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  • By: Maria Papadopoulos, MD; Peng Tee Khaw, MD
    Glaucoma

    Aim

    The aim of trabeculectomy surgery is to create a pathway for external drainage of aqueous from the anterior chamber.1

    Indications

    Trabeculectomy can be indicated following failed angle surgery, especially for primary congenital glaucoma (PCG). It can be considered as a primary procedure if a surgeon is unfamiliar with angle surgery, if angle surgery is not possible, or if a patient is unlikely to respond sufficiently to angle surgery as with very early or late presentations. Trabeculectomy can be indicated when very low target pressures are required, as in advanced optic-disc damage or to improve corneal clarity. Angle surgery has lower success rates for secondary childhood glaucomas compared to PCG,2,3 so it can be considered as a procedure of choice for many secondary glaucomas. Contraindications for trabeculectomy include phakia/pseudophakia, the presence of a cataract that might need removal in the near future, and corneal pathology that might require transplantation in the near future.

    Technique

    Traditionally, trabeculectomy in children was associated with significant complications largely related to early hypotony and adverse bleb morphology i.e. cystic, avascular blebs. These and other challenges of pediatric trabeculectomy, stimulated the re‑evaluation of the technique. There are many ways to perform trabeculectomy surgery in children, but Moorfield's Safer Surgery System (MSSS),4 which introduced simple modifications to the technique, and intraoperative application of Mitomycin C (MMC) have been found to encourage diffuse bleb formation (Figure 1).

    Figure 1. Contemporary pediatric trabeculectomy: Moorfield's Safer Surgery System.

    The MSSS emphasises a large area of treatment with antiscarring agent and posterior flow through a fornix based conjunctival flap and short scleral flap radial incisions to achieve posterior flow and a diffuse bleb (Figure 2).5,6

    Figure 2. Diffuse, elevated bleb with contemporary surgical trabeculectomy technique.

    "Titration" of postoperative intraocular pressure (IOP) is possible with releasable/adjustable sutures. This technique has been shown in adults and infants to be associated with favorable bleb morphology, reduced complications, and satisfactory outcomes.6,7 Buphthalmic eyes are especially prone to hypotony, flat anterior chambers, choroidal effusions, and suprachoroidal hemorrhage due to low scleral rigidity if aqueous flow is not well controlled. Measures to minimize hypotony are essential in trabeculectomy surgery especially in cases such as aniridia and Sturge Weber syndrome. For example, we recommend an anterior chamber (AC) maintainer to minimize any period of intraoperative hypotony and also to facilitate the accurate judgement of flow through the scleral flap.

    Postoperative Management

    Just as in adults, trabeculectomy requires frequent postoperative review to monitor the presence and degree of bleb inflammation. Potentially intensive steroid topical therapy might be required, which can be challenging for caregivers who might have difficulty gaining co-operation from young children. Additionally caregivers need to commit to frequent visits to the ophthalmologist for postoperative monitoring, which affects the child's schooling and potentially the caregiver's ability to commit to work or care for the rest of the family.

    The surgeon's challenges include adequate examination of the child and the ability to perform postoperative manipulations such as suture removal or application of further antiscarring agent. Examinations under anaesthesia (EUA) might be required for this purpose, often on a repeated basis. Remember that IOP measurement can be inaccurate with inhalational anesthetics, which reduce IOP.

    Failure tends to occur early in children, so frequent monitoring in the early postoperative period is vital. Examine children the first postoperative week and then weekly for the first month followed by greater intervals depending on bleb appearance and IOP control. In infants, at least 1 EUA is required within the first month after surgery preferably within the first 2 weeks. While under anaesthesia, you can take the opportunity to manipulate or remove sutures, inject subconjunctival 5Fluorouracil (5FU, 0.2–0.3 ml of 50 mg/ml 5FU), and to inject steroids such as betamethasone and local anesthetic adjacent to the bleb. Adjust topical steroids depending on the degree of inflammation and IOP, and in general, follow a weaning regimen for 3–4 months.

    Success and Complications

    Trabeculectomy is more likely to fail in children than adults8,9 due to the child's more vigorous wound healing.10 This propensity to failure necessitates using MMC, which you can use at varying potencies and requires only intraoperative exposure, a major advantage over 5FU in children. However, MMC is associated with higher complication rates. Early complications relate to hypotony (shallow or flat AC), hypotony maculopathy, choroidal effusion, suprachoroidal hemorrhage, and late complications are associated with thin, avascular, cystic blebs prone to leakage and potentially blinding infection.11–16

    The potential for complications after trabeculectomy, especially with MMC, cannot be overstated in children. The most appropriate MMC dose and duration of exposure for children is unknown, but most surgeons use 0.2–0.5 mg/ml depending on the number of risk factors for scarring and familiarity with specific concentrations. If an avascular cystic bleb develops, inform parents of the risk and seriousness of bleb-related infection. Advise them to report immediately to an ophthalmologist if symptoms or signs of bleb-related infection occur.

    With MMC, trabeculectomy cumulative success rates of 59%–90% at 2 years reducing to 51% at 5 years have been reported.12,14,17 Compared to GDDs, trabeculectomy surgery can achieve lower mean IOP,12 depend less on medication for IOP control,6,12,18 and require less postoperative surgical revision.18,19

    A reported risk factor for trabeculectomy failure, even with MMC, is glaucoma following congenital cataract surgery.12,20,21 Furthermore, success in infants, especially in those younger than 1 year, has been reported to be lower than older age groups11,13,16 and when compared to glaucoma drainage implants (GDDs).19 However, a more recent study suggests that with appropriate case selection (phakic patients) and regular follow-up, success can be comparable to GDDs.6 When trabeculectomy fails to control IOP, you can try bleb needling with an antiscarring agent if the bleb architecture allows and the sclerostomy is patent. You can repeat trabeculectomy with a stronger dose of MMC or consider a GDD if further surgery is required.

    References

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    18. Chen TC, Chen PP, Francis BA, et al. Pediatricglaucoma surgery: a report by the American Academy of Ophthalmology. 2014 Nov;121:2107-15.
    19. Beck AD, Freedman S, Kammer J, Jin J. Aqueous shunt devices compared to trabeculectomy with mitomycin C for children in the first two years of life. Am J Ophthalmol 2003; 136: 994-1000.
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