Nonpenetrating deep sclerectomy: Challenges, innovations, and current evidence

Abstract

Nonpenetrating deep sclerectomy (NPDS) was initially developed back in 1989. The procedure stands out in the field of glaucoma for its significant safety profile and good efficacy. Unlike other surgical alternatives, evidence has noted that NPDS results in a controlled and gradual reduction of intraocular pressure. The purpose of this literature review is to summarize the technique, challenges posed, current innovations, and overall outcomes mentioned in the literature on NPDS for various types of glaucomas and its various disease stages.

Introduction

Nonpenetrating deep sclerectomy (NPDS), first described by Fodorov and Koslov in 1989, stands out in the field of glaucoma surgery due to its efficacy and significant safety profile. Unlike traditional penetrating procedures, NPDS allows for a controlled and gradual reduction of intraocular pressure (IOP) during the surgical process. This slow decompression minimizes the risk of complications often associated with rapid changes in IOP, such as hemorrhagic events affecting the retina and choroid.[1,2]

One of the most compelling benefits of NPDS is its remarkably low risk of late intraocular infections. This aspect, along with the aforementioned advantages, has led to a growing interest among surgeons in nonpenetrating glaucoma surgery (NPGS) as a preferred option for managing different types of glaucoma.[3]

NPGS effectively lowers IOP by facilitating the flow of aqueous humor through an intact trabeculo-Descemet’s membrane (TDM). This flow occurs after the unroofing of Schlemm’s canal (SC) and the excision of the deep scleral tissue, which includes peripheral corneal tissue at the surgical site. Among the various procedures classified as NPGS, deep sclerectomy (DS) and viscocanalostomy (VC) are the primary techniques utilized.[1]

NPDS is generally indicated in open-angle glaucoma types: primary open-angle glaucoma (POAG), juvenile open-angle glaucoma (JOAG), pediatric glaucomas, and certain types of secondary glaucomas such as pseudoexfoliation, pigmentary, and steroid-induced glaucomas.

Surgical Anatomy

The surgical limbus is a transition zone having a blue–gray appearance when viewed externally after the conjunctiva has been reflected away from the limbus. The limbal blue–gray zone runs circumferentially over 360° with a width of about 1.2 mm between the white criss-cross fibers of the sclera posteriorly and the transparency of the cornea anteriorly. The posterior border of the blue–gray zone is the most consistent external limbal landmark of internal structures. It corresponds to the internal junction of the cornea and sclera which usually overlies the anterior trabecular meshwork (TM). Under a scleral flap, the blue–gray transition zone is relatively displaced posteriorly compared to the appearance through the full limbus thickness. The tissue appears gray over the trabeculum giving way to clear cornea at about the level of Schwalbe’s line. At a deeper level (about 90%), advancing from the sclera to the cornea, a well-delineated white line is encountered that roughly corresponds to the level of the scleral spur, just anterior to this white line lies the SC. After unroofing of SC, the TM will be visible. Identification of the scleral spur facilitates the peeling of the inner wall of SC.

Therefore, during the deep flap dissection, the following structures are visible from the sclera towards the cornea, (A) scleral spur, (B) SC, (C) TM, (D) Schwalbe’s line, and (E) Descemet’s membrane [Figure 1].[4]

Figure 1.

Anatomical landmarks during deep sclerectomy

How Does Nonpenetrating Glaucoma Surgery Reduce the Intraocular Pressure?

NPDS and VC are glaucoma surgical procedures, in which the natural anatomical angle structures for aqueous drainage are not penetrated nor excised. In both procedures, the exposed TDM, after unroofing of the SC, allows gradual filtration of aqueous humor from the anterior chamber (AC). Following its passage through the TDM, the aqueous humor resorption takes place through four hypothetical pathways: (A) intrascleral bleb, (B) subconjunctival filtration, (C) suprachoroidal space, and (D) episcleral drainage via SC ostia.[5]

Surgical Technique

A 7/0 Vicryl superior corneal traction suture is placed to allow proper exposure. A 0.1 ml of diluted mitomycin-C (MMC) (0.04mg–0.1mg/ml) is injected into the superior sub-tenon’s space and massaged throughout the whole region using a cellulose sponge. A fornix-based conjunctival incision is prepared, and blunt superior dissection is carried out to open the upper sub-tenon and sub-conjunctival spaces. Tenon’s layer is not excised unless it is very fleshy and redundant; in which case, it can be trimmed. Diathermy is applied to the bleeders as necessary. A large superficial scleral flap, 5 mm in width, is dissected using a crescent blade. Dissection is carried out forward till the corneal periphery is exposed. The flap can be placed at 12 o’clock or decentered nasally; care must be taken to avoid premature entry into the AC.

A second, smaller scleral flap is then dissected deeper to the superficial flap. Dissection begins at the distal end, possibly with exposure of the ciliary body or the choroid at the right posterior corner, then dissection is continued proximally. It is important to dissect as deep as possible leaving a thin scleral layer that transmits the blue color of the underlying ciliary body and choroid. The tip of the knife is oriented slightly upward during the forward dissection to avoid AC entry. Diathermy can be applied at this stage as well to ensure adequate hemostasis. The important landmark at that point is the scleral spur, being identified as a sharp white line that bounds the sclera proximally. Immediately anterior to the scleral spur, the SC posterior aspect is incised, exposing the TM, and the percolation starts. A dry cellulose sponge is used to wipe the TM cells and enhance further percolation. The floor of SC is peeled using fine forceps if needed [Figure 2]. The anterior landmark is Schwalbe’s line, which bounds the end of the dissection; this will expose the percolating TDM. A dry cellulose sponge is usually used to separate the TDM from the overlying corneal tissue. The deep flap is then excised [Figure 3], and the superficial flap is tightly sutured. Conjunctiva is then closed with inverted 10/0 nylon sutures. Rounded needles are very helpful to avoid conjunctival buttonholes. The wound is tested for any leak, and a combination of gentamycin and dexamethasone is injected into the inferior conjunctival fornix.[1,6]

Figure 2.

Peeling of the floor of Schlemm’s canal

Figure 3.

The deep scleral flap is excised, and the aqueous is percolating through the trabeculo-Descemet’s membrane

NPDS has a steep learning curve, which is attributed to the challenges of identifying SC intraoperatively; dissections above and below SC plane are not desirable. Besides that, the surgeon should be able to manage the IOP postoperatively, should the IOP become elevated above the patient’s target pressure.

In case, the IOP becomes elevated postoperatively, goniopuncture is performed using yttrium aluminum garnet [YAG] laser to create a full-thickness hole through the TM. Other causes of elevated IOP are excluded before goniopuncture [Figure 4]. Goniopuncture is associated with significant IOP reduction. The most frequent post-goniopuncture complication is iris prolapse [Figure 5].[7] Figure 6 shows the flow chart of elevated IOP after NPDS.

Figure 4.

The trabeculo-Descemet’s membrane, seen through gonioscopy, and the site of goniopuncture are marked by the asterisk

Figure 5.

The pupil is peaked due to iris prolapse following yttrium aluminum garnet goniopuncture

Figure 6.

The flow chart for management of elevated intraocular pressure after nonpenetrating deep sclerectomy

Challenges and Innovations

The common concerns with NPGS include:

• (1) How to make SC identification easier?

• (2) How to keep the cut ends of the SC patent postoperatively to enhance the internal drainage through the circumference of the canal? and

• (3) How to keep the decompression space open as anti-metabolites alone might not sufficiently achieve this goal.[8]

An essential step in NPGS is the proper dissection of the deep scleral flap to end up in a sufficiently percolating TDM. Deep dissection will leave almost up to 10% of the sclera over the uvea. In this way, SC will be deroofed with subsequent exposure the anterior trabeculum, Schwalbe’s line, and peripheral Descemet’s membrane. Thus, the outer wall of SC should be included in the excised deep flap. Dietlein et al. reported that NPDS, even when performed by an experienced glaucoma surgeon, might not show the SC endothelium.[9] They found out that 48% of the examined deep flaps specimens did not show SC endothelium, indicating the absence of proper unroofing.

To facilitate SC identification, Trabeculotome-guided unroofing of SC was introduced, a step that could be applied to all NPGS procedures. Simply, the Trabeculotome (Katena) is preplaced inside the SC before deep scleral flap fashioning, and canal unroofing is facilitated and guided by the instrument.[10] The Trabeculotome-guided approach was evaluated through a prospective study on 15 eyes with various types of glaucoma, SC endothelium was identified in all the examined specimens. Clinically, the mean IOP was reduced from 26.66 ± 4.54 mm Hg to 12.2 ± 3.5 mm Hg at the end of a mean follow-up of 9.4 ± 2.9 months.[11]

The next concern was the ability to keep SC ends patent postoperatively; this was accomplished using a 10 mm long segment of polypropylene 5/0 (Ethicon, Somerville, NJ, USA) was used to stent both cut ends of SC, Prolene canalo-stenting procedure. We reported a statistically highly significant drop in the mean IOP and the anti-glaucoma medications. YAG laser goniopuncture (LGP) was not required in any case.[12]

Sutureless DS (SDS) was introduced in 2017.[13] In this procedure, no sutures were added at the conclusion of the surgery, neither to the superficial scleral flap nor to the conjunctiva. The conjunctival edges were made adherent using low-power diathermy [Figure 7].

Figure 7.

The conjunctival edges are approximated with low-power diathermy in sutureless deep sclerectomy

A statistically significant reduction of the IOP was reported during all the follow-up visits without serious complications. The mean preoperative IOP was 31.72 ± 10.71 mm Hg and 15.07 ± 3.22 mmHg 6^th months postoperatively. The mean IOP was reduced 47% ± 24.9% compared with the preoperative IOP. The mean preoperative medication was 2.88 ± 1.36 and was reduced to 0.29 ± 0.469 at the 6^th postoperative month.

A temporary dellen in one eye, Tenon cysts in two eyes, minimal conjunctival recession in one eye. No otherwise serious complications were reported.

The hypothesis behind SDS is that NPDS a low-flow filtration filtration surgery with mild diffuse conjunctival elevation, so the conjunctival edges remain adherent, without retraction, under the adhesive effect of the low-power diathermy. Additional advantages of SDS include shorter operative time, no ocular irritation by the sutures, no need for conjunctival suture removal which may be difficult in some patients, and obviously slightly more economical.[13]

Through a prospective interventional study on 84 eyes in POAG and JOAG, SDS achieved a statistically significant reduction in IOP compared with the preoperative IOP (mean IOP = 26.21 ± 10.46 mmHg) starting from 1^st postoperative day (mean IOP = 7.18 ± 1.8 mmHg) till the end of follow-up period at 2 years (mean IOP = 15.85 ± 4.46) (P < 0.001). Furthermore, the number of medications dropped significantly from 3.27 ± 1.14 to 0.82 ± 0.97 at the end of follow-up period.[14]

In another interventional study that compared SDS (Group A) to conventional DS (Group B) on 60 eyes with POAG. Both surgeries showed significant reduction of IOP all through the study period: in Group A, mean reduction was 71.37%, 53.35%, 50.3%, and 44.33% at 1^st day, 1 month, 3 months, and 6 months, respectively, and in Group B, mean reduction was 57.62%, 40.63%, 37.41%, and 31.68% at 1^st day, 1 month, 3 months, and 6 months, respectively. Comparison between the percentage of reduction in both groups showed no statistically significant difference.[15] Another modification was the use of fibrin glue as a sealant to the conjunctival edges.[16]

In 2020, a novel simple economical step was introduced that enhances the efficacy of DS in lowering the elevated IOP by adding a sub-flap mattress 10/0 Nylon suture after excision of the deep scleral flap (Ahmed’s suture). Initially, we obtained additional 12.5% reduction in the IOP compared to the standard surgery.[17]

In the literature, various attempts have been made to preserve the scleral space under the superficial scleral flap: collagen implants, reticulated hyaluronic acid implant, nonabsorbable hydrophilic acrylic implant, and viscoelastic implant.[18,19] Many of those modifications are costly and not available in our practice. Other NPDS-enhancing procedures include antimetabolites, Canaloplasty with insertion of a circumferential tightening Prolene 10/0 was also described.[20] Other reports described adding trabeculectomy[21] and trabeculotomy.[22]

The surgical details are available in the literature.[17] In summary, A 10/0 nylon suture (Ethilon)^® mattress suture that extended 2 mm beyond the superficial scleral flap edge was secured under the flap [Figures 8a, b and 9]. The suture is non-absorbable and widely available.

Figure 8.

(a) The transverse mattress 10-0 nylon sub-flap Ahmed’s suture, (b) Ahmed’s suture seen with the gonioscope, The arrow points to the black 10/0 nylon suture being visible during gonioscopy

Figure 9.

Dimensions measured by the UBM: (a) Bleb length: whole anteroposterior length of the conjunctival bleb. - bleb height: the height of the conjunctival bleb. (b) lake length: antero-posterior length of the intrascleral lake. - lake height: the height of the intrascleral lake.[23]

The enhanced IOP-lowering effect Ahmed’s suture is explained by the following mechanisms: (1) the mechanical elevation of the proximal part of the superficial scleral flap, which in turn enhances the aqueous percolation, (2) the slight elevation of the scleral flap, without sutures at the edges, would induce some tissue separation, thereby enhancing aqueous movement to the subconjunctival space, and (3) tightening the suture by the tangential traction to the limbus would widen the TDM. 4-the proximal limb lies of the suture lies in the SC; this helps visualization of the TDM should YAG goniopuncture is needed [Figure 8b].

Through a randomized controlled study comparing 52 eyes with a sub-flap Ahmed’s suture modified NPDS (Group A) and 51 with a conventional NPDS (Group B). Success of surgery was categorized as complete success if the IOP remained between 6 and 18 mmHg without medications and as qualified if topical medications were required.

The postoperative IOP at the 1^st week, 3^rd, 6^th, 9^th and 12^th-month follow-ups in Group A were significantly lower (7.3 ± 2.1, 12.0 ± 2.3, 12.6 ± 2.7, 13.6 ± 3.4 and 13.8 ± 3.8 mmHg) than in B (9.2 ± 1.9, 14.0 ± 3.1, 14.8 ± 2.9, 15.4 ± 2.6 and 15.7 ± 2.7 mmHg) (P = 0.001, P = 0.001, P = 0.002, P = 0.027, and P = 0.029, respectively). The percentage of IOP reduction after 1 year was significantly higher in Group A than in Group B (49% vs. 36.5%). At the end of the 12-month follow-up, 81% of Group A and 69% of Group B were considered complete success. The study concluded that adding Ahmed’s suture is 30% more effective in reducing the IOP.[23]

In a more recent publication, forty eyes with open-angle glaucoma were assigned randomly into two groups: Group A underwent DS with Ahmed’s sub-flap mattress suture. Group B underwent conventional DS. Patients were followed up closely for 6 months with serial IOP measurements, and ultrasound biomicroscopy (UBM) was used to assess the surgical site functionally and anatomically at the 1^st and 6^th month.

Adding Ahmed’s sub-flap mattress suture improved the IOP-lowering effect of DS significantly from 43% in Group B to 53% in Group A at 6 months (P = 0.027). IOP in Group A was at 1 week, 1 month, and 6-month visits (7.9 ± 1.3, 11.7 ± 2.2, and 13.3 ± 1.9 mmHg, respectively) compared to Group B (10.1 ± 4.6, 14.1 ± 5.2, and 16.8 ± 4.1 mmHg, respectively) (P = 0.025, 0.041, and 0.001, respectively). UBM parameters were significantly larger in Group A at 1 and 6 months. Strong statistically significant negative correlations were established between IOP and all the UBM parameters apart from intrascleral lake height at the 1^st and 6^th months (P < 0.01 in all of them). Finally, significant correlations were found between IOP at 6 months and whole bleb anteroposterior length and height at 1 month (P = 0.001) [Figures 9 and 10].[24]

Figure 10.

Mean intraocular pressure follow-up chart[23]

Deep Sclerectomy Outcomes

In a large meta-analysis that included five studies with a total of 311 eyes (247 participants), of which 133 eyes (participants) were quasi-randomized. One hundred and sixty eyes that had trabeculectomy were compared to 151 eyes that had NPGS (of which 101 eyes had DS and 50 eyes had VC). The authors concluded that the review provides some limited evidence that control of IOP is better with trabeculectomy than VC. For DS, they could not draw any useful conclusions.[25]

Correia Barbosa et al.[26] reported that deep nonpenetrating sclerectomy showed a slightly lower long-term hypotensive effect compared to standard trabeculectomy, with significant differences at 12 months but not at 24 months of follow-up. The absolute and qualified success rates were 51.85% and 65.43% for the trabeculectomy group and 50.83% and 60.83% for the deep nonpenetrating sclerectomy, without significant differences. Regarding postoperative complications, mainly due to postoperative hypotonia, or related to the filtration bleb, they were significantly different between groups, with 10.8% and 24.7%, in deep-nonpenetrating sclerectomy and trabeculectomy groups, respectively. The authors concluded that deep non-penetrating sclerectomy seems to be an effective and safe surgical option for patients with open-angle glaucoma unable to be controlled by non-invasive strategies, and the data suggest that the IOP-lowering effect of this technique may be marginally lower than that of trabeculectomy, but the achieved efficacy outcomes were similar, with a significantly lower risk of complications.

In a retrospective study results 80 eyes of 69 patients underwent DS, with a mean follow-up period of 53.5 months. The mean preoperative IOP was 23.55 mmHg (range 11–52, standard deviation [SD] 8.46); the mean final IOP was 13.61 mmHg (range: 5–35, SD 4.73), with a mean reduction of 42.21%. The mean change in glaucoma medications was −1.64. 78.40% experienced a reduction in glaucoma treatment. Postoperatively, 43.80% had no complications; this improved to 85.0% when numerical hypotony and raised IOP without visual sequelae were excluded. Further procedures required included Nd: YAG goniopuncture (10%), bleb needling (13.75%) or revision (7.5%), iridectomy (3.75%), goniosynechiolysis (1.25%), and autologous blood injection (1.25%). Two eyes were converted to trabeculectomy perioperatively, with seven overall (8.75%) requiring trabeculectomy over the course of follow-up. 3.75% underwent glaucoma drainage device implantation, and 3.75% underwent cyclodiode laser. The authors concluded that DS is a safe, effective procedure for selected patients where trabeculectomy has a high likelihood of failure or where a higher IOP can be tolerated.[27]

In a retrospective cohort study that reported the incidence, risk factors, and long-term outcomes of LGP in patients with previous DS. 1765 eyes (1385 patients) underwent DS with or without cataract surgery between 2001 and 2020 in two UK institutions. Kaplan–Meier was used to estimate LGP incidence. DS success after LGP was calculated for criteria A, B, and C defined as IOP of ≤18, ≤15, and ≤12 mm Hg with 20%, 25%, and 30% reduction, respectively.

LGP had an estimated incidence of 33.3% (30.9%–35.6%), 56.3% (53.5%–58.9%), and 62.8% (59.7%–65.6%) at 1, 3, and 5 years, respectively. Mean (± SD) IOP significantly (P < 0.001) decreased from 21.2 (±6.0) mm Hg pre-LGP to 13.8 (±5.2) mm Hg and 12.9 (±4.7) mm Hg at 3 and 5 years post-LGP, respectively. Success rates at three and 5 years were, respectively, 40.9% (37.5%–44.6%) and 33.7% (30.3%–37.6%) for criterion A; 27.1% (24.0%–30.5%) and 22.3% (19.3%–25.7%) for criterion B; and 13.9% (11.6%–16.7%) and 11.6% (9.5%–14.3%) for criterion C. In all models, higher pre-LGP IOP (P < 0.001) and higher pre-LGP medication number (P < 0.001) were associated with increased failure, while male gender (P ≤ 0.004), intraoperative MMC (P ≤ 0.031), longer interval between DS, and LGP (P ≤ 0.01) with reduced failure.[28]

Outcomes of Nonpenetrating Glaucoma Surgery in Childhood and Juvenile Glaucoma

NPGS has been suggested as a surgical option in childhood glaucoma, based on its high safety profile with a lower incidence of intraoperative and postoperative complications, including hypotony, ischemic avascular blebs, and intraocular infection. Despite the high safety profile, it has not been widely adopted in children being technically challenging in buphthalmic eyes with thin sclera.[29]

Alkhalifah et al. evaluated 83 eyes of 68 patients. The mean (SD) age of participants was 11.1 (4.0) years (range: 5–25 years). The mean age at surgery was 5.9 months, and the mean follow-up period was 10.75 years. The majority of cases (83.1%) were primary congenital glaucoma. Visual acuity was ≥20/40 in 56.6% of cases, ranged between 20/40 and 20/200 in 18.1%, and was ≤20/200 in 25.3% of the operated eyes. Complete success rate (IOP ≤ 21 mmHg without medications) after one surgery was achieved in 53 eyes (63.86%). Qualified success rate (IOP ≤ 21 mmHg with medications) was achieved in 8 eyes (9.6%), while 22 eyes (26.5%) failed to achieve the target IOP of ≤21 mmHg or needed additional surgery to achieve it. Nine eyes (10.74%) had postoperative complications. The authors concluded that DS is a reasonable option for pediatric glaucoma that can provide good long-term visual outcomes and IOP control with a lower risk of surgical complications.[30]

In the retrospective study by Alharbi et al. who evaluated the safety and efficacy of MMC-augmented DS in 50 eyes (37 patients) with JOAG, with a mean age of 27.1 ± 11.3 years at the time of surgery. They reported a significant reduction in the mean IOP from 26.1 ± 13.4 mmHg on 3.8 ± 0.5 glaucoma medications at baseline to 15.2 ± 6.4 mmHg on 0.8 ± 1.2 medications at the last follow-up visit. Success was defined as postoperative IOP of 6 mmHg or more and below 18 mmHg. They reported success rates of 94% at 12 months, 85% at 24 months, and 72% at 36 months. The authors reported no vision-threatening complications; however, four eyes had postoperative hypotony.[31]

The literature has shown some other forms of childhood glaucomas that benefited from the NPGS, including Sturge–Weber Syndrome,[32] steroid-induced glaucoma,[33] and Aniridia-associated glaucoma.[34]

Regarding childhood glaucoma:

• (1) Originally, congenital and juvenile glaucomas were considered relative contraindications to NPDS. Later, the scientific evidence has shown relatively good results with NPDS, but the literature is lacking large controlled clinical trials and meta-analyses. Accordingly, evidence-based recommendations are yet to be determined

• (2) Goniopuncture which is an ancillary procedure performed if the postoperative IOP is not adequately controlled or elevated, is not an option in young children. Other measures could take over, like subconjunctival needling

• (3) There is a growing appreciation for combination procedures; DS-Trabeculotomy and VC-Trabeculotomy, and

• (4) In the author’s opinion (unpublished data), NPDS is more effective when combined with trabeculotomy in various stages of childhood glaucoma. [29]

Conclusion

NPDS is a valuable procedure for reducing IOP and minimizing reliance on medications in various forms of open-angle glaucoma. Its safety profile is notably high, both during and after the surgery, making it an appropriate option for patients across all stages of the disease. This is especially critical in advanced stages where complications such as sudden globe decompression and postoperative hypotony can lead to significant and serious long-term effects. Moreover, juvenile and pediatric patients are also well suited for this procedure, especially when combined with various modifications and approaches tailored to their needs.

The evolution of NPGS has seen numerous technique enhancements, elevating the overall success rates, cost-effectiveness, and patient comfort. These advancements underscore the potential of NPDS as an integral part of glaucoma management, facilitating better outcomes for patients in diverse demographics and disease stages.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.