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

PURPOSE: To compare Icare ONE rebound self-tonometer (ICRBT) measurements with Goldman applanation tonometry (GAT). METHODS: 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. Bland­Altman 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. RESULTS: 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: 0.30­0.68, 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. CONCLUSION: 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.

Comparison of dynamic contour tonometry with Goldmann applanation tonometry in glaucoma practice.

PURPOSE: To compare intraocular pressure (IOP) readings taken using dynamic contour tonometry (DCT) with IOP readings taken with Goldmann applanation tonometry (GAT) in eyes with glaucoma or ocular hypertension. METHODS: The present study included 100 eyes in 100 patients with glaucoma or ocular hypertension. After pachymetry DCT and GAT were performed. Intraocular pressures as measured with DCT and GAT were compared with one another and with central corneal thickness (CCT). RESULTS: Mean DCT IOP measurements (20.1 +/- 4.3 mmHg) were significantly (p < 0.001) higher than GAT IOP values (17.9 +/- 4.7 mmHg). The mean difference between DCT and GAT measurements was 2.1 mmHg (range -3.4 to 9.7 mmHg). The difference followed a normal distribution. Measurements made with DCT and GAT correlated significantly with one another (Spearman's rho = 0.761, p < 0.001). Neither GAT nor DCT measurements showed a significant correlation with CCT (537 +/- 39 microm, range 458-656 microm). Multivariate regression analysis has shown that the difference between DCT and GAT is influenced significantly by ocular pulse amplitude (r = -0.334, p = 0.001) and it is not influenced by CCT (r = -0.106, p = 0.292). CONCLUSIONS: In eyes with glaucoma or ocular hypertension, DCT facilitates suitable and reliable IOP measurements which are in good concordance with GAT readings. Variation in CCT cannot by itself explain the differences in measurements taken with DCT and GAT in a number of eyes.