Intrascleral Concentration vs Depth Profile of Mitomycin-C after Episcleral Application: Impact of Irrigation

Abstract

Mitomycin-C has been reported to cause toxic effects on the ciliary body after episcleral application during glaucoma surgery. We investigated the intrascleral diffusion of mitomycin-C in an experimental model. The episcleral sides of scleral quadrants of 14 human donor eyes were exposed for 5 min to sponges (corneal light shield, Merocel corp., Mystic, CT, U.S.A.) soaked with 200 μg ml−1mitomycin-C. After the exposure one of four quadrants was not irrigated and the episcleral sides of three quadrants were irrigated with 40, 100 and 200 ml saline. A 9 mm scleral disk was punched out with a trephine and frozen on a kryotome plate 2 min after the end of mitomycin-C exposure. An 8 mm diameter scleral disk was then cut with a trephine, again frozen on a kryotome plate and then horizontally dissected with a kryotome. For analysis purposes seven cuts of 20 μm thickness were combined to one layer of 140 μm. Six layers could be reproduced and were analysed. The mitomycin-C concentrations of these layers were analysed by high-performance liquid chromatography. A concentration vs depth profile was calculated for each group, and the half-width of concentration was calculated by log-linear regression.The mitomycin-C concentration of layer 1 was 24.51 μg g−1(±7.52) without irrigation, 13.15 μg g−1(±4.38) after 40 ml irrigation, 10.29 (±3.53) after 100 ml irrigation and 8.4 μg g−1(±1.62) after 200 ml irrigation. In layers 1–3 the concentration of mitomycin-C was significantly reduced by irrigation (ANOVA). In the deeper intrascleral layers irrigation had no effect on the mitomycin-C concentrations. Between layers 2 and 6 the half-width of the mitomycin-C concentration was 101 μm (no-irrigation group), 141 μm (40 ml irrigation group), 153 μm (100 ml irrigation group), and 164 μm (200 ml irrigation group). Irrigation reduced the mitomycin-C concentration only down to half of the scleral thickness, leaving the deep intrascleral concentrations unchanged.