The relative effects of corneal thickness and age on Goldmann applanation tonometry and dynamic contour tonometry

AIMS: To establish the effects of central corneal thickness (CCT) on intraocular pressure (IOP) measured with a prototype Pascal dynamic contour tonometer (DCT), to evaluate the effect of CCT and age on the agreement between IOP measured with the Pascal DCT and Goldmann applanation tonometer (GAT), and to compare the interobserver and intraobserver variation of the DCT with the GAT. METHODS: GAT and DCT IOP measurements were made on 130 eyes of 130 patients and agreement was assessed by means of Bland-Altman plots. The effect of CCT and age on GAT/DCT IOP differences was assessed by linear regression analysis. Interobserver and intraobserver variations for GAT and DCT were assessed in 100 eyes of 100 patients. RESULTS: The mean difference (95% limits of agreement) between GAT and DCT was -0.7 (-6.3 to 4.9) mm Hg. GAT/DCT IOP differences increased with thicker CCT (slope 0.017 mm Hg/microm, 95% CI 0.004 to 0.03, r2 = 0.05, p = 0.01), and with greater age, slope 0.05 mm Hg/year (95% CI 0.012 to 0.084, r2 = 0.05, p = 0.01). The intraobserver variability of GAT and DCT was 1.7 mm Hg and 3.2 mm Hg, respectively. The interobserver variability was (mean difference (95% limits of agreement)) 0.4 (-3.5 to 4.2) mm Hg for GAT and 0.2 (-4.9 to 5.3) mm Hg for DCT. CONCLUSIONS: GAT is significantly more affected than DCT by both CCT and subject age. The effect of age suggests an age related corneal biomechanical change that may induce measurement error additional to that of CCT. The prototype DCT has greater measurement variability than the GAT.     

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.     

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.     

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.     

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.     

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.     

Dynamic contour tonometry: a new way to assess intraocular pressure in ectatic corneas

PURPOSE: To compare intraocular pressure (IOP) measurements in patients with keratoconus (KC), pellucid marginal degeneration (PMD), and unilateral penetrating keratoplasty (PK) for KC by Goldmann applanation tonometry (GAT), Tono-Pen tonometry (TP), and Pascal dynamic contour tonometry (DCT). METHODS: Patients with KC, PMD, or PK were included in a prospective study. IOPs were measured by GAT, TP, and DCT. Severity of ectasia was determined by the steep curvature by corneal topography and central thinning by contact ultrasound pachymetry. IOP measurements were compared and correlated with disease severity. RESULTS: Fifty-three eyes of 36 patients were enrolled. Mean age was 45.3 +/- 12.5 years (range: 28-72 years). Twenty-nine eyes had KC, 21 eyes had a PK for KC, and 3 eyes had PMD. Mean DCT, GAT, and TP readings were 16.1 +/- 2.9, 14.3 +/- 4.1, and 13.8 +/- 4.1 mm Hg, respectively. The differences of mean IOP between GAT and DCT and TP and DCT were statistically significant, whereas the difference between GAT and TP was not. Both GAT and TP readings were significantly higher in the PK eyes than the KC and PMD eyes, whereas DCT readings were not. DCT measurements were not significantly different in PK versus non-PK eyes. CONCLUSION: DCT is a newly Food and Drug Administration (FDA)-approved device that is designed to measure IOP, independent of corneal thickness, corneal curvature, and ocular rigidity. DCT gave significantly higher IOP readings than GAT and TP in this study. DCT readings were not affected by corneal thickness. DCT may be more accurate in IOP measurement in eyes with KC and PMD.     

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.     

Comparison of dynamic contour tonometry with Goldmann applanation tonometry in glaucoma practice

Purpose: To compare intraocular pressure (IOP) readings taken using dynamic contour tonometry (DCT) with IOP readings taken with Goldmann applanation tonometry (GAT) in eyes with glaucoma or ocular hypertension. Methods: The present study included 100 eyes in 100 patients with glaucoma or ocular hypertension. After pachymetry DCT and GAT were performed. Intraocular pressures as measured with DCT and GAT were compared with one another and with central corneal thickness (CCT). Results: Mean DCT IOP measurements (20.1 ± 4.3 mmHg) were significantly (p < 0.001) higher than GAT IOP values (17.9 ± 4.7 mmHg). The mean difference between DCT and GAT measurements was 2.1 mmHg (range ? 3.4 to 9.7 mmHg). The difference followed a normal distribution. Measurements made with DCT and GAT correlated significantly with one another (Spearman’s rho = 0.761, p < 0.001). Neither GAT nor DCT measurements showed a significant correlation with CCT (537 ± 39 μm, range 458–656 μm). Multivariate regression analysis has shown that the difference between DCT and GAT is influenced significantly by ocular pulse amplitude (r = ? 0.334, p = 0.001) and it is not influenced by CCT (r = ? 0.106, p = 0.292). Conclusions: In eyes with glaucoma or ocular hypertension, DCT facilitates suitable and reliable IOP measurements which are in good concordance with GAT readings. Variation in CCT cannot by itself explain the differences in measurements taken with DCT and GAT in a number of eyes.     

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.     

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.     

中央角膜厚度、角膜曲率对Goldmann压平眼压计和非接触眼压计测量结果的影响

目的 探讨中央角膜厚度和角膜曲率对Goldmann压平眼压计(GAT)和非接触眼压计(NCT)测量结果 的影响.方法 比较性研究.选择120例门诊患者作为研究对象.应用超声角膜测厚仪测量患者中央角膜厚度,采用多功能验光仪测量角膜曲率,应用GAT和NCT测量受检者双眼眼压.应用SPSS 12.0统计学软件进行数据处理.采用直线回归法比较两种眼压计的测量结果 ,采用多重线性同归法分析中央角膜厚度、角膜曲率与两种眼压计所测眼压值的关系,应用Bland-Altman法比较NCT和GAT两种方法 对眼压测最结果 的影响.结果 GAT与NCT测量的平均眼压值分别为(18.4±4.0)mm Hg(1 mm Hg=0.133 kPa)和(17.0±4.6)mm Hg,差异有统计学意义(r=0.835,P=0.000).GAT和NCT测量的眼压值均受中央角膜厚度和角膜曲率的影响.中央角膜厚度每增加1μm,GAT测量眼压值增加0.039 mm Hg,而NCT测量眼压值增加0.064 mm Hg.角膜曲率半径每增加1 mm,GAT测最眼压值减少2.648 mm Hg,NCT测量眼压值减少3.190 nun Hg.中央角膜厚度对NCT测量眼压值的影响较其对于GAT测量眼压值的影响大.随着眼压的升高,NCT测最眼压值呈现出由低于GAT测量值到高于GAT测量值的逐渐变化趋势.结论 中央角膜厚度和角膜曲率均会影响NCT和GAT测量眼压值,而且中央角膜厚度对NCT测量眼压值的影响较其对GAT测量眼压值的影响大.     

动态轮廓眼压计与非接触式眼压计的比较

目的探讨中央角膜厚度和角膜曲率对轮廓动态眼压计以及非接触式眼压计眼压测量结果的影响。方法接受准分子激光原位角膜磨镶术(LASIK)的近视患者27例(54只眼),分别于术前和术后第4周使用非接触式眼压计(NCT)和动态轮廓眼压计(DCT)进行眼压测量。多元线性相关分析研究NCT、DCT测量值和角膜曲率及角膜中央厚度(CCT)之间的相关性。结果LASIK术后NCT测量值降低,而DCT测量值和术前比较差异则无统计学意义。角膜曲率、CCT和NCT读数呈线性相关,而与DCT读数无关。结论DCT测量眼压不受角膜曲率和中央角膜厚度影响,因此更适合于正常眼以及曾经接受角膜屈光手术眼的眼压测量。     

Tono-Pen versus Goldmann tonometry after excimer laser photorefractive keratectomy

PURPOSE: To compare intraocular pressure (IOP) measurements by the Tono-Pen 2 tonometer and Goldmann applanation tonometer (GAT) in post-photorefractive keratectomy (PRK) patients. SETTING: Refractive Surgery Center, Assaf Harofeh Medical Center, Zerifin, Israel. METHODS: In 18 patients, IOP was measured by GAT and then by Tono-Pen 2 tonometer 2 to 18 months following PRK (mean 6.6 months +/- 5.1 [SD]). Photorefractive keratectomy had been performed in 1 eye of each patient; the fellow eyes served as controls. Corneal curvature and thickness were evaluated. Ten of the 18 patients were treated with topical steroids. RESULTS: In the post-PRK eyes, mean GAT IOP was 1.8 +/- 3.1 mm Hg lower than mean Tono-Pen IOP (P = .012); there was no significant IOP difference in the control (fellow) eyes. In steroid-treated post-PRK eyes, mean GAT IOP (12.2 mm Hg) was 2.2 +/- 1.3 mm Hg lower than mean Tono-Pen IOP (14.4 mm Hg) (P = .0007). Mean Tono-Pen IOP in steroid-treated post-PRK eyes was 4.3 +/- 3 mm Hg higher than in the fellow eyes (P = .0014); mean GAT IOP was only 2.3 +/- 3.5 mm Hg higher (P = .04). In post-PRK eyes without topical steroid treatment, mean GAT IOP was 2.0 +/- 1.18 mm Hg lower than in the fellow eyes (P = .001); there was no significant difference in Tono-Pen IOP. There was a negative correlation between the difference in IOP values (Tono-Pen minus GAT) and corneal curvature in post-PRK eyes (r = 0.76, P = .0108, n = 15). CONCLUSIONS: The Tono-Pen tonometer appeared to be less affected than the GAT by the relative flattening, thinning, and anterior stromal decreased rigidity of the central cornea that occur following PRK. Post-PRK steroid-induced IOP elevation may be masked by the artifactual decrease in GAT IOP.     

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.     

Clinical comparison of the Icare tonometer and Goldmann applanation tonometry

PURPOSE: To compare a new method of intraocular pressure (IOP) measurement, using the Icare tonometer, with Goldmann applanation tonometry (GAT). PATIENTS AND METHODS: Two observers obtained IOP readings in 292 eyes (143 right and 149 left) of 153 subjects, using the Icare without topical anesthetic. A GAT reading was subsequently obtained by a consultant ophthalmologist, without the knowledge of the Icare readings. Central corneal thickness (CCT) was obtained on all eyes with ultrasound pachymetry. Patient comfort after IOP measurement was assessed in a consecutive subset of patients. RESULTS: The intraclass correlation coefficient between the 2 modalities of IOP measurement was r=0.95 for the right and r=0.93 for the left eye. The mean difference (Icare-GAT) between the IOP measured by the 2 methods was 0.4 mm Hg in the right eye (SD 3.0, 95% confidence interval -5.5 to 6.3), and 0.8 mm Hg in the left eye (SD 3.0, confidence interval -4.7 to 6.2). GAT measurements did not vary with CCT [correlation coefficient=0.09 (P=0.25) right and 0.14 (P=0.09) left eyes]. However, IOP measured with Icare tonometry increased with increasing CCT [correlation coefficient=0.16 (P=0.05) right and 0.21 (P=0.01) left eyes]. For every 100-microm increase in CCT, the difference (Icare-GAT) increased by 1 mm Hg. Of the 38 consecutive patients surveyed, 28 (73.7%) rated the Icare more comfortable than GAT, with only 2 (5.3%) rating it less comfortable (P<0.001). CONCLUSIONS: There is good correlation between the 2 methods of IOP measurement, even at extremes of IOP. The Icare instrument was easy to use and recorded rapid and consistent readings with minimal training. It seems to be more comfortable than GAT and obviates the need for topical anesthesia.     

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.     

Reproducibility and clinical evaluation of rebound tonometry

PURPOSE: To establish the reproducibility of a rebound tonometer in humans and the effect of corneal thickness on measurements, comparing it with Goldmann applanation tonometer. METHODS: In a first study designed to examine the reliability of the RBT, three experienced ophthalmologists undertook three consecutive intraocular pressure (IOP) measurements in 12 eyes of 12 normal subjects. A cross-sectional study was then performed to compare measurements obtained using the two tonometers in 147 eyes of 85 patients with ocular hypertension or glaucoma. RESULTS: Intraobserver coefficients of correlation obtained in the reproducibility study were 0.82, 0.73, and 0.87. Interobserver correlation was 0.82. There was a good correlation between IOP readings obtained by the RBT and the GAT (r = 0.865, P < 0.0001). RBT readings were consistently higher than GAT measurements (median difference, 1.8 +/- 2.8 mm Hg). A Bland-Altman plot indicated the 95% limits of agreement between the two methods were -3.7 to 7.3 mm Hg (slope = -0.022, P = 0.618). Using RBT, the point that best discriminated between patients with an IOP < or = 21 mm Hg and those with >21 mm Hg, as determined by the GAT was >23 mm Hg (sensitivity, 70.5%; specificity, 95.1%). In terms of pachymetry, the two tonometers behaved in a similar way, with correlation observed between IOP measurements and central corneal thickness. CONCLUSIONS: Rebound tonometry is a reproducible method of determining IOP in humans. In general, it tends to overestimate IOP compared with Goldmann applanation tonometry. The tonometers used in both methods are similarly affected by pachymetry.     

DCT和GAT对LASIK手术前后眼压的比较性研究

目的 评价动态轮廓眼压计(DCT)和Goldmann压平眼压计(GAT)对在准分子激光原位角膜磨镶术(LASIK)手术前后眼压测量值的变化.方法 取71例141只眼近视患者在LASIK术前和术后一周分别进行角膜厚度(CCT)、GAT、DCT测量.结果 ①LASIK手术前后DCT测得值尤显著性差异(P=0.062),GAT测得值有显著性差异(P＜0.001),CCT测得值有显著性差异(P＜0001).②Bland-Altman分析示LASIK手术前后DCT与GAT两种测量方法均呈现高度一致性.术前DCT测量值高于GAT测量值1.1mmHg,95%可信区间为(-0.6,2.8)mmHg;术后DCT测量值高于GAT测量值8.2mmHg,95%可信区间为(5.3,11.1)mmhg.③△GAT与△CCT呈正相关,△DCT与△CCT无统计相关性.结论 DCT测量值不受LASIK手术切削的影响,更适合于LASIK手术前后眼压的测量.