A novel method for controlling the quantity of mitomycin-C applied during filtering surgery for glaucoma

The use of a sponge impregnated with mitomycin-C is an increasingly common practice in glaucoma surgery. The appropriate antibiotic concentration and exposure lime have been considered in the literature, but not the exact amo unt to be used or the size of the sponge. The purpose of this study was to estimate the quantity of mitomycin-C contained in sponges prepared by diffe rent surgeons as compared to that in applicators of the type used in Schirm er's test graduation (5 x 5 mm). Four surgeons each cut and prepared 10 sponges for intraoperative use accor ding to their usual method. The same procedure was performed with 10 Schirm er's test graduations. Each sponge and each graduation was immersed in a so lution of mitomycin-C 0.2 mg/ml, and the quantity of antibiotic (mu g) in e ach was calculated as the difference between wet and dry weight. The mean quantity (+/- SEM) of mitomycin-C contained in cut sponges was 9.6 +/- 4.4 mu g (range 1.9-17.3), and the differences between surgeons were s tatistically significant (p<0.0001). The mean quantity of antibiotic in Sch irmer's test graduation was 1.7+/-0.3 mu g (range 1.1-2.5), and the differe nces between surgeons were not statistically significant (p=0.79). The quantities of mitomycin-C contained in sponges prepared for glaucoma su rgery differed for a given surgeon and between surgeons. Thus, variations i n the doses applied to the sclera could account for certain complications d ue to mitomycin-C. The use of a Schirmer's test graduation improves predict ability for the quantity of mitomycin-C applied to the sclera.