Оценка и лечение гипотонии с повреждением эндотелиального слоя после хирургии глаукомы с применением дренажных имплантатов

    Introduction

    Glaucoma is a leading cause of irreversible blindness worldwide, with the primary treatment strategy being the reduction of intraocular pressure (IOP). In cases where IOP cannot be medically controlled, glaucoma filtration surgeries are performed [1]. Today, trabeculectomy and glaucoma drainage devices (GDD) are the main surgical treatment methods [2]. GDDs are typically preferred as a second-line treatment after a failed trabeculectomy or as a primary procedure in clinical situations considered high-risk for trabeculectomy failure, such as previous vitreoretinal surgery, penetrating keratoplasty, uveitic glaucoma, or neovascular glaucoma (NVG) [3]. In our cases, the selection of the Ahmed Glaucoma Valve (AGV) as the primary treatment option was guided by the specific types of glaucoma, the ages of the patients, and their extensive histories of medical treatment.

    Although the Ahmed Glaucoma Valve (AGV) is a valved device, ocular hypotony (temporary or permanent) can occur in the early postoperative period. Hypotony may be due to over-priming of the tube and valve insufficiency, leakage of aqueous humor around the silicone tube, or decreased aqueous production due to ciliary body dysfunction. In hypotonic eyes, hypotonic maculopathy, choroidal detachment, and a shallow or flat anterior chamber (AC) can develop. Therefore, to prevent early ocular hypotony, partial ligation of the silicone tube with a vicryl suture may be applied intraoperatively [4]. Despite these precautions, hypotony remains a frequent complication and often necessitates further interventions, particularly in cases of inflamed glaucomas. Corneal endothelial cell loss and subsequent corneal edema and decompensation are well-known complications of tube shunt surgery. The rate of corneal complications following tube shunt surgeries has been reported at high rates of 16 to 27% in previous reports [5–7]. Factors such as postoperative hypotony, a shallow anterior chamber (AC), tube-cornea contact, and chronic inflammation contribute significantly to the loss of corneal endothelial cells after these procedures [6, 8, 9]. The risk of endothelial loss increases notably when the tube is implanted into the AC [7, 10, 11]. In these cases, removal of the tube and repositioning it through a new route is usually the preferred treatment method, but the management of hypotony and endothelial loss, especially in complicated cases, can be challenging [12, 13].

    Our analysis delves into these complications associated with the Ahmed Glaucoma Valve (AGV), including hypotony and endothelial decompensation. We provide a comprehensive review of the existing literature and discuss two complex clinical scenarios, aiming to improve the understanding and management strategies for these serious complications in glaucoma treatment.

    Case Presentations

    Case 1: A 61-year-old woman with a long-standing history of diabetes mellitus presented with significant pain and visual impairment in her right eye. An extensive evaluation revealed her right eye’s visual acuity was notably reduced to 0.2, with an alarmingly high IOP of 60 mm Hg. The presence of neovascularization on both the iris and the angle indicated advanced NVG. Despite the severe presentation, her retinal nerve fiber layer (RNFL) maintained a thickness of 104 µm, showing no signs of deterioration. She was diagnosed with NVG and commenced on an intensive treatment regimen that included topical brinzolamide/timolol three times daily, topical brimonidine three times daily, and oral acetazolamide four times daily, complemented by panretinal photocoagulation to treat retinal ischemia. Subsequently, an AGV was implanted to enhance control over her condition, taking into account her high visual potential and stable RNFL.

    As the patient was phakic, the tube was inserted into the AC without ligation.

    However, her postoperative trajectory was fraught with complications. She returned on the tenth day with a significant decline in vision. Examination revealed a shallow anterior chamber, direct contact between the tube and the iris, and an edematous lens complicated by posterior synechiae.

    A Seidel test confirmed a leaking surgical wound, her IOP had dropped to 4 mmHg, and an ultrasound showed choroidal detachment (Figure 1).

    These developments required immediate attention to prevent further deterioration of her condition. Ophthalmic viscosurgical device (OVD) was introduced into the AC, and the conjunctiva was sutured to repair the wound site.

    Subsequent follow-ups indicated that the eye remained normotensive with signs of regressing choroidal detachment.

    However, swelling of the lens was observed, which pushed the tube forward, resulting in contact between the tube and the corneal endothelium. Pentacam corneal topography (Oculus, Germany) revealed a shallow anterior chamber and the development of diffuse corneal edema, underscoring the complexity of managing this patient’s postoperative recovery (Figure 2).

    The severity of these findings prompted additional surgical measures to address the complications. Phacoemulsification with intraocular lens implantation was performed, along with synechiotomy, to relieve mechanical pressure on the tube and restore the eye’s anatomical configuration. Follow-up examinations indicated that the direct contact between the tube and the endothelium in the primary position had been successfully resolved. However, localized non-healing edema persisted in the superior portion of the cornea. Suspecting that contact between the tube and the endothelium during blinking or other manipulations might be contributing to the problem, a decision was made to reposition the tube behind the iris into the ciliary sulcus (CS), as illustrated in Figure 3. This strategic adjustment aimed to enhance patient outcomes and stabilize the postoperative situation.

    Case 2: A 59-year-old male, currently undergoing oncology treatment for colon cancer, presented with a long-standing history of pseudoexfoliative glaucoma (PXG) and pigment dispersion syndrome (PDS). He had been adhering to a comprehensive anti-glaucoma regimen for 18 years, which included topical dorzolamide/timolol, brimonidine, and oral acetazolamide. During the ophthalmologic examination, the visual acuity in his left eye was recorded at 0.1, with an IOP of 36 mm Hg and a RNFL thickness of 35 µm. In contrast, his right eye showed a visual acuity of 1.0 with IOP well-controlled by the current treatment. Given his relatively young age, extensive history of medication use, and severe conjunctival inflammation, it was decided to implant an AGV in his left eye to achieve better IOP management. Being phakic, the AGV tube was positioned in the AC without ligation.

    Two days after the implantation of the AGV, the patient developed significant hypotony and choroidal detachment, which continued beyond the initial postoperative period. In an effort to address these complications, an OVD was administered into the AC on the fifth day post-surgery. This procedure successfully stabilized the choroidal detachment and restored the IOP to normal levels. During this intervention, a thorough inspection of the surgical site was also conducted to check for any potential leaks. The Seidel test was negative, confirming the integrity of the wound and indicating that there were no leaks.

    At the two-week follow-up, the patient was found to have developed extensive corneal edema due to contact between the tube and the endothelium. Fortunately, the earlier issue of hypotony had resolved by this time, which led to considerations for a surgical revision of the tube to prevent further complications. However, the patient’s complex systemic health issues contraindicated the use of general anesthesia, and his limited capacity to attend frequent follow-up visits necessitated a less invasive approach. Consequently, a simpler procedure was chosen involving the repositioning of the tube away from the endothelium using a polypropylene suture [14]. After obtaining informed consent, the procedure was performed under topical anesthesia for minimal discomfort. A 10/0 polypropylene suture equipped with double-armed 3-inch long straight needles was used to transcamerally secure the tube from limbus to limbus. This technique effectively depressed the tube into an optimal position, ensuring it did not contact any intraocular structures. The ends of the suture were then securely tied, with the knot buried under the conjunctiva in the limbal region to minimize any potential irritation or infection. This strategic adjustment aimed to stabilize the tube’s position while accommodating the patient’s health constraints and reducing the need for more invasive interventions (Figure 4).

    Three months following the suture-assisted revision of the tube, the sutures unfortunately loosened, resulting in the tube once again contacting the endothelium. Three months after the suture-assisted tube revision, the sutures loosened, and the tube contacted the endothelium, necessitating a procedure similar to the previous case to relocate the tube into the CS (Figure 5). Despite managing the hypotony and tube-endothelial contact, the patient developed established endothelial decompensation and was referred to the cornea unit.

    Discussion

    Glaucoma affects approximately 3.5% of the global population aged between 40 and 80, necessitating a variety of medical and surgical interventions aimed at slowing the disease’s progression. However, these treatments can inadvertently impact the corneal endothelium, a critical layer whose full response to such interventions remains inadequately explored [15]. The corneal endothelium itself is composed of a single layer of hexagonal cells essential for maintaining clear vision by regulating corneal hydration through active ion transport. Disruptions in this delicate balance can result in corneal swelling and a subsequent loss of visual clarity. Despite the prevalence of glaucoma and its treatments, the precise mechanisms by which it induces changes in corneal endothelial cells remain elusive, highlighting a significant gap in our current understanding [16]. Gagnon et al. have described three potential mechanisms for this: direct compression from higher IOP, congenital alterations in the endothelium and trabecular meshwork, and toxicity from glaucoma medications [17].

    Glaucoma drainage devices (GDDs) are increasingly favored for managing complex and refractory glaucoma, often being the first choice for surgical intervention among many clinicians [18]. According to the findings of the Tube Versus Trabeculectomy Study, GDDs generally show higher success rates than trabeculectomy with mitomycin C over a five-year follow-up, achieving similar reductions in IOP while reducing the reliance on additional glaucoma medications [7]. The use of GDDs is particularly growing among high-risk patients where alternative treatments like trabeculectomy are likely to fail [19]. Despite their benefits, the placement of GDDs into the AC angle can lead to significant complications, including corneal endothelial decompensation, with incidence rates reported between 7 and 27% [7, 18]. To mitigate these risks, inserting the tube through the CS has emer ged as a viable alternative, especially in pseudophakic/aphakic patients or those with peripheral anterior synechiae (PAS). This approach aims to preserve corneal health while effectively managing the glaucoma [20].

    Corneal decompensation is a well-documented complication of common glaucoma procedures, yet the specific causes and risk factors are not fully understood. It is increasingly evident that the pathophysiology extends beyond mere mechanical injury and involves ongoing processes. Research into corneal edema post-glaucoma interventions has identified multiple mechanisms for endothelial cell damage. These include mechanical trauma from the surgery itself, alterations in the composition of aqueous humor, and shifts in the dynamics of aqueous humor flow [21]. A notable two-year study demonstrated a significant and progressive decline in endothelial cell density (ECD) following AGV implantation, with an average loss of 18.6%. The most substantial decrease occurred in the superotemporal quadrant, directly impacted by the tube placement, showing a loss of 22.6%. Such declines are clinically significant, with corneal decompensation often being the most common complication arising from this procedure [6]. Comparatively, while other intraocular surgeries like cataract and vitreoretinal surgeries also cause endothelial cell loss, such losses are generally one-time events. In contrast, ECD loss from GDD implantations tends to be progressive [15, 22]. Additionally, studies indicate that the position of the tube relative to the cornea, which may shift over time, correlates with the degree of endothelial cell loss. For instance, a study tracking 70 eyes with Baerveldt tubes freely placed in the anterior chamber showed a significant decrease in the distance between the tube and the cornea over 24 months, suggesting that tube migration is a critical factor affecting endothelial health [23].

    Given the inflammatory nature of the glaucoma in our cases and the long-term medical treatment these patients had undergone, the likelihood of successful trabeculectomy was anticipated to be low; thus, AGV implantation was the preferred initial strategy. A significant limitation in our preoperative preparation was the absence of endothelial cell count and morphological analysis. Had specular microscopy been feasible before surgery, we might have considered alternative surgical approaches given the elevated risk of endothelial loss. Unfortunately, the high preoperative IOP in these patients caused corneal edema, which hindered such diagnostic assessments. Furthermore, research suggests that the incidence of corneal edema is comparably high following any IOP-lowering procedure, whether it involves device placement or not. This indicates that corneal edema is a potential risk inherent to all such interventions. To better understand the nuances of corneal decompensation across different treatments, it is crucial to conduct long-term follow-up studies comparing outcomes between GDD implantations and trabeculectomy [21].

    The relationship between glaucoma and endothelial damage extends beyond the effects of surgical intervention; our examination reveals that certain types of glaucoma inherently predispose patients to endothelial dysfunction. Particularly in complex cases like NVG and pseudoexfoliation (PEX), the endothelial cell count and functionality are notably inferior compared to those in healthy individuals [24].

    Research shows that patients on chronic therapy with multiple IOP-lowering medications experience molecular alterations in the corneal endothelium [15]. From a molecular perspective, these drugs are thought to affect endothelial cells particularly by altering intracellular calcium balance [25]. Therefore, the risk of endothelial decompensation following GDD implant surgery should be kept in mind for these patient groups [26].

    Anterior chamber (AC) tube placement, while effective in reducing IOP, poses corneal endothelial risks [12]. Conversely, CS and vitreous cavity placements reduces the risk of mechanical damage to the cornea, which can result from blinking, eye rubbing, or other external force on the eye [20, 27, 28]. Positioning the tube in the CS increases the distance between the tube and the corneal endothelium and the effects from the turbulent flow at the tip of the implant or intermittent tube-corneal touch are mitigated. The iris may also act as a barrier to mechanical factors that cause ECD loss [29]. Studies, including those by Zhang et al., have demonstrated that the iris effectively shields the endothelium from tube-related damage in CS placements, maintaining ECD across different corneal areas [28]. Retrospective and interventional studies have documented a lesser decline in ECD in CS placements over time, emphasizing its benefits over AC placements [30, 31]. For instance, a 2021 study noted a more pronounced decrease in ECD in the AC group compared to the CS group over 24 months, with the AC group experiencing a 20% reduction versus 10% in the CS group [29]. While CS tube placement offers considerable advantages in reducing endothelial cell loss, it does present challenges such as difficulty in accurately placing the tube during surgery, and the potential for iris pigmentation due to friction [32]. Because of these constraints, most GDDs are inserted into the AC [33]. In cases where the tube is placed in the AC, surgeons aim to minimize the tube’s length and align it as close and parallel to the iris as possible to reduce the risk of endothelial damage. However, progressive endothelial damage remains a concern with AC placements. While pars plana placement requires a vitrectomy, introducing potential complications, CS placement has been increasingly favored for its ability to preserve endothelial integrity by increasing the separation from the cornea and minimizing the effects of turbulent flow at the tube tip [29].

    Several hypotheses have been suggested to explain the loss of ECD following AGV surgery. The proposed theories include turbulent flow at the implant’s tip, postoperative inflammation, depletion of nutrients and oxygen, intermittent contact between the tube and the cornea or uveal tissue, and the foreign body effects of the silicone tube [29, 34].

    Rososinski and colleagues have posited that the mere presence of the tube in the AC can trigger inflammation, either from physical contact or simply from its presence, leading to the formation of peripheral anterior synechiae (PAS). PAS, in turn, has been negatively correlated with endothelial cell count, and can lead to endothelial decompensation either through direct iris-endothelial contact or indirectly by increasing IOP due to impaired outflow [30]. Inflammation alters the composition of the aqueous humor, increasing oxidative stress and endothelial loss. Research indicates that GDDs can themselves exacerbate inflammation and increase inflammatory cytokines within the aqueous humor, potentially intensifying inflammation [35]. Additionally, the jet stream of aqueous humor flowing through the silicone tube during the heartbeat could contribute to endothelial loss, even without direct mechanical contact [34, 36].

    Freedman and colleagues have reported that cytokines from a foreign-body reaction in the bleb of aqueous drainage implants can diffuse back into the AC. This interaction, combined with the altered flow dynamics near the tube’s internal tip—where back-and-forth motion due to pulse-induced IOP changes can occur—may mechanically damage the nearby corneal endothelium. Normally, aqueous fluid enters the AC through the pupil, flows forward toward the endothelium, and then peripherally to the trabecular meshwork, facilitating efficient nutrient delivery and waste removal. However, when flow is redirected through a GDD tube, these metabolic exchanges are likely compromised [37].

    Risk factors for endothelial decompensation when a shunt tube is present include high IOP, an initially low endothelial cell count (observed in conditions like Fuchs endothelial dystrophy or post-cataract surgery or trabeculectomy with mitomycin C), a shallow AC, synechial angle closure, direct tube-endothelial contact, and the presence of a corneal graft [38]. Even when direct endothelial contact is eliminated, endothelial loss may continue, suggesting the influence of the tube’s dynamic movements and intermittent endothelial contact. Dynamic tube migration, particularly prevalent in inflammatory glaucomas such as uveitis, can occur in various gaze positions, as exemplified by our cases [39]. Regarding the compensation mechanisms of corneal endothelial cells, it is expected that the central ECD reflects the superotemporal ECD to some extent. Since corneal endothelial cells cannot reproduce, they compensate for damage through sliding, rearrangement, and enlargement.

    Therefore, central ECD loss might not only result from direct central damage but also as a compensation for damage in the superotemporal area [11]. This might explain the diffuse corneal edema in such patients. Koo et al. have also focu sed on the mechanism of endothelial loss involving the aqueous jet stream, noting that the positioning of the tube end (‘bevel up’) exposes endothelial cells more directly to these currents, thereby increasing the risk of endothelial loss [5].

    Our initial case involved NVG, a form of secondary glaucoma characterized by inflammatory processes, where hypotony ensued following the placement of an AGV into the AC. Hypotony following drainage implantation commonly arises from leaks at the tube entry sites [40]. In this instance, a progressive sequence of events unfolded, involving tube-lens contact, the onset of cataract formation, and the tube exerting pressure against the endothelium due to lens swelling. Throughout the management process, cataract surgery was performed, and the tube’s position was initially assessed as appropriate and unchanged. However, given the inflammatory nature of NVG, compounded by the presence of synechiae, the likelihood of endothelial contact increased. Managing NVG poses significant challenges, and as time progresses, angle closure can potentially direct the tube end towards the endothelium, exacerbating the risk of endothelial damage [41].

    In cases involving AC AGV, immediate intervention is necessary upon noticing endothelial decompensation due to tube-endothelial contact. Prior to opting for tube placement in the CS, less invasive techniques might have been introduced. For instance, as demonstrated in our second case, suture-assisted tube revision serves as a feasible alternative for patients who cannot undergo anesthesia due to systemic conditions. On the other hand, if the conjunctiva is fibrosed, reopening it for tube reinsertion can be challenging. This technique, employed by Bochmann et al. in a patient with significant subconjunctival scarring and no scleral support , may induce complications such as astigmatism. In their case, while visual acuity remained stable, surgically induced astigmatism was noted. Other potential complications include suture erosion at the limbus, long-term degradation of prolene, or ocular infection [14]. Despite Bochmann et al. reporting no complications aside from induced astigmatism over a 20-month follow-up period, our case exhibited loosening of sutures shortly after the procedure.

    Ma et al. proposed a technique for repositioning the tube with scleral fixation, which does not necessitate dissection or retrieval from the original scleral pathway. This method involves creating a scleral flap at the fixation site and maintaining the AC with a chamber maintainer. A precise incision is made just above the point where the tube enters the AC, allowing the tube end to be carefully flipped out using a Sinskey hook. Subsequently, a double-armed 10/0 Prolene straight needle is employed to penetrate through the tube end, with one needle entering the AC through the incision and being drawn through the scleral flap, followed by the other needle. This meticulous technique aligns the tube end parallel to the corneal surface, thereby minimizing potential complications associated with conventional methods [13].

    Another suture assisted revision technique also involves using a scleral flap. Initially, the tube’s position is identified, typically situated in the superotemporal quadrant. Subsequently, a meticulous placement of a 9-0 Prolene (Ethicon; Johnson and Johnson, USA) straight transchamber needle is executed across the cornea to overlay the body of the AGV tube. Following this, fornix-based conjunctival peritomies are meticulously performed, and partial-thickness scleral flaps are created. The Prolene suture is then inserted at the 10 o’clock limbus under the scleral flap and exits at the 2 o’clock limbus. This precise needle placement ensures that it lies above the AGV tube. Subsequently, the suture is securely fastened to displace the tube away from the cornea. Both scleral flaps and conjunctival peritomies are carefully closed to ensure that the suture knot remains adequately covered [42]. In this technique, different from the one we applied, the sutures passing further back from the limbus and being held under the scleral flaps might increase the tension and flattening effect of the suture.

    In managing endothelial decompensation and tube-endothelial contact, revising the tube’s placement into the CS has been the definitive method in both cases presented. Initially, it might be questioned why placement in the sulcus was not chosen. One reason was the phakic nature of the patients. Additionally, it’s important to consider that sulcus implantation doesn’t entirely prevent endothelial loss and may contribute to inflammation. A recent study comparing endothelial loss after trabeculectomy and drainage implant surgery showed significantly higher endothelial loss post-implantation, even years later, with continued higher levels of inflammation indicated by persistent elevated flare levels [43]. In the study group with sulcus AGV, monthly ECD loss was notably higher in the superotemporal corneal region compared to the central and inferonasal areas. This suggests that, while CS placement reduces trauma to central endothelial cells, it still induces endothelial loss and corneal changes near the tube [28]. Hypotheses for this ongoing loss include turbulence from altered aqueous humor flow, immune reaction from foreign body presence, and intermittent tube contact with the endothelium [43, 44]. Moreover, CS placement could exacerbate intraocular inflammation in uveitic glaucoma cases due to microscopic and continual contact between the tube and the iris, thereby promoting further inflammation [18]. Therefore, AC implantation might be considered beneficial, especially in inflamed or complex glaucoma cases, and was deemed appropriate in our cases for this reason.

    Murakami et al. demonstrated that CS placement with a GDD led to decreased central endothelial cell density. Factors like previous ocular surgeries and high preoperative IOP were linked to this reduction. The long-standing glaucoma in our cases also posed a risk for post-surgical endothelial loss. They emphasized that the number of past intraocular surgeries was directly associated with endothelial decompensation. Hence, the suture revision surgery applied to our second case could have negatively impacted the process as an additional intraocular surgical intervention [10]. Mechanical contact between the tube and the endothelium is a primary cause of endothelial damage following the implantation of a GDD. If the tube is left excessively long, resulting in evident contact with the corneal endothelium, tube trimming should be considered. Traditionally, this procedure is viewed as a major surgical intervention involving multiple steps: dissection through scarred conjunctiva, navigating beneath the scleral patch graft, extracting the tube from the AC, cutting it to the appropriate length, and then reinserting and securing it with sutures. This comprehensive approach can be extensive and prone to complications.

    However, Asrani and colleagues [45] have proposed a less invasive method requiring just two paracenteses, while Soebijantoro and associates [46] have introduced an even more minimally invasive technique involving only a single paracentesis. This streamlined procedure minimizes the surgical footprint and potential for complications.

    Hypotony, characterized by IOP below 5 mmHg, poses a significant concern following glaucoma surgeries, including AGV implantation Factors such as insufficient capsule creation, excessively wide sclerostomy, or weak aqueous production due to postoperative iritis can contribute to hypotony [40]. In such cases, it is crucial first to investigate and rule out the possibility of leakage [40, 47]. The AGV is specifically designed to minimize postoperative hypotony through its valve mechanism, demonstrating fewer severe complications compared to the Baerveldt glaucoma implant [8].

    Despite the precautionary designs, studies indicate that while AGV effectively reduces hypotony risks, it does not eliminate them. Surgical precautions to prevent persistent hypotony include avoiding over-priming the tube and excessive manipulation of the valve housing during surgery [48]. In the realm of clinical outcomes and predictive factors for postoperative hypotony, Rachmiel et al. observed lower IOP levels in patients with uveitic glaucoma compared to those with primary open-angle glaucoma in the initial months post-surgery [41]. However, Kaderli et al. found no significant differences in risk factors such as age, sex, lens status, history of previous ocular surgeries, preoperative glaucoma medication usage, or type of glaucoma affecting the prevalence of postoperative hypotony [47]. Chronic hypotony, which persists beyond four weeks, can lead to serious complications such as accelerated cataract formation, choroidal detachments, hypotony maculopathy, and even suprachoroidal hemorrhages [49, 50]. In these situations, surgical interventions may be necessary, such as ligating sutures for tube shunts or revising the surgery to reduce outflow, ensuring vision preservation [51, 52]. Non-physiological IOP levels, whether high or low, can disrupt endothelial function.

    Elevated or decreased IOP can impair endothelial cell function, leading to decompensation through the disruption of desmosomes and junctional complexes [53]. Furthermore, long-term complications like mechanical tube corneal rubbing might go unrecognized. A long AC tube, more prone to movement in eyes with low IOP, could lead to intermittent corneal contact during eye movements such as blinking or rubbing, potentially exacerbating endothelial damage over time [21].

    Ophthalmic viscosurgical devices (OVDs) play a crucial role in managing complications associated with ocular surgeries by blocking the trabecular meshwork, closing ciliary body detachments, and interrupting the cycle of hypotony and choroidal effusion. These devices also increase the viscosity of aqueous humor, effectively slowing the rate of filtration through tube shunts or sclerotomies [51, 54]. In our cases, postoperative hypotony was managed by injecting OVD into the AC. For the first patient, a Seidel positive wound with leakage was identified and subsequently repaired. It is important to note that if wound leakage is not addressed, the effectiveness of the OVD injection will be limited, thus checking and repairing the wound site is crucial initially.

    In their research comparing AGVs placed in the AC and the CS, Bayer and colleagues observed that shallow AC and the need for AC revisions with OVD were more frequent in implants placed in the AC. They provided three possible explanations for this observation, suggesting that the AC tends to be deeper in pseudophakic or aphakic eyes compared to phakic eyes, influencing the rate of AC reformation. Secondly, the threshold for reforming the AC may have been lower in the AC group to prevent mechanical contact between the tube and the corneal endothelium or the crystalline lens. Thirdly, they noted that peritubular filtration of aqueous is less likely in CS implantations due to the longer pathway through sclera and ciliary body tissues, compared to the shorter pathway through just scleral tissue in AC implantations [18].

    Given the challenges associated with sulcus implantation, Chey and colleagues recently published a study on a technique to reduce endothelial damage by utilizing a guided-assisted AGV implantation in the AC. In this technique, a 4-0 nylon suture is used as an intraluminal guide to facilitate accurate placement. Their findings revealed that none of the cases with guided implantation required repositioning of the tube into the CS, in contrast to standard implantation where such repositioning was necessary in 10 out of 79 cases. The postoperative complications did not differ significantly between the two groups, except for instances of flat AC, potentially due to leakage at the sclerotomy site following multiple punctures made to achieve the desired tube positioning in the non guided AGV group. Furthermore, the study indicated that guided implantation resulted in less endothelial loss over a two-year follow-up period [55].

    Given that this is a recent and innovative technique, there is a need for long-term comparative studies with traditional sulcus implantation to fully evaluate its efficacy and safety.

    Research indicates that both CS and AC tube shunt placements are effective and safe for reducing IOP. However, studies also show that CS implantation leads to significantly lower rates of corneal endothelial cell loss compared to AC placements. This makes CS implantation particularly advantageous for patients at high risk of corneal decompensation [3, 18, 20, 29]. When complications such as tube-endothelial contact occur, the recommended interventions include trimming or repositioning the tube tip. Nonetheless, it is important to note that endothelial decompensation resulting from such contact may become irreversible, potentially necessitating corneal transplantation to restore vision [38].

    Conclusion

    The findings from this study underscore the critical nature of strategic AGV placement and postoperative management to optimize patient outcomes in glaucoma surgery. While AGV is effective in reducing IOP, its association with significant risks such as hypotony and corneal endothelial decompensation necessitates careful surgical planning and follow-up. The comparison between AC and CS placements reveals a clear preference for the latter, given its reduced impact on corneal endothelial health. Furthermore, the introduction of guided-assisted AGV implantation presents a promising technique to reduce endothelial damage, although long-term studies are required to establish its efficacy fully.

    Despite being a valved system, AGV implantation, especially in high-risk cases, may benefit from intraoperative ligation to prevent postoperative hypotony and subsequent tube-endothelial contact.

    These findings highlight the complexity of managing high-risk glaucoma cases and emphasize the importance of tailored surgical approaches that consider individual patient anatomy and disease severity. Future research should continue to explore innovative surgical techniques and postoperative management strategies to enhance the safety and effectiveness of glaucoma filtration surgeries, thereby improving quality of life for affected patients.

    Информация об авторах

    Умай Гювенч, д.м.н., Учебно-исследовательская больница Анкары, umay.guvenc@gmail.com, https://orcid.org/0000-0002-8993-1674

    Гюлизар Демирок, доцент, Учебно-исследовательская больница Анкары, gulizardemirok@hotmail.com, https://orcid.org/0000-0003- 4655-4669

    Author’s contribution:

    Umay Güvenç: significant contribution to the concept and design of the work, final approval of the version to be published.

    Gülizar Demirok: analysis and processing of material, writing the text, significant contribution to the concept and design of the work, editing.

    Вклад авторов в работу:

    Умай Гювенч: существенный вклад в концепцию и дизайн работы, окончательное утверждение версии, подлежащей публикации.

    Гюлизар Демирок: существенный вклад в концепцию и дизайн работы, анализ и обработка материала, написание текста, редактирование.

    Funding: The authors have not declared a specific grant for this research from any funding agency in the public, commercial, or non-profit sector.

    Финансирование: Авторы не получали конкретный грант на это исследование от какого-либо финансирующего агентства в государственном, коммерческом и некоммерческом секторе.

    Authorship: All authors confirm that they meet the current ICMJE authorship criteria.

    Авторство: Все авторы подтверждают, что они соответствуют действующим критериям авторства ICMJE.

    Patient consent for publication: No written consent was obtained for the publication of this material. It does not contain any personally identifying information.

    Согласие пациента на публикацию: Письменного согласия на публикацию этого материала получено не было. Он не содержит никакой личной идентифицирующей информации.

    Conflict of interest: There is no conflict of interest.

    Конфликт интересов: Отсутствует.

    Originally received: 26.04.2024

    Final revision: 10.05.2024

    Accepted: 13.05.2024

    Поступила: 26.04.2024

    Переработана: 10.05.2024

    Принята к печати: 13.05.2024