Evaluation on repeatability and accuracy of iCare IC100 tonometer in measuring intraocular pressure

AIM: To evaluate the repeatability and accuracy of iCare IC100 tonometer in measuring intraocular pressure(IOP)by comparing the correlation and difference with Goldmann applanation tonometry(GAT)and non-contact tonometer(NCT), and to compare the correlation of the three types of IOP measurement with the central corneal thickness(CCT).METHODS: Prospective study. A total of 90 outpatients(90 eyes)in Liaoning Aier Eye Hospital from March 2019 to May 2019 were randomly selected as study subjects. All patients were measured IOP using iCare IC100, NCT, and GAT. The interclass correlation coefficient(ICC)was used to evaluate the repeatability of IOP measured 3 times consecutively using an intraocular tonometer. The correlation and consistency of iCare IC100, GAT and NCT were compared by one-way ANOVA, Pearson linear correlation analysis and Bland-Altman analysis. The linear regression analysis was used to analyze the correlation of the three tonometers with CCT.RESULTS: The mean IOP measured with iCare IC100, GAT and NCT was 19.74±6.90, 19.88±7.07 and 18.47±6.31 mmHg, respectively(F=1.180, P=0.309). The measurements of iCare IC100 with GAT, iCare IC100 with NCT and GAT with NCT were all positively correlated(r=0.930, 0.946, 0.918, all P<0.05), the Bland-Altman analysis showed that the mean differences between iCare IC100 and GAT, iCare IC100 and NCT, GAT and NCT were -0.142±2.61, 1.27±2.24, and 1.41±2.81 mmHg, respectively, with 97%(87/90), 96%(86/90), and 97%(87/90)IOP differences distributed within their 95% confidence intervals. The IOP measured with iCare IC100 and CCT, GAT and CCT and NCT and CCT were all positively correlated(r=0.426, 0.353, 0.451, all P<0.01). The linear regression equations between iCare IC100, GAT and NCT measurement and CCT were iCare IC100 IOP=-19.62+0.074×CCT; GAT IOP=-13.54+0.063×CCT; NCT IOP=-19.65+0.072×CCT; that is, for every 10 μm increase in CCT, iCare IC100 measurement increased by 0.74 mmHg, GAT measurement increased by 0.63 mmHg, and NCT measurement increased by 0.72 mmHg.CONCLUSION: The iCare IC100 tonometer has good repeatability and accuracy in measuring IOP, and the CCT has a greater impact on the measurement of iCare IC100 than the GAT and NCT.