The ocular pulse amplitude (OPA) is the difference between the minimum and maximum values of the pulsatile intraocular pressure (IOP) wave contour. The OPA depends on ocular perfusion and IOP, which are both affected by a trabeculectomy (TE). The aim of this study was to investigate how the OPA changes after TE and whether an early change in OPA can be used as a prognostic marker for a successful long-term outcome.Fourteen consecutive patients (26-84 years old) with medically uncontrolled primary open-angle or pseudoexfoliation glaucoma were included in the study. IOP and OPA were measured with a dynamic contour tonometer before and after TE on days -1, +1, +7, +14, +21, +28, +42, +56, +70, and +84. The OPA of the contralateral eye was used to control for variations in systemic haemodynamics. TE was regarded as successful if a persistent drop in IOP of at least 20% without the use of IOP-lowering treatment was achieved. Data were analysed using receiver operating characteristic curves, Kaplan-Meier survival curves and Mann-Whitney two-sample analysis.Five out of 14 TEs had an entirely successful outcome. The other 9 patients required additional interventions such as suturolysis, needling of subconjunctival scar tissue and antimetabolite injections during the 3-month period after the TE. On the first day after surgery, OPA decreased in 12 patients and increased in 2 patients compared with the preoperative measurements. In the 5 patients with a successful long-term outcome, OPA dropped by 3.38+/-1.79 mmHg (mean+/-SE), whereas the initial OPA drop in those cases that required additional interventions was 0.62+/-1.81 mmHg only (p<0.01). IOP dropped by 13.10+/-2.14 mmHg in the successful group and by 5.84+/-2.51 mmHg in the unsuccessful group (p=0.19). Kaplan-Meier estimates of survival showed that patients with an initial OPA drop of more than 2.0 mmHg had a significantly better chance of an entirely uncomplicated 3-month outcome after TE than patients with an initial OPA drop of less than 2.0 mmHg (log rank p<0.01).This pilot study indicates that an early drop in OPA of more than 2.0 mmHg after TE may be a good prognostic parameter for successful long-term control of IOP.