The predictive value of post-operative intraocular pressures following trabeculectomy

The value of post-operative intraocular pressure (IOP) in predicting the outcome of trabeculectomy was investigated in a retrospective study of single eyes of 203 Caucasian patients with uncomplicated chronic open angle glaucoma from the Birmingham and Midland Eye Hospital. Post-operative IOPs were recorded on day 1, at 2 weeks, and at 3, 6, 12 and 24 months. Surgical failure, defined as an IOP of 21 mmHg or above throughout the study period, occurred in 66 eyes by 24 months (32.5% failure). Discriminant analysis for the first day post-operative IOP showed a reliability of prediction of success (RPS) and failure (RPF) of 76.4% and 74.4% respectively, with an accuracy of prediction of success (APS) and failure (APF) of 92.6% and 42.6%. At 2 weeks, APS remained high (90.3%) and APF increased with time (63.2%). Certainty of success prediction at any stage is high and certainty of failure prediction becomes greater with time. In terms of IOP on the first post-operative day, 92.6% of successes may be correctly predicted if the IOP < 17 mmHg and 42.6% of failures may be predicted if the IOP > or = 17 mmHg. This study suggests that identification of patients at risk of failure on the basis of IOP in the early post-operative period is possible and that closer follow-up and early medical or surgical intervention may be indicated.