Modifying subsceral fluid pressure in an experimental model of mitomycin-C diffusion

BACKGROUND: Episcleral application of mitomycin-C (MMC) during glaucoma filtration surgery hinders the post-operative wound healing. Diffusion through the sclera might result in a toxic effect on the ciliary body resulting in reduced aqueous humor production leading to post-operative hypotony. We developed an experimental model to investigate the influence of intraocular pressure on the diffusion of MMC through the sclera and in subscleral compartments. METHODS: Scleral quadrants of 10 human donor eyes were mounted on PMMA tubes filled with saline imitating the intraocular volume. By height variation of a coupled infusion line different intraocular pressures were simulated (0, 8, 23 and 80 mmHg). Additionally the model included a subscleral sponge to mimic the compartment of the ciliary body. The episcleral sides of the scleral quadrants were exposed for 1 min to sponges soaked with 200 microg ml(-1) MMC. An 8-mm-diameter scleral disk was punched out with a trephine and horizontally dissected with a kryotome. The MMC concentrations of scleral layers, epi-and subscleral sponges and the fluid within the tubes were analysed by means of high-performance liquid chromatography. RESULTS: The MMC concentration gradually declined from the episcleral sponge (165 microg ml(-1)) to the superficial (3.3 microg ml(-1)) and deep scleral layers (1.2 microg ml(-1)), and to the subscleral sponge (0.2 microg ml(-1)). We were able to detect very small concentrations of MMC in the fluid within the PMMA tubes (0.01 microg ml(-1)). CONCLUSION: We developed a new experimental in vitro model for investigating transscleral MMC diffusion. The different simulated intraocular pressures had no effect on the concentration gradient through the investigated compartments of our model.