Long-term effects of postoperative subconjunctival injections of mitomycin-C in the rabbit eye

Single or multiple subconjunctival injections of mitomycin-C (MMC) may offer one way of establishing the total dosage of MMC more accurately. The method also allows re-applications later postoperatively. In this experimental, randomized prospective study we compared the effects of a single intraoperative application of MMC at the filtering site and a single postoperative subconjunctival injection of the drug.

The left eyes of 32 pigmented rabbits were divided into two groups. In the first group we applied MMC intraoperatively (IO) with a 4 x 1 mm surgical sponge soaked in a MMC solution (0.5 mg/ml). In the second group we injected 0.4 ml of the same solution subconjunctivally (SC) immediately after (conjunctival) suture. Post-operative evaluation was carried out every day during the first week, then every three days until day 58. Survival analyses were done for intraocular pressure (IOP) and bleb failure. Log-rank tests were used to compare survival differences between the groups.

The IO group showed longer survival parameters than the SC group (p < 0.05), both in the control of IOP and as regards blebs. The histological persistence of fistulas was similar. The IO group, however, had a higher incidence of undesirable side effects.

Our findings suggest IO application of MMC is more effective in reducing fibroblast ingrowth. However, subconjunctival application offers certain advantages such as the possibility of repeating the treatment postoperatively and, therefore, using a smaller initial dose.