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Abstract
Background/aims To introduce a novel ab interno 360° trabeculotomy for treating primary congenital glaucoma (PCG) and juvenile open angle glaucoma (JOAG) and report preliminary results.
Methods A retrospective chart review of patients who underwent a gonioscopy assisted transluminal trabeculotomy (GATT) procedure by four of the authors (DSG, OS, RLF and DGG) between October 2011 and October 2013. The surgery was performed in patients ≤30 years old with a dysgenic anterior segment angle and uncontrolled PCG and JOAG.
Results Fourteen eyes of 10 patients underwent GATT with follow-up >12 months (12–33 months; mean 20.4). Patients ranged in age from 17 months to 30 years (mean=18.4 years), and five (50%) were female patients. No complications occurred during or following surgery except for early postoperative hyphema in five (36%) of eyes, all cleared by 1 month. The mean intraocular pressure (IOP) decreased from 27.3 to 14.8 mm Hg and the mean number of medications required decreased from 2.6 to 0.86. Five eyes had a drop in IOP ≥15 mm Hg (range 15–39).
Conclusions The preliminary results and safety for GATT, a minimally invasive conjunctival sparing circumferential trabeculotomy, are promising and at least equivalent to previous results for ab externo trabeculotomy for the treatment of PCG and JOAG. All eyes in the study were considered a clinical success.
- Angle
- Glaucoma
- Intraocular pressure
- Treatment Surgery
- Child health (paediatrics)
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Introduction
Since the 1960s, the popularity of trabeculotomy ab externo for the treatment of developmental glaucoma has continued to rise. Several paediatric glaucoma specialists consider 360° circumferential trabeculotomy ab externo as their initial surgical treatment for primary congenital glaucoma (PCG) and juvenile open angle glaucoma (JOAG).1–3 Trabeculotomy lowers intraocular pressure (IOP) by improving the flow of aqueous through Schlemm's canal and adjacent collector channels without bleb formation.4–8 This bleb-less technique is especially desirable in children who would otherwise be subject to a lifetime risk of blebitis and endophthalmitis if a trabeculectomy was to be performed. Over the past two decades, improvements in trabeculotomy include circumferential suture techniques1–3 and a flexible illuminated microcatheter (iTrack, Ellex, Menlo Park, California, USA), which aids in the identification and cannulation of Schlemm's canal.9 ,10
Currently, the most common approach to circumferential trabeculotomy is ab externo, which requires an extensive conjunctival and scleral flap dissection and may diminish the success rate of a subsequent trabeculectomy. Grover et al10 recently reported on a novel ab interno conjunctival sparing approach for circumferential trabeculotomy for the treatment of open angle glaucomas in adults termed gonioscopy assisted transluminal trabeculotomy (GATT). The authors now report on the use of the GATT technique in patients with PCG and JOAG associated with anterior segment angle dysgenesis.
Methods
A retrospective chart review was performed for all patients who underwent a GATT procedure by four of the authors (DSG, OS, RLF and DGG) at Glaucoma Associates of Texas between October 2011 and October 2013. The study followed the tenants of the Declaration of Helsinki and was approved by the affiliated hospital's institutional review board. Written consent was obtained from all patients before surgery.
All patients had a preoperative gonioscopic exam that revealed an anterior insertion of the iris with non-distinct trabecular meshwork and Schwalbe's line. The surgery was performed in patients under the age of 30 years with a cornea sufficiently clear to allow intraoperative visualisation of the anterior segment angle. Despite mild corneal oedema with Haab's striae in some cases, all eyes successfully underwent an ab interno trabeculotomy. Throughout the study period, there were no patients who were considered good candidates for the GATT surgery who could not have the GATT surgery performed due to a cloudy cornea.
Surgical procedure
The detailed surgical procedure has previously been described by Grover et al10, including illustrations of the procedure. Briefly, a 23-gauge needle paracentesis track, oriented tangentially, is placed in either the supero-nasal or infero-nasal quadrant. Viscoelastic (sodium hyaluronate) is injected into the anterior chamber through this site. A temporal paracentesis is created. A microcatheter is inserted into the anterior chamber through the entry site. A 1–2 mm goniotomy is created in the nasal angle with a microsurgical blade (25-guage microvitreoretinal blade). Microsurgical forceps are then used to grasp the microcatheter within the anterior chamber. The distal tip of the microcatheter is then inserted into Schlemm's canal at the goniotomy incision. The microsurgical forceps are used to advance the catheter through the canal circumferentially 360° within the anterior chamber. The progress of the microcatheter is noted by observing the illuminated tip. Upon retrieving the distal tip, after the catheter has passed 360° around the canal, the catheter tip is externalised from the temporal corneal incision creating the first half of the 360° trabeculotomy. Then, traction is placed on the proximal aspect of the catheter, thus creating a 360° ab interno trabeculotomy (see figure 1). The viscoelastic is then removed from the anterior chamber. A 25% anterior chamber fill with viscoelastic can be instilled to help tamponade bleeding from the canal. The wounds are hydrated and checked to ensure a watertight closure. Some surgeons, because of the elastic nature of a paediatric cornea, preferred to place a suture through the corneal paracenteses. Postoperative corticosteroid (subconjunctival or intracameral) and antibiotic drops are given per the surgeon's discretion. Figure 1 summarises the key surgical steps.
Intraoperative photographs demonstrating the key portions of the gonioscopy assisted transluminal trabeculotomy surgery. (A) Initially a goniotomy is created with a microvitreoretinal blade. (B) Schlemm's canal is then cannulated with a microcatheter, using microsurgical forceps. (C) One can appreciate that the catheter has already been passed 2–3 clock hours around Schlemm's canal. (D) Given the blinking red light on the distal end of the tip, one can follow the path of the catheter as it travels circumferentially around the canal. The catheter has passed 180° around the canal. (E) One can now appreciate that the microcatheter has come full circle around the canal. (F) The distal tip of the catheter is retrieved within the anterior chamber using microsurgical forceps. Blood reflux from Schlemm's canal is normal and usually a prognostic indicator of a successful outcome as well as an intact distal collector system.
In certain cases, the microcatheter cannot be passed 360° in one direction and stops at around 180°–270°. In these cases, a limited trabeculotomy is created by performing a goniotomy at the site where the catheter stopped, retrieving the distal end. A microcatheter can then be passed in the opposite direction through an additional 23-gauge needle incision thus completing a 360° trabeculotomy.
Postoperative care and follow-up
After surgery, all patients were given topical broad-spectrum antibiotics and topical steroids. The use of pilocarpine in the immediate postoperative period was per the surgeon's discretion. The topical antibiotics were stopped at postoperative week 1. The topical steroids were tapered per the surgeons’ discretion, with the main goal of controlling inflammation and preventing a steroid IOP response. The patient's IOP was treated during the postoperative period per the surgeons’ discretion. Clinical information, obtained through chart review, was collected for the following postoperative visits: 1 day, 1 week, 2–3 weeks, 1 month, 3 months, 6 months and thereafter every 3–6 months. At each follow-up visit, the following data were collected: visual acuity, IOP, number of glaucoma medications, surgery related complications and gonioscopic findings. If a reliable exam and IOP measurement could not be obtained in clinic, exam under anaesthesia was performed. In the exam lane, Goldmann applanation was used when possible. If the patient could not tolerate applanation, the iCare tonometer (iCare, Vantaa, Finland) was used. If the patient was not able to cooperate with any exam, a Tonopen (Reichert, DePew, New York, New York, USA) was used during an exam under anaesthesia.
Results
Fourteen eyes of 10 patients underwent a GATT surgery. Patients ranged in age from 17 months to 30 years (mean=18.4 years), and five (50%) were female patients. Table 1 presents ocular and clinical characteristics.
Clinical characteristics of PCG and JOAG cases following a GATT surgery
Five eyes had a decrease in IOP >15 mm Hg (15–39) when comparing preoperative IOP to IOP at last follow-up. In all eyes, the mean number of preoperative IOP lowering medications was 2.6 and the mean number of postoperative IOP lowering medications was 0.86. In all eyes, the mean decrease in IOP was 12.5 mm Hg and the mean decrease in IOP lowering medications was 1.8. The mean follow up time was 20.4 months (range 12–33 months).
No complications occurred during or following surgery except for early postoperative hyphema in five (36%) of eyes, all of which had cleared by 1 month. Gonioscopy performed at last follow-up revealed open trabecular shelves in >180° of the angle in all eyes (figure 2). None of the operated eyes required subsequent pressure lowering surgery.
(A) Gonioscopic photograph demonstrating a trabecular shelf with blood reflux into the angle. (B) Ultrasound biomicroscope revealing a prominent posterior leaflet or trabecular shelf following cleavage with a microcatheter. The arrow demarks the trabecular shelf.
A 360° trabeculotomy was accomplished in all eyes except one eye (8/OS (left eye)) where only 180° of the angle could be treated given the degree of angle dysgenesis. In this eye (8/OS), a first-stage glaucoma drainage tube was implanted while the patient underwent subsequent GATT surgery on the contralateral eye in the event that pressure control failed in the left eye, but this has not been needed to date.
In patient 6/OD (right eye), although his IOP was controlled preoperatively, he was on maximal tolerated topical therapy as well as 500 mg of acetezolamide twice daily. The treating surgeon did not think this was a reasonable long-term treatment option for a 17-year-old patient. He subsequently underwent a 360° GATT surgery. At this last follow up, his IOP was controlled on a combination drop of timolol and brimonidine as well as a prostaglandin analogue.
In patient 3/OD, the goal of the surgery was to decrease the patient's dependence on IOP lowering medications. In this case, the surgery was not able to accomplish this goal. The patient has a controlled IOP at post-operative month 3 (IOP 12 mm Hg on two medications). He then was lost to follow-up and did not receive any ophthalmic care. The authors were able to convince him to return for an exam, 17 months later, at which time his IOP was found to be elevated. Given his loss to follow up for this long period of time, it is unclear why his surgical outcome was different from other subjects in this study.
Patients 2/OD, 3/OD, 4/OD and 6/OD all had IOPs below 21 mm Hg preoperatively. Patient 3/OD and 6/OD were discussed above. The decision to proceed with surgery in patient 2/OD and 4/OD was based on the patients’ strong desire to be off medication, the patients’ inability to reliably use medications, the cosmetic effects of the drops on the patients’ eyes and the strong feeling by the authors that PCG and JOAG are surgical diseases.
Discussion
Trabeculotomy ab externo was developed in the 1960s for the treatment of childhood and adult glaucomas.4–6 Performed under a scleral flap with a metal trabeculotome, the technique was unique as it aimed to optimise a segment of the inherent outflow system of the eye as opposed to creating a bleb with external filtration.7 Advances by several authors including Redmond Smith, John Lynn and Ronald Fellman allowed for the evolution of trabeculotomy with a trabeculotome to a suture trabeculotomy in order to control IOP in patients with developmental glaucoma.1 ,8 ,11 In most situations, circumferential suture trabeculotomy has largely replaced limited segmental metal trabeculotomy and is now considered by some specialists to be the gold standard for PCGs although there is no general consensus.2 ,3 ,12 Some paediatric glaucoma specialists still use goniotomy for PCG and JOAG as there is no general agreement as to which surgery provides better outcomes.13 However, Mendicino et al3 reported on the long-term surgical outcomes of 360 trabeculotomy versus goniotomy in PCG and found that the trabeculotomy group had successful IOP control in 92% of eyes compared with 58% of eyes in the goniotomy group. There is also evidence that 360° trabeculotomy is superior to a limited trabeculotomy with a trabeculotome.14 Given the observations that greater IOP lowering is associated with a great degree of angle surgery, the authors feel that 360° trabeculotomy provides the best chance of successful IOP control.
Recently, there have been advancements in the approach of a trabeculotomy that have increased the ease of the surgery. First, a flexible illuminated microcatheter (iTrack), which aids in the identification and cannulation of Schlemm's canal, has been developed and extensively used for circumferential trabeculotomy9 ,15 ,16 Second, the GATT surgery, initially described by Grover et al10, is a continuation of the evolution of trabeculotomy and allows for an ab interno approach to trabeculotomy. This study demonstrated that the GATT procedure can be used successfully to treat PCG and JOAG.
Every patient underwent a postoperative gonioscopy after postoperative month 3. All eyes in the study had an open trabecular shelf (see figure 2) in >180° of the angle. This shelf of tissue forms as a result of very anterior cleavage in the canal, close to Schwalbe's line and can be seen at the time of GATT. This long posterior leaflet may become tethered to a small area of the peripheral iris, seen especially superiorly, causing the leaflet to remain open and be easily seen gonioscopically protruding over the iris. Redmond Smith was the first to report on this suspension of tissue16 which we have termed a trabecular shelf. The authors feel that an open shelf signifies an open collector system, which is usually associated with a favourable postoperative outcome.
Given the small nature of our case series (table 1), the authors did not feel it was appropriate or meaningful to report a proportion of success or failure. While in case 6/OD there was not a substantial difference between the preoperative and postoperative IOPs, the authors felt this case was a clinical success as the patient was able to be taken off of oral acetazolamide.
One weakness of our study is the limited follow-up. However, several authors have reported on the long-term follow-up in many cases of primary congenital and JOAG treated with external circumferential trabeculotomy with relatively good success.3 ,9 ,14 ,17–19 Our group's clinical experience over the past 30 years with ab externo trabeculotomy has mirrored the high success rates of the published studies. We expect similar results with our ab interno, minimally invasive approach. The ability to circumnavigate the trabecular meshwork without violating the conjunctiva is a major advancement, especially since it does not cause scarring of the conjunctiva and therefore should not interfere with future filtration or drainage implant surgery. Given the novel nature of this surgery, having follow-up from 12 to 33 months is the best we can provide.
This study also has the weaknesses inherent to all retrospective clinical studies. The decision for a surgical intervention was purely at the individual surgeon's discretion. However, most paediatric glaucoma specialists consider PCG and JOAG to be a surgical disease.20 Given the relatively low incidence of paediatric glaucoma, a prospective study would be very challenging.
The authors feel that the GATT procedure is superior to the traditional ab externo approach because it does not involve an extensive conjunctival dissection or an invasive scleral flap. This theoretically would allow for a better outcome if traditional glaucoma surgeries are required as there would be no conjunctival or scleral scarring. As stated above, the authors feel this procedure is superior to a goniotomy as it opens 360° of the angle as oppose to a limited area.
The GATT surgery has a learning curve. There are surgeons outside of Glaucoma Associates of Texas who have and are currently performing GATT procedures. The surgery is relatively challenging but teachable and after 5–10 surgeries, one should attain a certain level of comfort with the procedure. The surgery is not without risk or complications. The learning surgeon should be comfortable with anterior segment angle anatomy, angle-based surgery and operating with a gonioprism.
In conclusion, we introduce a minimally invasive surgical technique (the GATT procedure) that improves upon conventional ab externo trabeculotomy by avoiding conjunctival and scleral incisions. The IOP lowering effect of this surgical technique, demonstrated in this study, as well as in our previously reported study on adult open angle glaucomas, are at least equivalent to (if not better than) previously published studies of ab externo circumferential trabeculotomy.8 ,12 ,16 ,18 ,19 The procedure was safe and found to be clinically successful in all eyes in our case series.
References
Footnotes
Competing interests None.
Ethics approval Texas Health Resources IRB.
Provenance and peer review Not commissioned; externally peer reviewed.
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