1. Historical Development of Angle Surgery Techniques

Angle surgery, including goniotomy and trabeculotomy, have been historically utilized as first-line procedures in pediatric glaucomatous eyes without additional ocular or systemic abnormalities and with corneal diameters less than 14 mm. Goniotomy, first utilized in 1893, is the oldest surgical treatment option for congenital glaucoma, utilizing sharp instruments through a clear corneal incision to incise the trabecular meshwork for an arc of 110–120° opposite the corneal incision site [45]. This procedure allows for direct visualization of TM, more targeted cutting of abnormal tissue, and may be subsequently repeated. Goniotomy demonstrated success in management of congenital glaucoma; initial reports detailed an 80% success rate, defined by adequate IOP control without topical IOP lowering therapy ^[1]. Trabeculotomy (ab externo) was first described in 1960, and involved dissection through an incision radial to the limbus to unroof Schlemm’s canal using a trabeculotome to allow increased aqueous humor drainage ^[2]. In 1966, the procedure was modified to use an external scleral flap similar to trabeculectomy, and the trabeculotome was modified to have two parallel arms, one to guide direction of the trabeculotome, and the other to open Schlemm’s canal (now known as the Harm’s trabeculotome) ^[3]. Both goniotomy and trabeculotomy require pre-operative or intracameral miotic agents to reduce risk of lens damage during the procedure. When compared to goniotomy, trabeculotomy was found to have similar success rates, without a clear consensus on one procedure being superior to the other in management of congenital glaucoma ^[4]. Goniotomy has, however, demonstrated decreased success in patients with cloudy corneas, as well as patients beyond the first three years of life, which represents a great segment of patients with GFCS ^[5]. Trabeculotomy may be the procedure of choice in such patient populations. The outcomes of angle surgery in congenital glaucoma have been thoroughly described in the literature, but there are few studies that discuss outcomes of these procedures specifically in GFCS.

2. Goniotomy vs. Trabeculotomy as Initial Procedure

In Chen et al. (2004), it was noted that 24 out of 97 eyes with aphakic glaucoma received goniotomy or trabeculotomy with a success rate of 16.0%, as defined by IOP ≤ 21 mmHg with or without medications and no need for further surgery ^[6]. These results, however, were not stratified by goniotomy vs. trabeculotomy as initial procedure, and only 9 of these eyes had these angle surgery procedures alone. In addition, the degree of trabeculotomy and surgical method was not explicitly stated. In order to compare success rates between goniotomy and trabeculotomy in patients with GFCS, Bothun et al. (2010) conducted a retrospective case series consisting of 14 eyes with aphakic GFCS ^[7]. Patients with anterior segment dysgenesis, microcornea, and glaucoma at time of cataract surgery were excluded. Procedures were performed by 4 different surgeons between 1990 and 2006 in the US with 10 right eyes and 4 left eyes as operative eyes. Patients received a 180° goniotomy or trabeculotomy as initial surgery, with the lateral 180° manipulated on initial trabeculotomy (one patient, however, received 360° suture trabeculotomy, the rest received trabeculotomy with Harm’s trabectome). The procedure for each eye was chosen according to the different surgeons’ standard first choice at the time of the study. After the completion of each case, dexamethasone and cefazolin were given, and a combination antibiotic/steroid drop given for up to 1 month after the procedure, with all IOP-lowering drops discontinued post-operatively and reinitiated for IOP > 21 mmHg associated with increased optic disc cupping or axial length. Patients were aged 3 months to 9.5 years, with a median age of 3 years with initial surgery occurring at a median of 2.9 years after initial cataract surgery. Follow-up occurred for an average of 4.7 years after the procedure. Success was defined as IOP ≤ 24 mmHg with or without topical medication, lack of sight-threatening complication, and avoidance of trabeculectomy or tube shunt. 2 Eyes had goniotomy alone, 3 eyes had goniotomy followed by trabeculotomy and 9 eyes had trabeculotomy. Eight eyes achieved treatment success, with 6 eyes, achieving treatment success after one surgery (all of which received trabeculotomy first). IOP was lowered from an average of 35 mmHg preoperatively to 22 mmHg postoperatively (p = 0.0005). Three eyes needed subsequent shunt placement after the last angle surgery because of progression of glaucoma and uncontrolled cupping; all 3 of these eyes had goniotomy first. The only complication was a subretinal prolene suture passage which was removed uneventfully. Results were not given stratified by which initial procedure patients had, but the necessitation of future tube shunting procedures only in patients receiving goniotomy first hints at the increased success of trabeculotomy as a more promising initial surgical procedure for pediatric GFCS. The subsequently emerging literature on the topic is largely focused on trabeculotomy for management of pediatric GFCS.

3. Microcatheter Trabeculotomy

A variant of the rigid probe trabeculectomy, a 360° trabeculotomy was developed in 1960, and refined in 1995, in which a 6-0 polypropylene suture was passed through the 360° circumference of Schlemm’s canal with the attempts of yielding a lower IOP than with partial opening of the lumen ^[8][9]. An illuminated microcatheter is used to continuously demonstrate the location of the suture in the canal to aid in correct placement of the suture and prevent placement in the suprachoroidal space [61]. Among the first reports of this procedure in GFCS eyes (aside from the one eye that received this procedure in Bothun et al., 2010) was conducted by Beck et al., which was a retrospective case series investigating success of microcatheter-guided 360° trabeculotomy in 29 eyes with various glaucomatous processes, including 4 eyes with GFCS at an average age of 5 months [53]. While this study has limited power due to low sample size of the condition at interest, and there is little information about the subgroup of GFCS patients, such as laterality, and time after initial cataract surgery, it was seen that this procedure can eliminate the need for IOP lowering therapy (2 out of 4 eyes) and can lower IOP and prevent progression of GFCS (3 of 4 eyes) without devastating complication. Bothun and Hansen also described a case of a 5 month old child with GFCS who received 300° trabeculotomy with combined pars plana capsulotomy with anterior vitrectomy for retained cortical material 4 months after cataract surgery and experienced a decrease in IOP (<20 mmHg) and had no need for further surgery ^[10].

To further investigate the success in microcatheter-facilitated 360° trabeculotomy in GFCS, Dao et al. conducted a retrospective chart review of 13 GFCS eyes (all aphakic) and 10 JOAG eyes ^[11]. Patients with anterior segment anomalies, extensive synechiae, congenital glaucoma, < 6 months of post-operative follow-up, and additional surgeries planned during study period were excluded. All surgeries were performed at two sites by one of two surgeons Out of 13 total eyes, 8 were able to receive full 360° cannulation (62%), and 1 required a second site for full cannulation. Of the remaining 5 eyes, 1 had 270° cannulation opened with the catheter and 4 had 180° rigid probe trabeculotomy. Patients were an average of 3.1 years old and mean preoperative IOP was 35.4 mmHg (±3.9) on a median of 2.5 glaucoma medications, with post-operative IOP of 21.9 mmHg (±8.6, p = 0.0004). Average number of IOP lowering agents was decreased from 2.8 to 1.9, but this change did not meet statistical significance. Complications included transient hypotony with choroidal effusions, recurrent scleral cyst at cutdown site, localized Descemet scar, and 2 cases of vitreous hemorrhage both requiring pars plana vitrectomy (PPV). Failure occurred in 5 eyes, only one of which had received the 180° trabeculotomy.

A larger retrospective chart review on 360° trabeculotomy in medically refractory pediatric glaucomatous eyes was subsequently conducted by Lim et al. in 2017, including 25 GFCS eyes, of which, 21 were aphakic and 4 were pseudophakic ^[12]. Patients with prior surgery, prior suture trabeculotomy, coexisting ocular or systemic syndromes, and insufficient follow-up time were excluded. All procedures were performed by a single surgeon at an institution where 360° trabeculotomy was standard of care for medically refractory GFCS and JOAG. All trabeculotomy procedures were performed in a standardized fashion with utilization of the iTrack microcatheter (Iscience Interventional, Menlo Park, CA, USA). If the Schlemm canal was unable to be cannulated the full 360°, either goniotomy and/or trabeculotomy with Harms trabeculotome was to be performed instead. Subconjunctival dexamethasone and cefazolin were administered, the eye was dressed in antibiotic/steroid ointment and patched. Postoperative eyes were treated with antibiotic drops, pilocarpine, and steroid drops for several weeks, and follow-up was conducted at day 1, weeks 1 and 3, and every 3–4 months as deemed medically appropriate. Success was defined as IOP ≤ 22 mm, or IOP reduction > 20% from baseline, with or without topical glaucoma medications, and without additional glaucoma surgery or devastating complications. Median patient age was 3.4 years of age, and the average length of follow-up was 31.9 months. Time since cataract surgery was not reported. Average pre-operative IOP was 31.5 (±7.5) mmHg, and patients were on an average of three drops pre-operatively. Post-operative IOP subsequently lowered to 19.7 mmHg (15.6 in eyes that achieved success, p < 0.001), and patients were on an average of 2.4 drops postoperatively (p = 0.015). No devastating post-operative complications occurred. These data suggest that microcatheter-assisted 360° trabeculotomy is a safe and effective initial surgical procedure for management of GFCS.