Current practice of trabeculectomy in a cohort of experienced glaucoma surgeons in Australia and New Zealand

Background/Objectives To evaluate current routine trabeculectomy technique preferences among Australian and New Zealand Glaucoma Society surgeons regularly performing trabeculectomy surgery. Subjects/Methods Survey of experienced surgeons who perform trabeculectomy. Results Forty-nine surgeons (33 male:16 female) participated in the survey. Trabeculectomy was performed as day surgery (39/47, 83.0%) under local anesthesia (44/47, 93.6%). The surgical techniques most commonly used were a corneal traction suture (44/47, 93.6%), fornix-based conjunctival flap (43/47, 91.5%) and half-thickness scleral flap (38/47, 81.0%). Mitomycin C antifibrotic agent was used in routine cases by 45/46 (97.8%) surgeons. Surgeons applied the antifibrotic agent under the Tenon layer with a pledget (36/46, 78.2%) with a concentration of 0.02% (37/46, 80.4%) for 2 (11/46, 23.9%) or 3 min (30/46, 65.2%). The Kelly (26/46, 56.5%) and the Khaw Descemet (19/46, 41.3%) punches were used to perform the sclerostomy. Most surgeons performed a peripheral iridectomy in all phakic patients (46/47, 97.9%), but less commonly in pseudophakic patients (34/47, 72.3%). Techniques for closure of the limbal conjunctival edge were quite varied with a combination of suturing including purse string (21/47, 57.4%), wing (20/47, 42.6%) and horizontal mattress sutures (33/47, 70.2%). Surgeons reviewed their routine patients four times in the first month (29/47, 61.7%) and continued the postoperative topical steroids for 3–4 months (28/47, 59.6%). Conclusions Although a wide range of techniques for trabeculectomy exists among surgeons, there are consistent procedures currently in use to optimize patient outcomes. This report will assist surgeons in choosing which surgical techniques fit their best practice.


INTRODUCTION
Trabeculectomy is designed to divert aqueous from the anterior chamber via a sclerostomy under a scleral flap to an external bleb. Filtration surgery is an option in patients who are using maximally tolerated medications and/or have had laser treatment and require further lowering of their intraocular pressures. It may also be considered as initial management for those presenting with advanced disease [1]. The technique has significantly evolved since it was introduced in 1968 by Cairns [2]. There are a number of different trabeculectomy techniques utilized by ophthalmologists in Australia and New Zealand, largely influenced by their glaucoma fellowship training. Each technique has been modified by individual surgeons according to their experience, preferences and specific clinical features and outcomes of the patients undergoing surgery. While there are numerous surveys that provide preferred practice patterns for glaucoma surgery [3][4][5], there is a paucity of data regarding preferred surgical techniques for trabeculectomy [6,7]. The aim of this study is to document the various techniques used by an experienced group of trabeculectomy surgeons in Australia and New Zealand.

METHODS
A survey of glaucoma surgeons attending an online meeting of the Australian and New Zealand Glaucoma Society (ANZGS) (as listed at the end of the paper) was conducted in February 2021. Participation was voluntary and no compensation was offered or provided for responding. The 39-question online survey, divided into five polls, was formulated and modified by the authors after trialing it on four trabeculectomy surgeons.
Participants were asked to recall their technique for a routine primary trabeculectomy performed in an adult. Questions on each step of the trabeculectomy were presented and respondents independently answered via an online polling software (Zoom, San Jose, USA). At the live presentation, after respondents answered each question, the results were displayed and discussed. During the presentation, participants were also able to type in questions and comments in a "chat box". This commentary was also recorded as part of the survey.

Data analysis
Data were collected and analyzed anonymously. Respondents reported their technique of choice for each surgical step. These data were collated for all respondents. The total number of responses and percentages are presented. Data from the returned questionnaires were tabulated and analyzed using Microsoft Excel (Microsoft Corporation, Seattle, WA, USA).

RESULTS
Forty-nine surgeons (33 male:16 female) participated in the study. Most surgeons were aged 30-49 years old (32/49, 65.3%) with the rest, 50-59 years old (14/49, 28.6%) and >60 years old (3/49, 6.1%). The majority did glaucoma fellowships in the UK (43/49, 87.8%) with the rest in the US (3/49, 6.1%) or elsewhere (3/49, 6.1%). The number of years in specialist practice was five or more for 32/49 (65.3%) of the surgeons, with the average number of trabeculectomies performed per year greater than 10 by 36 (73.5%) surgeons and greater than 20 by 21 (42.9%) surgeons. All participants answered the majority of the questions; however, there was a loss of two participants from Polls 2, 4 and 5 and a loss of three participants from Poll 3.

DISCUSSION
Although the practice patterns for trabeculectomy have been studied by a number of surveys [6][7][8], these studies did not address current practice preferences regarding surgical techniques for trabeculectomy in detail. This study aimed to evaluate current practice techniques for trabeculectomy among Australian and New Zealand glaucoma specialists. While the results of this survey demonstrate a wide range of techniques in trabeculectomy among glaucoma surgeons, it also suggests that there are many consistent features in surgical techniques that are undertaken by the majority of surgeons. This group of surgeons practice mainly in private clinics but have some public hospital appointments and/or academic positions. According to Australian Medicare statistics, there were 1987 trabeculectomies performed in the 12 months from July 2019 to June 2020 [9].
Pre-treatment with topical steroids was a routine part of trabeculectomy for a third of surgeons 16/47 (34.0%). It was used particularly in eyes with ocular surface inflammation and a history of previous uveitis. Most trabeculectomies were performed under  A corneal traction suture is an effective way of infraducting the eye to provide good exposure of the superior bulbar conjunctiva. Placing a superior rectus suture, although previously one of the most techniques [10], often results in subconjunctival hemorrhage or superior rectus hematoma that may trigger an excessive wound healing response in trabeculectomy [11]. The Ong eyelid speculum has a larger inferior blade that is able to push on the inferior conjunctival fornix resulting in the downwards rotation of the eyeball. This is effective in most eyes, although surgeons may still need a traction suture in some cases.
The Moorfields Safer Surgery System for Trabeculectomy was formulated by Professor Sir Peng Khaw [11]. This has had a direct influence on ANZGS surgeons' technique as many of the surgeons in this survey were trained in the United Kingdom either under Peng Khaw himself or by one of his many fellows. The key features of this system are to form a diffuse posteriorly draining bleb with normal conjunctival morphology. The use of MMC-soaked pledgets placed over a wide area under the Tenon layer, pre-placed scleral flap sutures, a small sclerostomy, intraoperative IOP titration and watertight closure of the limbal incision all contribute to the success of this technique [11]. The ability to control the fibrosis and allow long-term drainage of the bleb has revolutionized trabeculectomy surgery. The concentration of MMC depends on the anticipated scarring response of the conjunctiva and Tenon's layer, with a greater risk of fibrosis in younger patients, Asian/African-Caribbean ethnicity, previous surgery or active intra-or extraocular inflammation. Generally, a higher dose of MMC such as 0.03-0.04% for 3-4 min is indicated in cases at high risk of scarring and filtration failure. In a recent study by Seol et al., a concentration of 0.02% compared to 0.04% for 2 min resulted in no difference in efficacy or safety in a South-East Asian population; however, follow-up was for only 6 months [12]. The widespread use of antimetabolites in this survey is in contrast to the National Survey of Trabeculectomy in the United Kingdom conducted in 1996, where no antimetabolite was used in 83.6% [10].
The scleral flap has evolved over many years with various techniques [13]. The flap shape can be square, rectangular or trapezoidal and is generally a third to half thickness of the sclera. The purpose is to regulate the fluid egress from the anterior chamber to allow adequate pressure control, but also to prevent hypotony. Pre-placed scleral flap sutures allow for a rapid closure of the scleral flap reducing the intraoperative time of hypotony. A thicker flap (half thickness of the sclera) was preferable to reduce flap complications. Placement of the MMC under the flap also reduces closure from fibrosis. The application of the MMC varied from sub-Tenons pledgets (preferably polyvinyl alcohol [14]), injection at the beginning of the case and injection following dissection of the conjunctival flap. Injection of MMC is a less controlled technique than direct sponge application. Intravitreal and subconjunctival bevacizumab may also be used as an adjunctive agent to reduce postoperative fibrosis [15].
There are several areas where there is significant variability. The use of an anterior chamber maintainer was quite popular amongst the more recently trained of the group. The infusion of fluid maintains the anterior chamber after the sclerostomy so the eye pressure can be adjusted by titrating the flow through the scleral flap [11]. The size of the scleral flap was quite variable, with the other popular choice measuring 5 × 3 mm. Another one of the most variable steps in trabeculectomy technique was the closure of the scleral flap. There was a combination of fixed, releasable and/or adjustable sutures used. Fixed sutures often needed to undergo laser suture lysis postoperatively, whereas adjustment or removal of releasable sutures can be performed at the slit lamp [11]. Adjustable sutures utilizing a triple, quadruple or quintuple throw can be loosened postoperatively to titrate the flow rather than an "all or nothing" effect with releasable sutures. However, manipulation can be difficult through an edematous and inflamed conjunctiva and there is a risk of buttonholing the conjunctiva. Closure of the conjunctiva and Tenon's layer is critical to prevent wound leaks and postoperative hypotony. The variability in technique indicates there are many ways to achieve this result. The main principle is to avoid postoperative bleb leaks, especially following the use of an antifibrotic agent.
Postoperative guttae atropine 1% 19/47 (40.4%) was in common use and can relax the ciliary muscle with pain relief, may reduce postoperative bleeding, can reduce anterior chamber shallowing as well as reducing the risk of aqueous misdirection, stabilizes the blood aqueous barrier and prevents central posterior synechiae. Disadvantages of its use include a dilated pupil, which may blur vision and increase lens-corneal touch in shallow anterior chambers [11].
There are several limitations of this survey. A multiple-choice format may introduce bias by limiting possible responses to the options offered. However, the choices were carefully designed to include the most common techniques for each step and the chat box discussion further elucidated other options. Furthermore, answers given by some respondents may not accurately reflect their actual clinical practice because of errors in recall. Given that the results were anonymously collected, this would be unlikely. The study included most of the higher volume trabeculectomy surgeons in Australia and New Zealand, although it was not possible to obtain the opinions of every experienced trabeculectomy surgeon in the region. Ideally, trabeculectomy outcomes of all the surgeons involved could be compared to the various techniques in order to determine the most efficacious techniques. There was no attempt to compare the technique to trabeculectomy outcomes; however, the techniques used have been well documented with efficacy established [10].
The significant variations in practice preferences of trabeculectomy techniques among Australian and New Zealand glaucoma surgeons reflect a lack of good evidence to guide practice or maybe it reflects what works clinically, given the variable outcomes that one sees in our glaucoma surgery patients. Although the optimal clinical practice is poorly defined, the results of this survey provide a means for ophthalmologists to critically examine their own clinical preferences through comparison with those of their colleagues and adopt different techniques, given the variable nature of each eye's response to glaucoma surgery. This survey also provides a baseline against which clinical trends can be identified and assessed in future. It may stimulate consideration of a registry-base and potential randomized controlled trials that could lead to refinement of surgical techniques to improve success rates, ultimately reducing the complications of this highly effective surgical procedure.

Summary
What was known before • A wide range of techniques for trabeculectomy exists amongst surgeons.
• There are consistent procedures currently in use to optimize patient outcomes.