Comparison of dynamic contour tonometry with goldmann applanation tonometry

PURPOSE: The dynamic contour tonometer (DCT; Pascal tonometer) is a novel tonometer designed to measure intraocular pressure (IOP) independent of corneal properties. The purpose of this study was a comparison of the DCT with the Goldmann applanation tonometer (GAT) with respect to mean of IOP readings, the influence of ocular structural factors on IOP readings, and both intra- and interobserver variability, in a large group of healthy subjects. METHODS: In a prospective study of 228 eyes, IOP measurements by GAT and DCT were compared, and the effects of central corneal thickness (CCT), corneal curvature, axial length, and anterior chamber depth were analyzed. To evaluate intra- and interobserver variability, IOP was measured in eight eyes by four observers. RESULTS: There was a high concordance between the IOP readings obtained by DCT and GAT. However, IOP readings were consistently higher with DCT than with GAT (median difference: +1.7 mm Hg, interquartile range [25th-75th percentile] = 0.8-2.7 mm Hg). In contrast to GAT, multivariable regression analysis showed no significant effect of corneal thickness, corneal curvature, astigmatism, anterior chamber depth, and axial length on DCT readings. For repeated measurements the intraobserver variability was 0.65 mm Hg for the DCT and 1.1 mm Hg for the GAT (P = 0.008). Interobserver variability was 0.44 mm Hg for the DCT and 1.28 mm Hg for the GAT (P = 0.017). CONCLUSIONS: IOP measurements by DCT are highly concordant with IOP readings obtained from GAT but do not vary in CCT and have a lower intra- and interobserver variability. DCT seems to be an appropriate method of tonometry for routine clinical use.     

Comparison of dynamic contour tonometry with goldman applanation tonometry over a wide range of central corneal thickness

PURPOSE: To compare dynamic contour tonometry with Goldmann applanation tonometry in structurally normal corneas over a wide range of central corneal thickness (CCT). PATIENTS AND METHODS: Twenty-five patients each with normal CCT (group A), thin corneas (group B), and thick corneas (group C) had IOP measured with the Goldmann (GAT) and dynamic contour tonometer (DCT). RESULTS: In group A (mean CCT = 552 +/- 16 microm) the mean GAT was 15.9 +/- 3.1 mm Hg and mean DCT was 16 +/- 3.3 mm Hg (P = 0.91). In group B (mean CCT = 491 +/- 19 microm) the mean GAT was 13.2 +/- 3.5 mm Hg and the mean DCT was 15.9 +/- 3.5 mm Hg (P = 0.009). For group C (mean CCT = 615 +/- 22 microm), the mean GAT was 17.4 +/- 3.8 mm Hg and the mean DCT was 17.4 +/- 3.5 mm Hg (P = 0.95). The 95% agreement limits for DCT were -3.1 mm Hg to 2.9 mm Hg. The mean GAT-DCT difference was -2.6 mm Hg in thin corneas and -0.06 mm Hg in thick corneas. Below 520 microm reduction of 10 microm in CCT appears to result in a significant underestimation of the GAT IOP by 0.7 mm Hg (P < .001) and above 580 microm a non-significant overestimation of 0.2 mm Hg per 10 microm increase in CCT (P = 0.27). CONCLUSION: Dynamic contour tonometer agrees well on average with GAT but the agreement limits are wide. In structurally normal thin corneas DCT may give a more accurate assessment of the true IOP but it does not appear to have any benefit over GAT in thick corneas.     

The effect of corneal edema on dynamic contour and goldmann tonometry

PURPOSE: To determine the effect of contact lens-induced corneal edema on measurements of intraocular pressure (IOP) using the Pascal dynamic contour tonometer (DCT), compared with the Goldmann tonometer. METHODS: Thirty young healthy subjects (23.0 +/- 3.0 years) were recruited from the student population at the University of New South Wales. Thick hydroxyethyl methacrylate contact lenses were worn monocularly for 2 hours under closed-eye conditions to induce corneal edema via hypoxia. IOP (Goldmann and Pascal DCT), ocular pulse amplitude (OPA), and central corneal thickness (CCT) were measured in both eyes before and after lens wear. Paired t-tests, Pearson correlation, and Bland-Altman plots were used to identify changes in, and relationships between, these parameters resulting from corneal edema. RESULTS: Lens wear resulted in statistically significant changes in CCT (+48.3 +/- 14.4 microm, p < 0.001), Goldmann IOP (+1.5 +/- 2.8 mm Hg, p = 0.007), and Pascal DCT IOP (-0.7 +/- 1.1 mm Hg, p = 0.001) but not OPA (0.0 +/- 0.3 mm Hg, p = 0.721, two-tailed paired t-test). The Pascal DCT provided IOP readings that were 1.3 +/- 2.0 mm Hg higher than the Goldmann IOP readings when hydration was normal, but the Goldmann tonometer provided readings that were 0.8 +/- 2.5 mm Hg higher than the Pascal DCT readings when the cornea was edematous. The variation between the two instruments was weakly correlated to the change in CCT (r = -0.261, p = 0.044). CONCLUSIONS: Contact lens-induced corneal edema caused a small underestimation error in IOP measurements by the Pascal DCT, and an overestimation error in Goldmann tonometry measurements. The OPA measurement provided by the Pascal DCT is insensitive to corneal edema-induced changes in corneal properties.     

Comparisons between Pascal dynamic contour tonometry, the TonoPen, and Goldmann applanation tonometry in patients with glaucoma

PURPOSE: To compare intraocular pressure (IOP) measurements taken with Pascal dynamic contour tonometry (DCT), the TonoPen and the Goldmann applanation tonometry (GAT). The influence of central corneal thickness (CCT) on IOP measurements taken with Pascal DCT and the TonoPen was evaluated. METHODS: One eye in each of 101 consecutive patients with primary open-angle glaucoma (POAG) underwent ultrasonic CCT measurement and IOP evaluation with GAT, Pascal DCT and the TonoPen in random order. The agreement between results from Pascal DCT and the TonoPen and those of GAT was assessed using the Bland-Altman method. The deviation of Pascal DCT and TonoPen readings from GAT values, corrected for CCT, was calculated and correlated to CCT using a linear regression model. RESULTS: The mean of the differences in IOP measurements was 3.2 +/- 2.4 mmHg for Pascal DCT minus GAT readings and 0.5 +/- 4.5 mmHg for TonoPen minus GAT readings. The 95% confidence interval of differences in IOP measurements was higher between TonoPen and GAT readings (- 6 to 7 mmHg) than between Pascal and GAT readings (0.1-6.8 mmHg). Pascal DCT significantly overestimated IOP compared with GAT, especially for higher IOP readings. Bland-Altman scatterplots showed reasonable inter-method agreement between Pascal DCT and GAT measurements, and poor agreement between TonoPen and GAT measurements. The deviations of Pascal DCT and TonoPen readings from the corrected GAT values were both highly correlated with CCT values (linear regression analysis, p < 0.0001). The mean change in measured IOP for a 10-microm increase in CCT was 0.48 mmHg for Pascal DCT and 0.74 mmHg for the TonoPen. CONCLUSIONS: Agreement with GAT measurements was higher for Pascal DCT than for TonoPen readings; however, Pascal DCT significantly overestimated IOP values compared with GAT. Measurements of IOP obtained with both Pascal DCT and the TonoPen appeared to be influenced by CCT, and this influence appeared to be greater for the latter.     

Comparison of Goldmann applanation tonometry, rebound tonometry and dynamic contour tonometry in normal and glaucomatous eyes

AIM: To compare the intraocular pressure (IOP) measurements obtained with the rebound tonometry (RT), dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in normal and glaucomatous eyes and investigate the effects of central corneal thickness (CCT) and corneal curvature (CC) on IOP measurements. METHODS: One hundred and twenty-four eyes of 124 subjects were enrolled in this cross-sectional study. Fifty-six of participants were healthy individuals and 68 of them were glaucomatous patients. IOP was measured on each subject always in the same order, ICare RT-Pascal DCT-GAT, after a minimum interval of 10min between measurements. CCT and CC were measured using a rotating Scheimpflug camera before the IOP measurements in all subjects. One way repeated measures ANOVA, Pearson correlation coefficient and regression analysis, and Bland-Altman analysis was used for the statistical assessment. RESULTS: Mean IOP for all enrolled eyes was 16.00±3.80 mm Hg for GAT, 16.99±4.91 mm Hg for RT, and 20.40±4.44 mm Hg for DCT. Mean differences between GAT and RT was -1.75±3.41 mm Hg in normal (P<0.001) and -0.37±3.00 mm Hg in glaucomatous eyes (P=0.563). Mean differences between GAT and DCT was -4.06±3.42 mm Hg in normal (P<0.001) and -4.67±3.12 mm Hg in glaucomatous eyes (P<0.001). GAT and RT were significantly positive correlated with CCT in normal (r=0.317, P=0.017 and r=0.576, P<0.001, respectively) and glaucomatous eyes (r=0.290, P=0.016 and r=0.351, P=0.003, respectively). DCT was also significantly positive correlated with CCT in normal eyes (r=0.424, P=0.001) but not in glaucomatous eyes (r=0.170, P=0.165). All tonometers were unaffected by CC. CONCLUSION: IOP measurements by RT and DCT were significantly higher than GAT. DCT has highest IOP measurements among these tonometers. RT was most influenced tonometer from CCT although all tonometers were significantly positive correlated with CCT except DCT in glaucomatous eyes. CC did not influence IOP measurements.     

Comparison of dynamic contour tonometry and goldmann applanation tonometry in deep lamellar and penetrating keratoplasties

PURPOSE: To compare the measurements of intraocular pressure (IOP) with dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in eyes with corneal graft and to evaluate the influence of corneal thickness (CCT), corneal curvature (CC), and astigmatism on these methods. DESIGN: Prospective, observational cross-sectional study. METHODS: Eighteen eyes of 18 patients after penetrating keratoplasty (PKP) and 14 eyes of 14 patients after deep lamellar keratoplasty (DLKP) underwent IOP evaluation with DCT and GAT, and measurements of CCT, CC, and astigmatism. Bland-Altman plots were used to evaluate the agreement between tonometers. Multivariate regression analysis was used to evaluate the influence of ocular structural factors and running suture on IOP measurements obtained with both tonometers. RESULTS: IOP values obtained by DCT and GAT were strongly correlated in all eyes (r = .91; P < .001). DCT values measured 2.5 +/- 1.7 mm Hg higher than GAT readings (P < .001). A reduction of the mean IOP difference between DCT and GAT with an increase in IOP values (P < .001) was found. Regression analysis showed no effect of CCT, CC, astigmatism, and running suture on both DCT and GAT readings, either in DLKP or in PKP eyes. CONCLUSIONS: We found a good overall correlation between both tonometers but the agreement between instruments differs in high or low IOP ranges. The wide and varying 95% limits of agreement between DCT and GAT indicates that DCT provides IOP measurements on deep lamellar and penetrating keratoplasties which can be used in the clinical practice.     

Dynamic contour tonometry versus Goldmann applanation tonometry: a comparative study

Background Various sources of error, including central corneal thickness (CCT) and structural corneal rigidity, have been proposed for Goldmann applanation tonometry (GAT). The Pascal dynamic contour tonometer (DCT) is a novel device designed for intraocular pressure (IOP) measurements assumed to be largely independent of CCT and corneal curvature. We compared DCT with GAT in eyes with normal corneas of various thickness.Methods We prospectively measured IOP using DCT and GAT in random order in 100 eyes of 100 subjects (M:F=46:54; mean age 42±19, range 23–88 years).Results Mean DCT values were about 1mmHg higher than GAT readings (16±3 vs 15±3 mmHg, p=0.001). Bland–Altman analysis of individual pairs of DCT and GAT measurements revealed a bias of –1.0 mmHg [95% confidence interval (CI): ±1.2]. Neither GAT nor DCT showed a significant correlation with CCT (533±48, range 399–641 m).Conclusions In eyes with normal corneas, DCT allows suitable and reliable IOP measurements which are in good concordance with GAT. Comparison of DCT with intracameral manometry is desirable in the future.     

Comparison of intraocular pressure measured by Pascal dynamic contour tonometry and Goldmann applanation tonometry

AIMS: To compare the intraocular pressure (IOP) measurements obtained using the Pascal dynamic contour tonometer (PDCT) with the standard Goldmann applanation tonometer (GAT) and to correlate these with central corneal thickness (CCT) in patients with normal corneas. METHODS: A prospective, masked, comparative case series of 116 eyes from patients attending a glaucoma clinic. IOP was measured with PDCT by one examiner and with GAT by a masked, independent examiner. A mean of six CCT readings was used for analysis. RESULTS: IOP measured by the two instruments correlated significantly (r=0.77; P<0.0001). IOP measured by GAT correlated strongly with CCT (r=0.37, P=0.0001) whereas the relationship between IOP measured by PDCT and CCT approached significance (r=0.17, P=0.073). The differences between GAT and PDCT measured IOP also correlated strongly with CCT (r=0.37, P<0.0001). The 95% limits of agreement between GAT and PDCT were +/-4.2 mmHg. Dividing the eyes into three groups on the basis of CCT, demonstrated those in the thickest tertile showed a poorer agreement between instruments and the GAT measured significantly higher IOP in this group (P=0.003) while the PDCT showed no significant differences with different CCTs (P=0.37). CONCLUSION: Demonstration of the relative independence of PDCT IOP measurements from CCT supports a potential clinical role for this instrument, particularly for subjects with CCT outside the normal range.     

Dynamic contour tonometry in comparison to intracameral IOP measurements

PURPOSE: The purpose of the study was to examine the effect of central corneal thickness (CCT), corneal curvature, astigmatism, axial length (AL), and age on measurements with the Pascal Dynamic Contour Tonometer (DCT). METHODS: In a prospective clinical trial 75 eyes of 75 patients undergoing phacoemulsification were examined. Before phacoemulsification, the anterior chamber was cannulated at the temporal corneal limbus. In a closed system the IOP was directly set to 15, 20, or 35 mm Hg with a manometric water column. IOP measurements taken by DCT were compared to intracameral measurements with a precision reference pressure sensor. RESULTS: Measurements from 60 patients were suitable for statistical analysis. At IOP of 15 mm Hg, the mean difference between IOP measured by DCT and intracameral IOP was -0.02 +/- 1.32 mm Hg; at 20 mm Hg it was -0.2 +/- 1.44 mm Hg and at 35 mm Hg, -0.84 +/- 1.90 mm Hg. The concordance coefficient according to Lin was 0.9763, showing good agreement between DCT- and intracamerally measured IOP. There was a statistically significant correlation between the difference in IOP measured by DCT minus intracameral IOP and CCT (P = 0.0291, R2 = 0.00012). All other parameters had no statistically significant effect on the difference between DCT and intracameral IOP (corneal curvature, P = 0.6094, R2 = 0.00367; age, P = 0.9198, R2 = 0.000003; astigmatism, P = 0.1564, R2 = 0.08497; and axial length, P = 0.9484, R2 = 0.00008). CONCLUSIONS: Measurements with the DCT showed good concordance with intracameral IOP. CCT exerted a statistically significant but clinically irrelevant effect on measurements with the DCT.     

A comparison of four methods of tonometry: method agreement and interobserver variability

AIM: To compare the inter-method agreement in intraocular pressure (IOP) measurements made with four different tonometric methods. METHODS: IOP was measured with the Goldmann applanation tonometer (GAT), Tono-Pen XL, ocular blood flow tonograph (OBF), and Canon TX-10 non-contact tonometer (NCT) in a randomised order in one eye of each of 105 patients with ocular hypertension or glaucoma. Three measurements were made with each method, and by each of two independent GAT observers. GAT interobserver and tonometer inter-method agreement was assessed by the Bland-Altman method. The outcome measures were 95% limits of agreement for IOP measurements between GAT observers and between tonometric methods, and 95% confidence intervals for intra-session repeated measurements. RESULTS: The mean differences (bias) in IOP measurements were 0.4 mm Hg between GAT observers, and 0.6 mm Hg, 0.1 mm Hg, and 0.7 mm Hg between GAT and Tono-Pen, OBF, and NCT, respectively. The 95% limits of agreement were smallest (bias +/-2.6 mm Hg) between GAT observers, and larger for agreement between the GAT and the Tono-Pen, OBF, and NCT (bias +/-6.7, +/-5.5, and +/-4.8 mm Hg, respectively). The OBF and NCT significantly underestimated GAT measurements at lower IOP and overestimated these at higher IOP. The repeatability coefficients for intra-session repeated measurement for each method were +/-2.2 mm Hg and +/-2.5 mm Hg for the GAT, +/-4.3 mm Hg for the Tono-Pen, +/-3.7 mm Hg for the OBF, and +/-3.2 mm Hg for the NCT. CONCLUSIONS: There was good interobserver agreement with the GAT and moderate agreement between the NCT and GAT. The differences between the GAT and OBF and between the GAT and Tono-Pen probably preclude the OBF and Tono-Pen from routine clinical use as objective methods to measure IOP in normal adult eyes.     

Comparison of IOP measurements between ORA and GAT in normal Chinese.

PURPOSE: To compare intraocular pressure (IOP) obtained from the ocular response analyzer (ORA) and Goldmann applanation tonometer (GAT) on a group of normal Chinese. METHODS: One hundred twenty-five normal subjects were recruited, with one eye randomly selected for this study. Each eye was measured first with the noncontact tonometer ORA, followed by the GAT and ultrasound pachometry, in a randomized order. Four readings were obtained from the ORA, and three measurements were taken with the GAT. The mean was used for analysis. The ORA provided a Goldmann-correlated IOP (IOPg) and a corneal-compensated IOP (IOPcc). Three central corneal thickness (CCT) values were measured using an ultrasound pachometer, and the mean was used for analysis. RESULTS: IOP obtained from the ORA was similar to that from the GAT (IOPg minus GAT: mean difference = 0.33 mm Hg, 95% limits of agreement = 4.55 to -4.44 mm Hg; IOPcc minus GAT: mean difference = 0.24 mm Hg, 95% limits of agreement = 4.83 to -5.07 mm Hg). CCT was positively associated with corneal hysteresis (CH) (r2 = 0.30, p < 0.01), corneal resistance factor (r2 = 0.38, p < 0.01), GAT (r2 = 0.09, p < 0.01) and IOPg (r2 = 0.16, p < 0.01). IOPcc was not associated with CCT (r2 = 0.01, p = 0.33). CONCLUSIONS: Both IOPg and IOPcc have good agreement with GAT on normal subjects. The influence of CCT on IOPcc was insignificant.     

Comparison of dynamic contour tonometry and noncontact tonometry in ocular hypertension and glaucoma

PURPOSE: To assess the agreement in the measurement of intraocular pressure obtained by dynamic contour tonometer (DCT) and noncontact tonometer (NCT) in patients with glaucoma and ocular hypertension, to investigate the effect of corneal thickness on pressure readings by both instruments, and to assess the reproducibility of dynamic contour tonometer. METHODS: NCT and DCT measurements were made on 104 eyes of 104 patients with primary open-angle glaucoma (n=75) or ocular hypertension (n=29), and agreement was assessed by means of Bland-Altman plots. The effect of corneal thickness on both tonometers was assessed by linear regression analysis. Interobserver and intraobserver variations for dynamic contour tonometer were assessed in 41 eyes of 41 patients. RESULTS: The mean difference+/-SD (95% limits of agreement) between NCT and DCT was -0.80+/-2.98 (-6.6 to 5.1) mm Hg (P=0.009) and no relation between NCT/DCT differences and average was found. The intraocular pressure readings obtained by noncontact tonometer depended on central corneal thickness (P<0.001, adjusted r(2)=0.301). However, dynamic contour tonometer readings showed no effect of corneal thickness (P=0.388, adjusted r(2)=-0.002). The coefficient of repeatability for DCT was 0.92 (95% CI 0.85-0.96, P=0.001). CONCLUSION: In subjects with primary open-angle glaucoma and ocular hypertension, NCT and DCT readings are not interchangeable. DCT measurements, unlike NCT measurements, did not depend on corneal thickness.     

Comparison of dynamic contour tonometry and Goldmann applanation tonometry in relation to central corneal thickness in primary congenital glaucoma

Background

To compare intraocular pressure (IOP) measurements obtained with dynamic contour tonometer (DCT) and Goldmann applanation tonometer (GAT), and to investigate their relationship to central corneal thickness (CCT) in primary congenital glaucoma (PCG) eyes.

Methods

Thirty-one eyes of 31 PCG patients (25.7?±?7.2 years old) were examined. PCG was defined as elevated IOP, enlarged corneal diameter (buphthalmos), Haab’s striae and abnormal findings at gonioscopy. The mean of three measurements of GAT, DCT (quality scores 1 and 2), and CCT were obtained and assessed for agreement by means of Bland–Altman plot and for Spearman correlation test.

Results

Mean CCT was 534?±?72.3 μm (range: 430 to 610 μm). Mean IOP measurements were 15.1?±?4.2 mmHg (range: 5.5 to 22.7 mmHg) for DCT and 14.5?±?5.6 mmHg (range: 7.0 to 34.0 mmHg) for GAT (P?=?0.244). Spearman correlation tests showed that IOP difference (DCT ? GAT) was not correlated with CCT (r ²?=?0.023, P?=?0.417). IOP measurements by DCT were weakly but statistically correlated with those obtained with GAT (r²?=?0.213, P?=?0.0089). Bland–Altman analysis revealed poor agreement between DCT and GAT readings, considering the 95 % confidence intervals of ±10.45 mmHg.

Conclusions

The differences between DCT and GAT readings were not influenced by CCT in this series of patients. Considering the weak correlation and the poor agreement observed between GAT and DCT measurements and that they both may be affected by corneal biomechanical changes, these methods should not be used interchangeably, and may possibly give no meaningful IOP values in PCG patients.     

Ocular response analyzer versus Goldmann applanation tonometry for intraocular pressure measurements

PURPOSE: To establish correlations between intraocular pressure (IOP) measurements obtained with the ocular response analyzer (ORA) and the Goldmann applanation tonometer (GAT). The effects of central corneal thickness on the measures obtained were also examined. METHODS: This was a cross-sectional study. IOP was determined in 48 eyes of 48 patients with glaucoma In all patients, central corneal thickness (CCT) was measured by ultrasound pachymetry. RESULTS: ORA readings were consistently higher than GAT measurements (Goldmann-correlated IOP - IOP GAT mean difference, 7.2 +/- 3.5 mm Hg; corneal-compensated IOP - IOP GAT mean difference, 8.3 +/- 4.0 mm Hg) However, differences were not constant and increased with increasing IOP GAT readings, both with respect to Goldmann-correlated IOP (slope = 0.623, P < 0.0001) and corneal-compensated IOP (slope = 0.538, P < 0.0001). Both pressure measurements provided by the ORA showed significant correlation with CCT (CCT versus Goldmann-correlated IOP: r = 0.460, P = 0.001; CCT versus corneal-compensated IOP: r = 0.442, P = 0.001). No significant effects of corneal curvature or refraction on any of the pressures were observed. CONCLUSIONS: The ORA significantly overestimates IOP compared with the GAT. Differences between both sets of measures increase as the GAT-determined IOP increases. ORA readings seem to be affected by central corneal thickness.     

Agreement of iCare IC200 tonometry with Perkins applanation tonometry in healthy children

PurposeTo assess interdevice agreement between the iCare IC200 rebound tonometer and Perkins applanation tonometry (gold standard) in a healthy pediatric population.MethodsA total of 42 eyes of 42 healthy children were assessed using both tonometers. Data was collected on subject’s age, sex, best-corrected visual acuity, and central corneal thickness (CCT). Intraclass correlation coefficient (ICC) and Bland-Altman analyses were used to determine agreement between IC200 and Perkins applanation tonometers. Linear regression analyzed the effects of intraocular pressure (IOP) on device difference.ResultsThe mean age and standard deviation of healthy pediatric subjects was 10.0 ± 3.3 years. The mean difference between IC200 and Perkins tonometers (IC200-Perkins) was 0.72 mm Hg, with a mean of 17.1 ± 3.0 mm Hg and 16.4 ± 2.5 mm Hg, respectively. The absolute agreement, or ICC, between tonometers was 0.63 (95% CI, 0.56-0.70). Bland-Altman analysis showed 95% limits of agreement ranging from ?5.2 to +6.6 mm Hg. CCT was not correlated with IOP for either the IC200 (P = 0.35) or the Perkins tonometer (P = 0.052).ConclusionsCompared to applanation tonometry, IC200 overestimated IOP in healthy children, with a greater frequency of readings > +2 mm Hg than < ?2 mm Hg compared to Perkins. There was moderate agreement between tonometers. CCT was not found to influence IOP measurement for either tonometer.     

Comparison of ICare tonometer with Goldmann applanation tonometer in glaucoma patients

PURPOSE: To compare the intraocular pressure (IOP) readings taken with the new ICare tonometer and with the Goldmann applanation tonometer (GAT) and to evaluate the influence of central corneal thickness (CCT) on the IOP measurements. PATIENTS AND METHODS: One eye of 178 consecutive patients with primary open-angle glaucoma underwent ultrasonic CCT measurement, followed by IOP evaluation with the GAT and with the ICare tonometer. The deviation of ICare readings from GAT values, corrected according to the Doughty and Zaman formula, was calculated and correlated to CCT by a linear regression model. The agreement between the 2 devices was assessed by use of the Bland-Altman method. RESULTS: The average CCT was 552+/-39 mum. The mean IOP and the mean corrected IOP with GAT were 19.4+/-5.4 mm Hg, and 18.5+/-5.7 mm Hg, respectively. The mean ICare IOP reading was 18.4+/-5.2 mm Hg. The deviations of ICare readings from corrected GAT values were highly correlated with CCT values (r=0.63, P<0.01). Linear regression analysis showed that a CCT change of 10 mum resulted in an ICare reading deviation of 0.7 mm Hg. The Bland-Altman scatter-plot showed a reasonable agreement between the 2 tonometers. CONCLUSIONS: The ICare tonometer can be useful in a routine clinical setting. The IOP readings are quite in accordance with those obtained by GAT. The measurements seemed to be influenced by CCT variations, and thus pachymetry should always be taken into consideration.     

PASCAL动态轮廓眼压计与Goldmann压平眼压计在非青光眼人群中眼压测量值的比较及一致性分析

目的探讨在不同的中央角膜厚度(CCT)下PASCAL动态轮廓眼压计(DCT)与Goldmann压平眼压计(GAT)眼压(IOP)测量值的相关性,评价两者测量值的一致性及临床上两种眼压计测量值相互替换的可能性。方法非青光眼病例87例(168只眼)分别用DCT和GAT进行眼压测量,两种仪器的测量顺序随机。同时,用NIDEK UP-1000型角膜测厚仪测量CCT。DCT与GAT眼压测量值的相关性采用Spearson双变量相关分析,Bland-Altman分析法评价两种仪器IOP测量值的一致性。结果 (1)在不同的角膜厚度下DCT与GAT测得的IOP值均显著相关(CCT≤520μm,n=24,r=0.67,P<0.001;520μm580μm,n=44,r=0.61,P<0.001)。(2)DCT眼压测量值与CCT不相关(r=0.14,P=0.08),GAT眼压测量值与CCT显著相关(r=0.59,P<0.001)。(3)Bland-Altman一致性分析显示两种仪器的差值的均值为-0.9mm Hg,一致性界限为(-5.6 mm Hg,3.9 mm Hg)。结论 (1)在不同的角膜厚度下DCT与GAT的眼压测量值均显著相关。(2)DCT眼压测量值与CCT值不相关,GAT眼压测量值与CCT值显著相关。(3)一致性分析显示两者测量值的一致性界限跨度较宽,二者的IOP值不可简单地相互代替。     

Corneal thickness- and age-related biomechanical properties of the cornea measured with the ocular response analyzer

PURPOSE: The Ocular Response Analyzer (ORA) is a new instrument that measures the corneal biomechanical response (corneal hysteresis, CH) to rapid indentation by an air jet. CH is the difference in applanation pressures (P1, P2) between the rising and falling phases of the air jet. The investigation had two parts: a characterization study and a validation study. In the characterization study, the purposes were to investigate the intraocular pressure (IOP)-dependence of CH and to characterize the performance of the ORA. In the validation study, the purposes were to investigate the association between CH and both age and central corneal thickness (CCT) and the agreement between ORA and Goldmann applanation tonometer (GAT) IOP measurements. METHODS: For the characterization study, data were collected from 105 untreated subjects (45 ocular hypertensive patients and 60 normal subjects; mean age, 60 years, range, 26-82). GAT and ORA measurements were performed before and after IOP lowering of one randomly selected eye with apraclonidine drops. The change in P1 and P2 (arbitrary units) in relation to change in GAT IOP was analyzed to calibrate the instrument. The relation between P1, P2, and CCT was explored and ORA IOP was derived from the analyses. For the validation study, ORA and GAT IOP and CCT were measured in 144 eyes of 144 untreated subjects (mean age, 58 years; range, 19-83). The characterization calculations were applied to the dataset and values of CH and ORA IOP were calculated. The relationship between CH and both subject age and CCT was determined. The associations between CH and CCT and between ORA and GAT IOPs, were investigated by linear regression analysis. The agreement between measuring devices was calculated. RESULTS: In the characterization study, P1 changed by 6.41 arbitrary units for every 1-mm Hg change in GAT IOP. CH (P1 - P2) changed by -1.60 arbitrary units for every 1-mm Hg change in GAT IOP. For each unit change in P2, P1 changed by 1.27 units. From this association a new IOP-independent corneal factor was derived [P1 - (P2/1.27)] and is termed the corneal constant factor (CCF; mm Hg). ORA IOP normalized for CCF was defined as P2 - CCF (mm Hg). The CCF (mm Hg) was associated with CCT (micrometers) and with age: CCF = [(0.036 . CCT) - (0.028 . age)] + 1.06 (adjusted r2 = 0.34; P < 0.0001 for CCT, P = 0.007 for age). Normalized ORA IOP measurements were not associated with CCT. GAT IOP was associated with CCT and CCF-more strongly with the latter: GAT IOP = (0.03 . CCT)+1.52 (r2 = 0.06, P = 0.002); GAT IOP = (0.65 . CCF) + 4.5 (r2 = 0.13, P < 0.0001). The mean difference (95% limits of agreement) between GAT and normalized ORA IOP was 0.1 (-6.6 to +6.8) mm Hg. CONCLUSIONS: The CCF describes an IOP-independent biomechanical property of the cornea that increases with thicker CCT and decreases with greater age. It is moderately strongly associated with CCT and yet explains more of the interindividual variation in GAT IOP than does CCT. Normalized ORA IOP measurements are not associated with CCT.     

Agreement of rebound tonometer in measuring intraocular pressure with three types of applanation tonometers

PURPOSE: To evaluate the agreement of iCare rebound tonometer in measuring intraocular pressure (IOP) with Goldmann applanation tonometer (GAT), Tonopen XL, and noncontact tonometer, and the influence of the central corneal thickness (CCT) on IOP measurements made with these four tonometers in 45 (12 control and 33 glaucomatous or ocular hypertensive) eyes. DESIGN: Clinically relevant experimental study. METHODS: Tonometer intermethod agreement was assessed by the Bland-Altman method. The relations of CCT with absolute IOP values and intertonometer differences were analyzed by linear regression. RESULTS: The mean differences (95% limits of agreement) in IOP readings between iCare and GAT, Tonopen XL, and noncontact tonometer were 1.40 +/- 4.29, 0.00 +/- 4.78, and 2.22 +/- 4.19 mm Hg, respectively. All tonometries had a marked association with CCT. As the CCT got thicker, iCare considerably overestimated GAT and Tonopen XL. CONCLUSIONS: Although influenced by CCT, iCare agrees well with applanation tonometers.     

Intraocular pressure measurements using dynamic contour tonometry after laser in situ keratomileusis

PURPOSE: Thinning of the corneal stroma by laser in situ keratomileusis (LASIK) results in inaccurate low intraocular pressure (IOP) readings by Goldmann applanation tonometry (GAT). Dynamic contour tonometry (DCT) is a novel measuring technique, designed to measure IOP largely independent of corneal thickness and curvature. The purpose of this study was to compare IOP measurements using GAT and DCT in eyes undergoing LASIK for correction of myopia. METHODS: In a prospective, single-center study, central corneal thickness (CCT) and IOP were measured in patients undergoing first-time LASIK for myopia. IOP was measured before and after surgery using GAT and DCT. The untreated contralateral eyes served as paired controls. RESULTS: There was good concordance between the two tonometers in 62 normal eyes before LASIK. Corneal ablation of 90.0 +/- 49.18 micro m (median +/- SD) reduced IOP readings as measured by GAT by 3.0 +/- 1.9 mm Hg (P < 0.001). In contrast, no significant change in IOP readings was recorded by DCT (-0.2 mm Hg +/- 1.5 mm Hg, P = 0.30). There was no change in IOP in the untreated control eyes as measured by GAT and DCT. CONCLUSIONS: Significant decreases in IOP were recorded by GAT after LASIK for myopia. Measurements by DCT, however, did not reveal any significant changes in IOP.