Ocular hypotony is a recognized complication in glaucoma drainage device surgeries, with a higher incidence observed in non-valved tubes. ¹ Sequelae of ocular hypotony include choroidal detachment, hypotony maculopathy, and changes in refraction and visual acuity. ² Fortunately, most hypotony cases can be effectively managed through conservative measures. Studies have found the significance of certain risk factors in the development of choroidal detachment after glaucoma drainage device surgeries. These factors include older age, hypertension, pseudophakia, and specific glaucoma types such as pseudoexfoliation glaucoma. ³ Understanding and recognizing the relevance of these risk factors are crucial for both anticipating and managing potential complications associated with hypotony in glaucoma patients.

A 79-year-old female with advanced pseudoexfoliative open-angle glaucoma (SOAG) presented, having undergone trabeculectomy, multiple needling procedures, and cataract extraction with IOL implantation. The referral to our center at the McGill Academic Eye Center, was prompted by uncontrolled intraocular pressure (IOP) despite multiple hypotensive agents in both eyes. The anterior segment examination revealed a deep and quiet anterior chamber, a flat superonasal bleb, in-the-bag posterior chamber intraocular lens (PCIOL), superior iridotomy, and pseudo exfoliation material. Fundus examination demonstrated advanced optic nerve damage bilaterally. The initial IOP measured 20 mmHg in the right eye and 18 mmHg in the left eye, on 3 hypotensive eye drops (Latanoprost once a day, and a combined dorzolamide hydrochloride-timolol maleate twice a day) and oral Methazolamide (50 mg twice a day). The decision was made to proceed with Baerveldt tube implantation with a ripcord using a 4-0 nylon suture, starting with the right eye. The tube was implanted in the superotemporal area, and a wick suture using 8-0 Vicryl was placed through the tube to allow drainage while waiting for the spontaneous dissolution of the 7-0 Vicryl ligature suture. Antiglaucoma medication was halted in the operated eye immediately after surgery. The six-week follow-up examination revealed an open tube with an elevated bleb around the plate, and the IOP was 10 mmHg off anti-glaucoma medications. At postoperative month two, the IOP started to rise, reaching 20 mmHg, suggesting a hypertensive phase. The decision was made to remove the ripcord at the slit lamp, resulting in an immediate reduction of IOP to 12 mmHg. One week later, the IOP increased again, necessitating the initiation of antiglaucoma medications.

Three months later (postoperative month 6), the patient presented with persistent hypotony despite discontinuation of antiglaucoma medications. This hypotony was associated with choroidal folds and an impending kissing choroidal detachment. Multiple attempts of anterior chamber filling with dispersive or cohesive ophthalmic viscosurgical devices (OVD) and anti-inflammatory treatment resulted in temporary success. The hypotony recurred, leading to the decision for a more sustained intervention. An ab interno occlusion of the tube using a 7 mm segment of 3-0 nylon suture was performed. However, a subsequent recurrence of hypotony and choroidal detachment occurred. Additionally, the suture stent was observed to be descending, with a part passing beyond the tube bevel into the anterior chamber, see Figure 1. Consequently, the decision was made to perform plate truncation and stent the tube with a long segment extending beyond the plate, ultimately lifted under the conjunctiva.

Managing refractory hypotony in glaucoma drainage device cases can be challenging. Possible interventions include tube ligation, tube occlusion, plate truncation, or drainage of choroidal effusions. Reports highlight the successful control of delayed hypotony associated with Baerveldt tube or Ahmed glaucoma valve implantation through ab interno procedures using 4-0 polypropylene suture. ^{4 , 5} Another approach, as reported by Lim SH in 2018, involves stenting using two 5-0 nylon threads to effectively control hypotony in cases associated with Ahmed Glaucoma valve implantation. ⁶ Recognizing the impact on flow rates is essential in tube occlusion procedures. Studies have evaluated flow rates using different suture sizes, considering the cross-sectional area of each of the sutures. For example, 2-0 polypropylene suture led to complete occlusion of the Baerveldt tube, whereas 3-0 and 4-0 resulted in 44% and 26% occlusion, respectively. ⁷ It is noteworthy that even within the same type of suture, different manufacturers may introduce marginal size variability, potentially influencing flow rates. Furthermore, the utilization of multifilament nylon sutures, like Supramid, may additionally impact flow rates due to the expansion ability, and variability of suture diameter. ⁸

Delayed hypotony associated with a Baerveldt tube may arise from factors such as wound leaks or over filtration of the Baerveldt device, occurring in up to 5% of cases. ⁴ In the present case, delayed hypotony was observed six months post-operatively, significantly after the time that the ripcord had been removed.

Aligned with findings in previously published case reports, our case demonstrates the successful management of refractory hypotony and choroidal detachment through ripcord utilization. The unique aspect of our case involves the ab interno occlusion of the tube using 3-0 nylon. Previous literature mentions various dimensions of nylon and 3-0 Prolene, but the specific application of 3-0 nylon has not been reported before. This approach highlights the potential versatility of suture materials in managing refractory hypotony. Notably, Baerveldt tubes, unlike valved counterparts, are less frequently associated with a hypertensive phase, conventionally characterized by elevated intraocular pressure (IOP) in the initial three months post surgery. The pathophysiological understanding of this phenomenon remains elusive. Observations of increased congestion and dense fibrous encapsulation suggest a role for inflammatory mediators in the drained aqueous, inducing inflammatory reactions and fibrosis. While conversion to a steady phase usually occurs, the management of the hypertensive phase often involves aqueous suppressants to limit inflammatory mediator interaction with the capsule and reduce pressure, mitigating further optic nerve damage. ⁹ The utilization of an ab interno technique for the occlusion of the Baerveldt tube in this case offers several notable benefits compared to conventional ab externo approaches. The ab interno method is inherently less invasive, avoiding conjunctival dissection and minimizing the risk of eventual tube exposure. This approach also requires less anesthesia and is associated with a shorter operative time, compared to other ab externo approaches to the management of delayed hypotony. ¹⁰

In our case, we hypothesized that the spontaneous resolution of the hypertensive phase led to hypotony, resulting in a lower IOP than before ripcord removal. This speculation prompts a critical consideration regarding the optimal timing for ripcord removal. Accordingly, we propose a cautious approach of delaying ripcord removal in cases with hypotony risk factors until resolution of the hypertensive phase, unless the target pressure cannot be achieved with tolerable medical therapy. This recommendation aims to balance the need for IOP control with the potential risks associated with premature ripcord removal, adding a layer of individualized decision-making to optimize outcomes in complex glaucoma cases.

The ab interno occlusion of the Baerveldt tube using a 3-0 nylon suture demonstrated successful control in a case of refractory hypotony accompanied by maculopathy and choroidal detachment. However, the observation of suture descent cautions against using a short segment of ripcord.

Written informed consent for publication of their clinical details and clinical images was obtained from the patient.

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