BACKGROUND The purpose of this study was to assess the accuracy of the ICare tonometer, using the Perkins applanation tonometer (AT) as the reference, in a sample population being treated with travaprost 0.004% for glaucoma. METHODS Twenty-eight consecutive patients with open-angle glaucoma or ocular hypertension who had been receiving travaprost 0.004% to control elevated intraocular pressure (IOP) were included in the study. IOP was measured in the entire sample with ICare and Perkins AT. The difference between the methods was plotted against the mean to compare the tonometers. The hypothesis of zero bias was examined by a paired t-test. The 95% limits of agreement (LoA) were also calculated. RESULTS As previously found in young healthy subjects, ICare showed a tendency to overestimate Perkins IOP measurements by a mean of 3.57 mmHg. The agreement between the two methods is shown by the 95% LoA which was from -9.37 to +2.23 mmHg: 53% of the IOP differences fell within +/-3 mmHg. CONCLUSIONS The performance of the ICare tonometer in glaucomatous patients being treated with travaprost 0.004% to lower the IOP appears to be similar to that of young healthy patients. The tendency of ICare to overestimate the IOP readings should be considered when the instrument is used in the follow-up of glaucomatous patients.