Trabeculectomy
Brenda L. Bohnsack, MD, PhD
PREOPERATIVE CONSIDERATIONS
Trabeculectomy surgery has been a mainstay for refractory glaucoma in children and adults since the 1960s.1,2 While trabeculectomy surgery can provide excellent IOP control, careful preoperative screening is required to identify good surgical candidates.2 In children, cooperation with slit lamp examinations for monitoring of the bleb is required. In addition, a preoperative conversation with the patient and family about the lifelong risk of infection due to trauma and even swimming is important. This, combined with the introduction of glaucoma drainage devices (see Chapter 11), has made trabeculectomy a less common surgery in the pediatric population.3
The morphology of the trabeculectomy bleb is important to understand.4 A diffuse, slightly elevated bleb with microcysts and low conjunctival vascularization is desirable for IOP control and less risk of leaks. In contrast, a focal, highly elevated vascular bleb is likely to be encapsulated and not provide adequate IOP control. An elevated, thin cystic bleb at or near the limbus is caused by scarring posterior to the scleral flap and is at higher risk for leak and infection, which can be visually devastating.5 Much attention has been directed at intraoperative factors that influence bleb morphology in order to improve the functionality and longevity of the trabeculectomy.
Intraoperative antifibrotic medications: The use of antifibrotics, namely mitomycin C (MMC) and 5-fluorouracil (5FU), has become standard with trabeculectomy surgery. While many studies show better long-term IOP control with MMC, these blebs tend to have more early postoperative complications.6,7,8,9 The traditional method of application consists of sponges soaked in MMC (0.2-0.4 mg/mL) or 5FU (50 mg/mL), which are applied for 1-5 minutes to the prepared scleral bed prior to creation of the flap.10,11,12 Increased time of MMC exposure in adults may lead to complications such as cataract formation; however, the data in children are limited.13 MMC (0.2 mg/mL) can also be injected (0.1 mL) sub-Tenon’s prior to conjunctival incision in the desired area of the bleb. This approach may encourage a diffuse, posterior low-lying bleb.14,15 More recently the collagen matrix, Ologen (Aeon Astron), has been used to augment trabeculectomy surgery either as a substitute for or with low-dose MMC. The collagen matrix is placed under and posterior to the scleral flap and is hypothesized to prevent fibroblast organization and subsequent scar formation. Limited studies show that Ologen has similar efficacy to MMC in obtaining IOP control.
Conjunctival incision: Fornix-based and limbus-based incisions are the typical approaches for glaucoma surgery.16 Limbus-based incisions (conjunctival incisions made in the fornix) produce more avascular, thin cystic blebs that are localized at the limbus and prone for infection.17 However, fornix-based incisions (conjunctival incisions made at the limbus) are at higher risk for early bleb leaks.18 A hybrid approach may be used by creating the conjunctival incision ˜2-3 mm posterior to the limbus, which promotes posterior filtration by decreasing flow anterior to the suture line and has less early wound leaks.
SURGICAL PROCEDURE (VIDEO 12.1)Trabeculectomy With MMC (Fig. 12.1)
For subconjunctival injection of MMC: Mix 1 mL of MMC (0.5 mg/mL) with 1 mL of lidocaine (2%) for a final concentration of 0.2 mg/mL of MMC and 1% lidocaine. Inject 0.1 mL of MMC and lidocaine mixture sub-Tenon’s in the area of the anticipated bleb, ˜6 mm posterior to the superior limbus. Use a cotton-tipped applicator to spread the MMC and lidocaine mixture (Fig. 12.1).
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