The Clinical Study Of Intraocular Pressure Measurement By Rebound Tonometer In Healthy Individuals

Objectives:To evaluate the accuracy of introcular pressure(IOP) measured by Icare rebound tonometer and IOPen rebound tonometer compared to Goldmann applanation tonometry,as well as to compare and analyze the influence of central corneal thickness (CCT) on the IOP measurements measured by rebound tonometer.Method:We selected 244 eyes of 124 healthy individuals for intraocular pressure measurement from March to May in 2009 in a ran-dom order.First,Icare and IOPen tonometer was performed in a random order, followed by GAT tonometer.Central corneal thickness (CCT) was also measured by Hand-held ultrasonic corneal pachymeter in every eye. Then compared the measurements of the three tonomet-ries with each other and correlated them with CCT seperately.Results:The average age of 124 subjects was 40.22±14.47 years (range,16-76 years). The mean IOP readings obtained by Icare, IOPen and GAT tonometer were 15.46±3.52mmHg,13.05±3.59mmHg, and 15.64±2.57mmHg,respectively IOP readings by IOPen tonometer were consistently lower than those by Icare and Goldmann tonometer. The IOP readings between Icare and GAT was not significantly different(Z=-1.193,P=0.233>0.05),the mean difference was-0.19±2.68 mmHg. There was a significant difference between IOPen and GAT (Z=-8.437,P=0.000<0.01),the mean difference was-2.60±4.17mmHg. Comparison with IOP readings of Goldmann applanation tonometry (GAT),Icare tonometer show good agreement,whereas IOPen tonom- eter understimate IOP readings.The differences between corresponding measures (Icare value minus GAT value) had a mean of-0.2mmHg, a standard deviation of 2.68mmHg, a 95% limits of agreement of-5.4 to 5.1mmHg. The maximum of absolute value of difference was 5.4mmHg. In almost 84% of differences between Icare and GAT measurements were within±3mmHg,68% were within±2 mmHg, and 47% within±1 mmHg. The differences between corresponding measures (IOPen value minus GAT value) had a mean of-2.6mmHg, a standard deviation of 4.17mmHg, a 95% limits of agreement of-10.8 to 5.6mmHg. The maximum of absolute value of difference was 10.8mmHg. The IOPen readings were within±3mmHg of the GAT readings in 49% of eyes, within±2mmHg in 34% of eyes, and within±1mm Hg in 16% of eyes. Icare and GAT displayed good correlation (rs=0.656,p<0.01), and no significantly correlation between IOPen and GAT (rs=0.122,p>0.05). The mean CCT values was 539.90±31.85μm The linear correlation showed Icare and GAT were influenced by CCT, the correlation coefficient were 0.382 and 0.342 (P<0.01). IOPen and CCT had no significant linear correlation(rs=-0.073,P>0.05).The readings of the Icare minus GAT were correlated with the CCT readings(rs=0.180, P<0.01). For every 10mm increase in CCT, the difference (Icare-GAT) increased by 0.17mmHg.Conclusion:There are good correlation and agreement with IOP readings between Icare and GAT tonometer. The Icare instrument is easy to use and without topical anesthesia,but it is still affected by CCT. However, the accuracy of IOPen tonometer was not good.