This study investigated the rate and degree of reduction in intraocular pressure (IOP) obtained with an external ocular compression device. Following removal of the device, the subsequent recovery in IOP was monitored. We aimed to establish the time course of IOP changes, and thereby to optimise our use of such devices prior to cataract surgery. A rapid initial reduction over the first 10 minutes of compression was followed by a more gradual reduction to a mean reduction of 6.97 mmHg at 40 minutes. Recovery of IOP was rapid and complete by 20 minutes. We conclude that compression of up to 40 minutes duration is beneficial, and suggest such devices should be left on until immediately prior to surgery to preserve the reduction achieved.