Subconjunctival Versus Direct Mitomycin C in Trabeculectomy

Trabeculectomy is routinely used as a surgical treatment for open angle glaucoma. Success of trabeculectomy is greatly augmented by the use of antimetabolites to inhibit wound healing, specifically Mitomycin C (MMC). MMC can be applied to the eye at various sites, concentrations and times. This study aims to compare the two application routes that are commonly employed: subconjunctival pre-operative injection and intraoperative direct scleral application in terms of IOP lowering effect, bleb appearance and complications.

Trabeculectomy is widely used as a surgical treatment of uncontrolled open glaucoma. Success of trabeculectomy at halting or slowing glaucoma progression primarily relies on the extent of conjunctival and sclera wound healing. The success rates of trabeculectomy increased dramatically with the introduction of anti-metabolites. For more than two decades mitomycin-c (MMC), a chemotherapeutic agent capable of decreasing fibroblast activity and modulating wound healing at the bleb, has been used with trabeculectomy. The complications of MMC are well known and several studies have described various methods of application based on exposure time, dose and surface area. Numerous retrospective and prospective studies have compared the efficacy of MMC applied beneath the conjunctival flap with soaked sponges versus intrascleral application. In 2008, Lee et al. first described an alternative route of application: subconjunctival injection of MMC directly into the intra-Tenon area. Seventy-six eyes with primary and secondary open angle glaucoma underwent trabeculectomy with this approach and were followed for one year post-operatively. Eighty-six percent of eyes achieved an IOP <21 mm Hg and 57% an IOP<14 mm Hg at one year without adjunctive drops. Transient complications included hyphema, bleb leak and choroidal detachment. The advantages of injected MMC are primarily in controlling the exact dosage and area of application and reduced surgical time. Lim et al. retrospectively reviewed the outcomes of trabeculectomy in 57 eyes using sponge application directly to the sclera versus intra-tenon injection. IOP was significantly lower in the injection group at 1 month, 1, 2, and 3 years. Trabeculectomy success (IOP<21mm Hg or IOP >20% below baseline without medications or additional surgery) was greater in the injection group at 3 years. The sponge group experienced more encapsulated blebs but complication rates were similar in both groups. To date, there have been no prospective studies comparing the IOP-lowering efficacy and safety of intra-tenon injection versus direct scleral application of MMC.

Percentage of patients achieving at least a 30% mean intraocular pressure reductions from baseline and with an intraocular pressure <21 mm Hg. Subjects that met this criteria without the use of intraocular pressure lowering medications were classified as "Complete Success." Subjects that met this criteria but required the use of intraocular pressure lowering medications were classified as "Qualified Success." Subjects that failed to meet this criteria were classified as "Failure." Subjects that failed to meet this criteria and required additional glaucoma surgery were classified as "Complete Failure."

Bleb morphology at 6 months was graded using Indiana Bleb Appearance Grading Scale. Bleb height was graded on a scale of 0 to 3 (0: flat bleb without visible elevation, 1: low bleb elevation, 2: moderate bleb elevation, 3: high bleb elevation). Bleb extent was graded on a scale of 0 to 3 (0: no visible bleb extent to less than 1 clock hour, 1: extent equal to or greater than 1 clock hour but less than 2 clock hours, 2: extent equal to or greater than 2 clock hours but less than 4 clock hours, 3: extent equal to or greater than 4 clock hours). Bleb vascularity was graded on a scale of 0 to 4 (0: avascular/white, 1: avascular/cystic, 2: mild vascularity, 3: moderate vascularity, 4: extensive vascularity). Scales are descriptive and do not necessarily represent better or worse outcomes.

Mean number of postoperative interventions (needling, antifibrotic injections) performed in each group

Inclusion Criteria: medically uncontrolled glaucoma healthy and freely mobile conjunctiva in superior bulbar region Exclusion Criteria: previous incisional glaucoma surgery no light perception vision pregnant or nursing women iris neovascularization or proliferative retinopathy iridocorneal endothelial syndrome chronic or recurrent uveitis steroid-induced glaucoma pathologic myopia or refractive error less than -6.00 diopters unwillingness or inability to give consent inability to return for scheduled protocol visits