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 subconjunctival mitomycin-C (MMC) using an adapted rabbit model of filtration surgery.

METHODS

Twenty-four New Zealand White rabbits underwent filtration surgery, with random allocation to one of three treatments: 5-minute subconjunctival applications of MMC (0.4 mg/ml) with either a large (8 x 10 mm) or small (4 x 2 mm) sponge or no treatment (control). Drainage was achieved by placing an intravenous cannula through a scleral tunnel into the anterior chamber. Rabbits were examined at set intervals for up to 30 days after surgery. Measurements of appearance, 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

Statistical analysis showed a significant difference in bleb survival among all groups (log rank P = 0.0054, with 100% survival with large areas of MMC treatment). Comparison between large and small treatment area groups revealed significant differences in bleb survival (log rank P = 0.0388); bleb area (between-subject analysis, P = 0.009), and bleb height (between-subject analysis, P = 0.005). These differences were seen clinically, with large areas of MMC treatment producing diffuse and elevated blebs, small areas of treatment producing thin-walled and localized blebs with scarring at 21 days, and no treatment resulting in comparatively vascularized and scarred blebs before 14 days. Histologic analysis revealed clear differences among groups, with an increase in subconjunctival cellularity and scar tissue in eyes with failed blebs.

CONCLUSIONS

The size of the area of subconjunctival MMC treatment significantly affects surgical outcome. Histologic features mirror differences observed clinically. Alteration of the size of the MMC treatment area may provide an alternative and more controllable approach to modulating the wound-healing response after drainage surgery and, more important in the clinical context, to modifying bleb morphology.