OCULAR HYPOTONY AFTER TRABECULECTOMY WITH MITOMYCIN-C

Because mitomycin C reduces the resistance to aqueous outflow normally provided by postoperative subconjunctival fibrosis, we would expect t o see more frequent hypotony after trabeculectomy with mitomycin C tha n after standard trabeculectomy. To evaluate the incidence of hypotony in trabeculectomy with intraoperative mitomycin C use, we performed a retrospective analysis on 52 eyes of 48 patients who underwent trabec ulectomy with mitomycin C. Mitomycin C concentration was 0.4 mg/ml in all eyes, and treatment time ranged from 3 1/2 to seven minutes. We de fined hypotony as intraocular pressure lower than 5 mm Hg on two exami nations at least four weeks apart and six weeks or more postoperativel y. Overall, average intraocular pressure was 22.7 +/- 10.7 mm Hg preop eratively and 10.4 +/- 5.0 mm Hg postoperatively (P < .001), a mean re duction in intraocular pressure of 12.3 +/- 11.5 mm Hg (47.0%). Hypoto ny occurred in 17 of 52 eyes (32.7%). Seven eyes required trabeculecto my revision for hypotony. Hypotonous eyes received longer treatment wi th mitomycin C intraoperatively, with a mean application time of 5.3 /- 1.0 minutes for hypotonous eyes and 4.7 +/- 0.8 minutes for nonhypo tonous eyes (P = .03). Sixteen of 43 eyes (37.2%) undergoing primary f iltration became hypotonous, as compared to one of nine (11.1%) eyes t hat had previous filtering procedures (chi2 = 2.30, P = .13). Nine of 17 hypotonous eyes (52.7%) and five of 35 nonhypotonous eyes (14.3%) h ad loss of two or more lines of Snellen visual acuity. Hypotony occurr ed in nearly one third of eyes treated with mitomycin C during trabecu lectomy in our study. There was a statistically significant (P = .03) association of hypotony with longer application time of mitomycin C, a nd a trend toward increased incidence of hypotony in primary filtratio n.