Impact of irrigation in a new model for in vitro diffusion of mitomycin-C after episcleral application

Abstract

Purpose. Episcleral application of mitomycin-C (MMC) during glaucoma surgery hinders the post-operative wound healing but may lead to side effects to the ciliary body. We present an experimental model to investigate the influence of irrigation on diffusion of MMC through the sclera and into subscleral compartments. Materials and Methods. Scleral quadrants of 10 human donor eyes were mounted on PMMA tubes filled with saline imitating the intraocular fluid. Beneath the sclera a subscleral sponge was fixed to mimic the ciliary body. The episcleral sides of the scleral quadrants were exposed to sponges soaked with 0.2 mg/ml MMC and thereafter irrigated with 0, 40, 100 and 200 ml saline. Mitomycin-C concentrations of the sclera and the subscleral compartments were analyzed by means of high-performance liquid chromatography. In a second experiment, after the application time of one minute, different times of free diffusion until analysis were allowed, to evaluate the time-course of MMC penetration. Results. MMC concentrations declined from the scleral layers (1-13 µg/ml, depending on depth and irrigation) to the subscleral sponge (0.17-0.27 µg/ml) and to the subscleral fluid (0.002-0.05 µg/ml). Irrigation significantly reduced MMC concentrations in the superficial scleral layers and in the subscleral fluid to 10-30% of the no irrigation value. No effect was noted in the deep scleral layers and subscleral sponges. In the second experiment, the subscleral compartments showed higher MMC concentrations with longer diffusion times, whereas no effect on intrascleral MMC concentrations was observed. Conclusion. Irrigation reduced MMC concentrations in the superficial scleral layers and in the subscleral fluid by the same amount. The clinical value of irrigation should be reconsidered; a lower dose MMC application without irrigation might be a more rationale approach.