Dynamic Contour Tonometry

Safety and performance of a suprachoroidal sensor for telemetric measurement of intraocular pressure in the EYEMATE-SC trial

AIM

To investigate the safety and performance of a telemetric suprachoroidal intraocular pressure (IOP) sensor (EYEMATE-SC) and the accuracy of its IOP measurements in open angle glaucoma (OAG) patients undergoing simultaneous non-penetrating glaucoma surgery (NPGS).

METHODS

Prospective, multicentre, open-label, single-arm, interventional clinical trial. Twenty-four eyes of 24 patients with OAG regularly scheduled for NPGS (canaloplasty or deep sclerectomy) were simultaneously implanted with an EYEMATE-SC sensor. Six-month follow-up on the sensor's safety and performance as well as on the level of agreement between the EYEMATE-SC measurements and IOP measurements with Goldmann applanation tonometry (GAT).

RESULTS

The eyes underwent canaloplasty (n=15) or deep sclerectomy (n=9) and achieved successful implantation of the sensor. No device migration, dislocation or serious device-related complications occurred. A total of 367 comparisons were included in the IOP agreement analysis. The overall mean difference between GAT and EYEMATE-SC measurements was 1.31 mm Hg (lower limit of agreement (LoA) 7.55 mm Hg; upper LoA -4.92 mm Hg). The maximum difference of 2.5 mm Hg ±3.96 (LoA 0.30-2.29) was reached on day 10 and continuously improved to an agreement of -0.15 mm Hg ±2.28 (LoA -1.24 to 0.89) after 6 months. Accordingly, the percentage of eyes within an IOP difference of ±5 mm Hg improved from 78% (day 3) to 100% (6 months).

CONCLUSIONS

After 6 months, the EYEMATE-SC sensor was safe and well tolerated, and allowed continual IOP monitoring.

TRIAL REGISTRATION NUMBER

NCT03756662.

Comparison between dynamic contour tonometry and Goldmann applanation tonometry correcting equations

In order to investigate the reliability of correcting GAT formulas in comparison with dynamic contour tonometry (DCT), this study included 112 right eyes of 112 healthy subjects aged from 21 to 77 years, whose eyes underwent to a full ophthalmologic exam. IOP was measured in each eye with DCT and then with GAT. IOP values obtained with GAT were corrected with 10 equations and then compared with those provided by DCT. Participants mean age was 42.24 ± 14.08 years; mean IOP measured with DCT was 17.61 ± 2.87 and 15.50 ± 2.47 mmHg, measured with GAT. The mean discordance between DCT and GAT measurements was 2.11 ± 2.24 mmHg. All the correcting formulas, but Srodka one (p ˂ 0.001), tend to increase the difference between GAT and DCT. According to these results Śródka equation provides the best correction, reducing the difference between the two IOP measurement methods of - 0.03 ± 0.85 mmHg. Other equations do not provide a valid improvement of the agreement between the two methods or they provide a worsening of the agreement.

Corneal Biomechanics for Ocular Hypertension, Primary Open-Angle Glaucoma, and Amyloidotic Glaucoma: A Comparative Study by Corvis ST

BACKGROUND

To evaluate biomechanical parameters of the cornea provided by Corvis ST in patients with ocular hypertension, primary open-angle glaucoma, and amyloidotic glaucoma and to compare with healthy controls.

METHODS

This was a cross-sectional study of patients with ocular hypertension, primary open-angle glaucoma, and amyloidotic glaucoma that underwent Corvis ST imaging. Primary outcome was the comparison of corneal biomechanical parameters between study groups after adjusting for age, gender, Goldmann intraocular pressure (GAT-IOP), and prostaglandin analogues medication. Secondary outcome was the comparison of different IOP measurements in each group.

RESULTS

One hundred and eighty-three eyes from 115 patients were included: 61 with primary open-angle glaucoma, 32 with amyloidotic glaucoma, 37 with ocular hypertension and 53 were healthy controls. Amyloidotic glaucoma group had smaller radius (p=0.025), lower deflection amplitude at highest concavity (p=0.019), and higher integrated radius (p=0.014) than controls. Ocular hypertension group had higher stiffness parameter at first applanation (p=0.043) than those with primary open-angle glaucoma, and higher stress-strain index (p=0.049) than those with amyloidotic glaucoma. Biomechanically corrected intraocular pressure was significantly lower than Goldmann intraocular pressure in group with primary open-angle glaucoma (p=0.005) and control group (p=0.013), and Goldmann intraocular pressure adjusted for pachymetry in group with primary open-angle glaucoma (p=0.01).

CONCLUSION

Eyes with amyloidotic glaucoma have more deformable corneas, while eyes with ocular hypertension have less deformable corneas. These findings may be linked to the susceptibility to glaucomatous damage and progression. There were significant differences between Goldmann applanation tonometry and biomechanically corrected intraocular ocular pressure provided by Corvis ST.

Risk Factors for the Structural Progression of Myopic Glaucomatous Eyes with a History of Laser Refractive Surgery

As laser refractive surgeries (LRS) have been widely performed to correct myopia, ophthalmologists easily encounter patients with glaucoma who have a history of LRS. It is well known that intraocular pressure (IOP) in eyes with glaucoma is not accurate when measured using Goldmann applanation tonometry. However, risk factors for glaucoma progression, particularly those associated with measured IOP, have rarely been studied. We analysed data for 40 patients with a history of LRS and 50 age-matched patients without a history of LRS. Structural progression was defined as significant changes in thickness in the peripapillary retinal nerve fibre layer as identified using optical coherence tomography event-based guided progression analysis. Risk factors were determined via Cox regression analysis. Disc haemorrhage (DH) was associated with glaucoma progression in both the non-LRS group and LRS group (hazard ratio (HR): 4.650, p = 0.012 and HR: 8.666, p = 0.019, respectively). However, IOP fluctuation was associated with glaucoma progression only in the LRS group (HR: 1.452, p = 0.023). Our results show that DH was a significant sign of progression in myopic glaucoma eyes. When treating patients with myopia and glaucoma, IOP fluctuation should be monitored more carefully, even if IOP seems to be well controlled.

Evaluating the Relationship of Intraocular Pressure and Anterior Chamber Volume With Use of Prostaglandin Analogues

PRCIS

In this prospective study, naive prostaglandin use in primary open-angle glaucoma was associated with scleral biomechanical alteration and intraocular pressure (IOP) measuring errors.

PURPOSE

The purpose of this study is to determine the effects of naïve use of prostaglandin analogues (PGA) on IOP and anterior chamber volume (ACV), as well as investigate how PGAs might affect corneal and scleral stiffness and their impact on ocular rigidity.

MATERIALS AND METHODS

This study was a prospective study of 21 recently diagnosed open-angle glaucoma patients (33 eyes) initiating medical therapy with a topical prostaglandin eye drop. Corneal morphologic and biomechanical parameters as well as IOP were measured at 3 visits over a 4-month period with the following equipment: Pentacam, Corvis ST, Ocular Response Analyzer, Goldmann applanation tonometry (GAT) and Pascal dynamic contour tonometry.

RESULTS

The study demonstrated a significant decrease in mean IOP with initiation of PGA in all 4 tonometers (P<0.0001). The greatest change in IOP occurred in the first 4 weeks of treatment (P<0.0001). The mean ACV showed a significant decrease at visit 2 (P<0.02) and visit 3 (P<0.04) compared with baseline visit 1. However, there was a paradoxical increase in ACV in 37% of eyes at visit 2, despite a significant mean reduction in IOP by GAT and dynamic contour tonometry.The IOP/ACV ratio at visit 1 significantly predicted the reduction in respective measures of IOP, as well as scleral stiffness measured by stiffness parameter-highest concavity.

CONCLUSION

In clinical practice, GAT may not be the most appropriate tonometer for measuring IOP in PGA treated eyes due the measurement errors from ocular biomechanical alteration. The IOP/ACV ratio could potentially serve as a new diagnostic parameter to determine the likelihood of PGA treatment success.

Comparison of Biomechanically Corrected Intraocular Pressure Obtained by Corvis ST and Goldmann Applanation Tonometry in Patients With Open-angle Glaucoma and Ocular Hypertension

PRECIS

Biomechanically corrected intraocular pressure (bIOP) measurements provided by the new Corvis ST (CST) were higher than measurements obtained with Goldman applanation tonometry (GAT) in eyes with ocular hypertension (OHT) or open-angle glaucoma (OAG).

PURPOSE

To compare bIOP obtained with a new version of CST with GAT measurements in patients with OAG and OHT, and to identify factors affecting IOP measurement differences between these methods.

METHODS

A total of 122 eyes with OAG or OHT were enrolled. Sixty eyes were treated with prostaglandin analogs (PGA) and 62 eyes with selective laser trabeculoplasty (SLT). IOP was measured with CST, followed by GAT. Central corneal thickness (CCT) was measured with ultrasound pachymetry. Measurements obtained with these 2 approaches were compared.

RESULTS

The overall mean IOP was 15.2±3.0 mm Hg and 14.1±3.2 mm Hg with the CST and GAT, respectively (r=0.74; P<0.0001). There was a 1.17 mm Hg bias between tonometers, with 95% limits of agreement of -2.66 to 5.01 mm Hg. According to multivariate regression analysis, differences between bIOP and GAT-IOP were associated with CCT (P=0.001) and age (P=0.007) in the PGA group, but only with CCT in the SLT group (P=0.002). bIOP and GAT-IOP values were influenced by age (PGA: P=0.014; SLT: P=0.006) and CCT (PGA: P=0.007; SLT: P=0.032), respectively.

CONCLUSIONS

BIOP values were higher and less affected by CCT than GAT-IOP values in eyes with OAG and OHT. However, these measurements may not be interchangeable in the clinic.

A clinical method for estimating the modulus of elasticity of the human cornea in vivo

BACKGROUND

To develop a method, using current clinical instrumentation, to estimate the Young's modulus of the human cornea in vivo.

METHODS

Central corneal curvature (CCC), central corneal thickness(CCT), intraocular pressure (IOP) was measured with the Goldmann tonometer (IOPG) and the Pascal Dynamic Corneal Tonometer(PDCT) in one eye of 100 normal young human subjects (21.07 ± 2.94 years) in vivo. The Orssengo and Pye algorithm was used to calculate the Young's modulus of the corneas of these subjects.

RESULTS

The Young's modulus(E) of the corneas of the subjects using the PDCT and IOPG results (Ecalc) was 0.25 ± 0.10MPa, and without the PDCT results (Eiopg) was 0.29 ± 0.06MPa. The difference in these results is due to the difference in tonometry results between the two instruments, as the mean PDCT result for the subjects was 16.89 ± 2.49mmHg and the IOPG result 15.06 ± 2.71mmHg. E was affected by the CCC of the subjects but more particularly by the CCT and IOP measurements. Corneal stiffness results are also presented.

CONCLUSION

Two methods have been developed to estimate the Young's modulus of the human cornea in vivo using current clinical instrumentation. One method (Ecalc) is applicable to the general corneal condition, and Eiopg to the normal cornea, and these results can be used to calculate corneal stiffness.

Effectiveness of the Goldmann Applanation Tonometer, the Dynamic Contour Tonometer, the Ocular Response Analyzer and the Corvis ST in Measuring Intraocular Pressure following FS-LASIK

Purpose: To test the performance of the four tonometers in providing IOP measurements that were free of the effects of corneal biomechanics changes caused by refractive surgery.Methods: Four tonometers were employed to provide IOP measurements for 65 participants who accepted Femtosecond laser-assisted LASIK (FS-LASIK). The measurements included GAT-IOP by the Goldmann Applanation Tonometer, DCT-IOP by the Dynamic Contour Tonometer, Goldmann-correlated IOP (ORA-IOPg) and corneal-compensated IOP (ORA-IOPcc) by the Ocular Response Analyzer, and uncorrected IOP (CVS-IOP) and biomechanically corrected IOP (CVS-bIOP) by the Corvis ST. Statistical analyses were performed to assess the association of the differences in IOP caused by FS-LASIK with central corneal thickness (CCT), mean corneal curvature (Km), age, refractive error correction (REC), optical zone diameter (OZD), ablation zone diameter (AZD), residual stromal bed thickness (RSB) and RSB ratio (RSB/CCT). Multiple linear regression models were constructed to explore factors influencing IOP changes.Results: All four tonometers exhibited significant differences between IOP measurements taken pre and post-surgery except for CVS-bIOP in the low to moderate myopia group (t = 1.602, p = .12). CVS-bIOP, followed by DCT-IOP, provided the best agreement between pre and post-FS-LASIK measurements with the lowest differences in IOP and the narrowest limits of agreement. The pre-post IOP differences were also significantly associated with the reduction in CCT in only GAT-IOP, ORA-IOPg, and CVS-IOP. CVS-bIOP and ORA-IOPcc were the only measurements that were not correlated with CCT, Km or age both before and after FS-LASIK.Conclusions: The biomechanically corrected bIOP from the Corvis ST provided post-FS-LASIK measurements that were in closest agreement with those obtained before surgery. In comparison, GAT-IOP, ORA-IOPg, ORA-IOPcc, and CVS-IOP appeared to be more influenced by the changes in corneal biomechanics caused by FS-LASIK.

Significance of dynamic contour tonometry in evaluation of progression of glaucoma in patients with a history of laser refractive surgery

AIMS

In this study, we tested the hypothesis that intraocular pressure (IOP) parameters measured by dynamic contour tonometry (DCT) would be more relevant in progression of glaucoma when there is a history of laser refractive surgery (LRS) than the IOP parameters measured by Goldmann applanation tonometry (GAT) or calculated by correction formulae.

METHODS

Ninety-eight eyes in 54 patients with open-angle glaucoma and a history of LRS were included in this retrospective study. IOP was measured by both GAT and DCT during follow-up. Baseline, mean, and peak IOP, IOP fluctuation, and IOP reduction were measured by each tonometry method. Corrected IOP parameters using central corneal thickness and mean keratometry values were also analysed. Clustered logistic regression was used to identify variables correlated with progression of glaucoma. Areas under the curve (AUCs) for correlated variables were also compared.

RESULTS

The mean DCT value (OR 1.36, p=0.024), peak DCT value (OR 1.19, p=0.02) and pattern SD (OR 1.10, p=0.016) were significant risk factors for progression. There was a significant difference in the predictive ability of the mean DCT and GAT values (AUC 0.63 and 0.514, respectively; p=0.01) and of the peak DCT and GAT values (0.646 and 0.503, respectively, p=0.009). The AUCs for corrected IOP did not exceed those of DCT.

CONCLUSIONS

IOP measurements were more associated with progression of glaucoma when measurements were obtained by DCT than by GAT or correction formulae in eyes with a history of LRS.

Ex-vivo experimental validation of biomechanically-corrected intraocular pressure measurements on human eyes using the CorVis ST

The purpose of this study was to assess the validity of the Corvis ST (Oculus; Wetzlar, Germany) biomechanical correction algorithm (bIOP) in determining intraocular pressure (IOP) using experiments on ex-vivo human eyes. Five ex-vivo human ocular globes (age 69 ± 3 years) were obtained and tested within 3-5 days post mortem. Using a custom-built inflation rig, the internal pressure of the eyes was controlled mechanically and measured using the CorVis ST (CVS-IOP). The CVS-IOP measurements were then corrected to produce bIOP, which was developed for being less affected by variations in corneal biomechanical parameters, including tissue thickness and material properties. True IOP (IOPt) was defined as the pressure inside of the globe as monitored using a fixed pressure transducer. Statistical analyses were performed to assess the accuracy of both CVS-IOP and bIOP, and their correlation with corneal thickness. While no significant differences were found between bIOP and IOP_t (0.3 ± 1.6 mmHg, P = 0.989) using ANOVA and Bonferroni Post-Hoc test, the differences between CVS-IOP and IOPt were significant (7.5 ± 3.2 mmHg, P < 0.001). Similarly, bIOP exhibited no significant correlation with central corneal thickness (p = 0.756), whereas CVS-IOP was significantly correlated with the thickness (p < 0.001). The bIOP correction has been successful in providing close estimates of true IOP in ex-vivo tests conducted on human donor eye globes, and in reducing association with the cornea's thickness.

The thick and thin of the central corneal thickness in glaucoma

Central corneal thickness (CCT) is an important parameter in the assessment of any potential glaucoma patient. While it affects prognosis in ocular hypertension, its value in patients diagnosed with glaucoma is less certain. There are several biological factors and genetic components that may influence glaucoma progression, which have been associated with thinner CCT. The CCT itself can be affected by several factors including ethnicity, age, sex, glaucoma medications, genetics, and the subtype of glaucoma. Besides, there is variability in the measurement of CCT between difference types of devices. These factors need to be considered in the evaluation of glaucoma patients' CCT and its effect on interpretation of intraocular pressure levels and risk stratification.

Utility of Goldmann applanation tonometry for monitoring intraocular pressure in glaucoma patients with a history of laser refractive surgery

The utility of Goldmann applanation tonometry (GAT) for monitoring intraocular pressure (IOP) in open-angle glaucoma (OAG) patients with a history of laser refractive surgery was investigated by comparing IOP fluctuations measured using GAT and dynamic contour tonometry (DCT) on the same day. In this retrospective study, patients were divided into one of two subgroups according to IOP fluctuation values using GAT: 43 eyes in the low IOP fluctuation group (LIFG [GAT fluctuation ≤1.7 mmHg]); and 55 eyes in the high IOP fluctuation group (HIFG [GAT fluctuation >1.7 mmHg]). IOP fluctuation was defined as the standard deviation of all IOP values during follow-up. IOP parameters using GAT were compared with those of DCT. Correlation analyses were performed among IOP parameters, and between IOP fluctuation and associated factors including central corneal thickness, corneal curvature, and axial length. All IOP parameters demonstrated significantly high values in the HIFG compared with those in the LIFG. Mean and peak IOP using DCT were significantly higher than those using GAT in both groups. However, there were no significant differences in IOP fluctuation and reduction using both tonometry methods in the HIFG (p = 0.946 and p = 0.986, respectively). Bland-Altman analysis revealed similar fluctuations using GAT and DCT. In multivariate analyses, there was a significant correlation between fluctuations using GAT and DCT in the HIFG (p = 0.043). These results suggest that IOP monitoring using GAT is a reliable method of monitoring IOP change in glaucoma patients with a history of laser refractive surgery, especially those exhibiting high IOP fluctuation. Nevertheless, several factors, including central corneal thickness, corneal curvature, and axial length, should be considered when using GAT for IOP monitoring.

Goldmann tonometry tear film error and partial correction with a shaped applanation surface

Purpose

The aim of the study was to quantify the isolated tear film adhesion error in a Goldmann applanation tonometer (GAT) prism and in a correcting applanation tonometry surface (CATS) prism.

Methods

The separation force of a tonometer prism adhered by a tear film to a simulated cornea was measured to quantify an isolated tear film adhesion force. Acrylic hemispheres (7.8 mm radius) used as corneas were lathed over the apical 3.06 mm diameter to simulate full applanation contact with the prism surface for both GAT and CATS prisms. Tear film separation measurements were completed with both an artificial tear and fluorescein solutions as a fluid bridge. The applanation mire thicknesses were measured and correlated with the tear film separation measurements. Human cadaver eyes were used to validate simulated cornea tear film separation measurement differences between the GAT and CATS prisms.

Results

The CATS prism tear film adhesion error (2.74±0.21 mmHg) was significantly less than the GAT prism (4.57±0.18 mmHg, p<0.001). Tear film adhesion error was independent of applanation mire thickness (R²=0.09, p=0.04). Fluorescein produces more tear film error than artificial tears (+0.51±0.04 mmHg; p<0.001). Cadaver eye validation indicated the CATS prism's tear film adhesion error (1.40±0.51 mmHg) was significantly less than that of the GAT prism (3.30±0.38 mmHg; p=0.002).

Conclusion

Measured GAT tear film adhesion error is more than previously predicted. A CATS prism significantly reduced tear film adhesion error bŷ41%. Fluorescein solution increases the tear film adhesion compared to artificial tears, while mire thickness has a negligible effect.

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

Purpose

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.

Methods

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).

Results

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.

Conclusions

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.

Goldmann and error correcting tonometry prisms compared to intracameral pressure

Background

Compare Goldmann applanation tonometer (GAT) prism and correcting applanation tonometry surface (CATS) prism to intracameral intraocular pressure (IOP), in vivo and in vitro.

Methods

Pressure transducer intracameral IOP was measured on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically to 10, 20, and 40 mmHg. Simultaneously, IOP was measured using a Perkins tonometer with a standard GAT prism and a CATS prism at each of the intracameral pressures. Statistical comparison was made between true intracameral pressures and the two prism measurements. Differences between the two prism measurements were correlated to central corneal thickness (CCT) and corneal resistance factor (CRF). Human cadaver eyes were used to assess measurement repeatability.

Results

The CATS tonometer prism measured closer to true intracameral IOP than the GAT prism by 1.7+/−2.7 mmHg across all pressures and corneal properties. The difference in CATS and GAT measurements was greater in thin CCT corneas (2.7+/−1.9 mmHg) and low resistance (CRF) corneas (2.8+/−2.1 mmHg). The difference in prisms was negligible at high CCT and CRF values. No difference was seen in measurement repeatability between the two prisms.

Conclusion

A CATS prism in Goldmann tonometer armatures significantly improve the accuracy of IOP measurement compared to true intracameral pressure across a physiologic range of IOP values. The CATS prism is significantly more accurate compared to the GAT prism in thin and less rigid corneas. The in vivo intracameral study validates mathematical models and clinical findings in IOP measurement between the GAT and CATS prisms.

Goldmann applanation tonometry error relative to true intracameral intraocular pressure in vitro and in vivo

BACKGROUND

Goldmann applanation tonometry (GAT) error relative to intracameral intraocular pressure (IOP) has not been examined comparatively in both human cadaver eyes and in live human eyes. Futhermore, correlations to biomechanical corneal properties and positional changes have not been examined directly to intracameral IOP and GAT IOP.

METHODS

Intracameral IOP was measured via pressure transducer on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically on each patient alternately to 10, 20, and 40 mmHg. IOP was measured using a Perkins tonometer in the supine position on 58 eyes and upright on a subset of 8 eyes. Twenty one (21) fresh human cadaver globes were Intracamerally IOP adjusted and measured via pressure transducer. Intracameral IOP ranged between 5 and 60 mmHg. IOP was measured in the upright position with a Goldmann Applanation Tonometer (GAT) and supine position with a Perkins tonometer. Central corneal thickness (CCT) was also measured.

RESULTS

The Goldmann-type tonometer error measured on live human eyes was 5.2 +/-1.6 mmHg lower than intracameral IOP in the upright position and 7.9 +/- 2.3 mmHg lower in the supine position (p < .05). CCT also indicated a sloped correlation to error (correlation coeff. = 0.18). Cadaver eye IOP measurements were 3.1+/-2.5 mmHg lower than intracameral IOP in the upright position and 5.4+/- 3.1 mmHg in the supine position (p < .05).

CONCLUSION

Goldmann IOP measures significantly lower than true intracameral IOP by approximately 3 mmHg in vitro and 5 mmHg in vivo. The Goldmann IOP error is increased an additional 2.8 mmHg lower in the supine position. CCT appears to significantly affect the error by up to 4 mmHg over the sample size.

Clinical Evaluation of Methods to Correct Intraocular Pressure Measurements by the Goldmann Applanation Tonometer, Ocular Response Analyzer, and Corvis ST Tonometer for the Effects of Corneal Stiffness Parameters

PURPOSE

To evaluate the effectiveness of methods to correct intraocular pressure (IOP) measurements obtained using the Goldmann applanation tonometer (GAT), the ocular response analyzer (ORA), and the Corvis ST tonometer (CVS) for the effects of corneal stiffness parameters: central corneal thickness (CCT), corneal curvature (R), and age in a Chinese population.

PATIENTS AND METHODS

Data were collected for 99 eyes of 99 participants. Whereas cornea-corrected IOP was obtained directly from ORA (ORA-IOPcc), cornea correction in GAT and CVS was implemented using multiparameter equations developed earlier. The study also included IOP measurements by the dynamic contour tonometer, which is thought to be less affected by corneal stiffness parameters than other tonometers. Statistical analyses were performed to determine the association of both uncorrected and corrected IOP with the main stiffness parameters: CCT, R, and age.

RESULTS

After correction, a significantly decreased association between the GAT (from r=0.15 to r=-0.02), ORA (from r=0.24 to r=-0.19), and CVS (from r=0.47 to r=0.004) IOP measurements and the CCT was found, to levels below that with the dynamic contour tonometer-IOP (r=0.11). The IOP measurements made by the 4 tonometers, both uncorrected and corrected, did not correlate with age. The same was true for R except with ORA-IOPcc (r=0.23).

CONCLUSIONS

CCT accounted for the majority of variance in IOP, whereas age and R had a much smaller effect. The IOP correction processes studied were successful in reducing reliance of IOP measurements, especially those by GAT and CVS, on CCT in a healthy Chinese population.

Tonometry after Intrastromal Corneal Ring Segments for Keratoconus

SIGNIFICANCE

Reliable intraocular pressure (IOP) measurement after intrastromal corneal ring segments (ICRS) implantation is a challenge because of altered corneal morphology. In this study, IOP is measured with four tonometers, compared with Goldmann applanation tonometry (GAT) values and the influence of corneal parameters is established.

PURPOSE

This study compares IOP measurements made using different tonometers in patients implanted with ICRS and assesses the effects of central corneal thickness (CCT), corneal curvature, and corneal astigmatism on the IOP measurements obtained.

METHODS

In this cross-sectional study, IOP was measured using three different tonometers in 91 eyes of 91 patients with corneal ectasia implanted at least 6 months previously with ICRS. The tonometers tested were the TonoPen XL, Pascal dynamic contour tonometer (DCT), and iCare Pro rebound tonometer. GAT measurements were used as reference. Agreement among the IOPs provided by the different tonometers and the influence of corneal variables on the IOP measurements obtained were assessed using the Bland-Altman method, intraclass correlation coefficients, and multiple linear regression analysis.

RESULTS

Mean IOP differences were GAT versus TonoPen XL -0.8 ± 3.07 mm Hg, GAT versus DCT -1.0 ± 3.26 mm Hg, and GAT versus iCare Pro 0.8 ± 2.92 mm Hg. Our multiple linear regression analysis identified CCT as a confounding factor affecting all the tonometer readings but DCT-IOP.

CONCLUSIONS

In patients fitted with ICRS, IOP measurements made using the iCare Pro and TonoPen XL showed most agreement with GAT. Intraocular pressure measurements made by DCT were unaffected by corneal topographic factors though this procedure slightly overestimated GAT readings.

Correlation Between Dynamic Contour Tonometry, Uncorrected and Corrected Goldmann Applanation Tonometry, and Stage of Glaucoma

Importance

Accurate determination of intraocular pressure (IOP) is crucial for the diagnosis and management of glaucoma. Objective clinical evaluation of the correction equations for Goldmann applanation tonometry (GAT) is lacking.

Objectives

To investigate the difference between corrected and conventional GAT and Pascal dynamic contour tonometry (DCT) measurements, as well as the correlation between discordant IOP values and stage of glaucoma.

Design, Setting, and Participants

This prospective cross-sectional case series was conducted at the Department of Ophthalmology, University Hospital Zurich, and Talacker Eye Center between July 1, 2011, and May 31, 2016, among 112 white patients with glaucoma.

Interventions

Intraocular pressure measurements were performed with GAT and DCT in a randomized order. Goldmann applanation tonometry measurements were modified with 5 correction equations.

Main Outcomes and Measures

The primary end point was degree of concordance between corrected or uncorrected GAT and DCT measurements. The secondary end point was association between discordant IOP measurements and the stage of glaucoma, as assessed by the Glaucoma Severity Score.

Results

Among the 112 patients (67 women and 45 men; mean [SD] age, 66.3 [13.1] years), 63 of the eyes in the study (56.3%) were left eyes and 85 patients (75.9%) were taking ocular antihypertensive medications. Mean (SD) IOP was 20.3 (4.5) mm Hg (95% CI, 19.4-21.1) as measured by DCT and 17.0 [4.1] mm Hg (95% CI, 16.3-17.8) as measured by GAT. The mean (SD) discordance between DCT and GAT measurements was -3.3 (2.0) mm Hg (95% CI, 2.9-3.6). The 5 corrected GAT values ranged from -2.7 to -5.4 mm Hg compared with DCT. The mean (SD) result of the Dresdner correction formula (17.6 [4.1] mm Hg) was closer to the DCT measurement than the original GAT measurement. The mean (SD) Glaucoma Severity Score was 4.7 (3.4) (95% CI, 4.1-5.4). The uncorrected discordance IOPDCT - IOPGAT showed a positive correlation with the Glaucoma Severity Score (rs = 0.33; P < .001) and a negative correlation with central corneal thickness (rs = -0.22; P = .02).

Conclusions and Relevance

In comparison with DCT measurements, these data suggest that GAT values are significantly discordant in eyes with thin corneas and advanced glaucoma. Application of GAT-based correction formulas involves a possible risk of creating an even greater number of unpredictable measurement errors. Hence, we advise with caution, especially pertaining to eyes with thin corneas, to not place reliance on GAT readings, and abandon any correction formula.

Trial Registration

clinicaltrials.gov Identifier: NCT01474070.

Goldmann tonometer error correcting prism: clinical evaluation

Purpose

Clinically evaluate a modified applanating surface Goldmann tonometer prism designed to substantially negate errors due to patient variability in biomechanics.

Methods

A modified Goldmann prism with a correcting applanation tonometry surface (CATS) was mathematically optimized to minimize the intraocular pressure (IOP) measurement error due to patient variability in corneal thickness, stiffness, curvature, and tear film adhesion force. A comparative clinical study of 109 eyes measured IOP with CATS and Goldmann prisms. The IOP measurement differences between the CATS and Goldmann prisms were correlated to corneal thickness, hysteresis, and curvature.

Results

The CATS tonometer prism in correcting for Goldmann central corneal thickness (CCT) error demonstrated a reduction to <±2 mmHg in 97% of a standard CCT population. This compares to only 54% with CCT error <±2 mmHg using the Goldmann prism. Equal reductions of ~50% in errors due to corneal rigidity and curvature were also demonstrated.

Conclusion

The results validate the CATS prism’s improved accuracy and expected reduced sensitivity to Goldmann errors without IOP bias as predicted by mathematical modeling. The CATS replacement for the Goldmann prism does not change Goldmann measurement technique or interpretation.

Evaluation of Goldmann applanation tonometry, rebound tonometry and dynamic contour tonometry in keratoconus

PURPOSE

To compare the intraocular pressure (IOP) measurements obtained with the rebound tonometry (RT), dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in keratoconic corneas and to investigate the effects of central corneal thickness (CCT) and corneal radius of curvature (CR) on IOP measurements.

METHODS

Sixty-three eyes of 63 keratoconus patients were enrolled in this cross-sectional study. 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 CR were measured using a rotating Scheimpflug camera before the IOP measurements in all subjects. One way repeated measures ANOVA and Pearson correlation coefficient analysis was used for the statistical assessment.

RESULTS

Mean IOP for all enrolled eyes was 11.72±2.59mmHg for GAT, 9.34±3.29mmHg for RT, and 15.42±3.31mmHg for DCT. There were statistically significant differences among the three tonometers; GAT and RT (P<0.001), GAT and DCT (P<0.001), and RT and DCT (P<0.001). GAT and RT were significantly positively correlated with CCT (r=0.288, P=0.025 and r=0.483, P<0.001, respectively). RT was also significantly positively correlated with CR (r=0.550, P<0.001). DCT was not significantly correlated with CCT (r=0.115, P=0.377) nor CR (r=-0.179, P=0.168).

CONCLUSIONS

DCT has overestimated but RT has underestimated IOP readings according to GAT measurements in keratoconic corneas. DCT may be the most appropriate tonometer to use in keratoconus for the measurements of IOP, because DCT do not appear to be dependent upon CCT and CR.

[Intraocular pressure measurement inside the anterior chamber: a new technical solution and results]

AIM

To develop a new manometric device for intravital measurement of intraocular pressure (IOP) in the anterior chamber and to assess tonometric data reliability, including post-radial keratotomy (RK) measurements.

MATERIAL AND METHODS

The experiment was conducted in 2 isolated cadaver eyes, while the clinical study enrolled 20 patients (21 eyes) scheduled for cataract phacoemulsification surgery. Of them, 10 patients (10 eyes) with immature cataract and mild to moderate myopia constituted the control group. The study group consisted of the other 10 patients (11 eyes) with immature cataract, who had undergone RK more than 15 years earlier. The following tonometry methods were used: dynamic bi-directional corneal applanation (ORA, Reichert, USA), dynamic contour tonometry (Pascal tonometer, Zeimer, Switzerland), and rebound tonometry (ICare Pro, Tiolat, Finland). An original device was developed for intravital manometric measurements.

RESULTS

Manometric data obtained during the experiment matched the preset pressure in the anterior eye chamber. The median manometry results in the control and study groups were similar and equaled 21.5 and 21.0 mmHg, respectively. Preoperative tonometry readings ranged from 14.9 to 16.5 mmHg in the control group and from 19.7 to 23.3 mmHg - in the study group (with the exception of midperipheral rebound tonometry that showed 15.8 mmHg).

CONCLUSION

The developed device can well be used in experimental research. Midperipheral rebound tonometry was found to be the most informative method for post-RK IOP assessment. Manometry results in the study group mismatched tonometry readings in the controls, which might be due to the specifics of equipment calibration and requires further investigation.

[Reduction of intraocular pressure and ocular pulse amplitude during general anesthesia]

AIM

Measurement of the intraocular pressure (IOP) is an important tool for glaucoma diagnostics in children or patients with impaired cooperation. General anesthesia (GA) may significantly influence the IOP. This study aimed to evaluate the reduction of IOP during GA.

PATIENTS AND METHODS

The IOP was measured in 229 patients in a recumbent position in the non-operated eye prior to and 5 min after the beginning of GA with a dynamic contour tonometer (DCT).

RESULTS

The average IOP decreased from 19.9 ± 3.7 mmHg prior to GA to 14.1 ± 3.5 mmHg 5 min after beginning GA (p < 0.0001, IOP decrease 30 %). The GA caused a decrease of up to 2 mmHg in 6.1 %, 2-4 mmHg in 18.8 %, 4-6 mmHg in 21.0 %, 6-8 mmHg in 36.6 %, 8-10 mmHg in 13.6 %, 10-12 mmHg in 2.2 % and more than 12 mmHg in 1.7 % of the eyes. The ocular pulse amplitude (OPA) decreased from a mean of 3.4 ± 1.5 mmHg to 1.9 ± 1.0 mmHg (p < 0.0001, OPA decrease 41 %) under GA.

CONCLUSION

A significant decrease of IOP (mean 6 mmHg) occurs during GA and under extreme conditions up to 13.8 mmHg. A decrease of OPA of 1.5 mmHg should be taken into consideration for patients under general anesthesia and under extreme conditions up to 7 mmHg.

Comparison of Goldmann applanation tonometry and Pascal dynamic contour tonometry in relation to central corneal thickness and corneal curvature

Purpose

The aim of the study was to assess the influence of central corneal thickness (CCT) and corneal curvature in tonometry measurements taken by Goldmann applanation tonometry (GAT) and Pascal dynamic contour tonometry (DCT).

Methods

This was a prospective study of 185 eyes from 97 subjects, attending outpatient ophthalmology appointments, who underwent intraocular pressure measurements by GAT and Pascal DCT. CCT and corneal curvature were obtained using ultrasound pachymetry and Orbscan topography, respectively. All measurements were carried out among males and females during the period 2009–2012. Apart from the usual descriptive and exploratory data analysis, one-way analysis of variance and agreement analysis were performed, linear as well as intraclass correlation coefficients were estimated, and multiple scatter and Bland–Altman plots were produced.

Results

Mean IOP measurements obtained were 17.21±4.10 mmHg by DCT and 13.23±4.07 mmHg by GAT. Mean difference between the GAT and DCT measurements was 3.88±2.8 mmHg. Mean CCT and corneal curvature were 522.78±52 μm and 43.83±2.9823 D, respectively.

Conclusion

Intraocular pressure measured by GAT was consistently lower when compared with DCT, and this difference was greatest with thinner CCT. Flat corneas seem to influence GAT measurements compared to DCT.

Comparison of ICare and IOPen vs Goldmann applanation tonometry according to international standards 8612 in glaucoma patients

AIM

To compare IOPen and ICare rebound tonometry to Goldmann applanation tonometry (GAT) according to International Standards Organization (ISO) 8612 criteria.

METHODS

Totally 191 eyes (n=107 individuals) were included. Criteria of ISO 8612 were fulfilled: 3 clusters of IOP, measured by GAT, were formed. The GAT results were given as mean±standard deviation.

RESULTS

GAT (19.7±0.5 mm Hg) showed a significant correlation to ICare (19.8±0.5 mm Hg) (r=0.547, P<0.001) and IOPen (19.5±0.5 mm Hg) (r=0.526, P<0.001). According to ISO 8612 criteria in all 3 IOP groups the number of outliers (of the 95% limits of agreement) exceeded 5% for ICare and IOPen vs GAT: No.1 (n=68) 29.4% and 22.1%, No.2 (n=62) 35.5% and 37.1%, No.3 (n=61) 26.2% and 42.6%, respectively.

CONCLUSION

The strict requirements of the ISO 8612 are not fulfilled in a glaucoma collective by ICare and IOPen at present. As long as the Goldmann tonometry is applicable it should be used first of all for reproducible IOP readings. ICare and IOPen tonometry should be considered as an alternative tool, if application of Goldmann tonometry is not possible.

Goldmann Tonometer Prism with an Optimized Error Correcting Applanation Surface

Purpose

We evaluate solutions for an applanating surface modification to the Goldmann tonometer prism, which substantially negates the errors due to patient variability in biomechanics.

Methods

A modified Goldmann or correcting applanation tonometry surface (CATS) prism is presented which was optimized to minimize the intraocular pressure (IOP) error due to corneal thickness, stiffness, curvature, and tear film. Mathematical modeling with finite element analysis (FEA) and manometric IOP referenced cadaver eyes were used to optimize and validate the design.

Results

Mathematical modeling of the optimized CATS prism indicates an approximate 50% reduction in each of the corneal biomechanical and tear film errors. Manometric IOP referenced pressure in cadaveric eyes demonstrates substantial equivalence to GAT in nominal eyes with the CATS prism as predicted by modeling theory.

Conclusion

A CATS modified Goldmann prism is theoretically able to significantly improve the accuracy of IOP measurement without changing Goldmann measurement technique or interpretation. Clinical validation is needed but the analysis indicates a reduction in CCT error alone to less than ±2 mm Hg using the CATS prism in 100% of a standard population compared to only 54% less than ±2 mm Hg error with the present Goldmann prism.

Translational Relevance

This article presents an easily adopted novel approach and critical design parameters to improve the accuracy of a Goldmann applanating tonometer.

Non-continuous measurement of intraocular pressure in laboratory animals

Glaucoma is a leading cause of blindness, which is treatable but currently incurable. Numerous animal models therefore have both been and continue to be utilized in the study of numerous aspects of this condition. One important facet associated with the use of such models is the ability to accurately and reproducibly measure (by cannulation) or estimate (by tonometry) intraocular pressure (IOP). At this juncture there are several different approaches to IOP measurement in different experimental animal species, and the list continues to grow. We feel therefore that a review of this subject matter is timely and should prove useful to others who wish to perform similar measurements. The general principles underlying various types of tonometric and non-tonometric techniques for non-continuous determination of IOP are considered. There follows discussion of specific details as to how these techniques are applied to experimental animal species involved in the research of this disease. Specific comments regarding anesthesia, circadian rhythm, and animal handling are also included, especially in the case of rodents. Brief consideration is also given to possible future developments.

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.

The impact of corneal edema on intraocular pressure measurements using goldmann applanation tonometry, Tono-Pen XL, iCare, and ORA: an in vitro model

PURPOSE

Among other corneal biomechanical properties, Goldmann applanation tonometry (GAT) has been shown to depend on corneal edema. New tonometry devices have been designed, such as the Tono-Pen XL, iCare, and ocular response analyzer (ORA), to measure the intraocular pressure (IOP) accurately. This study aims to investigate the influence of corneal edema on the accuracy of these IOP-measuring devices in an in vitro model.

METHODS

A model of an artificial anterior chamber was developed using a guided trephination system. Eight donor corneas not suitable for keratoplasty were clamped into this artificial anterior chamber. All corneas showed signs of stromal edema. Intracameral pressure (ICP) was adjusted manometrically to 10, 20, 30, 40, and 50 mm Hg. The central corneal thickness (CCT) was determined by ultrasonic pachymetry. For each manometrically defined ICP, tonometry was performed using the iCare, Tono-Pen XL, GAT, and ORA.

RESULTS

The mean CCT increased from 616.1±29.6 µm to 626.9±36.1 µm. At 10 mm Hg, GAT yielded a higher ICP than those manometrically adjusted (10.4±3.3 mm Hg); at all other ICP levels, GAT yielded lower ICP levels than those adjusted. The Tono-Pen XL and iCare showed the greatest difference at 10 mm Hg, with the Tono-Pen XL yielding a value of 14.0±4.0 mm Hg and the iCare yielding a value of 12.5±2.6 mm Hg. All other results of the 2 devices fell within a range of ±2 mm Hg from the adjusted ICP. The ORA provided accurate results only at "physiological" ICP levels with a maximum difference of 2.6 mm Hg at 30 mm Hg. At higher ICP levels, corneal hysteresis decreased significantly with increasing ICP. None of the measurement devices revealed a statistically relevant dependence on CCT in this experimental setting.

CONCLUSIONS

The Tono-Pen XL and the iCare yielded the most accurate ICP values across all the adjusted ICP values. This may be because of their relatively small contact area with the cornea and, consequently, greater independence from corneal biomechanical properties. The ORA yielded accurate measurement results only at physiological ICP levels. As anticipated, GAT underestimated ICP. The Tono-Pen XL and the iCare should therefore be used to determine IOP in patients suffering from corneal edema, such as bullous keratopathy or Fuchs endothelial dystrophy.

Dynamic contour tonometry in primary open angle glaucoma and pseudoexfoliation glaucoma: factors associated with intraocular pressure and ocular pulse amplitude

Purpose:

To compare the intraocular pressures (IOP) and ocular pulse amplitudes (OPAs) in patients with primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PXG), and to evaluate ocular and systemic factors associated with the OPA.

Materials and Methods:

In this prospective study, on 28 POAG and 30 PXG patients, IOP was measured with the Goldmann applanation tonometry (GAT) and the Pascal dynamic contour tonometry (DCT). Other measurements included central corneal thickness (CCT), vertical cup-to-disc ratio (CDR), and systolic and diastolic blood pressure. Statistical significance was defined as P < 0.05.

Results:

In each of the POAG and PXG groups, GAT IOP was correlated with CCT (r = 0.40, P = 0.03 and r = 0.35, P = 0.05, respectively), whereas DCT IOP and CCT were not correlated. In all patients and in the POAG group, OPA was positively correlated with DCT IOP (r = 0.39, P = 0.002). OPA was not correlated with CCT in the POAG (P = 0.80), nor in the PXG (P = 0.20) group, after adjusting for DCT IOP. When corrected for DCT IOP and CCT, there was a significant negative correlation between OPA and vertical CDR in all patients (r = −0.41, P = 0.002). There was no significant difference in OPA between groups (P = 0.55), even when OPA was adjusted for IOP and systolic and diastolic pressure (P = 0.40), in a linear regression model.

Conclusion:

DCT IOP and OPA are not correlated with CCT. There is no significant difference between the OPA of PXG and POAG eyes. OPA is correlated with DCT IOP, and is lower in eyes with more advanced glaucomatous cupping.

Comparison of Goldmann Tonometry and Dynamic Contour Tonometry in Normal and Descemet Stripping Endothelial Keratoplasty Eyes

PURPOSE

This study aimed to compare intraocular pressures (IOP) measured by dynamic contour tonometry (DCT) with Goldmann tonometry (GAT) in Descemet stripping endothelial keratoplasty (DSEK) eyes. The agreeability between the 2 established methods and their relation to central corneal thickness (CCT) was also studied.

DESIGN

A comparative case series.

METHODS

Forty-six eyes of DSEK were enrolled at least 3 months after the procedure. Thirty-five other eyes of the same patient cohort served as control. Intraocular pressures were measured by DCT and GAT by 2 different examiners in a randomized manner. Central corneal thickness was measured by ultrasonic pachymetry. Statistical analysis was used for the calculation of means, SD, coefficient of determination, linear regression, and Bland and Altman plot. Statistical significance was considered as P < 0.05.

RESULTS

Mean CCT was 624.49 μm and 518.41 μm in DSEK and control eyes, respectively. Mean IOP by GAT and DCT, respectively, was 19.4 and 21.5 mm Hg in DSEK eyes and 15.12 and 17.6 mm Hg in controls. Descemet stripping endothelial keratoplasty eyes showed universally higher IOP by either method in comparison with normal controls. Dynamic contour tonometry reading was significantly higher than GAT in both (P < 0.05) groups. The correlation between IOP and CCT was not significant in DSEK eyes (P > 0.05).

CONCLUSIONS

A higher baseline IOP is to be expected in DSEK eyes, which is independent of corneal thickness. Both GAT and DCT can be used as a standard method to measure IOP in DSEK eyes, but their readings cannot be used interchangeably.

Comparison of Goldmann applanation and dynamic contour tonometry in a population of Mexican open-angle glaucoma patients

To compare intraocular pressure (IOP) measurements obtained with Goldmann applanation (GAT) and dynamic contour tonometry (DCT) in a Mexican population. 40 glaucoma patients were included in this cross-sectional observational cohort study. IOP measurements were performed in the following order: DCT, ultrasonic pachymetry and GAT, with a 5-minute difference between each measurement, between 8 am and 2 pm. Only DCT measurements of good quality (Q ≤ 3) were accepted. GAT measurements were made three times with the same Goldmann tonometer, previously checked for calibration errors, and the mean was used for statistical purposes. The IOP (mean [standard deviation], 95 % confidence interval [CI]) measured with the Goldmann tonometer (13.2 [2.4], 12.4-14.0 mmHg) was significantly lower than that obtained with the DCT (18.4 [3.3], 17.0-19.2 mmHg), p < 0.0001. Pearson's correlation coefficients between CCT and IOP measured with GAT and DCT were (r = 0.24, 95 % CI = 0.07-0.52, p = 0.133) and (r = 0.13, 95 % CI = -0.19 to 0.43, p = 0.412), respectively. The concordance correlation coefficient between GAT and DCT was r c = 0.3, 95 % CI = 0.17-0.41). DCT seems to overestimate the IOP as compared to GAT. Additionally, although there was a good correlation between the IOP measurements assessed with either GAT or DCT, the agreement was poor.

Association of ocular hypotensive medication types with dynamic contour tonometry and Goldmann applanation tonometry measurements in a glaucoma and ocular hypertensive population

PURPOSE

The aim of this study was to evaluate the association between different intraocular pressure (IOP)-lowering medications and IOP measurements by dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in a glaucoma and ocular hypertensive population.

METHODS

In a prospective, observational case series study, 410 eyes from 410 consecutive patients with open-angle glaucoma (OAG) or ocular hypertension (OHT), were enrolled. All eyes included in the study received unaltered ocular hypotensive medication for at least 6 months before IOP measurement. All eyes underwent 2 GAT and 3 DCT measurements, and their means were used for the analysis.

RESULTS

DCT-GAT IOP difference (ΔIOP) did not differ statistically significantly (P=0.49) between OAG and OHT group yielding a mean±SD of 4.26±2.02 mmHg and 4.41±2.25 mmHg, respectively. The number of IOP-lowering agents did not have any statistically significant influence on ΔIOP (p=0.177), DCT (P=0.28) and GAT (P=0.13) measurements. A statistically higher ΔIOP was revealed in monotherapy patients receiving Carbonic Anhydrase Inhibitors (CAIs) (ΔIOP=5.75 mmHg) in comparison to patients receiving Prostaglandin Analogs (ΔIOP=4.09 mm Hg) or beta Blockers (ΔIOP=3.78 mmHg) as single topical therapy (F=4.373, P=0.005). Eyes treated with CAIs as a part of the ocular hypotensive therapy yielded a significantly greater ΔIOP (P=0.0035) than those without CAIs in the therapeutic schema.

CONCLUSIONS

The difference between DCT and GAT IOP measurements is found to be statistically significantly higher in patients receiving CAIs either as monotherapy or as a part of a combined ocular hypotensive treatment, while DCT and GAT readings remain unaffected. The type of diagnosis and the number of ocular hypotensive medications had no statistically significant influence on ΔIOP.

Spectral analysis of intraocular pressure pulse wave in open angle glaucomas and healthy eyes

PURPOSE

To investigate the spectral content of intraocular pressure (IOP) pulse wave by advanced spectral signal processing of continuous IOP readings obtained by dynamic contour tonometry.

PATIENTS AND METHODS

A non-interventional case-control study included 20 healthy subjects, 20 previously untreated primary open angle glaucoma patients, and 20 previously untreated normal tension glaucoma patients. The continuous IOP reading obtained by dynamic contour tonometry was submitted to Fast Fourier Transform signal analysis and further statistical data processing.

RESULTS

The spectral components of the IOP pulse wave were discerned up to the fifth harmonic. Highly statistically significant difference was found between the control group and the primary open angle group, and between the primary open angle glaucoma group and the normal tension glaucoma group in the first, second and the third harmonic amplitude (p < 0.01). Glaucoma patients had significantly higher ocular pulse volume values.

CONCLUSIONS

It is possible to determine spectral components of the IOP pulse wave up to the fifth harmonic by a spectral analysis of dynamic contour tonometry continuous readings. We found that high Ocular Pulse Amplitude values in primary open angle glaucoma group was associated with high harmonics amplitude, which indicates low rigidity of blood vessels.

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 (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.

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.

The effect of thin, thick, and normal corneas on Goldmann intraocular pressure measurements and correction formulae in individual eyes

OBJECTIVE

To evaluate the usefulness of the central corneal thickness (CCT)-based correction formulae for stratified CCT groups, with intraocular pressure (IOP) from the Pascal dynamic contour tonometer (PDCT) as the reference standard.

DESIGN

Retrospective case series.

PARTICIPANTS

Two hundred eighty-nine patients attending a specialist glaucoma practice and a mixture of normal subjects and subjects with confirmed glaucomatous optic neuropathy.

METHODS

Intraocular pressure was measured using PDCT, Goldmann applanation tonometry (GAT), and the Ocular Response Analyzer (ORA; Reichert Corp, Buffalo, NY). The GAT readings were obtained before automated readings and were adjusted for CCT using 4 different correction formulae. Discrepancies between GAT and CCT-corrected GAT readings were evaluated after stratification into thin, intermediate, and thick CCT groups. The IOP measurements from GAT, the ORA, and CCT-adjusted IOP were compared against PDCT IOP measurements using Bland-Altman analysis.

MAIN OUTCOME MEASURES

Mean, 95% limits of agreement, and proportion of patients with IOP difference of 20% or more between PDCT IOP and each of GAT IOP, Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), and adjusted IOP using CCT-based correction formulae.

RESULTS

Average PDCT IOP values were higher than GAT, IOPg, IOPcc, and CCT-adjusted IOP. The GAT IOP readings demonstrated poor agreement with PDCT IOP (95% limits of agreement, ± 4.7 mmHg); however, IOPg, IOPcc, and adjustment of GAT IOP with CCT-based formulae resulted in even poorer agreement (range of 95% limits of agreement, ± 5.1 to 6.7 mmHg). If PDCT was used as the reference standard, there was a 26% to 39% risk of making an erroneous IOP adjustment of magnitude of 20% or more at all levels of CCT. This risk was greatest in the patients with thicker corneas (CCT, ≥568 μm).

CONCLUSIONS

Adjusting IOP using CCT-based formulae resulted in poorer agreement with PDCT IOP when compared with unadjusted G AT IOP. If PDCT is the closest measure we have to intracameral IOP, there is a risk of creating clinically significant error after adjustment of GAT IOP with CCT-based correction formulae, especially in thicker corneas. This study suggests that although CCT may be useful in population analyses, CCT-based correction formulae should not be applied to individuals.

Dynamic contour tonometry and goldman 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.

A survey and comparative study on the instruments for glaucoma detection

Glaucoma is one of the leading causes of irreversible blindness worldwide. It has been proposed that the intraocular pressure is a causative factor in the development of glaucoma, which is an optic neuropathy. This paper surveys the use of tonometers, gonioscopes, optical coherence tomographs, scanning laser polarimeters, scanning laser ophthalmoscopes (also known as scanning laser tomographs) and corneal pachymeters for the diagnosis and management of glaucoma. The working mechanisms as well as the comparative advantages and disadvantages of each of these instruments are presented.

Comparison of Goldmann and Pascal tonometry in relation to corneal hysteresis and central corneal thickness in nonglaucomatous eyes

Objective:

To compare measurements obtained by Goldmann applanation tonometry (GAT) and Pascal dynamic contour tonometry (DCT), and to study their relationship to corneal thickness and biomechanical properties in nonglaucomatous eyes.

Methods:

This is a prospective and randomized study of 200 eyes from 200 non-glaucomatous subjects who underwent intraocular pressure (IOP) measurements by GAT and DCT. The two methods were compared and assessed for agreement by means of the Bland–Altman plot. Central corneal thickness (CCT) and corneal hysteresis (CH) were obtained by ultrasound pachymeter and Ocular Response Analyzer, respectively. The effect of CH and CCT was correlated with the DCT/GAT IOP differences.

Results:

Mean age was 57.4 ± 14.7 years (range 24–82 years). Mean IOP measurements obtained were 16.7 ± 3.2 mmHg by GAT and 19.4 ± 3.3 mmHg by DCT. DCT showed a statistically significant higher mean IOP (2.7 ± 1.9 mmHg, P < 0.001) compared with GAT. Mean CCT and CH were 546.5 ± 40 μm and 10.85 ± 2.0 mmHg, respectively. The differences in IOP (DCT – GAT) were significantly correlated with CCT and CH (Pearson’s correlation coefficient r = −0.517 and −0.355, P < 0.0001, respectively). The difference between the two correlation coefficients was statistically significant (P < 0.05, Z-statistic). According to the Bland–Altman plot, the results of the two methods were clinically different.

Conclusion:

Significantly higher IOP readings were obtained by DCT than by GAT in nonglaucomatous subjects. The IOP differences between the two methods were associated with CCT and CH, suggesting that DCT was less dependent on corneal parameters. Each method provides clinically different IOP values, indicating that DCT and GAT should not be used interchangeably.

The ocular pulse amplitude at different intraocular pressure: a prospective study

PURPOSE

To investigate changes in ocular pulse amplitude (OPA) during a short-term increase in intraocular pressure (IOP) and to assess possible influences of biometrical properties of the eye, including central corneal thickness (CCT) and axial length.

METHODS

In a prospective, single centre study, OPA and IOP as measured by dynamic contour tonometry (DCT) were taken before baseline- and post-OPA (delta) intravitreal injection of 0.05 ml anti-vascular endothelial growth factor agents. Analysis was performed employing linear regression with baseline- and post (delta)-OPA differences as the dependent and post-IOP as well as delta IOP as the independent variable. A multilinear regression analysis with delta OPA as the dependent variable and baseline IOP, post-IOP, CCT and axial length as independent variables was conducted.

RESULTS

Forty eyes of 40 patients were included. IOP and OPA increased significantly after injection (IOP mean increase ± SD: 17.83 ± 9.83 mmHg, p < 0.001; OPA mean increase ± SD: 1.39 ± 1.16 mmHg, p < 0.001). For every mmHg increase in IOP, the OPA showed a linear increase of 0.05 mmHg (slope 0.05, 95% CI: 0.02-0.09, p = 0.003, r(2) = 0.20). Multiple regression analysis with delta OPA as the dependent variable revealed a partial correlation coefficient of 0.47 (p = 0.003) for post-IOP as the only significant contribution.

CONCLUSION

A clear positive relationship between OPA measurements and IOP levels was shown in a clinical routine setting using DCT focusing on baseline and postinterventional comparisons of OPA values after intravitreal injections in patients with exudative age related macular degeneration. When considering the OPA for diagnostic purposes, we recommend indication of corresponding IOP values.

Poor utility of intraocular pressure correction formulae in individual glaucoma and glaucoma suspect patients

BACKGROUND

To compare Pascal dynamic contour tonometry (DCT) measurements with Goldmann applanation tonometry (GAT) readings after adjustment with correction formulae in a population of Caucasian glaucoma and glaucoma suspect patients.

DESIGN

Retrospective cross-sectional case series in a specialist glaucoma practice.

PARTICIPANTS

Consecutive glaucoma and glaucoma suspect Caucasian patients.

METHODS

Case notes review of the GAT and DCT intraocular pressure (IOP) measurements from patients who presented on a non-acute basis over a 30-month period. The GAT measurement was adjusted with six different correction formulae. Agreement between GAT IOP, adjusted GAT IOP and DCT IOP was evaluated with the Bland-Altman analysis.

MAIN OUTCOME MEASURES

Agreement between GAT IOP (both unadjusted and adjusted) and DCT IOP.

RESULTS

Data from 200 patients with a mean age of 58.4 (±12.7) years were analysed. The mean central corneal thickness was 554.8 (±36.9) µm and the mean corneal hysteresis was 9.8 (±1.9) mm Hg. Sixty five (32.5%) had confirmed glaucomatous optic neuropathy. GAT IOP demonstrated poor agreement with DCT IOP. GAT IOP was on average 2.1 mm Hg less than DCT IOP. None of the six correction formulae resulted in improved agreement with DCT IOP. General linear model analysis found no statistically significant measurement differences between the glaucoma and glaucoma suspect groups.

CONCLUSIONS

GAT demonstrated poor agreement with DCT, and agreement did not improve after adjustment with correction formulae. Our results suggest that correction formulae for GAT IOP are unsuitable to clinically approximate 'true' IOP in Caucasian glaucoma and glaucoma suspect patients.

A history of intraocular pressure and its measurement

Doctors have not always associated elevated intraocular pressure with the vision loss from glaucoma. Although several individuals appear to have noted firmness of the eye in this condition as far back as the 10th century, elevated intraocular pressure was not routinely assessed until the latter part of the 19th century. von Graefe developed the first instrument for measuring intraocular pressure in 1865. The first reasonably accurate instrument was the Maklakoff applanation tonometer of the late 19th century; it was in widespread use throughout Eastern Europe until relatively recently. Schiötz developed an indentation tonometer that was widely used throughout the world during the first two thirds of the 20th century. Goldmann's applanation tonometer of 1950 began the era of truly accurate intraocular pressure measurement. It is still the most widely used tonometer in the world. Other devices such as the McKay-Marg tonometer (or its offspring the Tono-Pen), the pneumatonometer, and airpuff applanation tonometers are gaining adherents. The dynamic contour tonometer is the first totally new concept in tonometry in over 100 years. It is probably the most accurate of all the tonometers and is relatively independent of corneal biomechanical properties unlike its predecessors. Transpalpebral tonometers are attractive as they do not require topical anesthesia; however, they add the biomechanical properties of the eyelid to the list of potential errors and have not proven very accurate. The future should, hopefully, bring tonometers that can give diurnal or even longer indications of intraocular pressure variation. Although intraocular pressure elevation (or its absence) no longer can be counted on for diagnostic purposes, the role of intraocular pressure in the management of glaucomatous optic neuropathy remains critical.

Effect of hevin deletion in mice and characterization in trabecular meshwork

PURPOSE

Hevin is a matricellular protein and the result of a gene duplication of SPARC. SPARC-null mice have lower intraocular pressure (IOP). The function of hevin in trabecular meshwork (TM) is unknown. The authors hypothesized that hevin is expressed in TM and has a functional consequence on IOP.

METHODS

Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoblotting were performed to identify transcription and protein expression in TM and cultured TM cells. Toluidine blue stain was performed to compare anterior segments in wild-type (WT) and hevin-null mice. Confocal microscopy localized the structural distribution of hevin in human TM and hevin/SPARC in mouse anterior segments. IOP was measured in WT (C57BL6 × 129SvJ) and hevin-null mice using both rebound tonometry and cannulation tonometry. Central corneal thickness (CCT) was measured by ocular coherence tomography. Cultured TM cells were treated with TGF-β2 because TGF-β2 is associated with primary open-angle glaucoma.

RESULTS

Hevin mRNA and protein were expressed in TM tissues but not in cultured TM cells. No structural differences were observed in anterior segments of WT and hevin-null mice. IOP between hevin-null (n = 46) and WT (n = 44) mice was equivalent (15.3 ± 1.92 mm Hg and 15.9 ± 2.01 mm Hg, respectively; P = 0.15). CCT was similar between hevin-null and WT mice (107.95 ± 5.06 μm and 106.76 ± 3.46 μm, respectively; P = 0.11). TGF-β2 did not induce hevin, whereas SPARC expression was induced in a dose-dependent manner in human TM cell cultures.

CONCLUSIONS

Hevin does not appear to be critical to regulating IOP. Hevin is expressed in TM but, in contrast to SPARC, does not appear to be regulated by TGF-β2.

Hand-held dynamic contour tonometry

PURPOSE

We present a prototype of the hand-held dynamic contour tonometer (HH-DCT) and prospectively compare this HH-DCT with the well-established Perkins applanation tonometer (PAT) and the TonoPenXL (TPXL).

METHODS

In a prospective, single-centre, randomized study, intraocular pressure (IOP) readings were taken in random order using HH-DCT, PAT and TPXL tonometers. Intra-observer variability was calculated for each observer and compared between three experienced ophthalmologists and an inexperienced medical student.

RESULTS

Ninety-two corneas of 92 healthy participants were enrolled. IOP [mean mmHg ± standard deviation (SD)] as measured by HH-DCT was 16.97 ± 2.71, by PAT 13.98 ± 2.52 and by TPXL 13.34 ± 2.68. The range of three consecutive IOP readings differed significantly between the devices [p < 0.001; mean range: 1.45 ± 1.07 (HH-DCT), 1.87 ± 0.97 (PAT) and 2.08 ± 1.77 (TPXL)]. There was no difference of the range in all devices between the ophthalmologists and the medical student (HH-DCT p = 0.68, PAT p = 0.54, TPXL p = 0.48).

CONCLUSION

IOP readings measured by HH-DCT are significantly higher than by PAT and TPXL. The differences of IOP measurements are in good accordance with previous studies using the slit-lamp-mounted DCT (SL-DCT) and Goldmann Applanation Tonometry, where SL-DCT readings were 1-3.2 mmHg higher. HH-DCT seems to give more constant results, which can be seen in the lower intra-observer variability compared to PAT and TPXL.