Dynamic Contour Tonometer Research Articles

Effect of Recipient Corneal Pathology on Pascal Tonometer and Goldmann Tonometer Readings in Eyes after Penetrating Keratoplasty

To assess the influence of recipient corneal pathology on the performance of the Pascal dynamic contour tonometer (PDCT) (Swiss Microtechnology AG) by comparing it to Goldmann applanation tonometry (GAT) in post-penetrating keratoplasty (PKP) eyes. Intraocular pressure (IOP) was measured in 40 post-PKP eyes of 40 patients using PDCT and GAT. The study patients were divided into two groups. Group A included patients who had undergone PKP for ectatic corneal disorders (keratoconus, n=20) and group B included patients who had undergone PKP for other non-ectatic corneal disorders (Fuchs, post-corneal ulcer, post-chemical burn,post-trauma, n=20). Keratometric measurements were obtained in all eyes using Orbscan II (Bausch &Lomb) and central corneal thickness (CCT) was measured using Corneo-Gaze Plus (Sonogaze). In group B, a correlation between PDCT and GAT IOP measurements was observed. In group A, GAT IOP measurements were significantly lower than PDCT measurements (3.7 +/- 1.8 mmHg,p<0.001). Additionally, CCT affected GAT IOP measurements much more than PDCT measurements,while corneal curvature did not significantly affect IOP measurements of any instrument in either group. In post-PKP eyes, PDCT appears to be less influenced than GAT by CCT and pre-existing recipient corneal pathology. Therefore, PDCT may be better suited for monitoring IOP in post-PKP eyes.

Intraocular pressure measured by dynamic contour tonometer and ocular response analyzer in normal tension glaucoma

Dear Editor, We read with interest the article by Morita T et al. on intraocular pressure (IOP) measured by dynamic contour tonometer (DCT) and ocular response analyzer (ORA) in normal tension glaucoma (NTG) [1]. In their paper, the authors presented that corneal-compensated IOP (IOPcc) measured by ORA was significantly greater than GAT-IOP, DCT-IOP and Goldmann-correlated IOP (IOPg) in NTG eyes, but not in normal eyes, which suggested the possibility of IOP values being underestimated. We would like to raise a few points with regard to this article that may help to broaden the discussion. It is well-recognized that IOP measurement can be affected by central corneal thickness (CCT) and the biomechanical properties of the cornea, such as corneal hysteresis (CH), corneal resistant factor (CRF) and so on [2]. Corneal hysteresis may vary from different subjects. Sunil et al. reported that corneal hysteresis was lowest in NTG eyes when comparing with POAG and OHT eyes [3]. On the other hand, Ang GS reported a small but statistically higher mean CH in NTG eyes than POAG eyes [4]. We are curious about whether there were any differences in corneal biomechanical properties between normal eyes and NTG eyes in this study, as well as any effect of corneal biomechanical properties on IOP measurement in NTG eyes [1]. Another point we would like to mention is that intraocular pressure, just as our blood pressure, has diastolic and systolic pressure [5]. Based on the principle of DCT and ORA, IOP measurement taken by DCT always disaplays as diastolic pressure, while ORA finishes IOP measurement in 20 miniseconds, so it is hard to distinguish whether the IOP measured by ORA is diastolic or systolic pressure. It was speculated that the repeatability of IOP measurement taken by ORA would be not so good as DCT and GAT, which can cause the difference between IOPcc and GAT-IOP and DCT-IOP to a certain extent. Once again, we appreciate the authors’ efforts in investigating IOP measurement with different modalities.

Intraocular pressure measured by dynamic contour tonometer and ocular response analyzer in normal tension glaucoma

Intraocular pressure measured by dynamic contour tonometer and ocular response analyzer in normal tension glaucoma

Changes in intraocular pressure and ocular pulse amplitude with accommodation

AimsTo investigate the change that occurs in intraocular pressure (IOP) and ocular pulse amplitude (OPA) with accommodation in young adult myopes and emmetropes.MethodsFifteen progressing myopic and 17 emmetropic young adult...

Comparison of ICare, Dynamic Contour Tonometer, and Ocular Response Analyzer with Goldmann Applanation Tonometer in Patients with Glaucoma

To compare the intraocular pressure (IOP) readings taken by ICare, Pascal dynamic contour tonometer (DCT), and ocular response analyzer (ORA) with those taken by Goldmann applanation tonometer (GAT). We sought to evaluate the influence of central corneal thickness (CCT) on IOP measurements and to compare patients' preferences for the four tonometers. In this prospective study, 93 eyes from 93 patients were examined. Patients were randomly divided into 4 groups to vary the order in which the tonometers were applied. CCT was measured with an ultrasound pachymeter. The average CCT was 558+/-47.4 microm. The mean +/- standard deviation IOP for GAT, ICare, DCT, and ORA (Goldmann-correlated IOP) (ORA(GC)) were 15.1+/-4.8, 15.7+/-5.7, 18.2+/-5.1, and 18.3+/-6.6 mmHg, respectively. There was no significant difference between the mean IOP obtained with GAT and ICare (p=0.14). There was also no difference in IOP levels between the mean IOP obtained with DCT and ORA (p=0.26). There was no correlation between IOP measurements and CCT for the 4 instruments. Bland-Altman graphs showed disagreement between the measurements taken by GAT and the other instruments. There was no significant difference in patients' preference among the 4 instruments (p=0.48). IOP readings from ICare were consistent with those from GAT, whereas DCT readings correspond well to ORA(GC) measurements. DCT and ORA readings both overestimated the GAT readings. There was no correlation between the IOP measurements and the CCT for the 4 instruments. There was no significant difference in patients' preference among the 4 instruments.

Intraocular pressure measured by dynamic contour tonometer and ocular response analyzer in normal tension glaucoma

To investigate intraocular pressure (IOP) measurement values in normal tension glaucoma (NTG) eyes using two different types of tonometer that are supposed to be little affected by corneal biochemical properties. This study included 30 normal eyes of 16 healthy subjects and 30 eyes of 16 patients with NTG. IOP was measured with a Goldmann applanation tonometer (GAT), a Pascal dynamic contour tonometer (DCT), and a Reichert ocular response analyzer (ORA) three times each for normal and NTG eyes. The main measures were GAT-IOP, DCT-IOP, corneal-compensated IOP (IOPcc), Goldmann-correlated IOP (IOPg), and central corneal thickness (CCT). In normal eyes, GAT-IOP was 13.2 +/- 1.4 mmHg; DCT-IOP, 13.0 +/- 1.6 mmHg; IOPcc, 13.6 +/- 2.0 mmHg; and IOPg, 12.4 +/- 2.0 mmHg. Multivariate analysis revealed no significant differences between the four measurements (p = 0.08). CCT was 524.6 +/- 27.3 microns. In NTG eyes, GAT-IOP was 13.1 +/- 1.3 mmHg; DCT-IOP, 13.7 +/- 1.3 mmHg; IOPcc, 15.2 +/- 2.0 mmHg; and IOPg, 12.7 +/- 2.0 mmHg. Multivariate analysis showed significant differences between the four measurements (p < 0.01). Sheffé's test showed that IOPcc was significantly higher than GAT-IOP, DCT-IOP, and IOPg (GAT-IOP vs IOPcc: p < 0.0001; DCT-IOP vs IOPcc: p = 0.01; IOPcc vs IOPg: p < 0.0001). CCT was 515.4 +/- 32.9 microns, with no significant difference between normal and NTG eyes (p = 0.15). We investigated the values of IOP in NTG eyes as measured by the DCT and ORA. IOPcc was significantly greater than GAT-IOP, DCT-IOP and IOPg in NTG eyes, suggesting the possibility that IOP values may be underestimated.

Dynamic Contour Tonometry: Handheld versus Slit-lamp–Mounted

To compare the newly developed handheld dynamic contour tonometer (hh-DCT) with the established slit-lamp-mounted DCT (sl-DCT) in terms of agreement for intraocular pressure (IOP) and ocular pulse amplitude (OPA) measurements, intraobserver variability, and tonography effect. Evaluation of diagnostic technology. Fifty eyes of 50 healthy volunteers were examined with the hh-DCT and sl-DCT. A paired t test was performed to analyze differences in IOP and OPA readings. Measurements were compared for bias and agreement according to the method of Bland and Altman. Intraclass correlation coefficients (ICCs) were calculated to compare intraobserver variability. A mixed model analysis was performed to assess a possible tonography effect. The differences in IOP and OPA measurements, intraobserver variability, and tonography effect between the hh-DCT and the sl-DCT were examined. No statistically significant differences in IOP (sl-DCT-hh-DCT: 0.1+/-1.43 mmHg, 95% confidence interval [CI], -0.31 to 0.5, P = 0.63) or OPA (sl-DCT-hh-DCT: -0.1+/-0.52 mmHg, 95% CI, -0.28 to 0.01, P = 0.08) measurements were detected. Bland-Altman analysis revealed a bias of 0.1 with the limits of agreement of IOP measurement differences ranging from -2.71 to +2.90 mmHg. With regard to IOP readings obtained by sl-DCT, hh-DCT overestimated IOPs less than 15.6 mmHg and underestimated IOPs more than 15.6 mmHg. ICCs calculated for IOP readings were 0.87 (95% CI, 0.8-0.92) for hh-DCT and 0.85 (95% CI, 0.78-0.90) for sl-DCT. ICCs for OPA readings were 0.86 (95% CI, 0.79-0.91) for hh-DCT and 0.87 (95% CI, 0.8-0.91) for sl-DCT. Comparing the ICCs revealed no statistically significant difference between the devices with regard to IOP and OPA measurements (P = 0.53 and P = 0.93, respectively). Mixed model analysis of 3 consecutive IOP measurements revealed a decrease in IOP of 0.5 mmHg after each measurement in both devices, which was not significant between the 2 methods (P = 0.68). IOP and OPA readings obtained by the novel hh-DCT were shown to be strongly concordant with measurements obtained by the sl-DCT device. The hh-DCT may be a valuable alternative to the sl-DCT in clinical practice.

Repeated measures of intraocular pressure result in higher heritability and greater power in genetic linkage studies.

To analyze the effect of using one reading, the mean of two readings (from the same eye), or the mean of four readings (two from each eye) on the heritability estimates of intraocular pressure (IOP). This was a cohort study in which 344 pairs of twins, 163 monozygotic (MZ) and 181 dizygotic (DZ), were enrolled. IOP was measured using three tonometers: the gold standard Goldmann applanation tonometer (GAT), the Ocular Response Analyzer (ORA; Reichert Buffalo, NY), and the Dynamic Contour Tonometer (DCT, Pascal; Swiss Microtechnology AG, Port, Switzerland). The main outcome measure was the heritability of IOP correlated with the number of measurements. The mean IOPs of all four readings with the three tonometers were: 14.1 +/- 2.9 mm Hg for GAT, 15.9 +/- 3.2 mm Hg for ORA, and 16.9 +/- 2.7 mm Hg for DCT. As the number of readings increased, the calculated heritability (h(2)) of IOP measured using the GAT readings increased from 0.56 for one reading (95% confidence interval [CI], 0.44-0.65) to 0.58 for the mean of two readings (95% CI, 0.46-0.67) to 0.64 for the mean of all four readings (two right and two left; 95% CI, 0.55-0.72). Similar results were seen with the other two instruments. The results demonstrated that the use of the mean of several readings from both eyes reduced measurement error, yielding a higher heritability estimate. The higher heritability would increase the power to detect linkage in a genome-wide analysis.

The Relationship between Diurnal Variations in Intraocular Pressure Measurements and Central Corneal Thickness and Corneal Hysteresis

To examine the relationship between office-hour changes in IOP, measured with the Goldmann applanation tonometer (GAT) and dynamic contour tonometer (DCT), and the corneal characteristics central corneal thickness (CCT) and corneal hysteresis (CH). Sixty-two eyes of 62 untreated normal subjects and patients with untreated glaucoma had IOP measurements performed with the GAT (mm Hg) and DCT (mm Hg) over an 8-hour period at 2-hour intervals beginning at 9 AM. CCT (micrometers) was measured using a noncontact optical low-coherence reflectometry (OLCR) pachymeter, and CH (mm Hg) was measured with an ocular response analyzer (ORA). The associations between IOP measurements and corneal characteristics for each patient over the measurement period were assessed by using multilevel modeling. GAT and DCT IOP and CCT changed significantly during office hours (ANOVA; GAT: F = 19.9, P < 0.001; DCT: F = 4.6, P = 0.001; CCT: F = 16.4; P < 0.001). No significant changes were observed in CH (ANOVA; F = 1.8, P = 0.13). Multilevel modeling analysis of the interrelationships between CCT, CH, and age on IOP measurements revealed that both CCT and CH changes were significantly associated with GAT IOP changes (GAT IOP/CCT slope, 0.04 mm Hg/microm; 95% confidence intervals [CIs], 0.02-0.06; GAT IOP/CH slope, 0.20 mm Hg/mm Hg; 95% CI, 0.01-0.39). CCT, but not CH, changes were significantly associated with DCT IOP changes (DCT IOP/CCT slope, 0.03 mm Hg/microm; 95% CI, 0.00-0.05). However, although the association between CCT and GAT IOP was relatively uniform between subjects, association between CCT and DCT IOP showed greater intersubject variability. Age had no effect on the diurnal variation of IOP measured with either device. Measured IOP and corneal characteristics covary during office hours. Changes in CCT and CH are associated with changes in GAT IOP and, less consistently, with DCT IOP. The data suggest that variations in corneal characteristics explain a small proportion of the change in IOP measurements made with the GAT during office hours.

PASCAL DYNAMIC CONTOUR TONOMETRY VERSUS GOLDMANN APPLANATION TONOMETRY IN GAS AND AIR-FILLED EYES AFTER VITRECTOMY SURGERY

To compare Pascal Dynamic Contour Tonometry with Goldmann Applanation Tonometry in eyes after vitrectomy surgery with intraocular tamponade of air, silicone oil or perfluorocarbon gas. Prospective clinical comparative study. Eighty-two consecutive patients undergoing vitrectomy surgery with postoperative air, gas or oil tamponade were recruited. Intraocular pressure was measured with both devices. Mean Goldmann intraocular pressure was 16.6 mmHg (range, 1.0-46.0; SD = 8.80) and the mean Pascal intraocular pressure was 21.70 (range, 4.7-58.5; SD = 9.8) The mean difference between the Pascal and Goldmann readings was 5.09 mmHg (range, -14.7 to +12.9; 95% CI = 4.2-6.0; SD, 4.0; P < 0.001). Mean differences for the different tamponades were 5.09 mmHg for silicone oil, 4.02 mmHg for air, and 5.38 mmHg for perfluorocarbon gas. Pascal dynamic contour tonometry gives readings that are highly correlated with Goldmann applanation tonometry, but on average 5 mmHg higher in eyes after vitrectomy surgery with air, gas or silicone oil tamponades. The difference between Goldmann and Pascal readings does not appear to be altered by the presence of a scleral buckle, or the size of the intraocular gas bubble.

Corrélation entre hystérèse cornéenne, facteur de résistance cornéen et amplitude de pulsation oculaire chez les sujets sains

The Ocular Response Analyzer (ORA) measures corneal biomechanical properties: corneal hysteresis (CH) and the corneal resistance factor (CRF). The Pascal Dynamic Contour Tonometer (PDCT) measures the ocular pulse amplitude (OPA), which represents the systolic-diastolic variation in intraocular pressure (IOP). Both ORA and OPA values are lower in glaucoma patients than in normal patients. Our purpose was to assess whether there is a correlation between CH, CRF, and OPA values in healthy subjects. Prospective observational study including 81 eyes of 41 healthy adult volunteers. Patients with ocular eye disease, previous refractive or intraocular surgery, contact lenses, or topical or general medications were excluded. Patients underwent four ORA, three OPA, and two Goldmann Applanation Tonometry (GAT) measurements. For each device, the mean of all measurements were considered for this study. The statistical analysis by Spearman rank correlations was performed for right (RE), left (LE), and both eyes. The correlation between the two eyes of each subject was taken into account and canonical correlations were calculated using the SAS statistical software to improve the power of the analysis. The mean age was 43.6 +/- 14.6 years. The mean central corneal thickness was 545 +/- 32 microm for RE, 553 +/- 34 microm for LE, and 550 +/- 32 microm for both eyes. The mean IOPGAT values for RE, LE, and both eyes were, respectively 14.3 +/- 2.9 mmHg, 14.0 +/- 2.9 mmHg, and 14.2 +/- 2.9 mmHg. Spearman correlations were not statistically significant for separated RE and LE analysis. For both eyes, these correlations were rS=0.210, p=0.193 for OPA/CH and rS=0.388, p=0.013 for OPA/CRF. The Spearman correlation was statistically significant for OPA/CRF. This result was confirmed by canonical correlations (p=0.002) and in addition, CH was statistically correlated to OPA in the latter analysis (p=0.010). A statistically significant correlation was found between corneal biomechanical property values as measured by ORA and ocular pulse amplitude values as measured by PDCT in healthy subjects.

Comparison of the quality score of intraocular pressure and ocular pulse amplitude values measured by the Pascal dynamic contour tonometer

The Pascal dynamic contour tonometer (PDCT) is designed to measure intraocular pressure (IOP) largely independent of the corneal properties. It is equipped with a digital LCD screen that displays the IOP, the ocular pulse amplitude (OPA) and the quality score (Q) of the measurements [range 1 (excellent) to 5 (poor)]. The manufacturer has recommended discarding the IOP and OPA values of Q4 and Q5. The aim of our study was to assess if IOP and OPA measurements with Q3 are acceptable for clinical and research purposes. This is a prospective, observational study in which both patients with ocular hypertension or glaucoma and healthy subjects were enrolled; three consecutive PDCT IOP measurements were performed on all participants. Only patients and subjects with Q1, Q2 and Q3 recorded together were eligible. Only one eye per subject was considered for statistical analysis. The mean PDCT IOP and OPA were taken for statistical analyses. An ANOVA test for repeated measures was used to compare the differences between PDCT IOP and OPA Q1, Q2, and Q3 scores. A total of 87 subjects met the inclusion criteria. Mean PDCT (+/-SD) IOP were 17.5 +/- 3.4 mmHg for Q1, 17.6 +/- 3.3 mmHg for Q2 and 17.9 +/- 3.3 mmHg for Q3 (P > 0.05). Mean OPA Q1, Q2 and Q3 were 2.5 +/- 0.9, 2.5 +/- 1.0 and 2.5 +/- 1.0 mmHg, respectively, and were not statistically different. Based on these results, we concluded that the IOP and OPA values with Q1, Q2 or Q3 measured by PDCT are not significantly different and can therefore be taken into account indiscriminately for clinical and research purposes.

Relationship of Intraocular Pulse Pressure and Spontaneous Venous Pulsations

To determine the influence of intraocular pulse pressure (IOPP) on the presence of spontaneous venous pulsations (SVP) in patients with normal intracranial pressure. Clinic-based cross-sectional study. Forty-seven patients without signs and symptoms of elevated intracranial pressure were recruited from a general ophthalmology clinic. Patients with glaucoma or retinal vascular disease were excluded from the study. IOP was determined by applanation, and IOPP was measured with the Pascal Dynamic Contour Tonometer (Ziemer Group, Port, Switzerland). SVP were assessed by undilated (direct) and dilated indirect ophthalmoscopy. Other variables assessed included age, cup-to-disc ratio, and refractive error (spherical equivalent). The main outcome measure was the presence of SVPs with normal IOPP. The incidence of SVPs declined with increasing age in a nonlinear manner. Dilated examinations yielded the greatest sensitivity for detecting SVPs, with 91.5% of subjects having SVPs. However, in subjects with IOPP of 1.2 mm Hg or more in at least one eye, the incidence of SVPs was 100%. A significant correlation exists between the amplitude of IOPP and the presence of SVPs, with SVPs detected in one or both eyes of all patients with IOPP of 1.2 mm Hg or more. When IOPP is 1.2 mm Hg or more, absent SVPs may be more predictive of elevated intracranial pressure than previously recognized.

Physiological short‐term variability of ocular pulse amplitude (OPA) measured by dynamic contour tonometer (DCT) in healthy subjects

Abstract Purpose The Pascal® dynamic tonometer is a new non‐applanation contact tonometer designed to be largely independent of the structural properties of the cornea. It measures the systolic and diastolic IOP and their difference to determine OPA. By recording the pulsatile component of ocular blood flow (heart pulse as a function of time) the OPA could provide an indirect measurement of the choroidal perfusion. It has been suggested that OPA could be an indirect risk factor for glaucoma progression. We aimed to assess the short‐time variability of OPA in healthy persons Methods The left eyes of 30 healthy subjects were included in this prospective study. The IOP was measured twice by Goldmann applanation tonometers (GAT) followed by 3 consecutive measurements by DCT 10 min later. Pachymetry, arterial blood pressure and pulse rate were measured after IOP measurements. These measurements were repeated with an interval of fifteen days at the same hour of the first measurements. The mean value of each parameter was taken into account for the statistical analysis. Student Test was used to assess the difference and the Pearson correlation was used to assess the correlation between the various parameters Results The mean age was 41 ± 12 years. The mean IOP at the first visit was 13.6 ± 2.9 mmHg by GAT and 14.3 ± 2.2 mmHg by DCT. The mean OPA was 2.4 ± 0.9 mmHg (0.8 to 4.3 mmHg) at the first visit. The mean IOP at the second visit was 13.4 ± 3.2 by GAT and 15.0 ± 2.5 mmHg by DCT. The mean OPA was 2.6 ± 1.0 (0.9 to 5.8) mmHg at the second visit. Conclusion There was no significant difference in both OPA measurements. This parameter remains stable in a short‐time interval in healthy subjects.

Assessment of the Pascal Dynamic Contour Tonometer in Measuring Intraocular Pressure in Keratoconic Eyes

To assess the performance of the Pascal dynamic contour tonometer (PDCT) (Swiss Microtechnology AG) by comparing it to Goldmann applanation tonometry (GAT) and noncontact air tonometry (NCT) in keratoconic eyes. Intraocular pressure (IOP) was measured in both eyes of 32 patients with keratoconus using PDCT, GAT, and NCT. IOP measurements were also obtained with all 3 instruments in 46 patients with healthy eyes in the same age range, which served as controls. Keratometric measurements were obtained in all eyes using Orbscan II (Bausch & Lomb) and central corneal thickness was measured using Corneo-gaze plus (Sonogaze). In the control group, a correlation between PDCT, GAT, and NCT IOP measurements was observed. In keratoconic eyes, GAT and NCT IOP measurements were significantly lower than PDCT measurements (5.3+/-2.2 mm Hg and 4.75+/-1.7 mm Hg, respectively). Unlike GAT and NCT, PDCT measurements in both groups were not significantly affected by central corneal thickness. Additionally, the mean IOP measurement in the keratoconic eyes was lower than that of the control group, particularly when measured with GAT and NCT. Corneal curvature, did not significantly affect IOP measurements of any instrument in either group. The corneal abnormalities characteristical of keratoconus seem to influence more GAT and NCT IOP measurements than PDCT IOP measurements. Therefore, PDCT may be better suited for monitoring IOP in keratoconic eyes.

Accuracy of Goldmann, ocular response analyser, Pascal and TonoPen XL tonometry in keratoconic and normal eyes

Aim:The aim of this study was to evaluate the practicality and accuracy of tonometers used in routine clinical practice for established keratoconus (KC).Methods:This was a prospective study of 118 normal...

Effect of Central Corneal Thickness and Corneal Hysteresis on Tonometry as Measured by Dynamic Contour Tonometry, Ocular Response Analyzer, and Goldmann Tonometry in Glaucomatous Eyes

The dynamic contour tonometer (DCT; Pascal tonometer) and the Ocular Response Analyzer (ORA) are novel tonometers designed to measure intraocular pressure (IOP) independent of corneal properties and central corneal thickness (CCT), respectively. We wanted to compare the corneal compensated IOP (IOPcc) as measured by ORA with IOP values measured by DCT and Goldmann applanation tonometry (GAT) with respect to IOP readings and the influence of corneal hysteresis (CH) and CCT in glaucoma patients. In a study of 94 glaucomatous eyes, IOP measurements by ORA, DCT, and GAT were compared, and the effects of CCT and CH were analyzed. All measurements were taken by 1 of the authors only. The Mean CCT was 550+/-44 mum and mean CH 10.24+/-3.3 mm Hg. The mean value for IOPcc was 17.94+/-5.9 mm Hg, 15.14+/-3.7 mm Hg for DCT, and 14.3+/-4.3 mm Hg for GAT. The mean difference was 3.65+/-3.85 mm Hg between IOPcc and GAT and 2.80+/-4.9 mm Hg between IOPcc and DCT (P<0.001) and -0.85+/-3.3 mm Hg between GAT and DCT (P=0.015). None of the methods was related to CCT. In contrast, CH was highly statistically significant related to IOPcc (P<0.0001), whereas GAT and DCT showed only weak relation to CH (P=0.05). IOP measurements with the ORA are significantly higher than DCT or GAT with no apparent linear correction factor. To date, we cannot estimate the impact of differences in CH in relation to IOP and its measurement.

Heritability of intraocular pressure: a classical twin study

Aims:To estimate the heritability of intraocular pressure (IOP) by performing a classical twin study and to determine whether the use of different instruments influences calculation of eye IOP heritability.Methods:Twin pairs...

The Effect of Corneal Edema on Dynamic Contour and Goldmann Tonometry

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. 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. 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). 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.

Clinical assessment of dynamic contour tonometer

To assess the applicability and reliability of Dynamic Contour Tonometry (DCT) in the measurement of intraocular pressure (IOP) and ocular pulse amplitude (OPA) in patients with primary open-angle glaucoma (POAG), ocular hypertension (OHT), normal tension glaucoma (NTG) and normal controls. 120 subjects were included in the present study as follows: 30 patients in each group, total four groups, i. e. , POAG, OHT, NTG and normal control. IOP measured by DCT was compared to that by Goldmann applanation tonometry (GAT). OPA, central cornea thickness (CCT), central cornea curve (CCV), heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP), other associated parameters, were also determined for the subjects of each group. The IOP of all groups measured by DCT was (21.68 +/- 2.02), (23.37 +/- 2.65), (18.43 +/- 3.08), (17.04 +/- 2.07) mm Hg (1 mm Hg = 0.133 kPa); and the IOP measured by GAT was (21.18 +/- 2.95), (23.28 +/- 5.95), (16.39 +/- 3.60), (14.66 +/- 2.27) mm Hg, there was no significant differences between the IOP measured by these two methods (t = 1.338, 1.445, 1.682, 1.803; P = 0.197, 0.151, 0.136, 0.081). Significant differences of OPA levels in different groups were observed (F = 21.311, P = 0.000). OPA reading was affected by HR, SBP, DBP, IOP and CCT, while there was no correlation with patients' age. Regarding to the IOP measurement, DCT was in concord with GAT readings. The differences in OPA among POAG, OHT and the normal groups and the lowest OPA reading in NTG patients indicate different intraocular hemodynamic status among these groups. OPA measurement may be useful to early detection and progression follow-up of glaucoma patients.