FormalPara Key Summary Points

The sulcus tube internal needle guidewire (STING) technique is a unique method for placing a glaucoma drainage device tube into the ciliary sulcus.

This technique leads to intraocular pressure (IOP) lowering at 6 months with a low complication rate.

This technique is readily adoptable and may increase surgical precision and ease of sulcus tube placement.

This technique may encourage adoption of sulcus tube-shunt placement.

Digital Features

This article is published with digital features, including a video, to facilitate understanding of the article. To view digital features for this article, go to https://doi.org/10.6084/m9.figshare.24427936.

Introduction

Despite the advent of MIGS, glaucoma drainage device placement for the treatment of glaucoma remains a mainstay of surgical glaucoma management particularly for refractory glaucoma. Many glaucoma drainage devices are available, and various techniques for tube placement have been described. These include placement of the tube into the anterior chamber (AC), ciliary sulcus (CS), or anterior vitreous cavity via the pars plana.

Placement of a tube into the AC is traditionally achieved by making a conjunctival peritomy, securing the plate to the sclera, and passage of a 22- or 23-gauge needle through the sclera into the mid-anterior chamber. After the needle is withdrawn, the tube is advanced through the scleral tunnel and adequate placement of the tube tip in the AC is confirmed [1]. This technique, while effective in lowering IOP, does present long-term risks to the cornea. Patients with tubes implanted in the AC are at risk of corneal endothelial damage, corneal edema, and, in patients who are status post keratoplasty, graft failure. The rate of corneal damage is much higher in those with keratoplasty than in patients who retain the native cornea [2].

Alternatively, tube placement in the CS or vitreous cavity reduces the risk of mechanical damage to the cornea, which can result from blinking, eye rubbing, or other external force on the eye. There is increased space for tube placement in the CS in pseudophakic eyes with a posterior chamber intraocular lens. In contrast to the risk of corneal damage in patients with AC device placement, a retrospective interventional case series by Weiner et al. showed that placement of a tube in the CS in pseudophakic eyes resulted in an insignificant change to corneal morphology and central corneal thickness [3].

Several studies have shown that CS tube placement results in less endothelial cell loss (ECL) compared to AC placement. A 2021 retrospective study found a significant decrease in endothelial cell density (ECD) from 12 to 48 months (3.10%/year) in AC tubes compared to CS tubes [4]. Similarly, a nonrandomized interventional study performed by Zhang et al., showed a significantly faster decrease in corneal ECD in eyes with tubes placed in the AC compared with eyes with CS tube placement [5]. In addition, in a 2021 retrospective review of 38 eyes receiving an AC Ahmed Glaucoma Valve (AGV) and 24 eyes receiving a CS AGV, Kim et al. showed that the AC group had a significantly higher mean monthly ECL. At 24 months the AC group ECD decreased 20% compared to 10% for the CS group [6].

Various techniques for placement of a tube into the sulcus have been described, including both ab externo and ab interno approaches.

Ab Externo Techniques

In the traditional ab externo sulcus approach, a 22- or 23-gauge needle is directed through the sclera starting approximately 2.5 mm posterior to the limbus and is leveled to be parallel with the iris plane as it is advanced into the sulcus [7]. However, with this approach it is difficult to estimate the site of needle entry into the posterior chamber since it cannot be directly visualized. It is therefore possible to inadvertently advance the needle into the iris, into the intraocular lens, through the zonules, or into the vitreous cavity.

In one variation of the ab externo approach, a 23-gauge needle is inserted into the sulcus and then withdrawn. Next, a 4-0 polypropylene suture is threaded into the tube lumen. With 2 mm of the polypropylene protruding from the tube tip to increase its rigidity, the tube is placed through the scleral tunnel. The polypropylene suture piece is subsequently removed from the tube intracamerally using microforceps [8].

Alobaida et al. demonstrated an ab externo technique wherein a 30-gauge needle is used to make an initial guiding sclerostomy into the sulcus followed by a larger 23-gauge needle pass into the sulcus. Compared to AC placement, this sulcus tube technique resulted in a similar reduction in both IOP and glaucoma medication use with a reduced rate of hyphema [9].

Another ab externo approach uses a 4-0 nylon suture as a guidewire inserted into the AC via a paracentesis 180° away from the tube location. A 23-gauge needle is then inserted ab externo into the sclera 2 mm from the limbus into the CS, the 4-0 nylon suture is introduced into the lumen of the 23G needle intracamerally, the needle is withdrawn, the tube is guided into the CS along the 4-0 nylon guidewire, and the guidewire is then removed from the paracentesis [10].

Ab Interno Techniques

In one ab interno method, a 23-gauge needle is inserted through the cornea into the eye 180° away from the planned tube insertion site, advanced into the CS and out of the eye through the sclera. The needle is withdrawn and the tube is then inserted into the sulcus through this scleral tunnel [11].

In another ab interno approach, a larger 21-gauge needle is inserted into the anterior chamber through a paracentesis 180° away from the tube position and advanced into the posterior chamber and through the sclera. The tube is then inserted into the lumen of the needle and pulled into the posterior chamber as the needle is withdrawn [12, 13].

In yet another ab interno variation, a 10-0 polypropylene suture on a straight needle is advanced across the anterior chamber into the sulcus and then through the sclera, the suture is tied around the tube with a sliding knot, the tip of the tube is pulled into the sulcus space, and the suture is then removed [14].

Purpose

The challenge of the ab externo techniques lies in the proper anatomical placement of the tube in the sulcus, while the ab interno approaches can be technically difficult or require the use of a large 21-gauge needle with the possibility of excessive peritubular flow and postoperative hypotony. The purpose of this study is to demonstrate that the STING technique can be easily used to place a tube in the sulcus with precision and is effective in lowering the IOP with minimal complications.

Methods

Study Design

This is a case series from a single center. This study was conducted under approval from the Institutional Review Board at the University of Missouri-Columbia (IRB Project Number 2096195, IRB Review Number 390918). Written informed consent for publication of clinical details and clinical images was obtained.

The study involved a comprehensive review of patient charts who underwent the STING technique using the Ahmed Clearpath, AGV, or Baerveldt glaucoma implant between 2021 and 2022, all performed by a single surgeon.

Patients were included if they had at least 6 months of follow-up. Patients who were undergoing tube repositioning to the sulcus from the AC using the STING technique for corneal complications (i.e., not de novo glaucoma tube implant) and patients with a history of medication noncompliance were excluded.

We collected preoperative data including sex, age at the time of surgery, type of glaucoma, previous surgical treatments, glaucoma medication count, and IOP measured using Goldmann applanation tonometry. In cases where applanation data were unavailable, Tonopen IOP measurements were recorded. Additionally, intraoperative complications and procedure duration were documented.

IOP, glaucoma medication numbers, and complications were recorded on postoperative day 1, week 1, month 1, and at each consecutive follow-up visit through the most recent visit. Surgical failure criteria consisted of IOP > 21 mmHg or < 20% reduction from baseline on two consecutive follow-up visits after 3 months, an IOP ≤ 5 mmHg on two consecutive follow-up visits after 3 months, reoperation for glaucoma, or loss of light perception.

The surgery was defined as a qualified success if the surgery did not meet the criteria for failure and required supplemental medical therapy to control IOP.

All the data collected in the study were inserted into an electronic database via Microsoft® Excel® for Microsoft 365 MSO Version 2306. Statistical analysis was performed using SPSS Statistics. Related samples Wilcoxon signed-rank tests for comparison of the means were performed. P values < 0.05 were considered statistically significant.

Surgery Technique. Video demonstrating the placement of an Ahmed ClearPath Glaucoma Drainage Device using the STING technique.

Surgical Technique

Sulcus tube placement using the STING technique follows placement of the tube shunt baseplate and possible tube ligation if necessary. The tube is trimmed with a posteriorly facing bevel using Wescott or Vannas scissors at a length that will allow the tube to be visualized when the patient is dilated but avoiding obscuration of the visual axis by the tube tip. Calipers are used to estimate the distance between the dilated pupillary margin and the exit point of the needle and also the distance between the dilated pupillary margin and the paracentesis 180 degrees away from the tube's placement. A 22- or 23-gauge 1.5-inch needle is then bent toward the bevel at a 45- to 90-degree angle using hemostat forceps or a heavy needle driver at a distance from the needle tip between these two caliper measurements. A corresponding 45- to 90-degree bend is made in the opposite direction in similar fashion approximately 1 mm proximal to the first bend. If placement of the tube is in the superotemporal quadrant, an additional bend in the needle can be created to allow the needle to enter the anterior chamber from the inferonasal quadrant. A paracentesis is created 180° away from the location of desired tube entry. Cohesive viscoelastic is injected into the anterior chamber via the paracentesis and directed into the CS. The bent needle is placed through the paracentesis and directed into the CS, taking care to keep the distal section of the bent needle parallel with the iris plane. Counter traction on the sclera is used as the needle is advanced from the CS through the sclera. A piece of 6-0 polypropylene suture is then inserted into the lumen of the needle extrasclerally, and the needle is withdrawn from the eye leaving the polypropylene guidewire in place through-and-through the eye. The proximal end of the polypropylene suture is threaded into the trimmed tube, and the tube is advanced through the scleral tunnel along the polypropylene guidewire. Once the tube is visualized in the pupil and good tube placement confirmed, the guidewire is removed via the paracentesis. The closure proceeds per standard techniques, and at the conclusion of the case the cohesive viscoelastic in the anterior and posterior chambers is burped from the paracentesis.

The intraoperative sequence of the surgical procedure included slight variations from case to case reflecting the unique surgical history and clinical condition of each eye.

Results

A total of nine eyes from nine patients were included in this study, with an average patient age of 53.1 years. Among them, three patients had severe primary open-angle glaucoma (POAG), two patients had severe neovascular glaucoma (NVG), one patient had moderate NVG, one patient had mild NVG, one patient had mild mixed mechanism glaucoma, and one patient had moderate uveitic glaucoma. Concurrent cataract extraction with the implantation of an intraocular lens was performed in four patients, while all other eyes were previously pseudophakic.

Preoperative mean IOP averaged 23.8 ± 6.3 mmHg. Postoperative final IOP at the last follow-up averaged 14.9 ± 3.7 mmHg, representing a statistically significant reduction (p = 0.008). Figure 1 summarizes the IOP trends for the nine cases using the STING technique.

Fig. 1
figure 1

Postoperative IOP trends for nine cases using the STING technique. IOP values were taken at the nearest available time to the indicated timepoints, and no measurement was farther than 3 weeks from a given postoperative month.  IOP intraocular pressure, Preop preoperative, STING sulcus tube internal needle guidewire

Full size image

The average number of preoperative medications was 4.4 ± 0.7. At the last follow-up appointment, the mean number of medications was 3.6 ± 1.0, showing a statistically significant reduction (p = 0.039).

Table 1 provides a summary of patient ages, prior laser trabeculoplasty (LTP), implants, diagnoses, previous glaucoma surgeries, IOP, and complications.

Table 1 Demographics of eyes included in the study. Averages are represented as mean ± standard deviation
Full size table

Complications included one patient taking dasatinib who developed hemorrhagic chemosis, and another patient with a low IOP at postoperative week 3 with a Seidel positive area at the limbus, which resolved after an injection of cohesive viscoelastic and bandage contact lens placement.

The qualified success rate was seven out of nine cases (77.8%). The two failures occurred in patients with upper teen preoperative IOP values  wherein IOP decreased by < 20%. Of note, in one qualified success with adequate IOP control, tube repositioning from the sulcus to the pars plana was required. This particular patient with uveitis developed worsening inflammation possibly secondary to tube-iris chafing; therefore, the tube was repositioned to the pars plana around postoperative month 6.

Discussion

The STING technique is a novel method for tube-shunt placement in the sulcus for pseudophakic eyes that may reduce the risk of corneal damage by increasing the distance between the tube and endothelium [2,3,4]. In a 2022 AGS survey, 90% of the surveyed glaucoma surgeons reported commonly utilizing the AC for tube placement, but 61% reported that the available evidence suggests the superiority of sulcus placement over the AC in terms of ECL. Interestingly, 77% of surgeons reported that they would convert to placing tubes in the sulcus if a randomized controlled trial were to show its superiority in preventing ECL [15].

However, the ab externo variations of sulcus tube placement have inherent challenges, primarily due to anatomical differences among eyes, leading to uncertainty in tube placement and potential complications such as hyphema, iris trauma, zonular damage, or vitreous loss. A 2021 retrospective review of 104 sulcus tubes demonstrated that using the traditional ab externo approach required reinsertion of the tube due to malposition in 41% of cases, and sulcus insertion could not be accomplished at all in 4% of cases [16].

The ab interno techniques reduce some uncertainty regarding sulcus location but pose their own difficulties. These methods can be technically challenging to perform or they necessitate the use of a larger gauge needle, which increases the risk of unwanted peritubular flow and postoperative hypotony.

The STING technique may confer several advantages compared to previously described techniques. It utilizes an ab interno approach reducing uncertainty regarding the location of the ciliary sulcus. The polypropylene guidewire allows for continual maintenance of the sulcus pathway and therefore less risk of inadvertent iris or zonular trauma. The use of a standard gauge needle minimizes excess peritubular flow. Lastly, the double bend aids in positioning the tube parallel to the iris. A disadvantage of the STING technique is that it requires an additional polypropylene suture piece.

At 1 year, the tube group in the TVT study, which investigated BGI shunts, experienced treatment failure in 4% of patients [17]. Our study closely resembles a study conducted by Eslami et al. focusing on AGV implantation in the sulcus, which reported a success rate of 78.6% [18]. In comparison, our study achieved a success rate of 77.8% at an average follow-up of 11.8 months, which is similar to success rates observed in prior sulcus tube studies with similar success criteria and follow-up durations.

Regarding complications, we encountered similar issues as reported by Eslami et al., such as hyphema and iris chafing. However, their study had a larger sample size and documented additional and more severe complications, including endophthalmitis, vitreous blockage, conjunctival wound dehiscence, and choroidal effusions.

To gain a more accurate understanding of the frequency of complications, their prevention strategies, and the true effectiveness of the STING technique, a larger sample size and longer follow-up time are essential. While no cases of corneal decompensation have occurred, longer follow-up times are necessary to detect this complication. Measurement of ECL would also elucidate the risks to the cornea of this technique.

These findings are limited by short follow-up time, restricting the ability to fully assess the long-term outcomes and potential complications of this technique. Also, the study's retrospective nature and small sample size may influence its generalizability.

To validate the notion that the STING technique offers increased ease and surgical precision of sulcus placement, direct comparison with ab externo and ab interno sulcus techniques is warranted.

The STING technique utilizes a standard gauge needle and suture guidewire along which the tube can be advanced into the sulcus. The ease of implementation and low cost make it readily adoptable by glaucoma surgeons. These initial outcomes suggest good IOP control on fewer medications in pseudophakic eyes over a short follow-up period of approximately 12 months. The STING technique may encourage consideration of the sulcus space for glaucoma tube placement and decrease the corneal risks associated with glaucoma drainage devices.

Conclusions

In this preliminary study, we demonstrate that the novel STING technique is a method for placing a glaucoma drainage device tube into the sulcus, leading to IOP lowering and medication reduction with a low complication rate. This technique is readily adoptable and may increase surgical precision and ease of sulcus tube placement, warranting further investigation.