Impact of Mitomycin-C application time on the scleral Mitomycin-C concentration.

The aim of this study was to determine the effect of varying the application time of Mitomycin-C (MMC) on the scleral concentration of MMC. The sclerae of 14 human donor eyes were used for this study. The episcleral sides of the 4 scleral quadrants of each donor eye were exposed for 0.5, 1, 3 and 5 min to round, 8 mm-diameter sponges soaked with 50 microl of 0.2 mg/ml MMC. After 40-ml irrigation with saline, a central 8-mm diameter scleral disk was punched out, homogenized and analyzed with high performance liquid chromatography (HPLC). The scleral MMC concentrations (microg/g) after 0.5, 1, 3 and 5 min application times were 6.40 (+/-3.38), 9.02 (+/-2.40), 12.31 (+/-3.37), and 13.97 (+/-3.83). The differences of scleral MMC concentration in paired t-tests were statistically significant comparing 0.5 with 1 and 1 with 5 min application. However the effect was relatively small within the range of usual application times (1 to 5 min), and 64% of the MMC was delivered to the sclera within the first min.

In vitro diffusion of mitomycin-C into human sclera after episcleral application: impact of diffusion time.

The purpose of this study was to investigate the impact of different diffusion times of mitomycin-C (MMC) on the intrascleral concentration vs depth profile of MMC in an experimental model. Scleral quadrants of eight human donor eyes were exposed to sponges soaked with MMC for an application time of 1 min. After irrigation with 40 ml saline, we allowed further diffusion of MMC in the sclera for 1, 5, 14 and 29 min until the specimens were further processed. A central 8 mm diameter scleral disk was horizontally dissected with a kryotome at -20 degrees C. MMC concentrations of six layers of 140 microm thickness were analysed by means of high-performance liquid chromatography. The MMC concentrations (microg g(-1)) of layer 1 were: 13.45+/- 5.9 (mean +/- S.D. at 2 min diffusion time), 7.6+/-2.5 (6 min diffusion), 5.6+/-3.1 (15 min diffusion) and 3.6+/-1.7 (30 min diffusion). The corresponding MMC concentrations of layer 6 were: 0.61+/-0.48, 1.47 +/-0.66, 1.83+/-0.42 and 2.98+/-0.97 microg g(-1). The superficial concentration of intrascleral MMC decreased with increasing diffusion time, the deep concentrations increased. After 30 min of diffusion time, equal concentrations of MMC were found in all layers. Even with current low-dose application regimens of MMC the concentrations in the inner side of the sclera rapidly increase beyond the limits of the therapeutic range. Owing to this fast diffusion of MMC, the only means of reducing ciliary body concentrations of MMC is to reduce the dose.

Intrascleral concentration vs depth profile of mitomycin-C after episcleral application: impact of applied concentration and volume of mitomycin-C solution.

The purpose of this study was to investigate the impact of different concentrations and volumes of Mitomycin-C (MMC) on the intrascleral concentration vs depth profile of MMC in an experimental model. The episcleral sides of scleral quadrants of human donor eyes were exposed for 1 min to sponges (corneal light shield, Merocel Corp.) soaked with MMC. After irrigation with 40 ml saline a central 8 mm diameter scleral disk was horizontally dissected with a cryotome. MMC concentrations of six layers of 140 microns thickness were analysed by means of high-performance liquid chromatography. In Experiment 1 (11 eyes) the sponges were soaked with 50 microliters of 10, 100 and 200 micrograms ml-1 MMC solutions. In Experiment 2 (12 eyes) the sponges were soaked with 10, 30, 50 and 80 microliters of a 200 micrograms ml-1 isotonic MMC solution. In Experiment 1 the MMC concentrations (microgram g-1) of layer 1 were 0.35 (+/- 0.20; 10 micrograms ml-1 group) and 9.22 (+/- 2.92; 200 micrograms ml-1 group). In Experiment 2 the MMC concentrations were 2.57 (+/- 1.17; 10 microliters group), 7.35 (+/- 2.49; 30 microliters group) and 11.67 (+/- 3.25; 80 microliters group). The scleral MMC concentrations were significantly influenced by the applied concentrations (layers 1-5) and by the applied volumes (all layers) of MMC solution. The intrascleral MMC concentration increased linearly with increasing concentration and not linearly with increasing volume of the applied MMC solution. To achieve more predictable scleral concentrations of MMC after trabeculectomy with MMC it seems advisable to control both the concentration and the volume of the MMC solution used to soak the sponge.

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 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 microg ml(-1)mitomycin-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 microm thickness were combined to one layer of 140 microm. 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 microg g(-1)(+/-7.52) without irrigation, 13.15 microg g(-1)(+/-4.38) after 40 ml irrigation, 10.29 (+/-3.53) after 100 ml irrigation and 8.4 microg 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 microm (no-irrigation group), 141 microm (40 ml irrigation group), 153 microm (100 ml irrigation group), and 164 microm (200 ml irrigation group). Irrigation reduced the mitomycin-C concentration only down to half of the scleral thickness, leaving the deep intrascleral concentrations unchanged.