Gonioscopy-Assisted Transluminal Trabeculotomy, Ab Interno Trabeculotomy

Gonioscopy-Assisted Transluminal Trabeculotomy, A Novel Ab Interno Trabeculotomy Technique Report and Preliminary Results Davinder S. Grover, MD, MPH,1 David G. Godfrey, MD,1 Oluwatosin Smith, MD,1 William J. Feuer, MS,2 Ildamaris Montes de Oca, MD,3 Ronald L. Fellman, MD1 Purpose: To introduce a novel, minimally invasive, ab interno approach to a circumferential 360-degree trabeculotomy and to report the preliminary results. Design: Retrospective, noncomparative cases series. Participants: Eighty-five eyes of 85 consecutive patients who sought treatment at Glaucoma Associates of Texas with uncontrolled open-angle glaucoma and underwent gonioscopy-assisted transluminal trabeculotomy (GATT) for whom there was at least 6 months of follow-up data. Methods: Retrospective chart review of patients who underwent GATT by 4 of the authors (D.S.G., D.G.G., O.S., R.L.F.) between October 2011 and October 2012. The surgery was performed in adults with various openangle glaucomas. Main Outcome Measures: Intraocular pressure (IOP), glaucoma medications, visual acuity, and intraoperative as well as postoperative complications. Results: Eighty-five patients with an age range of 24 to 88 years underwent GATT with at least 6 months of follow-up. In 57 patients with primary open-angle glaucoma, the IOP decreased by 7.7 mmHg (standard deviation [SD], 6.2 mm Hg; 30.0% [SD, 22.7%]) with an average decrease in glaucoma medications of 0.9 (SD, 1.3) at 6 months. In this group, the IOP decreased by 11.1 mmHg (SD, 6.1 mmHg; 39.8% [SD, 16.0%]) with 1.1 fewer glaucoma medications at 12 months. In the secondary glaucoma group of 28 patients, IOP decreased by 17.2 mmHg (SD, 10.8 mmHg; 52.7% [SD, 15.8%]) with an average of 2.2 fewer glaucoma medications at 6 months. In this group, the IOP decreased by 19.9 mmHg (SD, 10.2 mmHg; 56.8% [SD, 17.4%]) with an average of 1.9 fewer medications (SD, 2.1) at 12 months. Treatment was considered to have failed in 9% (8/85) of patients because of the need for further glaucoma surgery. The cumulative proportion of failure at 1 year ranged from 0.1 to 0.32, depending on the group. Lens status or concurrent cataract surgery did not have a statistically significant effect on IOP in eyes that underwent GATT at either 6 or 12 months (P > 0.35). The most common complication was transient hyphema, seen in 30% of patients at the 1-week visit. Conclusions: The preliminary results and safety profile for GATT, a novel, minimally invasive circumferential trabeculotomy, are promising and at least equivalent to previously published results for ab externo trabeculotomy. Ophthalmology 2014;-:1e7 ª 2014 by the American Academy of Ophthalmology.

Trabeculotomy lowers intraocular pressure (IOP) by improving the flow of aqueous through Schlemm’s canal and adjacent collector channels without bleb formation.1e5 Over the past 2 decades, improvements in trabeculotomy include circumferential suture techniques6e8 and a flexible illuminated microcatheter (iScience Interventional Corp, Menlo Park, CA), which aids in the identification and cannulation of Schlemm’s canal.9,10 Currently, the most common approach to trabeculotomy is ab externo, which requires an extensive conjunctival and scleral flap dissection that may diminish the success rate of a subsequent trabeculectomy. The authors have developed a conjunctivalsparing, sutureless ab interno approach for circumferential trabeculotomy, termed gonioscopy-assisted transluminal  2014 by the American Academy of Ophthalmology Published by Elsevier Inc.

trabeculotomy (GATT), for the treatment of both adult and developmental open-angle glaucomas. The purpose of this study was to describe this novel approach and to present the preliminary results in adults with open-angle glaucoma.

Methods A retrospective chart review was performed for all patients who underwent GATT by 4 of the authors (D.S.G., D.G.G., R.L.F., O.S.) at Glaucoma Associates of Texas between October 2011 and October 2012. The study followed the tenets 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. ISSN 0161-6420/14/$ - see front matter http://dx.doi.org/10.1016/j.ophtha.2013.11.001

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Ophthalmology Volume -, Number -, Month 2014 All patients underwent a preoperative gonioscopic examination that revealed an open angle and identifiable landmarks, notably the scleral spur and trabecular meshwork. The surgery was performed in adults with various types of open-angle glaucomas. Patients either had this surgery performed in isolation or in combination with cataract surgery.

Surgical Procedure After a standard sterile preparation, the surgical eye was draped and an open wire nasal lid speculum was inserted to hold the eyelids open. A 23-gauge needle paracentesis track, oriented tangentially, was placed in either the superonasal or inferonasal quadrant. This initial track served as the entry site for the microcatheter or suture. A viscoelastic (sodium hyaluronate) was injected into the anterior chamber through this site. A temporal paracentesis was created. A suture or the microcatheter was inserted into the anterior chamber through the entry site with the tip resting in the nasal angle. The microscope and the patient’s head then were oriented to allow proper visualization of the nasal angle with a Swan-Jacob goniolens. A 1- to 2-mm goniotomy was created in the nasal angle with a microsurgical blade through the temporal site. Microsurgical forceps then were introduced through the temporal site and were used to grasp the microcatheter or suture within the anterior chamber. The distal tip of the microcatheter then was inserted into Schlemm’s canal at the goniotomy incision. Within the anterior chamber, the microsurgical forceps were used to advance the catheter through the canal circumferentially 360
. The progress of the microcatheter was noted by observing the illuminated tip. On retrieving the distal tip, after the catheter has passed 360
around the canal, the catheter tip was externalized from the temporal corneal incision creating the first half of the 360
trabeculotomy. Then, traction was placed on the proximal aspect of the catheter, thus creating a 360
ab interno trabeculotomy (see Fig 1). The viscoelastic then was removed from the anterior chamber by a 2-handed irrigation aspiration system to wash the anterior chamber of blood. Near the end of the procedure, a 25% anterior chamber fill with viscoelastic was instilled to help tamponade bleeding from the canal. The wounds were checked to ensure a watertight closure. Postoperative steroid (subconjunctival or intracameral) and antibiotic drops were given according to the surgeon’s discretion. In some cases, the suture or microcatheter could not be passed 360
in one direction and stopped at approximately 180
to 270
. In these cases, a limited trabeculotomy was created and the suture or microcatheter then was passed in the opposite direction through an additional 23-gauge needle incision. In nearly all of these cases in this study, 360
of the angle was treated successfully. For the cases in which cataract extraction (CE) and intraocular lens (IOL) implantation were performed, GATT was performed first, followed by CE and IOL implantation, which were performed with standard phacoemulsification with a slight enlargement of the temporal clear corneal incision.

Postoperative Care and Follow-up After surgery, all patients were given topical broad-spectrum antibiotics and topical steroids. The topical antibiotics were stopped at postoperative week 1. The topical steroids were tapered according to the surgeon’s discretion, with the main goal of controlling inflammation and preventing a steroid intraocular pressure (IOP) response. The patient’s IOP was treated during the postoperative period according to the surgeon’s discretion. Clinical information, obtained through chart review, was collected for the following postoperative visits: 1 day, 1 week, 2 to 3 weeks, 1 month, 3 months, 6 months, and thereafter every 3 to 6 months. At each follow-up visit, the following data were collected: visual acuity,

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Figure 1. Illustrations documenting the key steps of the gonioscopyassisted transluminal trabeculotomy procedure. A, Initial cannulation of Schlemm’s canal within the anterior chamber. B, The catheter (or suture) has been passed 360
around the canal. C, The distal tip of the catheter (or suture) has been retrieved and is being externalized, thus creating the circumferential trabeculotomy. 1 ¼ Schlemm’s canal; 2 ¼ initial goniotomy site; 3 ¼ microsurgical forceps; 4 ¼ either the suture or microcatheter; 5 ¼ distal end of the suture or microcatheter after it has been passed 360
around Schlemm’s canal; 6 ¼ path of the suture or microcatheter within Schlemm’s canal; 7 ¼ trabecular shelf that is created after this procedure; 8 ¼ trabeculotomy that is created when the distal end of the suture or catheter is retrieved and externalized.

IOP, number of glaucoma medications, surgery-related complications, and gonioscopic findings.

Statistical Methods In this report, we provide GATT outcomes for 5 groups of patients, all of whom had not undergone prior incisional glaucoma surgery and had preoperative IOP of 18 mmHg or more: group 1, primary open-angle glaucoma (POAG) with no prior CE and IOL implantation undergoing only GATT; group 2, POAG with no prior CE and IOL implantation undergoing combined GATT and CE and IOL implantation; group 3, POAG with prior CE and IOL

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Gonioscopy-Assisted Transluminal Trabeculotomy

implantation undergoing only GATT; group 4, other glaucoma with no prior CE and IOL implantation undergoing only GATT; and group 5, other glaucoma with no prior CE and IOL implantation undergoing combined GATT and CE and IOL implantation. For efficacy of evaluation, only 1 randomly selected eye with 6 months or more of follow-up per patient was included. However, to achieve the most comprehensive characterization of safety of the procedure, we included all eyes in which there was a surgical complication; this includes second eyes of certain patients and eyes with short follow-up ( 0.35). The difference in the decrease in medication by study group approached, but did not achieve, statistical significance at 6 months (P ¼ 0.13) or 12 months (P ¼ 0.052). In patients with glaucoma diagnoses other than POAG (study groups 4 and 5), on average, IOP decreased by 17.2 mmHg (SD, 10.8 mmHg) at 6 months (P < 0.001) and by 19.9 mmHg (SD, 10.2 mmHg) at 12 months (P < 0.001). In this group, the average percent lowering of IOP was 52.7% (SD, 15.8%) and 56.8% (SD, 17.4%) at 6 and 12 months, respectively. The percent reductions in IOP at 6 and 12 months were not statistically different from one another (P ¼ 0.43). For these patients, the number of pressure-lowering medications decreased by 2.2 (SD, 1.5) at month 6 (P < 0.001) and by 1.9 (SD, 2.1) at month 12 (P < 0.001). Patients undergoing GATT combined with CE did not differ from those undergoing primary GATT with respect to either pressure lowering or decrease in number of medications at either 6 or 12 months (all P > 0.15). There is a discrepancy in the number of study eyes between Tables 1 and 2. This difference is because we included both eyes of patients undergoing GATT as well as eyes with a short follow-up in assessing complications (Table 1), but only 1 eye of each patient and none with follow-up of fewer than 6 months in assessing the outcomes (Table 2). Table 3 represents the intraoperative and postoperative complications. Hyphema was a common occurrence within the first week, but nearly all cases resolved by the first postoperative month. Steroid-induced IOP spike did occur rarely at the firstmonth postoperative visit.

Table 1. Demographic Information Separated by Specific Study Groups Primary Open-Angle Glaucoma

No. of eyes (no. of patients) Mean age (SD) Range Female gender, no. (%) Diagnosis, no. (%) POAG CACG PXF Pigmentary Uveitic/inflammatory Mixed mechanism Other OAG Trauma Steroid

Other Glaucoma

Gonioscopy-Assisted Transluminal Trabeculotomy Only

Gonioscopy-Assisted Transluminal Trabeculotomy Plus Cataract Extraction with Intraocular Lens Implantation

Prior Cataract Extraction with Intraocular Lens Implantation and Gonioscopy-Assisted Transluminal Trabeculotomy Only

Gonioscopy-Assisted Transluminal Trabeculotomy Only

Gonioscopy-Assisted Transluminal Trabeculotomy Plus Cataract Extraction with Intraocular Lens Implantation

32 (29) 58.8 (10.2) 36e83 15 (52)

21 (17) 74.4 (7.1) 60e86 11 (65)

18 (17) 77.2 (6.6) 67e88 12 (71)

19 (18) 47.8 (14.7) 24e68 7 (39)

16 (15) 69.8 (14.5) 58e87 7 (47)

32 (100)

21 (100)

18 (100) 2 4 4 4 1

(11) (21) (21) (21) (5) 0 2 (11) 2 (11)

3 (19) 9 (56) 0 1 (6) 1 (6) 2 (13) 0 0

CACG ¼ chronic angle-closure glaucoma; OAG ¼ open-angle glaucoma; POAG ¼ primary open-angle glaucoma; PXF ¼ pseudoexfoliation glaucoma; SD ¼ standard deviation.

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Ophthalmology Volume -, Number -, Month 2014 Table 2. Efficacy Data for All Patients in the Study, Separated by Different Groups Primary Open-Angle Glaucoma GATT only (n ¼ 25) Months followed, mean (SD) Range Pts requiring further IOP-lowering surgery, no. (%) Pts at follow-up visit (mos), no. (%)* 3 6 12 Mean IOP (SD), mmHg Preoperative Month 3 Month 6 Month 12 Postop IOP >21 mmHg, no. (%) Month 3 Month 6 Month 12 Postop IOP >18 mmHg, no. (%) Month 3 Month 6 Month 12 Mean no. of meds Before surgery Month 3 Month 6 Month 12 No meds required, no. of eyes (%) Month 3 Month 6 Month 12

Prior CE þ IOL Implant GATT only (n ¼ 16)

GATT only (n ¼ 17)

9.2 (2.4) 6e15 0

10.7 (3.9) 6e17 2 (13%): 7.6 and 8.9 mos

12.4 (3.5) 6e18 2 (12%): 2 wks and 4.1 mos

10.5 (2.1) 7e14 1 (9%): 4.2 mos

16 (100) 16 (100) 4 (25)

16 (100) 16 (100) 5 (31)

16 (94) 15 (88) 10 (59)

11 (100) 10 (91) 5 (45)

11.4 (3.3) 6e17 3 (12%): 7 wks, 5.8 mos, and 6.2 mos 24 (96) 24 (96) 12 (48) 25.6 16.8 18.5 15.7

Other Glaucoma

GATT + CE with IOL Implant (n ¼ 16)

(6.1) (3.5) (7.1) (4.5)

23.9 (7.2) 12.5 (1.8) 16.9 (10.5) 15.5 (1.7)

23.8 16.8 17.4 16.2

(5.1) (2.6) (5.2) (4.4)

31.8 (11.5) 14.2 (5.9) 13.6 (5.2) 12.4 (3.4)

GATT þ CE with IOL Implant (n ¼ 11)

27.6 15.1 13.4 13.8

(8.0) (5.1) (3.6) (2.2)

2 (8) 5 (28) 1 (8)

0 1 (13) 0

1 (8) 3 (30) 0

2 (13) 1 (10) 0

2 (18) 0 0

6 (25) 6 (33) 4 (33)

0 1 (13) 0

2 (15) 4 (40) 2 (40)

3 (20) 2 (20) 0

2 (18) 1 (14) 0

3.2 1.6 2.3 1.5

(0.9) (1.1) (1.5) (1.2)

6 (25) 2 (11) 4 (33)

2.9 0.9 0.8 1.0

(1.1) (1.0) (1.1) (1.4)

7 (47) 5 (56) 2 (50)

2.2 1.3 1.9 2.6

(1.0) (1.2) (1.3) (1.5)

4 (31) 2 (20) 1 (20)

3.5 1.3 1.1 1.8

(1.0) (1.4) (1.3) (2.0)

7 (47) 5 (50) 5 (50)

2.9 0.7 1.1 1.2

(1.3) (1.1) (1.2) (1.3)

7 (64) 3 (43) 2 (40)

CE ¼ cataract extraction; GATT ¼ gonioscopy assisted transluminal trabeculotomy; IOL implant ¼ intraocular lens implantation; IOP ¼ intraocular pressure; meds ¼ medications; Postop ¼ postoperative; Pts ¼ patients; SD ¼ standard deviation. *Follow-up time censored after patient underwent glaucoma reoperation.

Figures 2 and 3 present the cumulative proportion of eyes that underwent reoperation for pressure control and in which treatment failed either by virtue of reoperation or uncontrolled pressure, defined as pressure not reduced by at least 20% from baseline or more than 21 mmHg at or after 6 months. The proportions at follow-up times of more than 12 months must be interpreted with caution for the 3 study groups involving CE because these groups all had fewer than 10 patients followed up beyond 1 year. Thus, a single treatment failure could result in a large change in the proportion.

Discussion Over the past decade, the indications for circumferential trabeculotomy have widened to encompass adult glaucomas.11e13 This is because of the desire to reduce complications from filtration surgery, particularly bleb-related issues, and instead to try to salvage the natural outflow channels of the eye. In addition, over the past decade, there has been a major surge in interest and innovation for angle-based procedures in the treatment of open-angle glaucoma, exemplified by Trabectome (NeoMedix Corporation, Tustin, CA), canaloplasty,

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iStent (Glaukos Corporation, Laguna Hills, CA), as well as newer investigational devices.14,15 These improvements in microinvasive angle surgery have led to a renaissance in adult canal surgery. This change in the treatment paradigm for glaucoma can be appreciated especially in countries like Japan, where many glaucoma specialists consider circumferential trabeculotomy as a first-line treatment for open-angle glaucomas.11e13 It is generally known that trabeculotomy with McPherson or Harms trabeculotomies yields suboptimal long-term results in adults.13 However, over the past decade, progress in technique and technology has improved outcomes in adult glaucomas, especially with circumferential trabeculotomy. For example, Chin et al found that 360
suture trabeculotomy ab externo was significantly more effective in lowering IOP in adult primary and secondary glaucomas than metal trabeculotomy.13 The success rate was higher with the circumferential trabeculotomy, 84% versus 31%. The IOP was lower with fewer medications in the circumferential group versus metal trabeculotomy, with a mean postoperative IOP of 13.1 mmHg with 0.5

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Gonioscopy-Assisted Transluminal Trabeculotomy

Table 3. Intraoperative and Postoperative Complications, Separated by Group Primary Open-Angle Glaucoma

Intraoperative complications Hyphema, no. (%) Week 1 Month 1 Month 3 Month 6 Other week-1 complications Other month-1 complications Other month-3 complications

Other Glaucoma

Gonioscopy-Assisted Transluminal Trabeculotomy Only

Gonioscopy-Assisted Transluminal Trabeculotomy plus Cataract Extraction with Intraocular Lens Implantation

Prior Cataract Extraction with Intraocular Lens Implantation, Gonioscopy-Assisted Transluminal Trabeculotomy Only

Gonioscopy-Assisted Transluminal Trabeculotomy Only

Gonioscopy-Assisted Transluminal Trabeculotomy plus Cataract Extraction with Intraocular Lens Implantation

None

None

None

None

1 bag dehiscence/AV

7 (23) 1 (3) 1 (3) 0 1 choroidal folds

6 (29) 0 0 1 (5) 0

5 (29) 1 (6) 0 0 0

7 (37) 1 (5) 0 0 2 IOP spike

5 (33) 0 0 0 0

2 steroid-induced IOP spikes 0

0

2 steroid-induced IOP spikes 0

0

1 steroid-induced spike, 1 shallow AC 0

0 1 CME

AC ¼ anterior chamber; AV ¼ anterior vitrectomy; CME ¼ cystoid macular edema; IOP ¼ intraocular pressure.

medications versus 15.2 mmHg with 1.4 at medications at 12 months, respectively. The higher success rate with 360
modern-day circumferential trabeculotomy is likely because of greater access to more collector channels, along with improved cleavage of the trabecular meshwork. Our results with circumferential ab interno trabeculotomy using a microcatheter in adults are similar to the previously published studies on trabeculotomies in adults.

In our study, patients with POAG (study groups 1e3) showed a decrease in IOP of 7.7 mmHg at 6 months and of 11.1 mmHg at 12 months with a decrease, on average, of 1 glaucoma medication. At 6 and 12 months, there was a 30.0% and 39.8% decrease in IOP from baseline, respectively. In these groups, at 12 months, the mean IOP ranged from 15.5 to 16.2 mmHg with 1.7 glaucoma medications. Figure 3 demonstrates that the cumulative proportion of

Figure 2. Kaplan-Meier curve representing the cumulative proportion of eyes that underwent reoperation for intraocular pressure control. CE ¼ cataract extraction with intraocular lens implantation; GATT ¼ gonioscopy-assisted transluminal trabeculotomy; IOP ¼ intraocular pressure; other ¼ other open-angle glaucomas; POAG ¼ primary open-angle glaucoma.

Figure 3. Kaplan-Meier curve representing the cumulative proportion of eyes that met the definition of failure. Failure was defined as intraocular pressure not reduced by at least 20% from baseline or more than 21 mmHg at or after 6 months or eyes that required further glaucoma surgery. CE ¼ cataract extraction with intraocular lens implantation; GATT ¼ gonioscopy-assisted transluminal trabeculotomy; other ¼ other open-angle glaucomas; POAG ¼ primary open-angle glaucoma.

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Ophthalmology Volume -, Number -, Month 2014 treatment failures in groups 1 through 3 at 9 to 12 months ranged from 0 to 0.3. In groups 4 and 5, the mean IOP at 6 and 12 months was between 13.4 and 13.6 mmHg and between 12.4 and 13.8 mmHg, respectively, with 1.6 glaucoma medications. In these 2 groups, there was a substantial decrease in the number of IOP medications required, from more than 3 to nearly 1.5. As demonstrated in Figure 3, the cumulative proportion of treatment failures for these 2 groups also ranged between 0.1 and 0.3 at 9 to 12 months. These results compare favorably with those of Tanito et al, who reported success rates near 58.7% at one year in patients who underwent trabeculotomy combined with phacoemulsification and intraocular lens implantation.16 More recently, Chin et al13 reported on a modified circumferential ab externo trabeculotomy with a mean postoperative IOP of 13.1 mmHg with a mean of 0.5 glaucoma medications at 1 year. Compared with these prior studies, our patient groups showed roughly similar IOP-lowering results and proportions of success. In this study, we considered a single IOP of more than 21 mmHg at last follow-up to be a treatment failure, whereas typically many retrospective and prospective studies require 2 consecutive high IOPs before classifying a treatment failure in a particular case. When more follow-up is available, the authors may consider incorporating this definition into the failure criteria. The authors believed it was important to use more conservative definitions of success and failure in this study to present the data in a standardized way, similar to other surgical studies. Gonioscopy revealed a number of pertinent findings. At the time of surgery, the entire trabecular meshwork, 360
, was cleaved open. After the hyphema cleared, gonioscopy was carried out and most of the trabecular cleft remained open. In many patients, the posterior leaflet of the trabecular meshwork became tethered to a small area of the peripheral iris, causing the leaflet of tissue easily to be seen protruding over the iris. Smith17 was the first to report on this suspension of tissue, which we have termed a trabecular shelf (Fig 4), a good indicator of an open, cleaved collector system typically associated with a good postoperative outcome. Interestingly, there were a few patients in whom treatment failed even though their circumferential trabeculotomy site appeared to be open. It is likely that these patients either have a dysfunctional collector orifice or a badly damaged distal collector system that is unable to accept the flow of aqueous. Currently, we have no way of clinically determining the function of one’s collector system. There have been reports of determining the patency of the downstream collector system during surgery; however, the clinical usefulness of these techniques have not been determined.18,19 One weakness of our study is the limited follow-up. However, several authors have reported on the long-term follow-up in many adults and children treated with external circumferential trabeculotomy with relatively good success.8,9,13,20e22 Our group’s clinical experience over the past 30 years has mirrored the high success rates of the

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Figure 4. Postoperative clinical gonioscopic photograph of the superior angle demonstrating the typical appearance of a trabecular shelf (arrow).

published studies. We expect similar results with our internal, minimally invasive approach. Moreover, we found the GATT procedure applicable to a wide variety of diagnoses and clinical situations. The ability to circumnavigate the trabecular meshwork without violating the conjunctiva is a major advancement, especially because it does not cause scarring of the conjunctiva and therefore should not interfere with future filtration surgery. 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. A wide variety of types of glaucomas were treated. Additionally, a broad spectrum of disease severity was treated. Over the course of this study, the surgical glaucoma patient who did not undergo GATT underwent either a trabeculectomy, glaucoma drainage device implantation, or a different minimally invasive glaucoma surgery such as Trabectome or endocyclophotocoagulation. We plan to perform a prospective clinical study to evaluate the success of this technique further, allowing us to determine prognostic indicators for success and failure better. Based on our initial experience, we believe that there are absolute and relative contraindications for this procedure. Absolute contraindications include an inability to stop anticoagulation medication, a bleeding diathesis, an unstable IOL, inability to identify angle structures (specifically, the trabecular meshwork), a closed angle, or severe endothelial compromise. Relative contraindications are a prior corneal transplant or inability to elevate the head 30
for the first 1-2 postoperative weeks. In conclusion, we introduced a minimally invasive surgical technique (GATT) that improves on conventional ab externo trabeculotomy by avoiding conjunctival and scleral incisions to identify the canal in adults and children. Success rates are at least equivalent to previously published studies of ab externo circumferential trabeculotomy. The procedure was safe and was found to be effective in 68% to 90% of eyes in a variety of clinical settings.

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Acknowledgment. The authors thank Alexandra B. Hernandez of Gory Details Illustration for Figure 1.

References 1. Harms H, Dannheim R. Epicritical consideration of 300 cases of trabeculotomy ‘ab externo’. Trans Ophthalmol Soc U K 1970;89:491–9. 2. Gregersen E, Kessing SV. Congenital glaucoma before and after the introduction of microsurgery: results of ‘macrosurgery’ 1943e1963 and of microsurgery (trabeculotomy/ectomy) 1970e1974. Acta Ophthalmol (Copenhn) 1977;55:422–30. 3. Haas J. Principles and problems of therapy in congenital glaucoma. Invest Ophthalmol Vis Sci 1968;7:140–6. 4. Smith R. A new technique for opening the canal of Schlemm: preliminary report. Br J Ophthalmol 1960;44:370–3. 5. McPherson SD Jr, McFarland D. External trabeculotomy for developmental glaucoma. Ophthalmology 1980;87:302–5. 6. Beck AD, Lynch MG. 360 degrees trabeculotomy for primary congenital glaucoma. Arch Ophthalmol 1995;113:1200–2. 7. Ikeda H, Ishigooka H, Muto T, et al. Long-term outcome of trabeculotomy for the treatment of developmental glaucoma. Arch Ophthalmol 2004;122:1122–8. 8. Mendicino ME, Lynch MG, Drack A, et al. Long-term surgical and visual outcomes in primary congenital glaucoma: 360 degrees trabeculotomy versus goniotomy. J AAPOS 2000;4: 205–10. 9. Girkin CA, Marchase N, Cogen MS. Circumferential trabeculotomy with an illuminated microcatheter in congenital glaucomas. J Glaucoma 2012;21:160–3. 10. Sarkisian SR Jr. An illuminated microcatheter for 360-degree trabeculotomy [corrected] in congenital glaucoma: a retrospective case series. J AAPOS 2010;14:412–6. 11. Tanihara H, Negi A, Akimoto M, et al. Surgical effects of trabeculotomy ab externo on adult eyes with primary open angle glaucoma and pseudoexfoliation syndrome. Arch Ophthalmol 1993;111:1653–61.

12. Iwao K, Inatani M, Tanihara H; Japanese Steroid-Induced Glaucoma Multicenter Study Group. Success rates of trabeculotomy for steroid-induced glaucoma: a comparative, multicenter, retrospective cohort study. Am J Ophthalmol 2011;151:1047–56. 13. Chin S, Nitta T, Shinmei Y, et al. Reduction of intraocular pressure using a modified 360-degree suture trabeculotomy technique in primary and secondary open-angle glaucoma: a pilot study. J Glaucoma 2012;21:401–7. 14. Godfrey DG, Fellman RL, Neelakantan A. Canal surgery in adult glaucomas. Curr Opin Ophthalmol 2009;20:116–21. 15. Craven ER, Katz LJ, Wells JM, Giamporcaro JE; iStent Study Group. Cataract surgery with trabecular micro-bypass stent implantation in patients with mild-to-moderate open-angle glaucoma and cataract: two-year follow-up. J Cataract Refract Surg 2012;38:1339–45. 16. Tanito M, Ohira A, Chihara E. Surgical outcome of combined trabeculotomy and cataract surgery. J Glaucoma 2001;10: 302–8. 17. Smith R. Nylon filament trabeculotomy. Comparison with the results of conventional drainage operations in glaucoma simplex. Trans Ophthalmol Soc N Z 1969;21:15–26. 18. Fellman RL, Grover DS. Episcleral venous fluid wave: intraoperative evidence for patency of the conventional outflow system. J Glaucoma. Dec 31 [Epub ahead of print]. 19. Grieshaber MC, Pienaar A, Olivier J, Stegmann R. Clinical evaluation of the aqueous outflow system in primary openangle glaucoma for canaloplasty. Invest Ophthalmol Vis Sci 2010;51:1498–504. 20. McPherson SD Jr. Results of external trabeculotomy. Am J Ophthalmol 1973;76:918–20. 21. Chihara E, Nishida A, Kodo M, et al. Trabeculotomy ab externo: an alternative treatment in adult patients with primary open-angle glaucoma. Ophthalmic Surg 1993;24: 735–9. 22. Luntz MH, Livingston DG. Trabeculotomy ab externo and trabeculotomy in congenital and adult-onset glaucoma. Am J Ophthalmol 1977;83:174–9.

Footnotes and Financial Disclosures Originally received: June 21, 2013. Final revision: October 24, 2013. Accepted: November 1, 2013. Available online: ---. Manuscript no. 2013-997. 1 Glaucoma Associates of Texas, Dallas, Texas. 2

Bascom Palmer Eye Institute, University of Miami, Miami, Florida.

3

Unidad Oftalmologica Montego c.a, Barquisimeto, Venezuela.

Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. Correspondence: Davinder S. Grover, MD, MPH, Glaucoma Associates of Texas, 10740 North Central Expressway, Suite 300, Dallas, TX 75231. E-mail: dgrover@ glaucomaassociates.com.

Presented at: American Academy of Ophthalmology Annual Meeting, November 2013, New Orleans, LA.

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