shunt implant). Sixty-two eyes were identified as having BGI implantation at the inferior limbus. Forty-five eyes were excluded from the analysis that did not satisfy the enrollment criteria (24 eyes had <6 mo of follow-up, 21 eyes had undergone prior GDD implant surgery). Fifty eyes (17 inferior, 33 superior) of the 43 patients (mean age 68.4 and 72.8 y, respectively) were enrolled (Table 1). Indications for performing inferior GDD surgery in these patients consisted of extensive superior limbal conjunctival scarring (n=10), poor exposure (n=2), superior bleb location (n=2), superior vitreous prolapse associated with inferior intraocular lens dislocation (n=1), and desire to preserve superior conjunctiva for future surgery (n=2).
Baseline clinical characteristics are presented in Table 1. All patient characteristics were similar between the superior and inferior groups expect for the mean preoperative IOP, which showed a significant difference (P=0.02) between the inferior GDD group (21±7 mm Hg) and the superior GDD group (26±11 mm Hg). One eye (6%) in the inferior group and 2 eyes (6%) in the superior group received a 250 mm BGI and there was no statistical difference between the groups (P=1.00).
Figure 1 illustrates the Kaplan-Meier survival plot of the cumulative probability of failure defining inadequate IOP reduction as IOP>21 mm Hg or not reduced by 20% below baseline, IOP≤5 mm Hg on 2 consecutive follow-up visits after 3 months, reoperation for glaucoma, or loss of light perception vision. There was no difference in the cumulative proportions of eyes failing between the groups (P=0.20, log-rank test). Success rates were similar (P>0.05) between the inferior and superior GDD groups during the study period, with 64.7% and 75.8% classified as successful at 1-year of follow-up and 43.1% and 65.7% at 2 years of follow-up, respectively.
(Enlarge Image)
Figure 1.
Kaplan-Meier plot of the cumulative probability of the failure defining inadequate intraocular pressure (IOP) reduction as IOP > 21mm Hg or not reduced by 20% below baseline, IOP≤5mm Hg on 2 consecutive follow-up visits after 3 months, reoperation for glaucoma, or loss of light perception vision (P = 0.20, using log-rank test).
The mean postoperative IOP (mm Hg) at 6, 12, 18, and 24 months (Table 2) was similar (all P>0.05) in the inferior GDD group (16±5, 15±5, 15±6, 15±5) and the superior GDD group (14±4, 13±4, 17±6, and 16±7) at 2 years. Mean postoperative IOP was significantly higher (P=0.046) in the inferior GDD group at the 3-year follow-up time point. Mean number of postoperative medications was similar in both the groups (P=0.5), averaging 2.4±1.6 in the inferior GDD group and 2.7±1.5 in the superior GDD group. All 10 (100%) of the failures in the superior GDD group were initially because of consecutive high IOPs, whereas in the inferior GDD group the reasons were: 8 (80%) high IOP, 1 (10%) reoperation to control pressure, and 1 (10%) hypotony. These differences between the groups were not statistically significant (P=1.00, exact χ test). When the groups were compared with respect to the incident reoperations for failure to control pressure, the inferior GDD group had a significantly higher rate (P=0.040, log-rank test). At 36-month follow-up, the cumulative proportion of reoperations to control pressure were 9.9% (SE=0.09) and 33.8% (SE=0.15) in the superior and inferior groups, respectively. The single eye reoperated in the superior GDD group received a second GDD, which was placed inferiorly. Of the 5 eyes reoperated in the inferior GDD group, 3 received a superior trabeculectomy and 2 eyes received a second GDD, both of which were implanted superiorly.
The overall incidence of postoperative complications was similar (Table 3), with 8 of the 17 inferior GDD eyes (47%) and 17 of the 33 superior GDD eyes (52%) experiencing either early-onset (≤1 mo after GDD implantation) or late-onset (>1 mo after GDD implantation) complications. Early complications consisted of choroidal effusion, hyphema, suprachoroidal hemorrhage, vitreous hemorrhage, shallow or flat anterior chamber, and cystoid macular edema. Late complications included persistent corneal edema, choroidal effusion, cystoid macular edema, chronic or recurrent iritis, and tube obstruction or malposition. The frequency and types of postoperative complications in both the groups were similar (all P>0.05) except for vitreous hemorrhage (P=0.04), which occurred in 2 patients from the inferior GDD group.
There were 2 reoperations for complications in the inferior GDD group. One patient underwent drainage of a suprachoroidal hemorrhage and 1 patient with a tube malposition required revision of the drainage tube. There were 4 reoperations for complications in the superior GDD group. Two of the eyes required tube revision (1 for malposition, 1 for obstruction) and 2 eyes underwent subsequent corneal transplantation. There was no difference in time to reoperation for complications between the 2 groups (P=0.99, log-rank test).
When reoperations for both pressure control and complications were combined into 1 incidence of "return to the operating room" outcome, there were no significant differences between the groups (P=0.18, log-rank test). At 36 months, the cumulative proportions requiring any reoperation were 24.6% (SE=0.12%) and 45.5% (SE=0.16%) in the superior and inferior groups, respectively (Fig. 2).
(Enlarge Image)
Figure 2.
Kaplan-Meier plot of the cumulative probability of the reoperation for inadequate intraocular pressure control or complications. There was no significant difference between the superior and inferior glaucoma drainage device groups with respect to total reoperations (P = 0.18, log-rank test).