Intrascleral concentration vs depth profile of mitomycin-C after episcleral application: Impact of irrigation

Mitomycin-C has been reported to cause toxic effects on the ciliary body af ter episcleral application during glaucoma surgery, We investigated the int rascleral diffusion of mitomycin-C in an experimental model. The episcleral sides of scleral quadrants of 14 human donor eyes were exposed for 5 min t o sponges (corneal light shield, Merocel corp., Mystic, CT, U.S.A.) soaked with 200 mu g ml(-1) mitomycin-C. After the exposure one of four quadrants was not irrigated and the episcleral sides of three quadrants were irrigate d 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, aga in frozen on a krgotome plate and then horizontally dissected with a kryoto me. For analysis purposes seven cuts of 20 mu m thickness were combined to one layer of 140 mu m. Six layers could be reproduced and were analysed. Th e mitomycin-C concentrations of these layers were analysed by high-performa nce liquid chromatography. A concentration vs depth profile was calculated for each group, and the half-width of concentration was calculated by log-l inear regression. The mitomycin-C concentration of layer 1 was 24.51 mu g g(-1) (+/-7.52) wit hout irrigation, 13.15 mu g g(-1) (+/- 4.38) after 40 ml irrigation, 10.29 (+/-3.53) after 100 ml irrigation and 8.4 mu g g(-1) (+/-1.62) after 200 ml irrigation. In layers 1-3 the concentration of mitomycin-C was significant ly reduced by irrigation (ANOVA). In the deeper intrascleral layers irrigat ion had no effect on the mitomycin-C concentrations. Between layers 2 and 6 the half-width of the mitomycin-C concentration was 101 mu m (no-irrigatio n group), 141 mu m (40 ml irrigation group), 153 mu m (100 ml irrigation gr oup), and 164 mu m (200 ml irrigation group). Irrigation reduced the mitomy cin-C concentration only down to half of the scleral thickness, leaving the deep intrascleral concentrations unchanged. (C) 2000 Academic Press.