Stand-Alone Xen Gel Microstent Implantation Compared With Kahook Dual Blade Goniotomy : Journal of Glaucoma

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New Understandings of Glaucoma: Original Studies

Stand-Alone Xen Gel Microstent Implantation Compared With Kahook Dual Blade Goniotomy

Duong, Ryan T. MD; Pittner, Andrew C. MD; Roa, Tina M. MD; Dirghangi, Arjun J. MD, MHS; Netland, Peter A. MD, PhD

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doi: 10.1097/IJG.0000000000002120
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Abstract

Minimally-invasive glaucoma surgeries (MIGS) are procedures with minimal scleral dissection that reduce intraocular pressure (IOP) and have an excellent safety profile.1 MIGS can be categorized based on the mechanism, by which they reduce IOP. Trabecular procedures enhance aqueous humor outflow through the Schlemm canal whereas transscleral procedures shunt aqueous humor from the anterior chamber into the subconjunctival space.1,2

The Kahook Dual Blade (KDB, New World Medical, Rancho Cucamonga, CA) is a goniotomy-like procedure, which utilizes a surgical knife to excise a strip of trabecular meshwork and improve outflow through the Schlemm canal.3 This procedure has been shown to be effective for mild to moderate open angle glaucoma (OAG) with IOP reduction and 40% glaucoma medication reduction when performed as a stand-alone procedure.4 When used in conjunction with phacoemulsification, KDB has been shown to reduce IOP by roughly 25% and glaucoma medication by 45%–65%.3–5 The Xen Gel Microstent (Allergan, Dublin, Ireland) is a transscleral hydrophilic gel stent tube that shunts aqueous humor into the subconjunctival space. After stand-alone Xen Gel Microstent implantation, IOP is reduced from 27%–41.8% and medications are reduced from 51%–76%.6 Xen Gel Microstent implantation is FDA approved as a stand-alone procedure or in combination with phacoemulsification cataract surgery.

Despite the growing popularity of MIGS procedures, literature comparing the safety and efficacy of different trabecular and transscleral MIGS devices remains limited. In addition, combination with cataract surgery can influence the results of MIGS procedures.2 This study aims to compare outcomes of stand-alone KDB goniotomy versus Xen Gel Microstent implantation for OAG independent of cataract surgery.

METHODS

This was a retrospective comparative case series of OAG patients treated with either stand-alone KDB goniotomy or Xen Gel Microstent implantation at the University of Virginia from January 2018 to December 2021. Institutional Review Board approval was obtained for the retrospective review of clinical records for all patients in a HIPAA-complaint database. This research adhered to the tenets of the Declaration of Helsinki and was conducted in accordance with regulations set forth by the Health Insurance Portability and Accountability Act.

Inclusion criteria were age older than 18 and follow-up of at least 24 months postoperatively. Primary open angle glaucoma and other open angle and secondary glaucomas were included as well as all subtypes of disease severity. For patients on medical therapy, no washout period was required for inclusion in the study. Patients were included regardless of previous laser or surgical treatment. Exclusion criteria included age younger than 18 years and if the glaucoma procedure was combined with cataract surgery.

Patient characteristics data were collected from the electronic medical record. Data were collected for a consecutive series of Xen Gel Microstent implantations and KDB goniotomy performed by 2 surgeons (P.A.N. and A.J.D.). The decision for surgical treatment was made by the surgeon and the patient. The indication for surgery was a failure to achieve target IOP using medical therapy and/or laser trabeculoplasty. In this retrospective study, the choice of the procedure was at the discretion of the surgeon, with no inclusion or exclusion criteria based on the clinician and patient choice of 1 procedure or the other. The preoperative number of medications and IOP were collected. The postoperative IOP, glaucoma medication, and complication data were collected at time points 1 day, 1 and 2 weeks, and 1, 3, 6, 9, 12, 18, and 24 months. Surgical success was defined as IOP<21 mm Hg, with or without glaucoma medications, and without additional glaucoma surgery. Surgical success was also calculated for a lower threshold of IOP (<18 mm Hg), with or without glaucoma medications, and without additional glaucoma surgery.

The KDB (New World Medical, Rancho Cucamonga, CA) and Xen Gel Microstent (Allergan, Dublin, Ireland) procedures were performed according to previously established protocols for each procedure.2,3,6 Xen Gel Stent procedures in this study included ab-externo and ab-interno approaches. Mitomycin C was administered as a subconjunctival injection of 0.1 mL of mitomycin C solution ranging in concentration from 0.2–0.4 mg/mL. The choice of concentration within this range was at the discretion of the surgeon.

Primary outcomes analyzed in this study included postoperative IOP, the number of glaucoma medications, and surgical success. Secondary outcomes included complications. Evaluation of IOP and glaucoma medication included both within-group comparisons of IOP and medication reduction from baseline for both procedures and between-group comparisons of outcomes at each follow-up time point. In the IOP and number of medication analyses, eyes were censored after failure (IOP<21 mm Hg, with or without glaucoma medications, and without additional glaucoma surgery). Continuous variables were compared with the t test. Discontinuous variables were compared with the Fisher exact test or the comparison of proportions test (z test). Kaplan-Meier survival analysis was used to compare success rates, with the log-rank test used for statistical comparisons. Statistical analyses were conducted in R (R Core Team, 2020), and P=0.05 was considered statistically significant.

RESULTS

A total of 75 eyes in 67 patients were included in the study comprising 57 Xen Gel Microstent and 18 KDB goniotomy procedures, with a 24-month postoperative follow-up period. Characteristics of subjects are shown in Table 1. Patients in this study were majority white with moderate to severe glaucoma, taking 2-3 glaucoma medications at baseline. There were no newly diagnosed or treatment naïve patients in this study. Overall, the mean age was ~70 years old. Xen Gel Microstent and KDB groups were similar with respect to glaucoma severity distribution (P=0.779) and other variables, but there was a significant difference in the type of glaucoma (P=0.033). Of the eyes treated with the Xen Gel Microstent, the majority were implanted ab-interno (54 eyes, 95%), whereas 3 eyes (5%) were ab-externo. The majority of patients in both groups had previous treatment with laser trabeculoplasty (P=0.522), and 2 eyes in each group had trabeculectomy before the study.

TABLE 1 - Characteristics of Subjects Treated With Xen Gel Microstent Implantation and Kahook Dual Blade (KDB) Goniotomy
Xen Gel Microstent KDB Goniotomy
N=57 (100%) N=18 (100%) P
Age, y (mean±SD) 70.3±16.4 70.7±14.7 0.925
Sex, N (%) 0.931
 Male 26 (45.6) 8 (44.4)
 Female 31 (54.4) 10 (55.6)
Race, N (%) 0.101
 White 45 (84.9) 11 (61.1)
 African-American 7 (13.2) 6 (33.3)
 Other* 5 (1.9) 1 (5.6)
Lens status, N (%) 0.525
 Phakic 19 (33.3) 4 (22.2)
 Pseudophakic 37 (64.9) 14 (77.8)
 Aphakic 1 (1.8) 0
Type of glaucoma, N (%) 0.033
 Primary open angle glaucoma 33 (57.9) 8 (44.4)
 Mixed mechanism glaucoma 9 (15.8) 0
 Other 15 (26.3) 10 (55.6)
Severity, N (%) 0.779
 Mild 6 (10.5) 3 (16.6)
 Moderate 24 (42.1) 7 (38.9)
 Severe 24 (42.1) 7 (38.9)
 Not specified 3 (5.3) 1 (5.6)
Baseline glaucoma medications, N (%) 0.196
 0-1 2 (3.5) 2 (11.1)
 2-3 31 (54.4) 6 (33.3)
 4+ 24 (42.1) 10 (55.6)
History of laser trabeculoplasty, N (%) 44 (77.2) 12 (66.7) 0.522
*Other included 1 Asian and 4 not specified in the Xen group and 1 not specified in the KDB group.
Other included pseudoexfoliation glaucoma, pigmentary glaucoma, juvenile-onset open angle glaucoma, chronic angle closure glaucoma, normal tension glaucoma, traumatic glaucoma, and uveitic glaucoma.

Mean baseline IOP was comparable between the Xen Gel Microstent and KDB goniotomy groups (23.7±8.4 and 25.9±7.9 mm Hg, respectively, P=0.32). Figure 1 shows the mean baseline and postoperative IOP. Both procedures significantly lowered IOP compared with baseline during the follow-up period. At 24 months after surgery, the mean IOP after Xen Gel Microstent was 14.7±3.2 mm Hg (32.7% reduction from baseline, P=0.018) and KDB goniotomy was 16.7±3.2 mm Hg (40.4% reduction from baseline, P=0.049). Between-group comparison showed a significantly greater reduction of IOP after Xen Gel Microstent implantation compared with KDB goniotomy from postoperative day 1 until 1 month after surgery, with no significant differences between groups from 3 months through the remainder of the follow-up period. At 24 months after surgery, there was no significant difference in mean IOP between the Xen Gel Microstent and KDB goniotomy groups (P=0.416).

F1
FIGURE 1:
Mean IOP. The IOP was significantly reduced in both groups compared with the baseline. The 1 day to 1-month time points (asterisks) were significantly lower in eyes treated with Xen Gel Microstent implantation compared with eyes treated with KDB goniotomy (P<0.05). After 1 month, there was no significant difference between groups. N values at baseline, 6 months, 12 months, and 24 months were 57, 35, 28, and 13 in the Xen Gel Microstent group and 18, 12, 6, and 3 in the KDB group. Error bars indicate SD. Time 0 was the baseline (preoperative) IOP. IOP indicates intraocular pressure; KDB, Kahook Dual Blade.

At baseline, there was no difference in the number of glaucoma medications in the Xen Gel Microstent and KDB goniotomy groups (3.3±1.1 and 3.4±1.4, respectively, P=0.721). Figure 2 shows the mean baseline and the postoperative number of medications. Both procedures reduced the number of medications compared with baseline during the postoperative period. At 24 months after surgery, the mean number of medications after Xen Gel Microstent was 1.5±1.5 (54% reduction from baseline, P=0.008) and KDB goniotomy was 1.7±0.6 (50% reduction from baseline, P=0.038). Between-group comparison showed a significantly greater reduction in glaucoma medication after Xen Gel Microstent implantation compared with KDB goniotomy from postoperative week 1 until 9 months after surgery, with no significant differences between groups from 12 months through the remainder of the follow-up period. At 24 months after surgery, there was no significant difference in the mean number of glaucoma medications after Xen Gel Microstent implantation compared with KDB goniotomy (P=0.710).

F2
FIGURE 2:
Mean number of glaucoma medications. The average number of medications was significantly lower in the Xen Gel Microstent group compared with the KDB group from week 1 to month 9 (*). After 9 months, there were no statistically significant differences between groups. N values at baseline, 6 months, 12 months, and 24 months were 57, 35, 28, and 13 in the Xen Gel Microstent group and 18, 12, 6, 3, and 3 in the KDB group. Error bars indicate SD. Time 0 was the baseline (preoperative) number of glaucoma medications. KDB indicates Kahook Dual Blade.

Analysis of mean IOP at 12 and 24 months including both eyes from the 8 patients with bilateral surgery compared with either eye or the average of both eyes from these patients showed no significant differences. In a subset of the patients treated with KDB goniotomy, pilocarpine 2% was used in the early postoperative period until postoperative week 3. Pilocarpine, when used as a postgoniotomy medication, was not considered in the total number of glaucoma medications. In the KDB goniotomy group, 11 eyes (61%) were treated with pilocarpine, whereas 7 eyes (39%) were not treated with pilocarpine. Analysis of these subgroups demonstrated no significant difference in IOP at any time point during the postoperative period through month 24 comparing eyes treated with pilocarpine and those not receiving pilocarpine.

Surgical success was defined at 2 IOP thresholds: IOP<21 mm Hg and IOP<18 mm Hg, both with or without glaucoma medication and without additional glaucoma surgery (Fig. 3). At the threshold of IOP<21 mm Hg, at both 1 and 2-year time points, success was achieved in 72% after Xen Gel Microstent and 61% after KDB goniotomy (P=0.06, log-rank). At the threshold of IOP<18 mm Hg, at both 1 and 2-year time points, success was 67% after Xen Gel Microstent implantation compared with 33% after KDB goniotomy (P=0.001, log-rank). Surgical success was not significantly associated with baseline glaucoma severity or diagnosis during the study period. Failures were due to IOP threshold criteria, in all instances of failure to meet success criteria. After failure to meet IOP success criteria, 8 (14%) eyes in the Xen Gel Microstent and 8 (44%) eyes in the KDB goniotomy groups were treated subsequently with additional glaucoma surgery (P=0.006). Except for transient hypotony (IOP<5 mm Hg) in the early postoperative period, no eyes in the study developed persistent hypotony.

F3
FIGURE 3:
Cumulative probability of success. A, Success was defined as IOP <21 mm Hg, with or without medications, and without further glaucoma surgery (P=0.06). B, Success was defined as IOP <18 mm Hg, with or without medications, and without further glaucoma surgery (P=0.001). The success of eyes after Xen Gel Microstent implantation compared with KDB goniotomy was significantly different at the lower IOP threshold criteria (<18 mm Hg), but not at the higher IOP threshold (<21 mm Hg). IOP indicates intraocular pressure; KDB, Kahook Dual Blade

Surgical success was further evaluated with criteria for the reduction of IOP and medications. There were 27 of 75 eyes (36%) with baseline IOP<21 mm Hg. With a success threshold of 10% reduction in IOP (with or without medications and no additional glaucoma surgery), there was no significant difference in survival after Xen Gel Microstent implantation and KDB goniotomy (P=0.08, log-rank). With a success threshold of 30% reduction in IOP (with or without medications and no additional glaucoma surgery), there was a significant difference in survival between the Xen Gel Microstent and KDB goniotomy groups (P=0.00001, log-rank). In addition, survival analysis using the threshold criteria in this study was identical compared with the analysis of survival using IOP thresholds, with 1 or more reduction in medication from baseline (without further glaucoma surgery). These results were consistent with results for surgical success using IOP thresholds.

Complications observed in this study were nonvision-threatening, and occurred in a low percentage of eyes (Table 2). Complications included hyphema in both groups, choroidal effusion in the Xen Gel Microstent group, and cystoid macular edema in 1 eye in the Xen Gel Microstent group. Hyphema was the most frequently reported complication, occurring in 8 eyes (14%) after Xen Gel Microstent implantation and 4 eyes (22%) after KDB goniotomy (P=0.409). One eye in the Xen Gel Microstent group required an anterior chamber washout procedure after hyphema. No surgical drainage was performed for choroidal effusions, and other complications were resolved without additional surgical intervention. The total complications observed in each group were not significantly different (P=0.550).

TABLE 2 - Postoperative Complications After Treatment With Xen Gel Microstent Implantation and Kahook Dual Blade (KDB) Goniotomy
Complication Xen Gel Microstent (N=57) KDB Goniotomy (N=18) P
Choroidal effusion,* N (%) 10 (17.5) 0 0.132
Hyphema, N (%) 8 (14.0) 4 (22.2) 0.646
Cystoid macular edema, N (%) 1 (1.8) 0 0.555
Total complications, § N (%) 19 (33.3) 4 (22.2) 0.550
*Choroidal effusion was mild and resolved without treatment in all subjects.
Hyphemas resolved without treatment in all subjects except 1 in the Xen group, who required anterior chamber washout.
More than 1 complication may have occurred in the same subject. The number of subjects with at least 1 complication was 16 (28.1%) and 4 (22.2%) after Xen implantation and KDB goniotomy, respectively (P=0.851).
§Needlings after Xen implantation were not included in complications. In the Xen gen microstent group, 21 subjects (36.8%) were treated with needling during the postoperative period. One patient in the KDB group (5.6%) was treated with Nd:YAG goniopuncture after KDB goniotomy, which was not included in the complications.

Needling revision of the Xen Gel Microstent implant was not considered a complication. The frequency of Xen Gel Microstent procedures requiring needling and revision was assessed. Needling was performed in 21 of 57 (37%) eyes in the Xen Gel Microstent group, and the average time to first needling was 4.6±5.3 months after surgery. All needlings were performed at the slit lamp in the clinic, and no complications were reported after the needling procedures. Of the 21 eyes treated with needling, 10 eyes (48%) met surgical success criteria of IOP<21 mm Hg and 9 eyes (43%) met success criteria of IOP<18 mm Hg at subsequent time points. Of the eyes treated with needling, 2 were treated more than once, both of whom subsequently met success criteria after the second needling. One eye (5.6%) after KDB goniotomy was treated with Nd:YAG goniopuncture for elevated IOP during the postoperative period, which was not considered a complication. Laser goniopuncture treatment improved the IOP during the subsequent follow-up period.

DISCUSSION

MIGS procedures have been increasingly used for primary surgical treatment for OAG.2,7 In this study, we performed a retrospective case series comparing stand-alone KDB goniotomy with stand-alone Xen Gel Microstent procedures. Both procedures effectively reduced IOP and the number of medications from baseline at the 24 months postoperative time point. Both procedures had a low percentage of non–vision-threatening complications. With a higher IOP threshold (<21 mm Hg), both procedures were able to achieve similar surgical success. However, at a lower IOP threshold (<18 mm Hg), the Xen Gel Microstent transscleral procedure had significantly higher success in reaching a lower IOP goal.

Our stand-alone Xen Gel Microstent efficacy results were similar to the 27–41% IOP reduction and 51–76% medication reduction previously reported with the stand-alone Xen Gel Microstent procedure.6 In addition, the needling revision rate for the stand-alone Xen procedure observed in this study was similar to the previously reported 30%–50% range.6 With stand-alone KDB goniotomy, we found similar efficacy results, although our results suggested greater medication reduction after stand-alone KDB goniotomy (50% reduction at 24 mo) compared with a previous study of stand-alone KDB goniotomy (36% reduction at 6 mo).4 We are unaware of prior studies comparing stand-alone KDB and Xen Gel Microstent procedures directly. A recent retrospective case series compared combination phacoemulsification with either KDB goniotomy or iStent implantation (a trabecular micro-bypass device for open angle glaucoma).8 This study demonstrated similar IOP reduction between the 2 approaches, but improved medication reduction and surgical success with less complications after KDB goniotomy with phacoemulsification compared with iStent implantation with phacoemulsification.8

Comparison of stand-alone MIGS versus combination procedures remains a challenge due to the heterogeneity of study populations, and studies include patients treated with combined glaucoma and cataract procedures, with some studies not differentiating outcomes from stand-alone and combination cases.2,6 Cataract surgery can influence the outcomes of combined cataract and glaucoma surgery. The Trabectome combined with cataract surgery was more effective compared with Trabectome alone.9 We have found similar results for Trabectome and KDB goniotomy,10 suggesting that combination with cataract surgery may influence the results of KDB goniotomy. The clinical indications for a stand-alone procedure may vary, but it is likely that the glaucoma indications predominate over indications for cataract surgery, for example, in a patient with elevated IOP and little to no cataract symptoms.

In this study, we compared the results of stand-alone KDB and stand-alone Xen Gel Microstent with moderate to severe glaucoma. Our findings of support the use of both Xen Gel Microstent and KDB goniotomy in glaucoma patients, for IOP and medication reduction as well as safety. The effects of the procedures on IOP and medications continued to change up to 9–12 months after surgery, which was more prolonged than expected, and may be further investigated in future studies. In our study, needling procedures after Xen Gel Microstent implantation were performed in approximately a third of eyes, were not included in complications, and likely influenced the results of the study. The frequency of needling after the Xen Gel Microstent may be a consideration for clinicians using this procedure.6 In this study, Nd:YAG goniopuncture was used to lower IOP after KDB goniotomy. Laser goniopuncture has been used as an adjunctive procedure after goniotomy with Trabectome.11 After KDB goniotomy, we performed the procedure as described previously,11 with the modification of a slightly higher pulse energy of 1–2 mJ. Although both Xen Gel Microstent implantation and KDB goniotomy reduced IOP to < 21 mm Hg, Xen Gel Microstent implantation had higher success in achieving a lower IOP target. This finding, if validated, may be relevant for clinicians considering these procedures with different goals for varying patients.

This study was limited by its retrospective design and possible selection bias. Procedure groups were not randomized, but baseline analysis reveals largely similar demographics and baselines between the 2 groups. Although primary open angle glaucoma was the most common diagnosis in this study, other types of secondary glaucomas with varying mechanisms for IOP elevation were included, which may have influenced the results of the study. Previous laser trabeculoplasty or conjunctival-based glaucoma procedures may have an effect on the results of the procedures in this study. We did not observe a significant difference of race in the eyes in this study, but future studies with larger numbers of patients may evaluate the influence of race on the outcomes of the procedures used in this study. The small sample size of KDB goniotomy cases in this study limited our ability to detect differences between groups, especially for complications. The higher rate of choroidal effusions after Xen Gel Microstent implantation compared with KDB goniotomy may be clinically relevant, although this difference was not statistically significant due to the low frequency of complications and the small sample size.

Surgeon selection bias may have led to a difference in the sample size between groups, and both eyes were included in the analysis from 8 patients with bilateral surgery. Both the Xen Gel Microstent and the KDB were FDA approved for use in stand-alone procedures or in combination with cataract surgery at the time of our study. We did not evaluate the influence of regulatory approvals for stand-alone procedures in this study. In addition, in our success analysis, thresholds for IOP were based on the previous studies, but are arbitrary thresholds. In our study, eyes with IOP>20 or >17 mm Hg would be classified as “failures” but may not have been clinical failures.

Despite these limitations, we concluded that both Xen Gel Microstent and KDB goniotomy result in improved postoperative IOP and reduction of glaucoma medications. Both procedures were found to have favorable safety profiles, with low complication rates in both groups. Xen Gel Microstent implantation was associated with more postoperative interventions (needling procedures) than the KDB goniotomy. In our study, there was no statistically significant difference in achieving surgical success with an IOP threshold <21 mm Hg. However, transscleral filtration with the Xen Gel Microstent was more likely to achieve a lower target IOP.

REFERENCES

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Keywords:

Xen Gel; Kahook Dual Blade; MIGS; glaucoma; goniotomy

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