EFFECT OF VARYING THE MITOMYCIN-C TREATMENT AREA IN GLAUCOMA FILTRATION SURGERY IN THE RABBIT

Purpose. To investigate the effect of varying the treatment area of su bconjunctival mitomycin-C (MMC) using an adapted rabbit model of filtr ation surgery. Methods. Twenty-four New Zealand White rabbits underwen t filtration surgery, with random allocation to one of three treatment s: 5-minute subconjunctival applications of MMC (0.4 mg/ml) with eithe r a large (8 x 10 mm) or small (4 x 2 mm) sponge or no treatment (cont rol). Drainage was achieved by placing an intravenous cannula through a scleral tunnel into the anterior chamber. Rabbits were examined at s et intervals for up to 30 days after surgery. Measurements of appearan ce, size, height, and vascularity of blebs and of intraocular pressure and anterior chamber depth were made by a masked observer. Histologic analysis of eyes was performed at 3, 14, and 30 days. Results. Statis tical analysis showed a significant difference in bleb survival among all groups (log rank P = 0.0054, with 100% survival with large areas o f MMC treatment). Comparison between large and small treatment area gr oups revealed significant differences in bleb survival (log rank P = 0 .0388), bleb area (between-subject analysis, P = 0.009), and bleb heig ht (between-subject analysis, P = 0.005). These differences were seen clinically, with large areas of MMC treatment producing diffuse and el evated blebs, small areas of treatment producing thin-walled and local ized blebs with scarring at 21 days, and no treatment resulting in com paratively vascularized and scarred blebs before 14 days. Histologic a nalysis revealed clear differences among groups, with an increase in s ubconjunctival cellularity and scar tissue in eyes with failed blebs. Conclusions. The size of the area of subconjunctival MMC treatment sig nificantly affects surgical outcome. Histologic features mirror differ ences observed clinically. Alteration of the size of the MMC treatment area may provide an alternative and more controllable approach to mod ulating the wound-healing response after drainage surgery and, more im portant in the clinical context, to modifying bleb morphology.