Evaluation of the Icare-ONE rebound tonometer as a self-measuring intraocular pressure device in normal subjects

To compare Icare ONE rebound self-tonometer (ICRBT) measurements with Goldman applanation tonometry (GAT). A trained examiner instructed each of 60 normal subjects on use of the ICRBT. Each subject then took two measurements of his/her own pressure using the ICRBT. Finally, a different examiner, who was masked to the earlier readings, measured IOP by GAT. Bland-Altman limits of agreement (LOA), intraclass correlation coefficients (ICCs), Kappa values, and paired t-test were used to assess the agreement between the two methods. Pearson's correlation coefficient was used for correlation analysis. All of the subjects were able to obtain correct measurements with ICRBT after three attempts. The mean intraocular pressure with ICRBT and GAT measurements were 16.0 +/- 3.3 mmHg and 13.7 +/- 2.5 mmHg respectively. The mean difference between patient's ICRBT and technician's GAT measurements was 2.3 mmHg (p < 0.001). In 63 % (38/60) of the cases the IOP difference (ICRBT - GAT) was within +/- 3 mmHg. The weighted Kappa for the IOP measurements of the two methods was 0.49 (95% CI: 0.30-0.68, p < 0.001), indicating acceptable agreement. A significantly positive correlation was found between ICRBT IOP measurements and central corneal thickness (CCT) (r = 0.48, p < 0.001). In addition, the difference in IOP measurements (ICRBT - GAT) between the two methods was positively correlated with CCT (r = 0.31, p = 0.015), indicating that greater thickness is associated with greater differences between the two methods. The ICRBT was reliable in the hands of normal subjects, and may be used for self-monitoring of IOP. ICRBT measurements generally overestimated GAT measurements.