Conditions for balance between lower normal pressure control and hypotony in mitomycin trabeculectomy

Striving for low to ultra-low postoperative intraocular pressure (IOP) through filtering surgery usually increases the incidence of prolonged hypotony. Early postoperative prognostic indicators for IOP control to lower normal level and prolonged hypotony in trabeculectomy with mitomycin C were examined to determine conditions required to obtain an optimum balance between them.

Records of initial trabeculectomy with mitomycin C (0.4 mg/ml, 3 min) in 59 consecutively operated Japanese patients with primary open-angle glaucoma who had used multiple medications before operation were retrospectively analyzed. IOP control to lower normal level was defined as having failed if IOP could not be maintained below 15 mm Hg without medication. Prolonged hypotony was defined as postoperative IOP below 5 mm Hg for more than 2 months, excluding the first month. The Cox proportional hazards model was applied to identify early postoperative factors contributing to the two surgical outcomes.

Among the factors studied, only the mean IOP on postoperative days 9-14 was significantly correlated with the surgical outcome. A receiver operating characteristic plot suggested that mean IOP of 8 mm Hg in this period would give an optimum balance between the two.

IOP of 8 mm Hg 9-14 days after surgery may be advisable in patients with preoperative multiple medications in whom IOP control to lower normal level is attempted with mitomycin C trabeculectomy. Knowledge of this may be helpful in deciding when laser lysis of sutures is indicated.