Abstract
Purpose
This retrospective cohort compared the cumulative probability of success for glaucoma drainage device (GDD) implantation in pediatric and adult patients.
Study Design
This retrospective study enrolled adult and pediatric patients who had received a GDD between January 1, 1985 and December 31, 2017.
Methods
Kaplan-Meier method was used to estimate the cumulative probability of success in pediatric and adult patients. Successful intraocular pressure (IOP) control was defined as i) a 20% reduction from baseline and ii) IOP>6 and <18. Inadequate IOP control and failure were defined as a violation of these two criteria for two consecutive visits. Cox proportional hazards models enabled assessing for the influence of sex, GDD location, and GDD type on IOP control.
Results:
A total of 425 adult eyes from 372 individuals and 41 pediatric eyes from 28 individuals were included. The median follow-up time was 55 months for adults and 87 months for children. Superior temporal GDD placement was most employed for both (p=0.16). Adults were more likely to receive a Baerveldt 350 (p=0.04) and children were more likely to receive an Ahmed S2 (p<0.001). Adults and children had a median survival time of 2.99 and 0.82, respectively, and did not have a statistically significant difference in GDD failure rate (p=0.18). Additionally, sex, GDD location, and GDD type did not affect the success rate.
Conclusions:
Children and adults had a similar cumulative probability of success following GDD implantation. This study found that GDD type, GDD location, and glaucoma type did not influence the probability of successful IOP control.
Keywords: Glaucoma, pediatric, glaucoma drainage device, success, intraocular pressure
Introduction
Trabeculectomy was previously considered the gold standard incisional surgery in adults.1 Clinical experience in patients with refractory glaucoma illustrated a superior probability of success with glaucoma drainage device (GDD) implantation, resulting in a rise in their use.2 GDDs are a form of aqueous shunt surgery relying on a silicone tube that inserts into either the anterior or posterior chamber to drain aqueous humor into a subconjunctival space maintained by a plate. GDDs are often classified based on the presence or absence of a valve that allows control of drainage following surgery to reduce the risk of postoperative hypotony. Non-valved devices such as the Baerveldt GDD can result in early post-operative hypotony and thus tube insertion may be postponed for a second procedure, or the tube may be temporarily ligated or occluded with an absorbable suture. On the other hand, the Ahmed glaucoma valve has a flow restricting mechanism that reduces the risk of postoperative hypotony.3
Increasingly, glaucoma drainage devices are employed for pediatric glaucoma.4,5 Yet, differences in pediatric and adult globe size, scleral elasticity, and glaucoma subtype can complicate surgical selection and have important implications for post-operative outcome.6 Enhanced wound healing capacity in children compared to adults may also complicate the success of surgical interventions reliant on alternative drainage conduits including GDD implants.7 However, there are a very limited number of studies that directly compare the post-operative IOP control success following glaucoma drainage device implantation in pediatric and adult patients,6 although, certain complications have been associated with age.8 Furthermore, such studies that directly compare GDD implantation in pediatric and adult patients have not thoroughly considered covariates that could influence success rate including glaucoma subtype or GDD location. Thus, this study aimed to report the compare the probability of successful IOP control in children and adults following GDD implantation. In addition, this study sought to identify potential factors that could adversely affect GDD success rate within each group including glaucoma type, GDD type, and GDD location.
Subjects and Methods
Cohort Selection
This study was approved by the Mayo Clinic Institutional Review Board (ID# 18–002182) and adhered to the tenets of the Declaration of Helsinki. Under the purview of the Mayo Clinic Institutional Board participants included in the study had given consent to have their medical records used for research. This retrospective cohort study recruited 372 patients receiving a GDD between January 1, 1985 and December 31, 2017 to ensure appropriate time for follow-up. Of these, 466 eyes were included based on research consent and availability of appropriate number of follow-up visits to allow for assessment of IOP control. Patients receiving a GDD while under 18 years of age were defined as pediatric. Patient age, race, and follow-up time were collected. Additionally, therapeutic, and surgical characteristics including number of IOP-modifying medications prior and following GDD implantation, GDD location, and prior surgeries were considered as potential covariates impacting IOP management success.
Surgery
All pediatric surgeries and most adult surgeries were conducted by internal surgeons (98%). Operating surgeons decided on the optimal GDD type, GDD location, and tube location based on individual clinical context.8 GDD implants used were the Baerveldt Glaucoma Implant (Advanced Medical Optics, Santa Ana, CA), Ahmed glaucoma valve (AGV) (New World Medical Inc., Rancho Cucamonga, CA), and Schocket tube.
Success Criteria
Successful IOP control was defined as i) a 20% reduction from baseline and ii) IOP>6 and <18.9,10 Inadequate IOP control and failure were defined as a violation of these two criteria for two consecutive visits. Baseline IOP was defined as the average IOP from the last three exam visits.
Statistical Analysis
Categorical demographic variables are reported as frequency and percentage. Following assessment of normality using a Wilk Shapiro test, median and range are used to report continuous variables unless otherwise noted. Generalized estimating equation models were used to compare baseline characteristics between the groups, compensating for the potential correlation between eyes from the same patient.8 Fisher’s exact test was used when a generalized estimating equation could not be fit due to an insufficient number of observations. The rate of successful IOP control was estimated using the Kaplan-Meier method. Potential covariates of IOP management including sex, glaucoma type, GDD type, and GDD location were assessed using a Cox proportional hazards model. Sandwich estimators within the Cox proportional hazards model compensated for the multiple eyes included for some subjects. All statistical analyses were conducted using SAS version 9.4 (Cary, NC).
Results
Demographics
The adult cohort consisted of 372 individuals with 425 eyes (213 male, 212 female). The median age (range) of adults was 68 (18,96) years. The pediatric cohort consisted of 28 individuals with 41 eyes (17 male, 24 female). The median age (range) of children was 9 (0,16) years. There was no significant difference in race (p=0.60) or sex (p=0.76) distribution between pediatric and adult patients in this cohort; although, most eyes (89%) were from White patients (Supplementary Table 1). Median follow-up time (range) was 55 (0, 260) months for adults and 87 (8, 205) months for children (Supplementary Table 1).
Glaucoma Subtype
Glaucoma subtype differed between adults and children (Table 1). Open glaucoma was the most common subtype of glaucoma in adults, accounting for 34% of eyes. In contrast, only 2% of pediatric eyes had open-angle glaucoma (Table 1.; p=0.01). Uveitic glaucoma was the most common glaucoma subtype in pediatric patients (29% of eyes), but only accounted for 5% of adult eyes (Table 1; p<0.001). Congenital glaucoma was the second most common subtype in children afflicting 22% of eyes, much more common than in adult eyes (Table 1; p<0.001). Less frequent subtypes of glaucoma in adult eyes included pseudoexfoliative (12%), neovascular (11%), angle closure (7%), mixed mechanism (6%), secondary (5%), steroid-induced (2%), steroid-induced uveitic, and ocular hypertension (Table 1; 1%). In pediatric eyes, less frequent subtypes included secondary (12%), mixed mechanism (7%), and steroid-induced uveitic (2%).
Table 1.
Glaucoma Etiology. Adults were more likely to have open angle glaucoma and children were more likely to have uveitic or congenital glaucoma.
| Glaucoma Etiology | Adults (N=425) | Pediatric (N=41) | P-value |
|---|---|---|---|
|
| |||
| Angle Closure | 32 (7%) | 0 (0%) | 0.098# |
| Congenital | 2 (1%) | 9 (22%) | <0.001 |
| Ocular Hypertension | 2 (1%) | 0 (0%) | 1.00# |
| Open Angle | 146 (34%) | 1 (2%) | 0.01 |
| Pigmentary | 10 (2%) | 0 (0%) | 1.00# |
| Pseudoexfoliation | 52 (12%) | 0 (0%) | 0.009# |
| Steroid-induced | 8 (2%) | 1 (2%) | 0.458 |
| Uveitic | 21 (5%) | 12 (29%) | <0.001 |
| Mixed Mechanism | 26 (6%) | 3 (7%) | 0.839 |
| Steroid-induced, uveitic | 4 (1%) | 1 (2%) | 0.393 |
| Neovascular | 46 (11%) | 0 (0%) | 0.024# |
| Secondary | 20 (5%) | 5 (12%) | 0.168 |
| Other | 56 (13%) | 9 (22%) | 0.271 |
N and % refer to number of eyes.
Prior Surgeries
On average (±standard deviation), adult and pediatric eyes had 0.62±0.94 and 0.66±0.96 incisional glaucoma surgeries before GDD implantation, respectively (Supplementary Table 1; p=0.87). Children (0.78±1.01) and adults (0.74±0.92) had a similar number of prior nonglaucoma incisional surgeries (Supplementary Table 1; p=0.88). Adults had a larger number of prior laser surgeries for glaucoma (0.61±0.90 versus 0.05±0.31; Supplementary Table 1; p<0.001) and nonglaucoma indications (0.28±0.57 versus 0.05±0.22; Supplementary Table 1; p<0.001). Classifications of surgeries are listed in Supplementary Table 1.
GDD Location
Only superior temporal GDD placement was favored for both pediatrics and adults (Table 2; p=0.16) with 92% of adult and 85% of pediatric eyes having only superior temporal placement. In adults, only superior nasal, only inferior nasal, only inferior temporal, and multiple placements accounted for 2%, 2%, 1%, and 2% of eyes, respectively. In pediatric eyes, 10% of eyes had multiple GDDs placed while no eyes had only superior nasal, only inferior nasal, or only inferior temporal placement (Table 2).
Table 2.
Surgical Characteristics.
| GDD Plate Location | Adults (N=425) | Pediatric (N=41) | P-value |
|---|---|---|---|
|
| |||
| Superior Nasal | 5 (2%) | 0 (0%) | 1.0# |
| Superior Temporal | 393 (92%) | 35 (85%) | 0.16 |
| Inferior Nasal | 8 (2%) | 0 (0%) | 1.0# |
| Inferior Temporal | 6 (1%) | 0 (0%) | 1.0# |
| Multiple | 11 (2%) | 4 (10%) | 0.05 |
| Unspecified | 2 (1%) | 2 (5%) | 0.02 |
| GDD Type | Adults (N=425) | Pediatric (N=41) | P-value |
|
| |||
| Baerveldt 250 | 55 (13%) | 9 (22%) | 0.21 |
| Baerveldt 350 | 230 (54%) | 13 (32%) | 0.04 |
| Ahmed FP7 | 105 (24%) | 5 (12%) | 0.11 |
| Ahmed S2 | 24 (6%) | 10 (24%) | <0.001 |
| Ahmed B1 | 11 (2%) | 4 (10%) | 0.05 |
N refers to number of eyes; GDD= Glaucoma Drainage device
denotes Fisher’s test as generalized estimating equation could not be fit to compensate for multiple eyes when value is 0.
GDD Type
The most commonly used GDD was the Baerveldt 350 which was used in 54% of adult eyes and 32% of pediatric eyes, reflective of a larger utilization rate in adults (Table 2; p=0.04). In pediatric eyes, a higher implantation rate of Ahmed S2 valves compared to adults was observed (24% versus 6%; p<0.001; Table 2). In adults, Baerveldt 250, Ahmed FP7, and Ahmed B1 GDDs accounted for 13%, 24%, and 2%, of eyes respectively (Table 2). In children, Baerveldt 250, Ahmed FP7, and Ahmed B1 GDDs were implanted in 22%, 12%, and 10% of eyes, respectively (Table 2).
GDD Success
Out of 425 adult eyes, inadequate IOP control was documented in 198 (15-year rate of 55%; Table 3) throughout the study. From the 41 pediatric eyes, inadequate IOP control was documented in 25 (15-year rate of 61%; Table 3). Before GDD implantation, the median (IQR) number of medications for adults and children were on 3.0 (2,4) and 2.0 (1,2) medications, respectively. Following GDD surgery, the median (IQR) number of medications reduced by 0 (0,2) and 0 (−0.5, 2.0) medications, highlighting similar improvement in the number of medications needed (p=0.35). No statistically significant difference in the cumulative probability of success following GDD implantation was observed between adult and pediatric patients (Fig. 1; p=0.18, HR=1.31, 95% CI: 0.88–1.95) with a median survival time of 2.99 years and 0.82 years, respectively (Fig. 1). The cumulative probability of success for adults was 74%, 65%, 49%, and 48% at 6 months, 1 year, 5 years, and 10 years, respectively (Figure 1). In children, the cumulative probability of success was 66%, 46%, 39%, and 39% at 6 months, 1 year, 5 years, and 10 years, respectively (Figure 1). A Cox proportional hazard model was used to adjust for potential confounders including sex, glaucoma type, GDD location, and GDD type. Even with the adjustment of these covariates, no difference was observed in the risk of GDD failure (Table 4; HR: 1.1, 95% CI [0.7–1.7], p=0.79). Sex did not impact the probability of GDD failure (Table 4; HR: 0.9, 95% CI [0.7–1.2], p=0.62). Glaucoma subtype did not appear to affect success in IOP control as closed-angle glaucoma (Table 4; HR: 0.9, 95% CI [0.5–1.6], p=0.62), pseudoexfoliative glaucoma (Table 4; HR: 0.7, 95% CI [0.4–1.2], p=0.16), neovascular glaucoma (Table 4; HR: 1.1, 95% CI [0.6–1.9], p=0.77), and other glaucoma (Table 4; HR: 1.2, 95% CI [0.8–1.7], p=0.37) and had a similar risk of GDD failure compared to open angle glaucoma. Implantation in the superior temporal position did not impact the probability of failure (Table 4; HR: 0.8, 95% CI [0.4–1.4], p=0.37). Compared to the Baerveldt 350, the use of the Baerveldt 250 (Table 4; HR: 1.2, 95% CI [0.8–1.7], p=0.48), Ahmed FP7 (Table 4; HR: 1.1, 95% CI [0.7–1.5], p=0.69), Ahmed S2 (Table 4; HR: 1.2, 95% CI [0.7–1.9], p=0.44), and Ahmed B1 (Table 4; HR: 1.0, 95% CI [0.4–2.6], p=0.96) did not influence failure probability.
Table 3.
Surgical Outcomes.
| Adults (N=425) | Pediatric (N=41) | P-value | |
|---|---|---|---|
|
| |||
| Outcome | |||
| Documented Failure | 198 | 25 | |
| No Documented Failure | 227 | 16 | |
| Medication Use | |||
| Median Number of Medications Before GDD (IQR) | 3.0 (2,4) | 2.0 (0,3) | |
| Median Number of Medications After GDD (IQR) | 2.0 (1,3) | 2.0 (1,2) | |
| Median Change in Medication Use (IQR) | 0 (0,2) | 0 (−0.5,2.0) | 0.35 |
Raw number of documented failures are reported. N refers to number of eyes; GDD=Glaucoma Drainage device; IQR=interquartile range
Fig 1.
Kaplan-Meier curve comparing the cumulative probability of successful intraocular pressure control following glaucoma drainage device implantation. No statistically significant difference was observed in the cumulative probability of success in pediatric or adult patients receiving a glaucoma drainage device. Median survival time was 2.99 years and 0.82 years for adults and children, respectively. p=0.81
Table 4.
Cox proportional hazards model assessing hazard for failure
| Parameter | P-value | Hazards Ratio (95% Confidence Interval) |
|---|---|---|
|
| ||
| Age | ||
| Adult | REF | 1 |
| Pediatric | 0.79 | 1.066 (0.673–1.690) |
| Sex | ||
| Female | REF | 1 |
| Male | 0.62 | 0.931 (0.704–1.232) |
| Glaucoma Type | ||
| Open Angle Glaucoma | REF | 1 |
| Other Glaucoma Types | 0.37 | 1.178 (0.826–1.681) |
| Closed Angle Glaucoma | 0.62 | 0.859 (0.470–1.569) |
| Pseudoexfoliative Glaucoma | 0.16 | 0.662 (0.373–1.176) |
| Neovascular Glaucoma | 0.77 | 1.087 (0.624–1.893) |
| GDD Location | ||
| All other locations | REF | 1 |
| Superior temporal location | 0.37 | 0.766 (0.427–1.374) |
| GDD Type | ||
| Baerveldt 350 | REF | 1 |
| Baerveldt 250 | 0.48 | 1.149 (0.785–1.682) |
| Ahmed FP7 | 0.69 | 1.076 (0.749–1.546) |
| Ahmed S2 | 0.44 | 1.209 (0.750–1.948) |
| Ahmed B1 | 0.95 | 1.031 (0.415–2.563) |
GDD= Glaucoma Drainage device
p<0.001
Discussion
Our study found no statistically significant difference in the cumulative probability of successful IOP control with GDD implantation in pediatric and adult patients. These findings are in line with a previous study conducted by Mandalos and Sung (2017) where no difference was observed in the cumulative probability of success in adult and pediatric patients. In this cohort, the cumulative probability of success was 74%, 65%, 49%, and 48% at 6 months, 1 year, 5 years, and 10 years, respectively. These values fall within the range of previously observed cumulative success probabilities. Previous studies have shown the cumulative probability of success for GDD implantation ranging from 59–97%, 59–79%, 24–76%, 73% at 1 year, 5 years, 7 years, and 10 years, respectively varying with underlying glaucoma subtype and GDD type.9–12 In this cohort, the cumulative probability of success for pediatric patients was 66%, 46%, 39%, and 39% at 6 months, 1 year, 5 years, and 10 years, respectively. Previous reports suggest the probability of success for GDD in pediatric glaucoma ranges from 78–93% at 6 months, 61–94% at 1 year, 49–94% at 2 years, and 32–65% at 5 years.13–21 The probability of success in this pediatric cohort appears lower than in other studies. The somewhat lower success in our study may be due to differences in the retention of more refractory or complex cases in a tertiary referral center.
Additionally, we considered other potential covariates that could influence success probability including sex, GDD type, GDD location, and glaucoma subtype. In this study, GDD location did not influence the probability of success in adults or children. The influence of valved versus nonvalved GDDs on the probability of success is still unclear. The Ahmed Baerveldt Comparison (ABC) was a randomized control trial that compared the probability of success in patients with the Ahmed and Baerveldt glaucoma implants. The overall probability of success was similar between both devices.22 However, the Ahmed Versus Baerveldt (AVB) study found a higher failure rate with Ahmed implantation.23 This difference likely lies in differing primary success criteria used by each study. In the ABC study, success was defined as maintenance of IOP between 6–21 mmHg; however, in the AVB study, success was defined as maintenance of IOP between 6–18 mmHg. When considering success as maintenance of IOP between 6–21 mm Hg, no difference in probability of success was observed with GDD type in the AVB study.24 Our retrospective study used 18 mmHg as the upper limit for success. However, even with this more stringent upper limit, no difference in failure risk was observed between the Ahmed or Baerveldt valves. Interestingly, Schocket tube, a nonvalved device, implantation was associated with a higher risk of failure compared to Baerveldt 350 implantation. Of note, this implantation was infrequently employed and may have been utilized in clinical contexts with an inherently high failure risk.
On the other hand, the results observed with GDD location are concordant with previous studies. In this cohort, GDD location did not appear to influence the cumulative probability of success, yet superior temporal placement was preferred for both pediatric and adult patients. Superior temporal placement may be preferred for surgical reasons including enhanced coverage by the upper eyelid and increased space to fit the blebbing over the plate.25 While available studies have shown that superior temporal placement does not affect the early probability of success, it may reduce the risk of complications and need for later revisions.11,26,27
This retrospective cohort study aimed to compare the cumulative probability of success with GDD implantation in pediatric and adult patients. Similar to a previous study, no difference was observed in the cumulative probability of success. However, differences in postoperative complications were previously observed and must be diligently considered.6,8 This study also aimed to identify other factors that could influence observed outcomes.
This study had several limitations including having a limited number of pediatric eyes which could influence the power of the study. Minimum detectable hazard ratio analysis revealed that that study was able to detect a hazard ratio of 1.77 with a power of 80% and alpha of 0.05. Additionally, the adult cohort was relatively heterogeneous with patients exhibiting multiple glaucoma subtypes, which was adjusted for in the Cox proportional hazards model. While sex, glaucoma subtype, GDD type, and GDD location appeared to have no impact on the cumulative probability of success, larger controlled trials are needed to tease out factors that could influence or negate differences in the cumulative probability of success. While no statistically significant difference in the cumulative probability of failure was observed between children and adults, additional studies are needed to enrich the limited available literature. Assessing the influence of covariates including GDD type, GDD location, and glaucoma subtype will require larger controlled trials.
Supplementary Material
Acknowledgments:
The authors would like to thank the Mayo Clinic Foundation for research support. A.G. and K.K. were supported by the National Institute of General Medical Sciences (T32 GM 145408).
Footnotes
Conflict of Interest:
The authors have no conflicts of interest to disclose.
Data Availability:
Deidentified data are available from the corresponding authors at reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
Deidentified data are available from the corresponding authors at reasonable request.