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Antonio M. Fea, 1 Andrea Gilardi, 1 Davide Bovone, 1 Michele Reibaldi, 1 Alessandro Rossi, 1 Earl R. Craven21 Diploma of the Scientific Ophthalmological University of Turin, Turin, Italy; 2 Johns Hopkins University, Baltimore, Maryland, USA Elmer Eye Institute Glaucoma Center of Excellence Corresponding author: Antonio M. Fea, +39 3495601674, email [email protected] Abstract: PRESERFLO™ MicroShunt is a new device for minimally invasive glaucoma surgery (MIGS) implanted ab externo, the aqueous humor is drained into the subconjunctival space. It has been developed as a safer and less invasive treatment for patients with medically uncontrolled primary open-angle glaucoma (POAG). The classic approach to MicroShunt implantation involves various critical steps, including creating a small scleral pocket with a 1mm blade, inserting a 25G (25G) needle through the scleral pocket into the anterior chamber (AC), and then thin-walled 23-gauge (23G ) The cannula flushes the stent. However, insertion of the needle into the scleral pocket creates an incorrect channel, making it difficult to thread the device. The purpose of this article is to propose a simplified method of implantation. Our method suggests making a scleral tunnel using a 25G needle directly and using this 25G needle in the limbus to slightly push the sclera into the AC. The MicroShunt was then assembled on a 23G cannula that was attached to a 1ml syringe. The device can then be flushed with a syringe. Thus, outflow can be confirmed immediately by observing water droplets seeping from the outer openings of the stent. This new approach may have various potential benefits such as better control of the entry site, avoidance of false passages, reduction or elimination of the risk of lateral outflow of aqueous humor, promotion of a parallel path to the iris plane, and greater speed. Key words: MIGS, open-angle glaucoma, Preserflo, MicroShunt, glaucoma surgery, subconjunctival filtration.
In the past few years, minimally invasive or minimally invasive surgery (MIGS) has emerged in the field of glaucoma surgery. 1-5 These MIGS devices were developed for the treatment of medically unsupervised patients with primary open-angle glaucoma (POAG) to improve safety while maintaining the effectiveness of lowering intraocular pressure (IOP). 1-5 MIGS devices can be divided into: trabecular, suprachoroidal, and subconjunctival. 1,3 Subconjunctival outflow mimics the mechanism of trabeculectomy. Compared to trabeculectomy, it provides lower postoperative intraocular pressure, offering standardized procedures and greater safety. 1-5 All subconjunctival devices are based on tubule implantation. The lumen dimensions of these devices were approximated using the Hagen-Poiseuille laminar flow equation. 1 Generally, the lumen is chosen to prevent chronic hypotension and is large enough to avoid occlusion.
Although there is some debate about considering MicroShunt as MIGS, for the purposes of this document, the term MIGS will be applied to it. The PreserfloTM MicroShunt implant has recently been introduced. 6 The shunt consists of a polystyrene block, an isobutylene block, a styrene polymer that was previously used as a coronary stent because it causes minimal inflammation and encapsulation. 7,8 The device is 8.5 mm long and has a lumen of 70 µm to control flow and maintain IOP above 5 mmHg. (with average water production). 8 The length of the device allows for greater posterior water outflow, so a wide posterior incision is recommended.
In general, the oblique quadrant is the preferred site for implantation as it avoids access to the superior rectus muscle. Mitomycin-C (MMC) concentrations and exposure times varied depending on risk factors or surgeon experience. 9-16
This brief overview is intended to outline further modifications to the procedure for faster and easier MicroShunt implantation.
The review of medical records was approved by the Ethics Committee of the University of Turin. Because this was a retrospective review of medical records, the ethics committee waived the requirement to obtain written informed consent to participate in the study. However, all participants provided written informed consent prior to surgery.
To ensure patient privacy, their information is anonymized through the use of unique identifiers. The study protocol followed the principles of the Declaration of Helsinki and the Guidelines for Good Clinical Practice/International Coordinating Committee.
The present study included consecutive POAG patients ≥18 years of age and drug-treated patients with preoperative IOP ≥23 mmHg who underwent independent MicroShunt implantation.
PRESERFLOTM MicroShunt (Santen ex Innfocus, Miami, FL, USA) is supplied in a sterile packaging kit containing a 3 mm scleral marker, a 1 mm triangular blade, 3 LASIK ShieldsTM (EYETEC, Antwerp, Belgium), a marker and a size 25 needle ( 25G).
Before using the MicroShunt, the manufacturer recommends refilling with a 23G cannula, which is not included in the kit.
While it is a plus that glaucoma surgeons are familiar with the classic implant procedure, some of the steps can be challenging. In particular, when the 25G needle slips, its tip may create an incorrect/incorrect channel in a different plane or enter the anterior chamber without reaching the top of the scleral tunnel. It is really difficult to control the path of the 25G needle because the space inside the scleral tunnel is virtual, or at least very thin (see Fig. 1).
Figure 1. Overview of the main stages of the new surgical technique. (A) The needle is designed to penetrate the sclera 3 mm from the edge. (B) Once the needle reaches the limbus, it is pushed down. (C) The needle enters the anterior chamber. (D) After creating a tunnel with a triangular blade, the path of the needle used to enter the anterior chamber may not follow the tunnel, creating a false passage.
In some cases, this problem can make inserting the microshunt into the anterior chamber (AC) difficult because its tip is blocked in the tunnel. In addition, this manipulation may be more difficult in eyes with abnormal limbal anatomy.
Also, if the second attempt still fails, the surgeon may be forced to implant the device in a more advantageous order. This site is more prone to subsequent scarring due to the presence of the superior rectus abdominis.
To avoid this problem, one option is to inject AK with the tip of a microknife used to create a scleral pocket. While this method saves time and prevents the creation of erroneous paragraphs, it can be difficult to estimate the length of an incoming AC. In addition, the triangular shape of the blade defines a larger path, which creates a lateral flow in the early postoperative period. According to Poiseuille’s law, the lateral flow also invalidates attempts to create a given outflow of water from the AC, which can contribute to the development of hypotension.
Our surgical technique provides two improvements over traditional surgical procedures. The first is to directly use a 25G needle as a tunnel. As a second improvement, our technique proposes attaching a 23G cannula, which is commonly used for silicone oil aspiration, to the posterior end of the MicroShunt. Thus, the surgeon can flush the device directly during the installation of the thread.
Using a 25G needle to create a tunnel simplifies the surgical procedure as it eliminates the need for a scleral pocket and significantly reduces the scleral area involved in the procedure. In addition, this improvement helps to minimize long-term potential damage to endothelial cells by compressing the sclera as it approaches the limbus, thereby entering the iris in a more parallel plane (see Figure 1 and supplemental video).
The second improvement offered by the new technology is the use of a 23 G cannula, similar to the cannula commonly used for silicone oil aspiration. This 23G cannula perfectly fixes the MicroShunt and makes it easy to flush. In addition, the fluid injected into the AC also increases the pressure, allowing aqueous humor to flow through the distal end of the device (see Figure 1 and supplementary video).
Our clinical experience included 15 eyes from 15 OAG patients who underwent an independent microshunt and were followed up for 3 months. Although there are data on intraocular pressure lowering drugs and intraocular pressure lowering drugs, our main goal was to focus on early postoperative complications.
All patients were Caucasian, median (interquartile range, IqR) age was 76.0 (range 71.8 to 84.3) years, 6 (40.0%) were women. Key demographic and clinical characteristics are summarized in Table 2.
Median (IqR) IOP decreased from 28.0 (27.0 to 32.5) mm Hg. Art. at the beginning of the study to 11.0 (10.0 to 12.0) mm Hg. Art. after 3 months (Hodges-Lehman median difference: -18.0 mmHg, 95% confidence interval: -22.0 to -14.0 mmHg, p=0.0010) (Fig. 2). Similarly, the number of ophthalmic antihypertensive drugs decreased significantly from 3.0 (2.2-3.0) drugs at baseline to 0.0 (0.0-0.12) drugs at 3 months (Hodges-Lehman mean difference: -2.5 drugs) Drug, 95% CI: -3.0 to -2.0 Drug, p = 0.0007). After 3 months, none of the patients took systemic drugs to lower IOP.
Figure 2 Mean intraocular pressure during follow-up. Vertical bars represent interquartile ranges. *p < 0.005 as compared to baseline (Friedman test and post hoc analysis for pairwise comparisons were done with the Conover method). *p < 0.005 as compared to baseline (Friedman test and post hoc analysis for pairwise comparisons were done with the Conover method). * p <0,005 по сравнению с исходным уровнем (критерий Фридмана и апостериорный анализ для попарных сравнений были выполнены по методу Коновера). * p < 0.005 compared with baseline (Friedman’s test and post hoc analysis for pairwise comparisons were performed by Conover’s method). *p < 0.005 与基线相比（弗里德曼检验和成对比较的事后分析是使用Conover 方法完成的）。 *p < 0.005 * p <0,005 по сравнению с исходным уровнем (критерий Фридмана и апостериорный анализ для парных сравнений были выполнены с использованием метода Коновера). * p < 0.005 compared to baseline (Friedman’s test and post hoc analysis for pairwise comparisons were performed using Conover’s method).
Visual acuity decreased significantly on day 1, week 1, and month 1 compared to preoperative values, but recovered and stabilized from month 2 (Fig. 3).
Rice. 3. Review of median maximally corrected distance visual acuity (BCDVA) during follow-up. Vertical bars represent interquartile ranges. *p < 0.01 as compared to baseline (Friedman test and post hoc analysis for pairwise comparisons were done with the Conover method). *p < 0.01 as compared to baseline (Friedman test and post hoc analysis for pairwise comparisons were done with the Conover method). *p < 0,01 по сравнению с исходным уровнем (критерий Фридмана и апостериорный анализ для попарных сравнений были выполнены по методу Коновера). *p < 0.01 compared with baseline (Friedman’s test and post hoc analysis for pairwise comparisons were performed using Conover’s method). *p < 0.01 与基线相比（Friedman 检验和成对比较的事后分析是使用Conover 方法完成的）。 *p < 0.01 *p < 0,01 по сравнению с исходным уровнем (критерий Фридмана и апостериорный анализ для парных сравнений были выполнены с использованием метода Коновера). *p < 0.01 compared to baseline (Friedman’s test and post hoc analysis for pairwise comparisons were performed using Conover’s method).
Regarding safety, two (13.3%) eyes developed a hyphema (approximately 1 mm) on the first postoperative day, which resolved completely within a week. Peripheral choroidal detachment occurred in three eyes (20.0%), which successfully resolved with medical therapy within one month. None of the patients required additional surgical intervention.
The data currently available evaluating the efficacy and safety of MicroShunt show promising results, albeit limited. 9-16 Surgeon experience and clinical outcomes are critical to the improvement and simplification of surgical technique.
In this article, we aim to demonstrate a faster, more consistent, and easier technique for implanting this device. Clinical data for the method was designed to look for early complications that may be associated with the method, and not to analyze its effectiveness.
The device has two side ribs, the theoretical function of which is to prevent possible side flow and movement of the MicroShunt. 6,8 Traditional methods involve the use of a triangular blade to create a shallow scleral pocket posterior to the limbus and 3 mm proximal to the limbus to accommodate these lateral fins. However, its length and the fact that the scleral pocket starts 3 mm from the limbus results in the device protruding significantly into the anterior chamber. Because of this, we rarely implant ribbed devices below the scleral pocket when using the classical technique to prevent overgrowth of the device in the anterior chamber.
With our technology, the stent is free to move and displace as the ribs are accessible under the Tenon capsule. However, it should be emphasized that no dislocation occurred in our sample.
The use of needles to create scleral tunnels for implanted drainage devices is nothing new. Albis-Donado et al. [17] reported good clinical outcomes in patients undergoing Ahmed valve implantation for glaucoma through a needle-created scleral tunnel without the use of a tube-covering patch.
In our technique, we used 25G with an outer diameter of 0.515 mm and a track length of 3 to 4 mm, which was sufficient to securely hold the device in place. Given the MicroShunt’s outer diameter of 0.35mm, using a smaller stylus can result in a more stable grip and less lateral flow. Needles 26 (0.466), 27G (0.413), or even 28G (0.362) can be used, but we have no experience with smaller diameter needles. Further medium- and long-term studies are needed to evaluate these options.
Another potential problem with this technique is scleral erosion. However, it should be noted that a similar technique using the 20G18 microvitreoretinal blade or the larger 22-23G17 needle has been described for Molteno implants without migration or erosion18 and Ahmed with minimal tube retraction (4/186). 17
The needle technique has several advantages over traditional transplant methods, such as a faster procedure, a flatter transition between the conjunctiva and the cornea, and a lower incidence of dellen and painful blisters. 17,18 In addition, both studies showed that the absence of corrosion was associated with a tight fit between the pipe and tunnel, resulting in less galling and wear. 17.18
In terms of safety, the rate of postoperative complications appears to be somewhat higher than reported in other articles, but it should be noted that we have taken special care to report even prosaic complications in this article, but none of these complications was of clinical importance.
Although the incidence of false tunnels has not been reported in previous studies9-16, this intraoperative complication may occur and cause the creation of another lateral tunnel, increasing the risk of hyphema and possibly taking up space. less favorable position.
This brief report has several limitations that need to be mentioned. Of these, the most important are the limited sample size, short follow-up time, and lack of a control group. However, this article describes a method that significantly improves the insertion of a microshunt with the same rate of intraoperative and early postoperative complications as with conventional methods. 9-16
In conclusion, the use of a needle to create an intrascleral pathway has shown promising results in this small group of patients. Its use can be especially useful when the presence of other equipment limits space. Further research is needed to determine the long-term stability of this technique and the potential benefits of smaller needles.
Medical writing and editorial services are provided by Antonio Martínez (MD), Ciencia y Deporte SL, with unrestricted funding from the University of Turin.
The authors would also like to thank A Mazzoleni, L Guazzone, C Caiafa, E Suozzo, M Pallotta, and M Grindi for their collaboration during the study.
Dr. Antonio M. Fea is a consultant for Glaukos, Ivantis, iSTAR, EyeD, and a paid consultant for AbbVie, in addition to the work presented. Dr. Earl R. Craven is currently an employee of AbbVie and reports personal expenses to Santen in addition to the work presented. The authors report no other conflicts of interest in this work.
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