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

Intraocular pressure(IOP) measurement is an important examination items in the clinical work of ophthalmology, but also plays a key role in the diagnosis, monitoring and follow-up of glaucoma. IOP charactrized with its diurnal fluctuations because it was vulnerable to a variety of factors. Eye puncture was the unique method to determinate the accurate IOP,while it could not be a routine diagnostic tool in clinical practice,IOP measurement usually carried out using all kind of tonometers in the clinical practice.There were many tonometers used currently in clinical,which including Goldmann applanation tonometer (GAT),PASCAL dynamic contour tonometer (DCT), non-contact tonometer (NCT),Schiotz tonometer, Proview tonometer, Perkins tonometer, Tono-pen tonometer and Diaton tonometer,etc.Because the design concepts and measurement methods were different from different tonometers, some characterized with their convenience during IOP measurement, such as Schiotz tonometer, Perkins tonometer, Tono-pen tonometer and Proview tonometer;some were safe to conduct IOP measurement,such as NCT;some have emphasized the standardization of measurement, such as GAT;others have underlined the authenticity of the measurement results,such as DCT;while others characterized with their convenience,safety and accuracy, such as Diaton and Icare. The measurement principle and methods are different from different tonometers,each tonometer had their own advantages and disadvantages.The IOP measurement results were vulnerable to a variety of factors,these factors including:1.environmental factors such as pressure, temperature,humidity and lighting conditions, etc;2.many factors could affect the IOP measurement results which including different tonometers and operators, anesthesia, also collar was too tight and the watching time had an effect on IOP; 3.some individual factors such as gender,age,body shape and general conditions (blood pressure, blood glucose, blood viscosity, hormone levels, plasma osmolality); 4.IOP in the same individual could change because it can be affected by time, sports, menstrual cycles and postular change.Some of these factors led to different IOP levels in the normal individuals,and some led to the IOP fluctuations in the same individual, and some can interfered the authenticity and accuratecy of the IOP measurement results. The IOP authenticity and accuratecy of varying digrees and diffetent ways which due to the above-mentioned factors were different from different tonometers.The IOP measurements using all kinds of tonometers can only be carried out on the eyeball indirectly, so that the IOP values obtained by tonometers were vulnerable to the physical characteristics of eyeball,such as scleral rigidity, corneal curvature,especially central corneal thickness (CCT), etc.GAT was commonly used and has been considered as the golden standard for IOP measurement in clinical, but its measurement results were significantly affected by CCT.While as a new tonometer, many studies have shown that the IOP value measured by DCT did not be affected by CCT and other corneal physical characteristics.The effect of 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.some of the IOP values measured by two different tonometers can be interchanged directly but some need to go through a correction.In order to get an truer IOP,the IOP measured by tonometers was usually corrected by an formula-related according to patients' CCT. As a new tonometer, Icare rebound tonometer (Icare) was designed following the magnetic rebound principles, and its convenient carrying and measurement have placed it into an advantage.At present, many foreign hospitals have been put it into using in clinical.Currently,a number of related research have been carried out at abroad. their research showed that:the IOP of Icare,GAT and DCT showed a good correlation between each other;CCT had a significant impact on the IOP values of Icare and GAT, while had little impact on the IOP value of DCT.However, there was little current Icare-related research in domestic, at the same time,there was yet no study which related to the exchange methods and the possibility of the IOP between each two different tonometers at home and abroad.In order to further evaluated the performance of Icare, especially to evaluate the effects of CCT on IOP values measured by Icare,and to fill gaps of Icare-related research in domestic;at tha same time,in oder to explore the exchange possibilities and methods of IOP between each two tonometers in clinical,we conducted the following study.Objectives1. Compared the IOP values obtained by Icare,GAT and DCT in a whole large samples and in high,medium and low IOP groups,then evaluating the accuracy of Icare in the IOP measurement;2. Compared the IOP values obtained by Icare,GAT and DCT in the thin,medium and thick CCT groups;then evaluated the effect of CCT on IOP values of Icare,GAT and DCT,especially to evaluated the effect of CCT on IOP values of Icare;3. Application of Bland-Altman analysis to evaluate the agreement among the IOP values obtained by Icare,GAT and DCT which were corrected according to CCT,then to explore the possibilities and methods of IOP exchange in clinical between each two tonometers.Methods1.IOP measurements were carried out with Icare, GAT, and DCT randomly in 152 eyes of 78 cases by the same person in the same darkroom, the IOP measurement of Icare, GAT, and DCT were carried out in the order, right eyes are first measured, left eyes are post-test. 2.CCT measurement were peformed on each eyes using corneal thickniss measuring instrument of model NIDEK-UP-1000.3.Statistical methods:ANOVA of repeated measurement data and LSD-t test 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; the conversion of IOP between two different tonometers was assessed by linear regression analysis;Bland-Altman analysis was applicated to evaluate the agreement of Icare, GAT and DCT.Results1. IOP measurements were carried out with Icare, GAT, and DCT randomly in 152 eyes of 78 cases,the mean IOP values of Icare,GAT and DCT were 19.16±5.03(mmHg),18.41±4.52(mmHg) and 17.23±3.69 (mmHg) respectively, there were significant differences among them(F=7.256,P=0.001), at the same time, there was significant differences between the IOP values of each two tonometers,however, there was significant correlation between each other at the same time(Icare/GAT:r=0.940,p<0.001;Icare/DCT:r=0.745,p<0.001;GAT/DCT:r=0.800;p< 0.001).2.IOP values measured with Icare, GAT, and DCT were higher in turn in the low IOP group, while lower in turn in the medium and high IOP groups.The mean IOP differences showed statistical significance in each two kinds of tonometers(low IOP group:F=7.610,P=0.001; medium IOP group:F=22.940, P＜0.001; high IOP group:F=15.285, P<0.001),which was same as those in all IOP groups.The mean IOP differences among the three IOP groups increased along with the increasing of IOP,meanwhile,the difference in high IOP group was about 2 times as much as those in the middle IOP group.3. The mean IOP value of DCT was the highest in the thin CCT group, while GAT was the lowest;in the normal CCT group and the thick CCT group,the mean IOP value of Icare,GAT,and DCT was in turn reduces.The IOP differences between Icare and GAT/DCT showed no statistical significance in the thin CCT group but it was quite the opposite in the other groups. The mean IOP difference of Icare/GAT, Icare/DCT and GAT/DCT increased along with the increasing of CCT.4. The same as the correlation between IOP values of Icare and CCT,IOP values of GAT showed a sinificant correlation with CCT(IOPIcare/CCT:r=0.341,P< 0.001;IOPGAT/CCT:r=0.333,P<0.001),while the correlation between IOP values of DCT with CCT was quite opposite(r=0.032,P=0.699).5. There was no significant differences among the IOP values of Icare,GAT and DCT after the correction according to CCT (F=0.775,P=0.461).Mutiple comparison shown that:the mean difference between IOP value of Icare and those of DCT after the correction according to CCT was-0.04±2.95 (mmHg),it shown no statistical significance(t=-0.162, p=0.879), meanwhile,the IOP values of Icare showed a close relationship with those of DCT(r=0.782,p<0.001).The mean difference in IOP value of Icare and GAT and in IOP value of GAT and DCT after the correction according to CCT were 0.51±1.71 (mmHg) and-0.54±2.33 (mmHg) respectively, although the differences were smaller than those before correction according to CCT,they still showed a statistical significance.6. The 95% limits of agreement between Icare and GAT was-2.62mmHg to 4.14mmHg before the correction according to CCT,while it was-2.85mmHg to 3.86 mmHg after the correction according to CCT;the 95% limits of agreement between Icare and DCT before and after the correction according to CCT were-4.65mmHg to 8.51 mmHg and-5.83mmHg to 5.75 mmHg respectively;the 95% limits of agreement between GAT and DCT was-4.15mmHg to 6.49 mmHg before the correction according to CCT, while it was-5.11mmHg to 4.02 mmHg after the correction according to CCT.The 95% limits of agreement after the correction according to CCT was all narrowed than those before the correction according to CCT.Conclusions1. There was small difference and close relationship between the IOP values of Icare and the IOP of GAT/DCT,thus the IOP values of Icare was believable in the clinical practice.2. The IOP values of Icare and GAT showed a significant dependency on CCT, but the extent and the ways of the dependency maybe different from Icare to GAT,while the IOP values of DCT showed little dependency on CCT.3. It was temporarily unable to evaluate the consistency between IOP values of Icare and DCT using the Bland-Altman analysis, but the mean difference between the IOP of Icare and DCT after being corrected according to CCT was less than 0.5mmHg,pearson correlation analysis have shown that there was closely correlation between IOP values of Icare and DCT,at the same time,meanwhile,t tests have shown that IOP values of Icare did not different from those of DCT significantly,so the IOP of Icare showed a good consistency with the IOP of DCT and they could be interchanged directly in clinical after the correction according to CCT,however, it was quite the opposite before the correction according to CCT.4. As same as the consistency between IOP of Icare and those of GAT which were both calculated out by a single formula according to CCT,the IOP values of Icare did not have a good consistency with those of GAT before the correction according to CCT,so they could not be interchanged directly both before and after the correction according to CCT in clinical;at the same time,the IOP values of GAT and DCT could not be interchanged directly both before and after the correction according to CCT.