The Comparison Of Intraocular Pressure Measured By Icare Rebound Tonometer, Goldmann Applanation Tonometer And PASCAL Dynamic Contour Tonometer In Healthy Subjects

Intraocular pressure(IOP) measurement is the most important examination items in the basic and clinical work of ophthalmology. IOP measured accurately, safely, quickly is of great significance in the diagnosis and treatment of glaucoma. There are various kinds of tonometers in clinical practice, which including Goldmann applanation tonometer (GAT), Icare rebound tonometer(Icare), PASCAL dynamic contour tonometer (DCT), non-contact tonometer (NCT), Schiotz tonometer, Proview tonometer, Perkins tonometer, Diaton tonometer and Tono-pen tonometer,etc. Because the design principles are different from different tonometers, advantages and disadvantages of them are not the same. Some emphasize measurement method is simple,such as Proview. tonometer, Tonopen tonometer.Some of the measured processes are safety,such as NCT. Some have emphasized the standardization of measurement, such as GAT. Others have emphasized the authenticity of the measurement results,such as DCT. Eye puncture is the unique method to determinate the accurate IOP,while it can not be a routine diagnostic tool in clinical practice. Measuring IOP indirectly by wall of eyeball is the method of tonometers, while the results are influenced by a number of factors,such as the tensity of eyelid and eye muscle,mental state, endocrine factors, temperature changes.IOP values obtained by tonometers are affected by the physical characteristics of the eyeball,such as scleral rigidity, corneal curvature,especially central corneal thickness (CCT). GAT was commonly used and has been considered as the gold standard for IOP measurement, but most of the scholars subscribed that its measurement results were significantly affected by CCT,and confirmd a linear correlation between the IOP value measured by GAT and CCT.DCT based on contour matching, its IOP values were independent of corneal characteristics, so the IOP value measured by DCT did not affected by CCT and other corneal physical-characteristics. Many studies have shown the veracity of DCT. Icare rebound tonometer (Icare) was designed following the magnetic rebound principles, it has the advantages of accurate measurement, easy operation and broad scope of application,ect. Research showed that CCT had a significant impact on the IOP values of Icare. At present, many foreign hospitals have been put it into using in clinical. The varying digrees which were vulnerable to the different CCT were different from different tonometers, so the IOP values of the same individual measured at the same time and on the same place may vary from different tonometers.Domestic and international research showed that IOP values obtained by Icare,GAT and DCT were different,but there were good correlation among them. CCT have a significant impact on the IOP values of Icare and GAT, but have little impact on the IOP value of DCT. Previous studies on glaucoma and intraocular hypertention of our department have confirmed that the IOP of Icare,GAT and DCT had a good correlation between each other for most population, IOP of Icare and GAT were affected by CCT,while DCT was not. Consistency evidenced a lack of agreement between both every two tonometers before CCT correction, and could not be interchanged in clinic. There was a agreement of IOP between Icare and DCT after CCT correction, while disagreement between the measurements taken by Icare and GAT, GAT and DCT after correcting according to CCT. The purpose of this study was to compare the IOP values measured by Icare, GAT and DCT in healthy subjects,to further evaluate the performance of Icare, especially to evaluate the effects of CCT on IOP values measured by Icare,and to explore the exchange possibilities and methods of IOP between each two tonometers in clinical,we conducted the following study.Objective1. Comparing the IOP values measured with Icare,GAT and DCT in healthy subjects,analysing the correlation between each other.2. Comparing the IOP values measured with Icare,GAT and DCT in the thin,normal and thick CCT groups,then evaluating the effect of CCT on IOP values of Icare,GAT and DCT.3. evaluating the agreement among the IOP values obtained by Icare,GAT and DCT before and after the correction according to CCT,then to explore the possibilities and methods of IOP exchange in clinical between each two tonometers.MethodsIOP measurements were carried out with Icare, GAT, and DCT in 185 eyes of 93 cases by the same person in the same darkroom, the IOP measurement of Icare, DCT, and GAT were carried out in the order, right eyes are first measured, left eyes are post-test. CCT measurement were peformed on each eyes using corneal thickniss measuring instrument of model NIDEK-UP-1000.Statistical methods:ANOVA of repeated measurement data and Mutiple comparison was applicated to compare the IOP values measured by Icare, GAT and DCT. The relevance of the three pairs of variables were evaluated by pearson correlation analysis. The effect of CCT on IOP of Icare, GAT and DCT was assessed by pearson correlation analysis and linear regression analysis. Paired t test, Pearson correlation analysis and Bland-Altman analysis were applicated to analyze the consistency of IOP measured with every two tonometers before and after CCT correction.Results 1. IOP measurements were carried out with Icare, GAT and DCT in 184 eyes of 92 cases,the mean IOP measured were (16.92±3.56) mmHg(1mmHg=0.133kP), (16.30±3.33) mmHg, (15.56±2.58) mmHg, respectively, which was significant difference(F=17.692, P<0.001). There was significant positive correlation between each other at the same time(Icare/GAT:r=0.878,p< 0.001;Icare/DCT:r=0.587,P<0.001;GAT/DCT:r=0.680,p<0.001).2. The mean IOP value has the order of GAT,Icare and DCT in the thin CCT group,while in the normal CCT group and the thick CCT group,the mean IOP value of DCT,GAT and Icare rose in turn.There was no significant difference among IOPs of eyes measured by Icare, GAT and DCT in the thin CCT group (Fright=0.859, Pright>0.05;Fleft=2.834, Pleft>0.05) but it was quite the opposite in the other groups (normal:Fright=5.013, Pright<0.05; Fleft=16.099, Pleft<0.001; thick:Fright=34.324,Pright<0.05; Fleft=15.907,Pleft<0.001). The IOP differences between Icare and GAT/DCT showed on satistical significance in the thin CCTgroup but it was quite opposite in the other groups. The mean IOP difference of Icare/GAT, Icare/DCT and GAT/DCT increase along with the increasing of CCT.3. The Pearson correlation analysis indicated that IOPs of Icare and GAT had a significant positive correlation with CCT(ricare=0.473,P<0.001; rGAT=0.439,p< 0.001, respectively),while the correlation between IOPs by DCT and CCT was quite opposite(r=0.101,p=0.171). The regression equation between IOPs of Icare and CCT is Icare=0.046CCT-8.531(F=52.346, P<0.001),and the regression equation between IOPs of GAT and CCT is GAT=0.040CCT-5.765(F=43.344, P <0.001).4. Paired t test, Pearson correlation analysis and Bland-Altman analysis were applicated to analyze the consistency of 93 normal person(185 eyes)'s IOP:①he difference of IOP by Icare and GAT,Icare and DCT, GAT and DCT was (0.61±1.71) mmHg,(1.33±2.94) mmHg,(0.71±2.47) mmHg respectively before CCT correction, and significant statistics difference was found in comparison(p<0.001). The difference of IOP by Icare and GAT,Icare and DCT, GAT.and DCT was (0.39±1.70) mmHg,(0.09±2.56) mmHg,(-0.30±2.15) mmHg respectively after CCT correction, and the difference of IOP value of Icare and GAT was obvious(P<0.05) after CCT correction, while the difference between Icare and DCT,GAT and DCT was quire opposite(P>0.05).②here were significantly correlation (p<0.001) between each two tonometers (before CCT correction:Icare/GAT:r=0.879, Icare/DCT:r=0.583, GAT/DCT:r=0.678; after CCT correction:Icare/GAT:r=0.848, Icare/DCT:r=0.615, GAT/DCT: r=0.713).③Before the correction according to CCT,the 95% limits of agreement between Icare and GAT was (-2.74,3.96) mmHg, the range was 6.70mmHg,while it was (-2.93,3.72) mmHg after the correction according to CCT,and the range was 6.65mmHg. Before the correction.according to CCT,the 95% limits of agreement between Icare and DCT was (-4.43,7.09) mmHg, the range was 11.52 mmHg,while it was (-4.93,5.11) mmHg after the correction according to CCT,and the range was 10.04 mmHg. Before the correction according to CCT,the 95% limits of agreement between GAT and DCT was (-3.11,5.53) mmHg, the range was 8.64 mmHg,while it was (-4.51,3.91) mmHg after the correction according to CCT,and the range was 8.42 mmHg.Conclusions1. There was good correlation between the IOP values of Icare and.the IOP of GAT or DCT,thus the IOP value measured by Icare rebound tonometer was believable.2. IOPs measurement by DCT did not correlate with CCT in healthy eyes,both Icare and GAT measurements are influenced by CCT, but the extent and the ways of the dependency maybe different from Icare to GAT.3. The IOP obtained with Icare,GAT and DCT can not be interchanged in clinic before CCT correction. However the IOP values of Icare and GAT,Icare and DCT can be exchanged after correcting according to CCT,the IOP values of GAT and DCT can not be interchanged after CCT correction.