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Scientific Reports volume 15, Article number: 2738 (2025 ) Cite this article Foot Valve
The purpose of this study was to evaluate the difference in the incidence of the hypertensive phase (HP) between Ahmed glaucoma valve (AGV) patients who received intracameral air injection and those who did not. A total of 78 patients who underwent AGV surgery between January 1, 2016 and June 30, 2023 were included in this retrospective study. HP was defined as intraocular pressure (IOP) greater than 21 mmHg within the first 6 postoperative months. Among baseline characteristics, except for neovascular glaucoma and baseline IOP, there were no differences between the air injection and control groups. In the air injection group, the rate of HP was 19%, which was significantly lower than 49.1% in the control group (p = 0.017). In multivariate logistic regression analysis, baseline IOP had a significant positive correlation (OR: 1.120, p = 0.026), while age and intracameral air injection had a significant negative correlation with the incidence of HP (OR: 0.938, p = 0.028, OR: 0.142, p = 0.029). Postoperative IOP at 1 year and surgical success rates were not different between the two groups. Intracameral air injection during AGV surgery can significantly reduce the risk of HP. Intracameral air injection can be a simple procedure in AGV surgery for reducing HP.
Hypertensive phase (HP), one of the clinical signs that can occur after glaucoma drainage device (GDD) surgery such as Ahmed Glaucoma Valve (AGV; New World Medical, Inc., Rancho Cucamonga, CA) and Baerveldt Glaucoma Implant (BGI; Abbott Medical Optics, Inc., Santa Ana, CA), is generally defined as IOP greater than 21mmHg within the first 3 to 6 postoperative months without tube obstruction, retraction, or malfunction1. HP has been reported in 56 ~ 82% of patients who underwent AGV surgery, with 72% of them not resolving spontaneously2. Whereas, 20 ~ 30% have been reported in BGI, which tend to be lower than AGV1,3,4.
Fibrous encapsulation around the GDD plate can lead to resistance in aqueous humor through the tube, resulting in increased postoperative IOP and the development of the HP5. In glaucomatous aqueous humor, pro-inflammatory cytokines such as transforming growth factor β2(TGF-β2), tumor necrosis factor- α (TNF-α), interleukin-6 (IL-6), and IL-8 have been found in high concentration6,7,8. Immediate aqueous outflow in non-ligated AGV may allow these cytokines-rich aqueous humor to reach surrounding tissue, facilitating bleb encapsulation around the AGV plate earlier and inducing HP more frequently compared with BGI4,9,10,11,12.
We previously reported cases where intracameral air injection could help prevent tube obstruction of AGV with a blood clot in neovascular glaucoma (NVG)13. From these cases, we suggested that air bubbles in the anterior chamber could restrict the flow of red blood cells (RBCs) and prevent clot formation near the tube opening. In this context, we hypothesize that, although temporary, intracameral air injection could decrease the cytokine levels in the anterior chamber. Additionally, an air bubble with air-fluid level may restrict the flow of not only RBCs, but also proinflammatory cytokines toward the tube in the early postoperative periods.
The objective of this study is to evaluate the difference in the incidence of HP, postoperative IOP, and surgical outcomes between AGV patients who received intracameral air injection and those who did not.
This was a retrospective comparative study from a tertiary academic medical center, Gachon University Gil Hospital, Incheon, Korea, from January 1, 2016 through June 30, 2023. The study was approved by the Institutional Review Board (IRB) of Gachon University, Incheon, Korea and adhered to the tenets of Declaration of Helsinki (IRB number: GBIRB2021132). Due to the retrospective nature of the study, the Institutional Review Board at Gachon university Gil hospital waived the need to obtain informed consent. All eyes that underwent AGV implantation during this period were included, regardless of glaucoma subtype or stage. All eyes that underwent AGV surgery were refractory to maximally tolerated medical therapy. Exclusion criteria included: failure to complete follow-up before 1 year after AGV implantation, the need for subsequent revision surgery or an ocular surgery other than glaucoma. Data, were collected retrospectively from electronic medical records (EMR) and, included basic demographics like, age, sex, diabetes; pre-existing ocular condition like lens status, prior history of ocular surgery (prior glaucoma or other surgery), axial length; subtype of glaucoma; baseline IOP. Data-related outcomes included: IOP at each follow up period (postoperative (POD) 1 week, 1,3,6 month, 1year), number of glaucoma medications at the end point (POD 1year), the incidence of hypertensive phase (HP), and surgical failure. HP was defined as IOP > 21mmHg within the first 6months and Failure was defined as IOP > 21mmHg despite glaucoma medication or the need for additional glaucoma surgery to control IOP. Eyes that had not failed but required glaucoma medication to control IOP < 21mmHg were defined as qualified success. Eyes that had not failed and did not need glaucoma medication for control IOP < 21mmHg were defined as complete success.
All surgeries were performed by a single surgeon (JYL). All subjects underwent similar steps of AGV surgery. The surgical site was prepared and draped in the usual sterile manner. After a subtenon injection of 2mL of 2% lidocaine for anesthesia, a corneal traction suture was placed at the superior cornea. A superior limbal incision was made and dissected toward the fornix, deep through subtenon space. The implant FP7 was primed with balanced salt solution (BSS) with a 27-G cannula and placed in sub-tenon posterior equator space. For fixing, the plate was secured with 10 − 0 nylon sutures 8 mm from the limbus. A scleral tunnel into the anterior chamber was created with a 23-G needle and the AGV tube was trimmed to the appropriate length and inserted into the anterior chamber through the scleral tunnel. An appropriately sized double layered pericardial patch graft was fixed to the sclera with 10 − 0 nylon sutures to cover the exposed tube. The conjunctiva and tenon were closed with 8 − 0 vicryl sutures. At the end of the procedure, if intracameral air injection was performed, filtered air was injected into the anterior chamber through the paracentesis site. The anterior chamber was filled with an 80 to 90% air fill.
All statistical analyses were performed with SPSS (IBM Corp. Released 2021. IBM SPSS Statistics for Windows, Version 29.0: IBM Corp). For evaluating baseline characteristics of subjects between air injection and control groups, descriptive statistics were used. For identifying which demographic and clinical characteristics were significantly related to HP, bivariate analysis was used. For identifying risk factors of HP, multivariate logistic regression analysis was used. We calculated the variance inflation factors to test the multicollinearity. For evaluating the interaction between IOP and time and IOP difference at each follow-up visit between the two groups, repeated measures of ANOVA and independent t-test were used. For identifying surgical success or failure between the two groups, the Chi-square test was used.
One hundred twelve patients were retrospectively screened for eligibility to analyze HP during the 1-year postoperative period. 34 cases were excluded due to subsequent revision surgeries, ocular surgeries unrelated to glaucoma, or failure to follow-up within the 1-year postoperative period. Among these, 30 cases were lost to follow-up, 3 cases underwent vitrectomy due to vitreous hemorrhage secondary to proliferative diabetic retinopathy, and 1 case required surgical revision due to tube occlusion by iris. Of the remaining 78 patients (69.6%), 21 received intracameral air injection, and 57 did not (Fig. 1). The ratio of patients who underwent intracameral air injection to those who did not was approximately 1:2.7.
Flow chart of subject screening and enrollment.
Of the 78 subjects in the study, 32 experienced HP (41.0%). Table 1 presents the baseline characteristics of total subjects (Table 1).
The air injection and control groups were compared in terms of demographic and preoperative clinical characteristics. There were no statistically significant differences in age, sex, diabetes, lens status (phakic or pseudophakic), axial length and history of prior glaucoma surgery. Among glaucoma subtypes, the proportion of NVG was significantly higher in the air injection group (81%, n = 17) compared to the control group (36.8%, n = 21) (p = 0.001). Baseline IOP was also significantly higher in the air injection group than in the control group (p = 0.004) (Table 2).
Bivariate analysis of baseline characteristics showed that age and air injection status were significantly associated with HP (age, p = 0.012, air injection, p = 0.017). Subjects in the HP group were significantly younger than those in the non-HP group (54.6 ± 11.9 vs. 61.8 ± 12.5, p = 0.012). The incidence of HP was 19% in the air injection group, significantly lower than 49.1% observed in the control group (p = 0.017). Other factors, including sex, diabetes, lens status (phakic or pseudophakic), NVG, axial length, history of prior glaucoma surgery and baseline IOP were not significantly related to HP (p = 0.423, p = 0.072, p = 0.271, p = 0.233, p = 0.169, p = 0.241) (Table 3).
Multivariate logistic regression analysis indicated that baseline IOP was significantly associated with the incidence of HP. (OR : 1.120, p = 0.026). Age and intracameral air injection had a significantly negative association with the incidence of HP. (OR : 0.938, p = 0.028, OR: 0.142, p = 0.029) (Table 4). The variance inflation factors of the regression model were less than 2 for all the covariates, indicating no multicollinearity.
Postoperative IOP after AGV surgery was significantly lower in the air injection group at 6 months postoperatively compared to control group (p = 0.026). However, the postoperative IOP at 1 week, 1 month, 3 months, and 1 year, as well as the number of glaucoma medication taken at 1 year, did not differ significantly between the air injection and control groups. (p = 0.073, p = 0.331, p = 0.242, p = 0.789, p = 0.565) (Table 5). Repeated measures of ANOVA revealed no significant time-IOP interaction between the air injection and control groups. (p = 0.064) (Fig. 2).
Mean intraocular pressure for air injection versus control group over time. There was no significant time-IOP interaction between air injection and control groups (p = 0.064, Greenhouse-Geisser). * Statistically significant difference in IOP at postoperative 6 months.
A comparison of surgical success rates at 1year postoperatively revealed no significant difference between the air injection and control groups. The overall surgical success rates, (95.3% vs. 93%), qualified success rates (81.0% vs. 77.2%), complete success rates (14.3% vs. 15.8%) and failure rates (4.8% vs. 7.0%) were comparable between the two groups. (p = 0.918)
The present study showed that intracameral air injection with AGV surgery could reduce the risk of the hypertensive phase following the procedure. To the best of our knowledge, this is the first report on the effectiveness of intracameral air injection in mitigating the risk of the hypertensive phase.
A possible explanation for this outcome is that when the anterior chamber is filled with air, the level of inflammatory cytokines in the anterior chamber may be low during the immediate postoperative period. Moreover, air bubbles around the tube with an air-fluid level could decrease the immediate flow of pro-inflammatory cytokines through the GDD tube to the sub-tenon space. In the same respect as us, a study reported that anterior chamber washout in AGV surgery could reduce the risk of HP10. In the study, anterior chamber washout could also decrease the immediate transport of pro-inflammatory cytokines through aqueous flow to the episclera. These findings suggest that the dilution of these cytokines in the anterior chamber and the reduction of immediate exposure of these factors to the tissue around the GDD plate may help mitigate the risk of HP.
In terms of HP incidence, in our study, 19% of eyes that underwent air injection experienced HP, which was a lower incidence compared to previous reports14,15,16,17. It is not appropriate to directly compare HP incidence rates across different studies with various baseline data. However, despite the air injection group in our study having higher baseline IOP and NVG proportions than the control group, a lower HP incidence was observed in the air injection group. Logistic regression analysis revealed non air injection as a risk factor for developing a hypertensive phase. Therefore, further prospective randomized controlled studies are necessary to validate the impact of intracameral air injection on HP.
Among baseline characteristics, younger age and higher baseline IOP were significant risk factors, while axial length, NVG, and prior surgical history of glaucoma were not significant risk factors in the development of HP after AGV surgery. The finding that younger age was associated with HP was consistent with previous studies11,18,19. The reason why younger patients experienced more HP may be due to a more prominent postsurgical inflammatory response, which could induce fibrous encapsulation compared to older patients20,21. Also, higher concentrations of pro-inflammatory cytokines in the aqueous humor of younger patients support this reason22,23,24. Previous studies reported axial length, NVG, and prior surgical history of glaucoma as risk factors but these were not significantly associated with HP in our study11,25,26. Higher baseline IOP also showed a significant correlation with the development of HP in many previous studies18,19,26,27. There are several explanations for that. A study reported a correlation between cytokine levels and intraocular pressure28. In addition, the early mechanical force from high IOP-induced immediate aqueous drainage leads to a thick capsule wall around the GDD9. Lastly, the IOP reduction capacity of AGV depends on the valve mechanism and small surface area, AGV may provide insufficient IOP control in patients with higher baseline IOP18,26,27.
In this study, IOP at 6 months was lower in the air injection group than in the control group, but IOP at 12 months and the success rates were not different. Many previous studies have reported variable results about the effect of HP on surgical outcomes.2,11,25,26,27,29,30,31,−32 Some short-term studies within the first postoperative year reported lower surgical success rates in the HP group, while others reported no difference.2,25,26,27,29,30,31,−32 The prevention of HP may enhance surgical outcomes in AGV surgery, which is beneficial for patients. However, most of the baseline risk factors such as age, baseline IOP, or NVG, mentioned above, associated with the development of HP are not modifiable. In this regard, intracameral air injection with GDD could be a simple and feasible procedure to reduce HP.
In long-term studies with a follow-up period of, more than 1 year, various success results have also been reported2,11,29,30,31 ,Some of these studies have indicated that the HP only reduces surgical success rates in the short-term but not in the long-term29,31. Interestingly, none of studies have reported the opposite results among the varied outcomes from previous studies. Regardless of the association between HP and long-term surgical outcomes, it has been commonly observed in previous long-term studies that postoperative IOP difference between the HP group and non-HP group decreases over time29,30,31,33. Even in studies, that have shown better long-term surgical outcomes in the non-HP group, there were no IOP differences at the final visit between the HP and non-HP group30,33. This suggests that the transient IOP rise characteristics of the HP may not be associated with better long-term IOP reduction and that controlling for HP may not ensure sustained IOP reduction because of underlying disease.
There are several limitations in this study. Firstly, the main limitations of this study were the small sample size, the bias of mixed glaucoma subtype, and different baseline data between the two groups which stem from retrospective design. NVG was included more prevalent in the air injection group than in the control group. Also, the mean baseline IOP of the air injection group was 36.3 ± 8.6mmHg which was higher than the control group. Therefore, our finding of the protective effect on HP of intracameral air injection may not be applicable to patients with relatively lower baseline IOP or without NVG. Prospective randomized controlled studies that enroll specific glaucoma subtypes are needed to clarify the issue. Secondly, intracameral air injection may be a temporary effective procedure for lowering the level of cytokines in anterior chamber during the postoperative periods after AGV surgery. So, the idea that the air in anterior chamber which dissolves within a few days could influence the development of HP which usually occurs several weeks after the surgery may be scientifically uncertain. However, as mentioned above, there has been indirect clinical evidence that the excessive aqueous outflow during the initial postoperative period and the early exposure of tissue to proinflammatory cytokines contained in the aqueous humor could influence the development of HP28,34,35. Therefore, further clinical and experimental studies are required to find more solid and scientific evidence that supports these results. Lastly, there was no statistical difference in postoperative time-IOP interaction, IOP at each postoperative visit, (except for 6 months), and surgical outcomes between the air injection and control groups. In our clinic, intracameral air injection was performed in severe NVG cases with intraocular hemorrhage, which are vulnerable to hyphema. Owing to these retrospective features of this study, an unbiased postoperative IOP comparison between two groups was impossible. However, higher baseline IOP and NVG have been reported as risk factors for surgical failure in many previous studies11,19,36,37. The outcome that postoperative IOP and surgical outcomes in the air injection group were comparable with the control group may be encouraging results despite the higher baseline IOP and a higher proportion of NVG. In addition, we did not experience any complications associated with intracameral air injection.
In conclusion, intracameral air injection can significantly reduce the risk of HP, especially in patients with high baseline IOP and NVG. Intracameral air injection can be a less invasive, simple and promising procedure in AGV surgery for reducing HP.
The data that support the findings of this study are available from the corresponding author, JYL, upon reasonable request.
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This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors
Onnuri Eye Hospital, Jeollabuk-do, South Korea
Department of Ophthalmology, College of Medicine Gil Medical Center, Gachon University, Incheon, South Korea
Hoang-at Eye Clinic, Seoul, South Korea
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JYL conceived of the presented idea, developed the hypothesis and designed the study. YSK collected clinical datas. YSK and SHK analyzed collected clinical datas. SHK wrote the main manuscript in consultation with JYLAll authors discussed the results and contributed to the final manuscript.
Correspondence to Jong Yeon Lee.
The authors declare no competing interests.
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Kim, S., Kwon, Y. & Lee, J.Y. Effect of intracameral air injection during Ahmed glaucoma valve implantation on hypertensive phase. Sci Rep 15, 2738 (2025). https://doi.org/10.1038/s41598-025-87222-1
DOI: https://doi.org/10.1038/s41598-025-87222-1
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