Impact of corneal parameters on intraocular pressure measurements in different tonometry methods

Analysis of Goldman Applanation Tonometry with and without fluorescein among glaucomatous and nonglaucomatous patients attending Mzuzu Central Hospital in Malawi: A cross-sectional study

Background and Aim

Goldman Applanation Tonometry (GAT), the gold standard of tonometry, is used without fluorescein in low-resource settings. Nevertheless, corneal biomechanics differ among population groups.

Purpose

The aim of the study is to assess the relationship between GAT findings with and without fluorescein among glaucomatous and nonglaucomatous adults in Malawi.

Methods

This was a cross-sectional quantitative study involving 22 glaucoma patients and 22 nonglaucoma patients at Mzuzu Central Hospital. We used a purposive sampling technique to select participants into the two groups. Next, we measured intraocular pressure using GAT with and without fluorescein. Then we entered the data into SPSS version 25. We employed the Wilcoxon test to make comparisons based on age and gender. We considered the value of p < 0.05 statistically significant.

Results

There is a statistically significant and strong positive correlation between nfGAT and fGAT among both glaucoma (r = 0.989, p < 0.001) and nonglaucoma (r = 0.955, p < 0.001). According to age, there is no significant difference in IOP value measured with nfGAT and fGAT for both glaucomas (p = 0.109) and nonglaucoma subjects (p = 0.076). However, significant differences were observed between nfGAT and fGAT mean IOP according to sex among both glaucomatous and nonglaucomatous subjects (p = 0.017 and p = 0.32, respectively).

Conclusion

The study suggests that the merits of intraocular pressure measured using GAT without fluorescein are not speculative, therefore the two techniques can be routinely used interchangeably in diagnosing and managing glaucoma.

Distribution and associated factors of intraocular pressure in the older population: Tehran Geriatric Eye Study

AIM

To determine the distribution and associated factors of intraocular pressure (IOP) in an Iranian elderly population 60 years of age and above.

METHODS

The present report is part of the Tehran Geriatric Eye study (TGES), a population-based cross-sectional study that was conducted on the residents of Tehran 60 years of age and above. The sampling was performed using multistage stratified random cluster sampling methods from 22 districts of Tehran, Iran. Demographic and history information, blood samples, and blood pressure were collected from all participants. Ocular examinations included measurement of uncorrected and best-corrected visual acuity, objective and subjective refraction, and slit-lamp biomicroscopy. The IOP was measured using Goldmann applanation tonometry (GAT). Corneal imaging and ocular biometry were performed using Pentacam AXL.

RESULTS

The data of 3892 eyes of 2124 individuals were analyzed for this report. The mean age of the study participants was 66.49±5.31y (range: 60 to 95y). The mean IOP was 15.2 mm Hg (95%CI: 15.1 to 15.4), 15.3 mm Hg (95%CI: 15.1 to 15.5) and 15.1 mm Hg (95%CI: 15.0 to 15.3) in all participants, males, and females, respectively. Of the study participants, 1.3% had an IOP of ≥20 mm Hg. The mean IOP increased from 15.1 mm Hg in the age group 60-64y to 16.3 mm Hg in the age group ≥80y. According to the final multiple GEE model, the IOP was statistically significantly higher in men than in women. All the studied age groups, except for the 75-79-year-old age group, had significantly higher IOP compared to the 60-64-year-old age group. The IOP was significantly higher in underweight compared to other body mass index groups. Moreover, the IOP had a statistically significant direct relationship with the mean corneal power (mean CP), central corneal thickness (CCT), and systolic blood pressure.

CONCLUSION

The present study presents the distribution of IOP in an Iranian elderly population. A higher IOP (within the range 14 to 17 mm Hg) is significantly associated with older age, male sex, high systolic blood pressure, increased mean CP, and CCT. These factors should be considered in the clinical interpretation of IOP.

Intraocular Pressure and Its Relation to Ocular Geometry: Results From the Gutenberg Health Study

Purpose

The purpose of this study was to investigate the association between intraocular pressure (IOP) and ocular geometry.

Methods

The Gutenberg Health Study is a population-based cohort study in Mainz, Germany. Study participants underwent a comprehensive ophthalmologic examination including noncontact tonometry, objective refraction, optical biometry, and Scheimpflug imaging of the anterior segment at the first 5-year follow-up examination (in 2012–2017). Multivariable linear regression analysis was carried out to determine associations of IOP and geometric parameter of the human phakic eye, namely central corneal thickness (CCT), corneal curvature, anterior chamber depth (ACD), lens thickness, and axial length. In addition, the relationship of IOP and the anterior chamber angle (ACA) width was analyzed.

Results

There were 6640 participants with phakia (age 57.3 ± 10.2 years, 49.1% women) that were included in this cross-sectional analysis. Mean IOP was 14.8 ± 2.9 mm Hg in the right eyes and 14.9 ± 2.9 mm Hg in the left eyes. IOP increased with higher CCT, greater posterior segment length, higher age (all P < 0.001), thicker lens (P = 0.003), and female sex (P = 0.05), whereas the ACD was not associated with higher IOP. The IOP increased with a narrower ACA in univariable analysis (P < 0.001), but not in adjusted analysis in subjects with an open angle.

Conclusions

IOP values are related to ocular geometry, as shown in this population-based study on Caucasian subjects. Thus, knowledge of the architecture of the eye is an important factor when measuring IOP. Longitudinal evaluation will analyze whether some of these parameters are also risk factors for the development of glaucoma.

Measures of disease activity in glaucoma

Glaucoma is the leading cause of irreversible blindness globally which significantly affects the quality of life and has a substantial economic impact. Effective detective methods are necessary to identify glaucoma as early as possible. Regular eye examinations are important for detecting the disease early and preventing deterioration of vision and quality of life. Current methods of measuring disease activity are powerful in describing the functional and structural changes in glaucomatous eyes. However, there is still a need for a novel tool to detect glaucoma earlier and more accurately. Tear fluid biomarker analysis and new imaging technology provide novel surrogate endpoints of glaucoma. Artificial intelligence is a post-diagnostic tool that can analyse ophthalmic test results. A detail review of currently used clinical tests in glaucoma include intraocular pressure test, visual field test and optical coherence tomography are presented. The advanced technologies for glaucoma measurement which can identify specific disease characteristics, as well as the mechanism, performance and future perspectives of these devices are highlighted. Applications of AI in diagnosis and prediction in glaucoma are mentioned. With the development in imaging tools, sensor technologies and artificial intelligence, diagnostic evaluation of glaucoma must assess more variables to facilitate earlier diagnosis and management in the future.

Different Effects of Aging on Intraocular Pressures Measured by Three Different Tonometers

This study aimed to compare intraocular pressures (IOP) using different tonometers, Goldmann applanation (IOP_GAT), non-contact (IOP_NCT), and rebound (IOP_RBT), and to assess the effects of aging and central corneal thickness (CCT) on the measurements. The IOP_GAT, IOP_NCT, IOP_RBT, mean patient age (65.1 ± 16.2 years), and CCT (521.7 ± 39.2 µm) were collected retrospectively from 1054 eyes. The differences among IOPs were compared by the paired t-test. Possible correlations between devices, age, and CCT were assessed by linear regression analyses. The effects of age and CCT on the IOP reading were assessed by mixed-effects regression models. The IOP_GAT values were 2.4 and 1.4 mmHg higher than IOP_NCT and IOP_RBT, respectively; the IOP_NCT was 1.0 mmHg lower than IOP_RBT (p < 0.0001 for all comparisons). The IOPs measured by each tonometer were highly correlated with each other (r = 0.81–0.90, t = 45.2–65.5). The linear regression analyses showed that age was negatively correlated with IOP_NCT (r = −0.12, t = −4.0) and IOP_RBT (r = −0.14, t = −4.5) but not IOP_GAT (r = 0.00, t = −0.2); the CCT was positively correlated with IOP_GAT (r = 0.13, t = 4.3), IOP_NCT (r = 0.29, t = 9.8), and IOP_RBT (r = 0.22, t = 7.2). The mixed-effect regression models showed significant negative correlations between age and IOP_NCT (t = −2.6) and IOP_RBT (t = −3.4), no correlation between age and IOP_GAT (t = 0.2), and a significant positive correlation between CCT and the tonometers (t = 3.4–7.3). No differences between IOP_GAT and IOP_RBT were seen at the age of 38.8 years. CCT affects IOPs from all tonometers; age affects IOP_NCT and IOP_RBT in different degrees. IOP_RBT tended to be higher than IOP_GAT in young subjects, but this stabilized in middle age and became higher in older subjects.

Comparison of intraocular pressure in healthy brachycephalic and nonbrachycephalic cats using the Icare® TONOVET Plus rebound tonometer

OBJECTIVE

To compare intraocular pressure using the Icare® TONOVET Plus rebound tonometer in healthy brachycephalic and nonbrachycephalic cats.

ANIMALS STUDIED

Both eyes of 78 healthy cats were investigated in this study. Cats were divided into two groups: brachycephalic (n = 39) and nonbrachycephalic (n = 39).

PROCEDURES

Nose position and muzzle ratio were photographically recorded and analyzed. Physical and ophthalmic examinations were performed. Intraocular pressure was measured using the Icare® TONOVET Plus rebound tonometry instrument. Quantitative mean values were statistically compared using an unpaired t-test at a significance level of p < .05.

RESULTS

Mean values of the nose position and muzzle ratio were significantly lower in the brachycephalic group (20.14 ± 5.43%, 9.61 ± 3.29%) compared with the nonbrachycephalic group (29.21 ± 4.30%, 13.97 ± 6.01%). The mean intraocular pressure for brachycephalic cats (15.76 ± 0.50 mmHg) was significantly lower (p < .001) than for nonbrachycephalic cats (18.77 ± 0.49 mmHg).

CONCLUSIONS

Intraocular pressure was significantly lower in brachycephalic cats using the Icare® TONOVET Plus rebound tonometer. Intraocular pressure values obtained in this study could be used as a guideline for measurements obtained using this tonometry device in healthy brachycephalic and nonbrachycephalic cats.

Reliability of iCare ic100 Rebound Tonometry and Agreement With Goldmann Applanation Tonometry in Healthy and Post-myopic LASIK Patients

PRECIS

Rebound tonometry offers excellent reliability for obtaining intraocular pressure (IOP) measurements in healthy and post-myopic laser-assisted in situ keratomileusis (LASIK) patients regardless of corneal parameters and axial length and regardless of the instillation of ocular topical anesthesia.

PURPOSE

The purpose of this study was to assess the reliability of rebound tonometry, its agreement with Goldmann applanation tonometry (GAT) and its concordance after topical anesthesia in a group of nonoperated healthy patients and a group of post-myopic LASIK patients.

PATIENTS AND METHODS

Fifty-four patients were included in this prospective observational, case-control study. Patients were divided into 2 groups: control (n=32, 26.7±6.1 y) and LASIK (n=22, 35.8±7.6 y). Measurements of IOP were carried out using the iCare ic100 tonometer and GAT. The repeatability, intersession and interobserver reproducibility, GAT interchangeability and concordance after topical anesthesia of the iCare ic100 tonometer were assessed.

RESULTS

Clinical reliability of the iCare ic100 was excellent in terms of repeatability [intraclass correlation coefficient (ICC)=0.909 and 0.951 in control and ICC=0.938 and 0.961 in LASIK] as well as interobserver reproducibility (ICC=0.896 in control and 0.916 in LASIK) and concordance after anesthesia (ICC=0.910 in control and 0.972 in LASIK) in both groups. Intersession reproducibility was clinically good in nonoperated patients (ICC=0.758 and 0.849) and excellent in LASIK patients (ICC=0.878 and 0.904), although statistically significant differences were obtained in the control group for both examiners (P=0.003 for examiner 1 and P=0.04 for examiner 2). Agreement with GAT was good in both groups (ICC=0.805 in control and 0.790 in LASIK), although statistically different (P<0.001 and P=0.02, respectively). Finally, the iCare ic100 reliability was independent of corneal parameters and axial length in both groups (P>0.05 for all parameters).

CONCLUSIONS

Rebound tonometry offers good or excellent clinical reliability in both healthy and post-myopic LASIK patients. This article highlights the efficacy of iCare ic100 rebound tonometry as a reliable tool for the measurement of IOP and the management of glaucoma in healthy patients and patients undergoing myopic LASIK surgery.

Comparative Evaluation of Rebound and Perkins Tonometers in Pediatric Glaucoma With Varied Corneal Characteristics

PRECIS

Icare tonometer overestimated intraocular pressure (IOP) as compared with Perkins and this variation was higher in IOP>19 mm Hg and corneal opacity in patients with pediatric glaucoma.

PURPOSE

To compare the IOP measured by Icare ic200 with Perkins tonometer in pediatric glaucoma with different corneal characteristics.

METHODS

Patients of pediatric glaucoma posted for routine examination under anesthesia, age below 12 years were enrolled. All patients underwent IOP measurement with Perkins and Icare ic200 tonometer by the same observer. Basic demographic data and other relevant clinical data were recorded. Central corneal thickness (CCT), horizontal corneal diameter, and corneal characteristics such as cornea clarity was recorded.

RESULTS

A total of 194 eyes of 105 patients were analyzed. The difference between Perkins and Icare IOP was -0.816 mm Hg with the Bland-Altman plot 95% limits of agreement (LoA) from -11.194 to 9.562 mm Hg and 5.1% (10) values lying outside LoA. At IOP <19 mm Hg, the difference was -0.65 mm Hg and IOP ≥19 mm Hg, the difference was higher, -1.12 mm Hg. In the clear cornea group (123 eyes), the difference in IOP by 2 tonometers was -0.776 mm Hg with the Bland-Altman plot 95% LoA between -10.679 and 9.128 mm Hg. In hazy corneas (36 eyes), the difference in IOP was 0.531 mm Hg. The Bland-Altman plot showed 95% LoA between -6.242 and 7.303 mm Hg. In the scarred cornea group (35 eyes), the difference in IOP between the 2 was -2.343 mm Hg and the Bland-Altman plot showed wide 95% LoA from -16.302 to 11.616 mm Hg.

CONCLUSION

Icare tonometer overestimated IOP as compared with Perkins and this variation was higher in eyes with IOP≥19 mm Hg, CCT >615 μm, and scarred corneas. A moderate correlation between IOP and CCT for both tonometers was noted.

Influence of Corneal Visualization Scheimpflug Technology Tonometry on Intraocular Pressure

Purpose

To investigate the effect of Corneal Visualization Scheimpflug Technology tonometry (CST) on intraocular pressure (IOP).

Design

Cohort study.

Participants

Patients with and without primary open-angle glaucoma (POAG) were included.

Methods

Intraocular pressure was measured using the Icare rebound tonometer (ICRT; Icare Finland Oy) and the biomechanically corrected IOP (bIOP) using the CST. Intraocular pressure was measured at baseline with ICRT, followed by a CST measurement in one eye with the fellow eye acting as a control. Icare measurements were repeated at 10 seconds and 1, 2, 4, 8, 15, 30, and 60 minutes in both eyes. The ratio of test eye IOP to fellow eye IOP was used to control for intrasubject variation.

Main Outcome Measures

Intraocular pressure change following Corneal Visualization Scheimflug Technology tonometry.

Results

Forty participants (mean age, 54.09 ± 20.08 years) were included comprising 20 patients with POAG and 20 patients with no ocular abnormalities other than cataract. Mean central corneal thickness was similar in those without POAG (547.4 ± 55.05 μm) and with POAG (520.22 ± 37.59 μm; P = 0.14). No significant change was found in IOP measured with the ICRT in the fellow eye versus the 1-hour period in either the healthy (P = 0.87) or POAG (P = 0.92) group. Significant changes were found in IOP after CST measurement for both healthy (P < 0.01) and glaucomatous (P < 0.01) eyes. After the CST measurement, the IOP reduced continuously from a mean of 13.75 mmHg to 10.84 mmHg at 4 minutes for healthy eyes and from 13.28 mmHg to 11.11 mmHg at 8 minutes for glaucomatous eyes before approaching (83% for healthy eyes and 92% POAG eyes) the pre-CST measurement at 1 hour.

Conclusions

Corneal Visualization Scheimpflug Technology tonometry causes a significant reduction in IOP in both glaucomatous and healthy eyes that lasts for at least 1 hour afterward.