Mitomycin C is routinely administered during trabeculectomy surgery to reduce conjunctival scarring and improve bleb survival. Mitomycin C is a potent alkylating agent that permanently changes exposed ocular tissues. The two most common MMC application methods are placing MMC-soaked cellulose sponges in the sub-Tenon space or injecting a lower concentration of MMC into the intra-Tenon space. While both methods are widely accepted and practiced, differences between the two approaches have only recently been studied.
This study by Swogger and colleagues compares clinical and histological outcomes after glaucoma filtering surgery in rabbits receiving either preoperative intra-Tenon injection (0.2 mL of 0.1 mg/mL) of MMC or intraoperative MMC application by sponge (0.4 mg/mL for four minutes). Ten rabbits total were randomized to the two MMC application methods during modified trabeculectomy surgery. Animals were followed for four weeks after surgery, at which point histopathology was performed. The authors observed a small but significant benefit in intraocular pressure (IOP) reduction in the injection compared to the sponge group. They also observed less goblet cell loss (beneficial in eyes with pre-existing ocular surface disease), less loss of vascularity (theoretically less prone to late surgical complications, including endophthalmitis), and lower collagen content (less scarring) in eyes receiving injection compared to sponge.
This study provides unique insight into the histological sequelae of both application methods, which favor injection over sponge. These findings are important as glaucoma surgeons may want to consider other effects of their surgeries outside of IOP lowering. However, the study is limited by its short follow-up duration and small sample size. Longer and better powered studies in human eyes did not find a significant difference in clinical outcomes between injection and sponge groups (Do et al., AJO, 2020). Therefore, longerterm animal studies would be beneficial to elucidate chronic outcome differences between injection and sponge.