Suppression of avascular bleb formation by a thin biodegradable film in a rabbit filtration surgery with mitomycin C

Abstract

Avascularity of the bleb is regarded as a risk of bleb infection, which is the most serious complication after filtration surgery with mitomycin C (MMC). There is no perfect way to prevent avascular bleb formation. We hypothesized that keeping the conjunctiva away from direct exposure to aqueous filtration may suppress avascular bleb formation after filtration surgery with MMC. In order to prove our hypothesis, we investigated whether a thin biodegradable, honeycomb-patterned film (HPF) can reduce bleb avascularity in a rabbit model of filtration surgery with mitomycin C (MMC). A fornix-based full-thickness filtration surgery was performed in one eye of each of five rabbits (control group). The same surgery with intraoperative MMC treatment was done in both eyes of six rabbits, with one eye receiving a 14-μm-thick HPF made from poly(L-lactide-co-ε-caprolactone), which was placed subconjunctivally over the filtration site with the honeycomb surface facing up. Intraocular pressure (IOP) measurements, bleb evaluations using ultrasound biomicroscopy (UBM), and in vivo confocal microscopy (IVCM) were performed periodically for 4weeks postoperatively followed by histological examination. The postoperative IOP decrease and bleb survival were significantly greater in MMC-treated eyes than in control eyes, and were similar between MMC-only and MMC + HPF eyes. The avascular area in the bleb persisted for 4weeks in MMC-only eyes. Postoperative IVCM showed morphological changes of the conjunctival epithelial cells (i.e., enlarged and variable in size and shape) and epithelial defects in MMC-only eyes, and significantly lower density of connective tissue and vascularity in the subepithelial space in MMC-only eyes compared to the control eyes. These IVCM findings agreed with those by UBM and histology. Bleb avascularity shown by clinical bleb appearance, IVCM and histology, conjunctival epithelial damage shown by IVCM and histology, and loose subepithelial connective tissue shown by UBM, IVCM, and histology were all reduced in MMC + HPF eyes compared to MMC-only eyes. IVCM successfully showed the characteristic conjunctival damage in MMC-treated blebs. The concomitant use of a thin biodegradable HPF reduced avascularity and conjunctival damage in blebs, without compromising filtration in rabbits following filtration surgery with MMC.