Microinvasive Glaucoma Surgery in Children

Microinvasive Glaucoma Surgery in Children

December 30, 2021

Pediatric glaucoma is a potentially sight-threatening disease and is considered the second leading cause of treatable childhood blindness.

Pediatric glaucoma is a clinical entity including a wide range of conditions: primary congenital glaucoma, glaucoma secondary to ocular (e.g., aniridia, Peter’s anomaly), or systemic disease (e.g., Sturge Weber) and glaucoma secondary to acquired condition (pseudophakic, traumatic, uveitic glaucoma).

The treatment algorithm of childhood glaucoma is a step-by-step approach, often starting with surgery, as in primary congenital glaucoma cases. Medical therapy is also crucial in the management of pediatric glaucoma.

Surgery is the first-line approach for the management of congenital glaucoma and is the mainstay in the childhood glaucoma treatment algorithm in patients showing an uncontrolled IOP despite medical therapy and progressive disease, despite an apparently controlled IOP.

Angle surgery is generally the first choice for the management of primary congenital glaucoma. The goal of this approach is to overcome the increased resistance to aqueous outflow due to trabecular dysgenesis. Angle surgery includes goniotomy and trabeculotomy.

Childhood glaucoma constitutes less than 0.1% of diagnoses in ophthalmic patients but is responsible for approximately 18% of blindness in schools for the blind. 

This rare, heterogeneous group of diseases can severely affect the developing visual system, as well as result in significant psychosocial and financial stress to both patients and families. Surgery is the first-line treatment in most cases, rather than conservative medical or laser therapy.

Angle surgery is often the preferred initial procedure, followed by glaucoma drainage devices (GDD) or other filtering surgery if intraocular pressure (IOP) remains uncontrolled.

The IOP-lowering effect of glaucoma surgery decreases with time, and multiple surgeries are often needed over a child’s lifetime for adequate IOP control.

Preserving conjunctival tissue during the initial surgery is important and could increase the chance of success with subsequent surgeries.

Further, traditional glaucoma surgery, such as GDD implantation and trabeculectomy, are associated with complications that are less readily detected and managed in children than in adults.

In 2012, Saheb and Ahmed defined microinvasive glaucoma surgery (MIGS) as having 5 features: an ab-interno microincisional approach, minimal tissue trauma, modest efficacy, rapid recovery, and a high safety profile.

These qualities make MIGS procedures attractive, conjunctiva-sparing options for the treatment of childhood glaucoma.

As of December 2021, there were no randomized clinical trial data available on the safety and efficacy of the various MIGS procedures in children, limiting their applicability.

The surgeon must consider efficacy, etiology, disease severity, corneal clarity, angle status, and cost.

Trabecular Incising Procedures

Based on the Saheb and Ahmed criteria, goniotomy was likely the original MIGS performed for childhood glaucoma. It has been used since the 1940s and is considered safe, simple, and efficacious. 

The electrosurgical trabeculectomy device (Trabectome; Neomedix Corporation) and dual blade trabeculectomy device (Kahook Dual Blade [KDB]; New World Medical) enhance traditional goniotomy by ablating or excising, respectively, the trabecular meshwork (TM) and inner wall of Schlemm’s canal.

It is performed similarly to goniotomy, whereby under direct gonioscopic visualization, the device is inserted through a clear corneal incision and passed across the anterior chamber to engage the TM. Approximately half of the angle can be treated.

These devices have a theoretical decreased risk of scarring-related closure of the trabecular cleft compared to goniotomy.

In a retrospective study examining Trabectome results at 72 months in 11 eyes of 8 patients age 26.8±7.7 years with childhood glaucoma, the baseline IOP was 30.5±7.8 and was maintained at 18.1±6.8 at 1 year and 16.8±2.5 at 6 years. 

In a prospective cohort study examining Trabectome outcomes in 60 eyes of 60 patients 30±8 years old with juvenile open angle glaucoma (JOAG), eyes with no prior history of surgery had an IOP reduction of 10.6 mmHg at 12 months from a baseline of 27.4 mmHg.8 KDB has been reported in case reports without long-term follow-up. 

Of note, the Goniotome is similar to the Trabectome electrosurgical trabeculectomy device, but no literature exists regarding its utility in childhood glaucoma patients.

Gonioscopy-assisted transluminal trabeculotomy (GATT) permits ab-interno circumferential angle incision without violation of the conjunctiva or sclera. Following a clear corneal incision, a traditional goniotomy incision is made in the TM.

Next, a filament (either a blunted polypropylene suture or illuminated microcatheter [iTrack; Nova Eye Medical]) is threaded through the goniotomy into Schlemm’s canal using intraocular microforceps.

The filament is advanced through the entire canal, and then the 2 ends of the filament are pulled to rupture the inner wall of Schlemm’s canal and create a circumferential incision of the TM.

In a retrospective series of 14 eyes of 10 patients ages 17 months to 30 years old with PCG and JOAG patients who underwent GATT, the mean IOP decreased from 27.3 mmHg to 14.8 mmHg after surgery, and all eyes in the study remained a clinical success for longer than 12 months.

Research suggests that circumferential angle treatment is superior to partial treatment with various devices/procedures.

In a retrospective study comparing 64 eyes of 38 patients ages 0.23 months to 14.2 years old with PCG who underwent circumferential trabeculotomy vs goniotomy as the initial procedure, the IOP was controlled in 92% of eyes in the trabeculotomy group and 58% in the goniotomy group through approximately 4 years to 9 years of follow-up.

Ab-interno viscocanalostomy/canaloplasty uses viscoelastic to dilate collector channels and Schlemm’s canal, and it may be advantageous in cases with post-trabecular outflow obstruction.

The OMNI surgical system (Sight Sciences) is a single-use, disposable handpiece that combines the VISCO360 and TRAB360 capabilities for cannulation and viscodilation of Schlemm’s canal, and can mechanically disrupt the TM.

After creation of a traditional goniotomy, the device is advanced to the opposite angle, and the retractable filament is deployed into approximately 6 clock-hours of Schlemm’s canal. Upon retraction, viscocanalostomy occurs.

The filament is then redeployed into the same 6 clock hours, then pulled into the anterior chamber to incise approximately 180° of the angle. The procedure is then repeated in the opposite direction, creating a pseudocircumferential ab-interno trabeculotomy.

The illuminated iTrack microcatheter is also capable of viscocanulostomy. There is no high-quality evidence on the effect of canaloplasty in childhood glaucoma.

However, a recent case report described the potential role of OMNI in a 4-month-old patient with congenital glaucoma associated with Sturge-Weber syndrome.

The patient’s IOP remained controlled without adjunctive medical therapy through 10 months of follow-up. The authors postulated that viscodilation of Schlemm’s canal and collector channels would be useful in addressing the post-trabecular outflow obstruction in some secondary open-angle glaucomas.

Trabecular Bypass With and Without Bleb-forming Procedures

The Xen gel stent (XEN45, Abbvie) is a transcamerally placed device of fixed channel size that shunts aqueous from the anterior chamber to a perilimbal bleb. This may offer an alternative to trabeculectomy or tube shunt surgery, with a fixed channel size decreasing the risk of hypotony.

There are a few case reports that found success with Xen in childhood glaucoma. However, no higher quality evidence exists regarding the long-term safety profile or efficacy compared with traditional bleb-forming procedures in children.

Other trabecular bypass devices, such as the iStent (Glaukos) and Hydrus microstent (Ivantis) similarly have no outcomes data in children, so there is unknown benefit.

Suprachoroidal shunts like the iStent Supra (Glaukos), which is not FDA approved as of 2021, are unlikely to outperform trabecular-incising surgeries, and also have no outcomes data in children.

Other MIGS Procedures

There is no consensus on the optimal surgical approach for angle closure in children and young adults. Goniosynechiolysis (GSL) under direct gonioscopic visualization is postulated to result in decent IOP reduction without GDD implantation or other more invasive procedures.

Goniosynechiolysis can be performed alone or in combination with lensectomy or endoscopic cyclophotocoagulation (ECP).

In a retrospective review of 11 eyes of 7 patients that examined the safety and efficacy of lens extraction with GSL in patients younger than 40 with angle-closure glaucoma, authors found that all patients were able to discontinue glaucoma medications and achieve significant improvements in IOP and visual acuity without requiring a bleb-forming procedure. 

This procedure meets the 5 criteria to define MIGS. Goniosynechiolysis is performed with microforceps through a clear corneal incision, while the surgeon gently peels the anterior synechiae open. Once the TM is visible, additional angle surgery can be considered.

Endoscopic cyclophotocoagulation is the only MIGS that does not require direct visualization of the angle through the surgical microscope.

Cyclodiode laser in childhood glaucoma patients can be considered a safe alternative for patients with high risk of surgical complications or poor visual prognosis. 

In a large, single-center cohort study examining ECP treatment in 80 eyes of 70 patients with childhood glaucoma following cataract surgery (60%), anterior-segment dysgenesis (13%), primary congenital glaucoma (9%), or other childhood glaucoma (19%), success for a single ECP treatment at 1, 3, and 5 years was 64%, 36%, and 16%, respectively.

Additional sequential ECP improved 1-, 3-, and 5-year success to 81%, 49%, and 34%, with a median time to failure of 2.9 years.

The mean patient age was 9.5±6.0 years old (range, 0.2-22.9), and 7 patients were older than 18 years at the time of initial ECP. 

A separate study of modest size (35 eyes of 24 patients under 16 years of age) found the success rate of ECP in childhood glaucoma following cataract surgery to be 54% after a mean of 7.2 years of follow-up.

The type of glaucoma may impact efficacy of some MIGS procedures in children, but further research is needed to evaluate this hypothesis.

Ab-interno trabecular-incising procedures, circumferential when possible, are the preferred initial treatment when the glaucoma involves an open angle, whereas GSL, with or without lensectomy or ECP, may be offered when the angle is closed.

There is no evidence to recommend MIGS procedures that leave permanent hardware. Minimally invasive glaucoma surgery offers conjunctiva-sparing alternatives to traditional glaucoma surgery, which is particularly important in the lifelong treatment of childhood glaucoma.

However, these procedures must be used with caution and with proper patient selection in the setting of no long-standing safety profile or large-scale clinical data.