To describe the intraocular pressure (IOP) changes resulting from scleral flap suture and scleral flap manipulation in an experimental model of conventional guarded filtration surgery. Experimental study. Trabeculectomy operations were performed with adjustable sutures on 5 donor human eyes connected to a constant flow infusion and a real-time IOP monitoring system. Three different manipulations: posterior lip massage, suture adjustment using special forceps, and suture release, were tested on the completed operation site. The success in lowering IOP to the target range of 7 to 15 mm Hg within 5 interventions, the time to reach equilibrium IOP, and the frequency of undesired outcomes. Posterior lip massage, suture release, and suture adjustment lowered the IOP after stabilization to the target range in less than 5 interventions in 9%, 14%, and 100% respectively (P < 0.001). The median time for IOP to stabilize at the new level after each intervention after correction for the flow rates used was 36.3 minutes for massage, 8.5 minutes for releasable sutures, and 3.7 minutes for adjustment of sutures (P < 0.001). These results suggest that suture adjustment may be superior to both posterior lip massage and releasable sutures for managing IOP in the early phase following glaucoma surgery. Following clinical interventions that result in loss of anterior chamber volume, IOP checks should be made at least 40 minutes post-intervention or at a later time afterwards if there is a clinical risk of low aqueous production. Manipulation of the scleral flap and associated sutures may only lower the IOP for minutes to hours if the suture tension is not decreased.