Dynamic Contour Tonometer Measurements Research Articles

Estimating pulsatile ocular blood volume from intraocular pressure, ocular pulse amplitude, and axial length.

The purpose of this study was to develop a method of estimating pulsatile ocular blood volume (POBV) from measurements taken during an ophthalmic exam, including axial length and using a tonometer capable of measuring intraocular pressure (IOP) and ocular pulse amplitude (OPA). Unpublished OPA data from a previous invasive study was used in the derivation, along with central corneal thickness (CCT) and axial length (AL), as well as IOP from the PASCAL dynamic contour tonometer (DCT) and intracameral (ICM) measurements of IOP for 60 cataract patients. Intracameral mean pressure was set to 15, 20, and 35 mmHg (randomized sequence) in the supine position, using a fluid-filled manometer. IOP and OPA measurements were acquired at each manometric setpoint (DCT and ICM simultaneously). In the current study, ocular rigidity (OR) was estimated using a published significant relationship of OR to the natural log of AL in which OR was invasively measured through fluid injection. Friedenwald's original pressure volume relationship was then used to derive the estimated POBV, delivered to the choroid with each heartbeat as a function of OR, systolic IOP (IOPsys), diastolic IOP (IOPdia), and OPA, according to the derived equation POBV = log (IOPsys/IOPdia) / OR. Linear regression analyses were performed comparing OPA to OR and calculated POBV at each of the three manometric setpoints. POBV was also compared to OPA/IOPdia with all data points combined. Significance threshold was p < 0.05. OR estimated from AL showed a significant positive relationship to OPA for both DCT (p < 0.011) and ICM (p < 0.006) at all three manometric pressure setpoints, with a greater slope for lower IOP. Calculated POBV also showed a significant positive relationship to OPA (p < 0.001) at all three setpoints with greater slope at lower IOP, and a significant negative relationship with IOPdia. In the combined analysis, POBV showed a significant positive relationship to OPA/ IOPdia (p < 0.001) in both ICM and DCT measurements with R2 = 0.9685, and R2 = 0.9589, respectively. POBV provides a straight-forward, clinically applicable method to estimate ocular blood supply noninvasively. Higher IOP in combination with lower OPA results in the lowest values of POBV. The simplified ratio, OPA/ IOPdia, may also provide a useful clinical tool for evaluating changes in ocular blood supply in diseases with a vascular component, such as diabetic retinopathy and normal tension glaucoma. Future studies are warranted.

Dynamic Contour Tonometer and Goldmann Applanation Tonometer Performance in a Developing World Setting

To examine tonometer usability and intraocular pressure (IOP) measurement precision in a general ophthalmology clinic in the developing world. A total of 100 eyes of 100 participants attending a charity ophthalmology walk-in clinic in Ghana, West Africa, had IOP measurements made with the Goldmann applanation tonometer (GAT) and the dynamic contour tonometer (DCT) in a randomized order by 2 clinicians. Both clinicians had extensive experience in using the GAT but were relatively inexperienced in using the DCT. The repeatability coefficient was calculated to determine intraobserver variability. Reproducibility of interobserver IOP measurements was calculated using Bland-Altman analysis. IOP could not be measured in 3% of eyes using the GAT and in 16% of eyes using the DCT. The repeatability coefficient for the GAT and DCT were 2.5 and 3.0 mm Hg, respectively. The DCT repeatability coefficient was 2.3 mm Hg when only "good quality" measurements were considered. The interobserver mean difference (limits of agreement) were -0.8 mm Hg (±3.9 mm Hg) for the GAT and 0.3 mm Hg (±3.3 mm Hg) for the DCT. DCT IOP measurements were unobtainable in eyes with corneal surface irregularities or excessive eye or lid movements. The DCT shows good measurement precision with comparable repeatability and superior reproducibility compared with the GAT. The DCT score is useful in its objectivity and improving repeatability. However, patient and ocular surface factors may impede DCT measurements, impacting upon its general usability in a high volume, walk-in community clinic.

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

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. 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. 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 (r(2) = 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. 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.

Dynamic Contour Tonometry and Goldmann Applanation Tonometry: Correlation with Intracameral Assessment of Intraocular Pressure

Purpose To compare intraocular pressure (IOP) measured using a dynamic contour tonometer (DCT) and a Goldmann applanation tonometer (GAT) with in vivo intracameral IOP, and establish the relationship between DCT, GAT and central corneal thickness (CCT) in patients with primary open-angle glaucoma (POAG). Materials and Methods We examined 50 eyes of 50 patients with POAG scheduled for glaucoma or cataract surgery. Immediately before surgery, CCT, GAT and DCT IOP were assessed, after which manometry of the anterior chamber was performed. A Bland-Altman plot was used to test the agreement among the 3 measurements of IOP, and univariate and multivariate regression analyses were used to evaluate the effect of CCT on DCT and GAT. Results On average, the DCT readings were 4.0±1.6 mmHg higher than the GAT readings and 2.3±2.4 mmHg higher than the manometric readings; the GAT measurements were generally a mean 1.7±1.8 mmHg lower than the manometric readings. The CCT had an almost similar influence on DCT and GAT measurements (p=0.84). Conclusions The DCT-measured IOP was significantly higher than that measured by means of GAT and anterior chamber manometry. The DCT and GAT readings were both influenced by CCT to the same extent.

The Impact of Intraocular Pressure Reduction on Retrobulbar Hemodynamic Parameters in Patients with Open-Angle Glaucoma

To assess the retrobulbar hemodynamic parameters in the ophthalmic artery (OA), central retinal artery (CRA), and short posterior ciliary arteries (PCA) after decreasing elevated intraocular pressure (IOP) in patients with open-angle glaucoma (OAG) by using color Doppler imaging. A total of 46 eyes from 46 patients with OAG, with elevated IOP, were consecutively included in this prospective study. Peak-systolic velocity, end-diastolic velocity, and Pourcelot resistivity index were assessed in the OA, CRA, and PCA. The IOP was measured with Goldmann applanation tonometer (GAT) and the dynamic contour tonometer (DCT), 3 times respectively. Ocular pulse amplitude (OPA) appeared during the DCT measurement. After decreasing the elevated IOP, measured with both GAT and DCT, the retrobulbar parameters showed no differences as compared with baseline measurements. After Bonferroni correction (p ≤ 0.0042, alpha/12), statistical significance appeared in retrobulbar hemodynamics only in DCT (29.3 ± 6.4 vs 15.5 ± 4.2 mmHg), GAT (33.0 ± 8.3 vs 15.8 ± 7.0 mmHg), and OPA measurements (4.1 ± 1.3 vs 2.7 ± 1.4 mmHg), in comparison to baseline. There was no correlation between the changes in IOP measured with either DCT or GAT and the changes in the retrobulbar hemodynamic parameters (p>0.05 for all). The results of our study suggested a lack of correlation between the changes in IOP, measured with either DCT or GAT, and the changes in the retrobulbar hemodynamic parameters. The results of our study might suggest that the blood flow disturbances found in glaucoma patients are independent of the IOP.

Intraocular pressure in keratoconus

This study aimed to investigate intraocular pressure (IOP) measurements taken using the dynamic contour tonometer (DCT) and the non-contact tonometer (NCT) in subjects with keratoconus. Intraocular pressure was measured in 20 keratoconus subjects and 20 age-matched control subjects using the DCT and NCT instruments. Central and off-centre measures were taken with the DCT in order to highlight any systematic errors associated with corneal biomechanical factors. Measures of anterior and posterior corneal topography and thickness were also taken in each subject. No significant difference was found between the central and off-centre DCT IOP readings for the keratoconus subjects and age-matched controls (p > 0.05). The average DCT IOP was 14.2 ± 1.4 mmHg in the keratoconus subjects and 14.2 ± 1.6 mmHg in the controls. However, the average NCT readings differed significantly (p < 0.001) between the keratoconus subjects (9.2 ± 1.5 mmHg) and the controls (12.9 ± 2.4 mmHg). Intraocular pressure measurements taken with the DCT showed no significant (p > 0.05) correlation with the severity of keratoconus as determined through measures of corneal topography and thickness. Equivalent IOP measurements taken with the NCT correlated significantly with certain measures of corneal curvature and thickness in the keratoconus population. The difference between DCT and NCT IOP was strongly correlated with measures of corneal topography and thickness, with differences increasing in more advanced keratoconus. The measurements obtained with the DCT do not appear to be dependent upon corneal factors, unlike those taken with the NCT. The presence or severity of keratoconus was not correlated with DCT IOP values.

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

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. 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. 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). 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.

Physiological diurnal variability and characteristics of the ocular pulse amplitude (OPA) with the dynamic contour tonometer (DCT-Pascal®)

The Pascal dynamic contour tonometer (DCT) allows measurement of intraocular pressure (IOP) independently of corneal properties. It records, simultaneously, haemodynamic IOP fluctuations and the difference between the systolic and the diastolic IOP corresponding to the ocular pulse amplitude (OPA). The OPA indirectly reflects choroidal perfusion and could be considered as an independent risk factor in glaucoma. We aimed to establish the physiological diurnal variability of the OPA and its correlations with other biophysical parameters because its characteristics remain partly unclear. Prospective study including 52 eyes of 28 normal subjects with Goldmann applanation tonometry (GAT) IOPs < 22 mmHg. Subjects treated with systemic medications that could interfere with blood pressure or heart rate were excluded. IOP was measured at 9:00 am, 1:00 pm, and 4:00 pm by GAT and DCT. Two consecutive GAT followed by three consecutive DCT measurements were performed in each session by the same clinician (SP). Only DCT measurements with quality 1 and 2 were taken into account. Blood pressure, pulse rate, and central corneal thickness (CCT) were recorded after the last IOP measurements. Spearman correlation coefficient was used for assessment of correlations. Mean age was 40 +/- 14 years. Mean DCT values were significantly higher than GAT readings (mean = 16.8 +/- 2.0 vs. 15.2 +/- 2.8 mmHg, P < 0.02). The mean OPA was 2.2 +/- 0.7 mmHg (range: 1-3.4 mmHg). The mean amplitude of diurnal OPA fluctuations was 0.4 mmHg. There was no significant difference in the mean OPA values at each time of the diurnal curve. The intraclass correlation (ICC) of only one OPA measurement in relation to part of total variance due to inter-measurement variation was 78%. Averaging over three independent readings of OPA improved ICC to 91%. The OPA was correlated with GAT (r = 0.31, P < 0.0001) and DCT IOP measurements (r = 0.49, P < 0.0001). It was correlated neither with blood pressure nor with age. OPA values of both eyes of the same individual were highly correlated (r = 0.89, P < 0.0001). In normal healthy eyes, the ocular pulse amplitude remains stable during normal outpatient office hours and was not correlated with blood pressure or age of patients.

Évaluation clinique du tonomètre dynamique de contour Pascal ®

Purpose: The Pascal (R) dynamic contour tonometer (DCT) was designed to measure IOP independently of corneal properties. This study aimed at 1) assessing the intra- and interindividual variability of DCT IOP measurements, the differences between DCT and applanation tonometry IOP measurements (APL), and their correlations with central corneal thickness (CCT); 2) analyzing the variability of the ocular pulse amplitude (OPA) and its correlations with age, blood pressure (BP), cardiac beat pulse (CP), diagnosis of glaucoma, IOP, and severity of glaucomatous visual field (VF) defects. Methods: Twenty-five normal subjects (25 eyes), 14 patients with ocular hypertension (27 eyes), and 54 glaucomatous patients (104 eyes) were included in this prospective study. In the first 12 normal subjects, three consecutive IOP measurements were taken by three different observers using DCT, directly followed by three measurements with APL by the same observer. In the following 13 subjects, the reverse sequence was followed. In the other group, the IOP measurements (three DCT and three APLs) were taken by the same observer. Only DCT measurements with quality levels 1-3 were considered for analysis. Results: In the normal group, DCT IOP measurement variability varied between 4.4%-7.3% (intraobserver variation coefficient) and 8% (interobserver variation coefficient). DCT IOP measurement was not influenced by the sequence of measurements or the observer. DCT overestimated IOP by a mean of 2.2mmHg compared with APL (p 0.05). Conclusions: IOP measurements with the Pascal (R) DCT and APL correlated well and were reproducible. DCT IOP measurement variability was slightly higher than APL with relatively wide 95% limits of agreement. Considering the entire study population, DCT overestimated IOP by a mean 2.0mmHg compared with APL. DCT was independent of CCT, especially in thin corneas. The DCT does not appear to be clinically advantageous over the Goldmann tonometer in the IOP measurement in thick corneas. Therefore an IOP follow-up by APL tonometry and pachymetry appeared to be mandatory for the interpretation of the true IOP. Interindividual OPA variations were high, as was measurement variability. OPA was correlated with BP, cardiac frequency, IOP, diagnosis of glaucoma, and severity of glaucomatous VF defects. These must be considered in the clinical interpretation of this parameter.

Dynamic contour tonometry versus Goldmann applanation tonometry: a comparative study

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. 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). Mean DCT values were about 1 mm Hg 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 microm). 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.