The influence of central corneal thickness and age on intraocular pressure measured by pneumotonometry, non-contact tonometry, the Tono-Pen XL, and Goldmann applanation tonometry

Meta-Analysis of Tonometer Correction Formulae to Determine True Normal Intraocular Pressures Across a Diverse Range of Species

OBJECTIVE

To utilize previously published tonometer correction formulae to investigate whether true intraocular pressure (IOP) is relatively conserved across a diverse range of vertebrate species.

ANIMALS STUDIED

Tonometer correction formulae for 21 species.

PROCEDURES

A literature search was performed to identify prior studies containing correction formulae for non-invasive tonometers used in normal animal and human subjects. In all cases, direct manometry was compared to non-invasive tonometry values. Where necessary, multiple correction regression formulae were combined to generate a single representative formula using a meta-analysis generic inverse variance method. A subsequent literature search was then performed to collect uncorrected IOP values of normal animals and humans using a variety of non-invasive tonometers. These IOP values were then corrected using the relevant correction formula.

RESULTS

Sixty-five tonometer correction formulae and 104 studies containing IOP values in normal animals and humans acquired using non-invasive tonometry met the inclusion criteria. Corrected IOP values were calculated for 21 species using 13 types of non-invasive tonometers. Overall corrected and uncorrected mean IOP values were typically within a range of 10 to 25 mmHg (corrected: 16/21 species, uncorrected: 14/21 species). Differences between overall mean corrected and uncorrected IOP values ranged from 0.2 to 15.3 mmHg with an average of 6.1 mmHg difference.

CONCLUSIONS

True normal IOP is relatively conserved across a diverse range of vertebrate species despite uncorrected values from individual tonometers suggesting otherwise. Maintaining true IOP between 10 and 25 mmHg appears to be important in ocular physiology in many vertebrates.

Association of digital eye strain with central corneal thickness: a cross-sectional observational pilot study

PURPOSE

This study aimed to evaluate whether the digital eye strain (DES) was associated with the low central corneal thickness (CCT).

METHODS

This observational cross-sectional pilot study was conducted from April 2023 to October 2023 at a tertiary eye care centre in North India, where CCT values were compared between subjects with DES and those without DES. Two hundred and eighty subjects (n = 280) aged 15-40 years with clear corneas and lenses were initially included in this study. Those with corneal opacity, corneal degeneration, pregnancy, and diabetes were excluded. These subjects were then assessed with a 'computer vision syndrome questionnaire (CVS-Q)' test. Participants having a score ≥ 6 were grouped as the "DES group" and participants having a score < 6 were grouped as the "Control group". The participants from each group were then examined with Spectral Domain Ocular Coherence Tomography (SD-OCT) to measure CCT. The primary outcome was to evaluate the comparative difference in CCT values between the two groups as well as the association of DES with CCT values.

RESULTS

The study included one hundred and forty (n = 140) subjects each in the DES group and the control group. The DES score assessed with the CVS-Q questionnaire ranged from 6 to 32 in the DES group, with a mean ± SD of 17.08 ± 7.01. The overall mean CCT was 507.31 ± 31.01 (median, 512 microns; range, 450-601 microns). There was a significant difference in the mean CCT between the two groups, with lower mean CCT values in the DES group (487.76 ± 23.61 microns) than the control group (526.87 ± 24.53 microns) (p < 0.0001). The CVS-Q test score had moderate inverse correlation in the DES group (Pearson's r = - 0.42, p < 0.01) and negligible correlation (Pearson's r = - 0.14, p = 0.12) in the control group with CCT.

CONCLUSION

Central corneal thickness was observed to be reduced among the subjects with digital eye strain (DES).

Validation of intraocular pressure measurement using tonometer AVIA across different postures: A Bland Altman analysis

AIMS/OBJECTIVES

Tonometry is a fundamental procedure in the diagnosis and management of glaucoma. Different tonometers have been proposed but none are as accurate as the Goldman applanation tonometry (GAT). Nonetheless, due to the limitations of GAT, mobile tonometry methods became prevalent. This study aims to examine the reliability of the Tono-Pen AVIA® (TPA) in measuring intraocular pressure (IOP) across different postures.

METHODS

A total of 196 eyes were prospectively examined for IOP changes using GAT and TPA. IOP measurements were taken across different postures using the TPA. Reliability of measurements was compared using interclass correlation coefficients (ICC), while agreement was represented using Bland-Altman analysis. Pearson r coefficient was used to measure correlations.

RESULTS

When compared to GAT (14.5 ± 4.4 mmHg), IOP readings were significantly higher for TPA at both seated (16.5 ± 4.5 mmHg; p < 0.001) and supine (16.9 ± 5.7; p < 0.001) positions. The ICC values for GAT and TPA among seated and supine patients were 0.79 (0.54-0.90) and 0.76 (0.48-0.87) indicating good reliability between the readings. There were significantly positive correlations between GAT and TPA at both seated (r = 0.626, p < 0.001) and supine (r = 0.727, p < 0.001) positions. Per Bland-Altman analysis, limits of agreement were -8.57 to 4.37 for GAT and seated TPA and -10.34 and 5.34 for GAT and supine TPA.

CONCLUSION

Good reliability exists between IOP measurements using GAT and TPA. However, the devices are not interchangeable and therefore cannot be used reciprocally in the same patient.

Agreement and Reliability of Transpalpebral Tonometers with Goldmann Applanation Tonometer: A Systematic Review and Meta-analysis

TOPIC

The systematic review and meta-analysis consolidates the extant body of evidence comparing reliability and agreement between transpalpebral tonometers (TTs) and Goldmann applanation tonometer (GAT).

CLINICAL RELEVANCE

With a global prevalence of 3.54 percent, glaucoma stands as the second leading cause of preventable blindness. Projections indicate a rise to 111 million cases by 2040. Existing literature presents inconsistent findings while comparing TT and GAT. The derivation of summary estimates assessing their agreement holds significance, given TT's multifaceted applicability in clinical, community, and home settings.

METHODS

Systematic review was conducted using PubMed, Cochrane Library, and Google Scholar from January 2000 to December 2022. Two reviewers independently evaluated, enumerated, and extracted studies and data based on eligibility criteria. The Quality Assessment for Diagnostic Accuracy Studies checklist was used to assess study quality. The summary measures were pooled using the random-effects model as mean difference (MD), and 95% limits of agreement (LoA). We assessed heterogeneity using the I2 statistic. The study protocol was registered with the International Prospective Register of Systematic Reviews (CRD42022321693).

RESULTS

A total of 26 methods comparison studies (3577 eyes) were included in the meta-analysis. The overall random-effects MD (TT - GAT) and standard deviation (SD) for intraocular pressure (IOP) were -0.70 ± 4.32 mmHg (95% LoA: -8.74 to 7.33 mmHg). In the subgroup analysis based on index test devices used, Easyton showed the lowest MD, SD, (-0.29 ± 2.35 mmHg), and 95% LoA (-4.90 to 4.32 mmHg). In the univariate meta-regression model, we found that, on average, studies examining normal eyes reported a statistically significant lower MD of 2.67 mmHg (95% confidence interval: 0.27-5.07 mmHg; P = 0.03) between TT and GAT, compared to studies that assessed eyes with mixed ocular condition.

CONCLUSION

In the current meta-analysis, we found a small MD in the measured IOP between the 2 tonometers. However, given the high heterogeneity and a wider LoA, it is not advisable to use TT interchangeably with GAT.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Influence of meteorological factors on intraocular pressure variability using a large-scale cohort

The effects of meteorological conditions on IOP using a large-scale health examination cohort were investigated. There were a total of 811,854 measurements from 126,630 eyes of 63,839 subjects in 9 years from a health checkup cohort followed up annually for age, sex, body height, body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), and IOP. The effects of these variables and the meteorological data of daily average temperature (TP), daily average local atmospheric pressure (AP), daily average volumetric humidity (VH), and daily amount of rainfall (RF) on the day of IOP measurement on IOP were investigated. Several variables were significantly associated with IOP, including sex, age, body height, BMI, SBP, DBP, average TP, average AP, average VH, RF, white blood cell count, red blood cell count, hemoglobin, aspartate aminotransferase, alanine aminotransferase, guanosine triphosphate, calcium, and HbA1c. This study indicated a correlation between meteorological factors and IOP. Higher AP and RF were associated with elevated IOP, whereas higher TP and VH were associated with decreased IOP.

Comparison of intraocular pressure measurements with the tono-pen, goldmann applanation tonometer, and noncontact tonometer in nonglaucomatous pseudophakic children

BACKGROUND

To evaluate the agreement between the Goldman applanation tonometer (GAT), Tono-Pen, and noncontact tonometer (NCT) in the measurement of intraocular pressure (IOP) in pseudophakic children.

METHODS

The medical records of nonglaucomatous pseudophakic children between 2009 and 2019 were retrospectively analyzed. A total of 46 eyes of 23 patients operated for bilateral pediatric cataract were included in the study. The patients' mean age was 13.4 ± 4.1 years. Central corneal thickness (CCT) and IOP values measured with the GAT, Tono-Pen, and NCT were recorded. Agreement between the tonometers was evaluated by intraclass correlation coefficients (ICC) and the Bland-Altman method.

RESULTS

The mean IOP of the 46 eyes included in the study was measured as 13.7 ± 2.3 mm Hg with the GAT, 16.0 ± 2.3 mm Hg with NCT, and 16.5 ± 2.3 mm Hg with the Tono-Pen (p < 0.001). There is no statistical difference between NCT and Tono-Pen measurements, while GAT measurements were significantly lower than those of the NCT and Tono-pen. ICC values showed fair agreement between NCT and Tono-Pen (ICC = 0.720), whereas there was poor agreement between GAT and NCT (ICC = 0.501) and Tono-pen (ICC = 0.314).

CONCLUSIONS

With all devices included in the study, thicker corneas were associated with higher IOP measurements. Although there was moderate agreement between the NCT and Tono-Pen, there was a statistically significant difference in the IOP values provided by the three devices. Our results suggest these devices should not be used interchangeably.

Evaluation of corneal densitometry values with Pentacam in cases of ocular hypertension and pseudoexfoliative glaucoma

BACKGROUND

Examination of corneal densitometry measurements using the Pentacam Scheimpflug imaging system in cases of pseudoexfoliative glaucoma (PEXG) and ocular hypertension (OHT).

METHODS

The study included 50 eyes of 29 PEXG patients, 25 eyes of 16 OHT patients, and 76 eyes of 38 healthy control subjects followed in the glaucoma clinic. Corneal densitometry values of all cases were measured using the Scheimpflug imaging system (Pentacam, Oculus, Germany). Corneal densitometry was assessed based on 4 concentric radial zones (0-2 mm, 2-6 mm, 6-10 mm, and 10-12 mm) and depths (anterior, central, posterior, and total) within the Scheimpflug imaging system. The results were statistically analyzed.

RESULTS

Corneal densitometry values examined between the OHT and control groups were higher in OHT and statistically significant (p < 0.05). Corneal densitometry values examined between the PEXG and control groups were higher in PEXG and statistically significant (p < 0.05). In comparison between the PEXG and OHT groups, corneal densitometry values in the central 0-2 mm, 2-6 mm, and 6-10 mm; posterior 0-2 mm and 2-6 mm radial zones were higher in PEXG and statistically significant (p < 0.05).

CONCLUSIONS

It was observed that elevated intraocular pressure levels in OHT cases could lead to changes in the cornea, consequently increasing corneal densitometry values. The higher corneal densitometry values in PEXG cases compared to OHT were attributed to the accumulation of pseudoexfoliative material in the cornea. Based on our study, corneal densitometry could serve as a potential biomarker for early glaucoma detection in OHT cases and could be employed to assess corneal transparency during the follow-up of PEXG cases.

The Finnish current care guideline for open-angle glaucoma

This article is an English translation of the 4th Finnish Current Care Guideline for diagnostics, treatment and follow-up of primary open-angle glaucoma, normal-tension glaucoma and pseudoexfoliative glaucoma. This guideline is based on systematic literature reviews and expert opinions with Finland's geographical and operational healthcare environment in mind.

Characterization of intraocular pressure variability in conscious rats

Elevation of mean intraocular pressure (IOP) has long been recognized as a leading risk factor for glaucoma. Less is known about the possible contribution of moment-to-moment variations in IOP to disease development and progression due to limitations of tonometry, the prevailing method of IOP measurement. Tonometry provides good estimates of mean IOP but not IOP variance. The aim of this study was to quantitatively characterize IOP variability via round-the-clock IOP telemetry in conscious unrestrained rats. The anterior chamber of one eye was implanted with a microcannula connected to a wireless backpack telemetry system, and IOP data were collected every 4 s for one week. The cannula was then repositioned under the conjunctiva, and control data were collected for an additional week. IOP statistics were computed in 30-min intervals over a 24-h period and averaged across days. All animals exhibited a diurnal variation in mean IOP, while deviations about the mean were independent of time of day. Correlation analysis of the deviations revealed transient and sustained components, which were respectively extracted from IOP records using an event detection algorithm. The amplitude and interval distributions of transient and sustained events were characterized, and their energy content was estimated based on outflow tissue resistance of rat eyes. Transient IOP events occurred ∼231 times per day and were typically ≤5 mmHg in amplitude and 2-8 min in duration, while sustained IOP events occurred ∼16 times per day and were typically ≤5 mmHg in amplitude and 20-60 min in duration. Both persisted but were greatly reduced in control recordings, implying minor contamination of IOP data by motion-induced telemetry noise. Sustained events were also often synchronous across implanted animals, indicating that they were driven by autonomic startle and stress responses or other physiological processes activated by sensory signals in the animal housing environment. Not surprisingly, the total daily fluidic energy applied to resistive outflow pathways was determined primarily by basal IOP level. Nevertheless, transient and sustained fluctuations collectively contributed 6% and diurnal fluctuations contributed 9% to daily IOP energy. It is therefore important to consider the cumulative impact of biomechanical stress that IOP fluctuations apply over time to ocular tissues.

Future research perspective on the interfacial physics of non-invasive glaucoma testing in pathogen transmission from the eyes

Non-contact tonometry (NCT) is a non-invasive ophthalmologic technique to measure intraocular pressure (IOP) using an air puff for routine glaucoma testing. Although IOP measurement using NCT has been perfected over many years, various phenomenological aspects of interfacial physics, fluid structure interaction, waves on corneal surface, and pathogen transmission routes to name a few are inherently unexplored. Research investigating the interdisciplinary physics of the ocular biointerface and of the NCT procedure is sparse and hence remains to be explored in sufficient depth. In this perspective piece, we introduce NCT and propose future research prospects that can be undertaken for a better understanding of the various hydrodynamic processes that occur during NCT from a pathogen transmission viewpoint. In particular, the research directions include the characterization and measurement of the incoming air puff, understanding the complex fluid-solid interactions occurring between the air puff and the human eye for measuring IOP, investigating the various waves that form and travel; tear film breakup and subsequent droplet formation mechanisms at various spatiotemporal length scales. Further, from an ocular disease transmission perspective, the disintegration of the tear film into droplets and aerosols poses a potential pathogen transmission route during NCT for pathogens residing in nasolacrimal and nasopharynx pathways. Adequate precautions by opthalmologist and medical practioners are therefore necessary to conduct the IOP measurements in a clinically safer way to prevent the risk associated with pathogen transmission from ocular diseases like conjunctivitis, keratitis, and COVID-19 during the NCT procedure.

Central Corneal Thickness and Intraocular Pressure in Children with Type 1 Diabetes Mellitus

PURPOSE

The aim of this study is to determine the mean central corneal thickness (CCT) and mean intraocular pressure (IOP) in children with type 1 diabetes mellitus (T1DM) and to determine the relationship between CCT and IOP on the one hand and age, sex, retinopathy hemoglobin A1c (HbA1c), and duration of diabetes on the other.

METHODS

This is a case-control, hospital-based study conducted at Hospital Universiti Sains Malaysia between January and November 2022. Thirty-eight children with T1DM were recruited as cases, and 38 healthy children were recruited as controls. The cases and controls then underwent ophthalmic examination, IOP measurement, and CCT measurement using optical coherence tomography (OCT) of the right eye. The IOP measurements were adjusted for CCT for further analysis.

RESULTS

The means of CCT and IOP values were significantly higher in the T1DM group than in the control group (all p = 0.02). The mean CCT was 542.18 ± 20.40 μm in the T1DM group, and 529.52 ± 26.17 μm in the control group. The mean IOP was 14.68 ± 1.98 mmHg in the T1DM group, and 13.52 ± 1.66 mmHg in the control group. The mean HbA1c was 10.68% ± 2.49% in the T1DM group. Age and duration of DM were found to have a significant association with CCT in children with T1DM. The duration of DM was also found to be significantly associated with the IOP. Sex and HbA1c levels were found to have no significant relationship with either CCT or IOP.

CONCLUSIONS

Children with T1DM have significantly higher CCT and IOP than the average child. The duration of DM is a significant factor that impacts both CCT and IOP. In addition, age is another factor that affects CCT in children with T1DM.

Comparison of Ocular Biomery in Primary Open Angle Glaucoma and Non-glaucoma in South West Nigeria

Background

Glaucoma is a public health problem in Nigeria. The number of individuals affected by glaucoma in Nigeria is much higher than the individuals known to have the disease. Ocular parameters such as intraocular pressure, central cornea thickness, axial length and refractive error have all been documented as risk factors of glaucoma especially among Caucasians and African Americans, with little documentation in Africa where there's an alarming rate of blindness.

Aim and Objectives

To compare central cornea thickness (CCT), intraocular pressure (IOP), axial length (AL) and refractive state in participants with primary open angle glaucoma (POAG) and non-glaucoma in South-West Nigeria.

Materials and Methods

This hospital-based case-control study was carried out among 184 newly diagnosed POAG and non-glaucoma adult participants attending the outpatient clinic of Eleta eye institute. The CCT, IOP, AL and refractive state were measured in each participant. Test of significance between proportions in categorical variables were assessed using chi square test (χ2) in both groups. The means were compared using independent t-test while correlation between parameters were analyzed using Pearson correlation coefficient.

Results

The mean age of the POAG participants was 57.16 + 13.3 years and the mean age of the non-glaucoma participants was 54.15 + 13.4 years. The mean IOP in the POAG group was 30.2 + 8.9mmHg while non- glaucoma group was 14.2 + 2.6mmHg (P < 0.001), other ocular parameters were not significantly different in both groups. In the POAG group, decreased spherical equivalent refractive error (i.e increasing myopia) was significantly associated with increased axial length (r= -0.252, P = 0.01), but not significant in the non- glaucoma group. However, in the non-glaucoma group, central cornea thickness increased with increasing intraocular pressure (r= 0.305, P = 0.003), which was not significant in the glaucoma group.

Conclusion

Patients with POAG had much higher IOP and thus, IOP remains a significant risk factor in its development. There was a significant relationship between refractive state and axial length in the POAG group while a significant relationship was identified between central cornea thickness and intraocular pressure in the non- glaucoma group.

Central Corneal Thickness and Intraocular Pressure in Women With Gestational Diabetes Mellitus

INTRODUCTION

Pregnancy causes an increase in central corneal thickness (CCT) and a reduction in intraocular pressure (IOP), especially in the third trimester. However, there is very limited published data regarding CCT and IOP in gestational diabetes mellitus (GDM) on diet control. This study is aimed to compare the means of CCT and IOP between pregnant women with GDM on diet control, healthy pregnant women, and healthy non-pregnant women.

METHODS

This is a comparative cross-sectional study. A total of 184 women were recruited and divided into the following three groups: 61 pregnant women with GDM on diet control, 63 healthy pregnant women, and 60 healthy non-pregnant women as control. All subjects have undergone ocular examination during their 36-40 weeks of gestation. CCT measurement was done using a specular microscope and IOP measurement using a non-contact tonometer. Data from the right eye were analyzed.

RESULTS

The mean age was 32 (4.0) years in GDM on diet control, 29 (3.0) years in healthy pregnant women, and 27 (5.4) years in healthy non-pregnant women. The number of gravidas was 2.5 (0.8) in women with GDM on diet control and 2.3 (0.8) in healthy pregnant women. There was a significant difference (p<0.05) in the mean CCT in women with GDM on diet control compared to healthy pregnant and healthy non-pregnant women. The mean IOP is significantly lower in both pregnant women with GDM on diet control and healthy pregnant groups, compared to the healthy non-pregnant women group.

CONCLUSION

Women with GDM showed significantly thicker mean CCT than healthy pregnant and non-pregnant women. The mean IOP is significantly lower in both pregnant women with GDM on diet control and healthy pregnant groups, compared to the healthy non-pregnant women group.

Analysis of the influence of corneal properties and densitometry on applanation and rebound tonometry in primary open angle glaucoma

PURPOSE

To evaluate the influence of corneal densitometry on portable applanation (Perkins) and rebound (iCare ic100 and PRO) tonometry. A secondary goal was to assess if there was a relationship between various corneal properties and the severity of primary open angle glaucoma (POAG).

MATERIAL AND METHODS

Seventy-five eyes of 75 patients with primary open angle glaucoma were studied, divided by severity into 3 groups: 25 mild, 25 moderate and 25 advanced. Intraocular pressure (IOP) was measured 3 times in each participant with a Perkins applanation tonometer (PAT), a handheld version of the Goldman applanation tonometer (GAT), an iCare PRO and an iCare ic100. Mean values were then calculated. Corneal topography with the Pentacam HR (Oculus, Wetzlar, Germany) was also performed in all individuals.

RESULTS

Mean age and sex were comparable in all groups, as were densitometry values (P>0.05). The mean visual field defect (MD) was 2.85 (±1.23) dB in the mild glaucoma group, 8.26 (±1.90) dB in the moderate group and 15.66 (±3.46) dB in the advanced group. Three multivariate regression analyses were performed. The first and second calculations assessed the effect of IOP obtained with iCare ic100 and PAT as dependent variables with age, sex, CCT and mean keratometry (Km) within the glaucoma subgroups and the global sample. The third analysis was carried out to assess the relationship between corneal densitometry as the dependant variable and the aforementioned corneal parameters among the glaucoma groups. In the first multivariate regression analysis, a statistically significant correlation was found between ic100 rebound tonometry and CCT in the POAG global sample (coef. 0.117; IC [-0.21-(-0.01)]; P=0.025). No statistically significant correlation was found in the subgroup analyses. In the second multivariate analysis, no significant correlation was found between PAT and CCT, Km, age or sex (P>0.05). In the third analysis, densitometry was correlated with age in all glaucoma subgroups (P<0.001) and with CCT in the moderate glaucoma subgroup (coef. -0.037; IC [-0.67-(-0.01)]; P=0.021). Tonometry appeared to be minimally influenced by corneal densitometry, with a mild positive linear correlation seen (R=0.03). IOP values were similar with 3 of the tonometers: PAT 16.07 (±3.18) mmHg, PRO 16.27 (±3.42) mmHg and ic100 15.17 (±4.28) mmHg. There was, however, a significant underestimation of IOP with ic100 (-0.89mmHg) compared to PAT (P=0.007).

CONCLUSION

Corneal densitometry did not show significant differences between glaucoma severity groups. A positive correlation was seen with CCT and both corneal densitometry and age. No correlation was found with keratometry or severity of glaucoma. The influence of corneal densitometry on IOP measurements appears weak, with little clinical relevance identified.

Eye Dynamics and Engineering Network Consortium: Baseline Characteristics of a Randomized Trial in Healthy Adults

PURPOSE

To improve understanding of intraocular pressure (IOP) and its variance, this project identifies systemic and ocular characteristics of healthy eyes of adult volunteers including IOP variation, ocular biometrics, and aqueous humor dynamics (AHDs). These data serve as baseline controls for further studies from the Eye Dynamics and Engineering Network (EDEN) Consortium.

DESIGN

Multicenter open-label clinical trial in healthy adults randomized to 1 week treatment with 2 approved glaucoma drugs in a crossover design.

PARTICIPANTS

Among 135 healthy participants, 122 participants (aged 55.2 ± 8.8 years; 92 females, 30 males) completed the protocol.

METHODS

Participants from the University of Michigan, Mayo Clinic, and University of Nebraska Medical Center underwent measurements of ocular biometrics, AHD, and IOP using 4 tonometers. Intraocular pressure data during 3 study visits without glaucoma medications were used in the analysis. The PhenX Toolkit survey acquired standardized data on medical history, surgical history, medications, smoking and alcohol exposures, and physical measures.

MAIN OUTCOME MEASURES

The variability of IOP measurements within eyes was assessed as visit-to-visit IOP variation, within-visit IOP variation, and within-visit positional IOP variation. The concordance (or correlation) between eyes was also assessed.

RESULTS

Average positional change of > 4.7 mmHg was detected with a range of 0.5-11.0 mmHg. Pearson correlation of IOP between eyes within a visit was 0.87 (95% confidence interval [CI], 0.82-0.91) for Goldmann applanation tonometry, 0.91 (95% CI, 0.88-0.94) for Icare rebound tonometry, and 0.91 (95% CI, 0.88-0.94) for pneumatonometry. There was a 4% to 12% asymmetric fluctuation of 3 mmHg or more between eyes between visits using rebound tonometry, 9% with Goldmann applanation tonometry, and 3% to 4% by pneumotonometry. The coefficient of variation between visits for the same eye ranged from 11.2% to 12.9% for pneumatonometry, from 13.6% to 17.4% for rebound tonometry, and 15.8% to 16.2% for Goldmann applanation tonometry.

CONCLUSIONS

The current study from the EDEN Consortium describes measurement methods and data analyses with emphasis on IOP variability. Future papers will focus on changes in ocular biometrics and AHD with timolol or latanoprost treatment.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Analysis of Various Modalities for Intraocular Pressure Measurement in Relation to Keratoconus Severity in 246 Eyes of the Homburg Keratoconus Center

PURPOSE

Intraocular pressure (IOP) measurement may be difficult in keratoconus (KC) due to corneal protrusion and irregular astigmatism. This study aimed to assess which IOP measurement modality is least affected by KC severity.

METHODS

Data from 246 corneas of 246 patients with KC were retrospectively analyzed. KC stages were determined using the Topographic KC (TKC) and ABCD KC classifications derived from Pentacam (Oculus, Germany). IOP was measured using Goldmann applanation tonometry (GAT), Ocular Response Analyzer (ORA, Reichert Instruments, USA), and Corvis ST (CST, Oculus, Germany). Cronbach alpha (CA), analysis of variance with Bonferroni correction, Dunnett T3, and Pearson correlation were performed.

RESULTS

Using CA, the reliability of measurements using various modalities increased to 0.764 to 0.943 when excluding IOP Goldmann overall and in each KC stage (TKC and ABCD). Analysis of variance revealed significant differences between TKC and ABCD stages for almost all IOP modalities. The Bonferroni post hoc test showed significant differences between the measured IOP in earlier and advanced KC stages, except for the biomechanically CST-corrected IOP (bIOP). Pearson correlation analysis showed a significant correlation between IOP and thinnest corneal thickness (TCT) for all IOP modalities except bIOP.

CONCLUSIONS

CST-based bIOP seems to be best suited for IOP measurement in KC because it did not correlate with TCT in contrast to IOP measurements by ORA or GAT. The measurement results from GAT in patients with KC should be interpreted with care and always in view of corneal thickness. As a thumb rule, we suggest to add at least 2 mm Hg to the measured GAT value.

Comparison of three rebound tonometers in normal and glaucomatous dogs

OBJECTIVE

The objectives of the study were to compare intraocular pressure (IOP) readings across a wide range and obtained via three rebound tonometers in ADAMTS10-mutant Beagle-derived dogs with different stages of open-angle glaucoma (OAG) and normal control dogs and to investigate the effect of central corneal thickness (CCT).

ANIMALS STUDIED

Measurements were performed on 99 eyes from 50 Beagle-derived dogs with variable genetics-16 non-glaucomatous and 34 with ADAMTS10-OAG. Seventeen OAG eyes were measured twice-with and without the use of IOP-lowering medications.

PROCEDURES

IOP was measured in each eye using three tonometers with their "dog" setting-ICare® Tonovet (TV), ICare® Tonovet Plus® (TVP), and the novel Reichert® Tono-Vera® Vet (TVA)-in randomized order. CCT was measured with the Accutome® PachPen. Statistical analyses included one-way ANOVA, Tukey pairwise comparisons, and regression analyses of tonometer readings and pairwise IOP-CCT Pearson correlations (MiniTab®).

RESULTS

A total of 116 IOP measurements were taken with each of the three tonometers. When comparing readings over a range of ~7-77 mmHg, mean IOPs from the TV were significantly lower compared with TVP (-4.6 mmHg, p < .001) and TVA (-3.7 mmHg, p = .001). We found no significant differences between TVA and TVP measurements (p = .695). There was a moderate positive correlation between CCT and IOP for TVA (r = 0.53, p < .001), TVP (r = 0.48, p < .001), and TV (r = 0.47, p < .001).

CONCLUSIONS

Our data demonstrate strong agreement between TVP and TVA, suggesting that the TVA may similarly reflect true IOP values in canines. CCT influenced IOP measurements of all three tonometers.

Comparison of Intraocular Pressure Measurements With Goldmann Applanation Tonometry, Tonopen XL, and Pascal Dynamic Contour Tonometry in Patients With Descemet Membrane Endothelial Keratoplasty

PRCIS

IOP measured with Tonopen and DCT was higher than GAT in eyes that underwent DMEK.

PURPOSE/AIM OF THE STUDY

To compare intraocular pressure (IOP) measurements measured based on Goldmann applanation tonometry (GAT), Tonopen XL, and Pascal Dynamic Contour Tonometry (DCT) in patients who had undergone descemet membrane endothelial keratoplasty (DMEK) and to appraise the influence of central corneal thickness (CCT) on IOP measurements.

MATERIALS AND METHODS

Thirty-four eyes (from 34 patients) who underwent DMEK at least 1 month before the study were included. We performed Tonopen XL, GAT, and DCT IOP measurements at 10 min intervals. Bland-Altman plots were used to assess agreement between GAT, Tonopen XL, and DCT. Spearman rank correlation was used to calculate the deviation from GAT readings by each device and correlate the readings with the CCT variable.

RESULTS

The mean IOP values with GAT, Tonopen XL, and DCT were 14.9±5.8, 16.2±5.5, and 19.2±5.0, respectively. Statistically significant differences between GAT and Tonopen XL and between GAT and DCT were noted ( r =0.942 [0.885-0.971]; P =0.0001 and r =0.942 [0.885-0.971]; P =0.0001, respectively). DCT tended to return a higher IOP relative to GAT and Tonopen XL. CCT and IOP readings obtained by GAT, Tonopen XL, and DCT did not show a statistically significant correlation with each other.

CONCLUSION

IOP as measured with both Tonopen and DCT was found to be higher than GAT in eyes that underwent DMEK surgery although the techniques showed a good correlation. After DMEK surgery, all 3 measurement techniques can be practical in routine postoperative examinations, however it is recommended to measure IOP with the same device during patient follow-up.

The Association Between Age and Systemic Variables and the Longitudinal Trend of Intraocular Pressure in a Large-Scale Health Examination Cohort

Purpose

The detailed effects of age and systemic factors on intraocular pressure (IOP) have not been fully understood because of the lack of a large-scale longitudinal investigation. This study aimed to investigate the effect of various systemic factors on the longitudinal change of IOP.

Methods

There were a total of 20,909 eyes of 10,471 subjects from a health checkup cohort that were followed up for systemic factors: (i) age at baseline, (ii) sex, (iii) time series body mass index (BMI), (iv) time series smoking habits, (v) time series systolic and diastolic blood pressures (SBP and DBP), and (vi) time series 19 blood examinations (all of the time series data was acquired at each annual visit), along with IOP annually for at least 8 years. Then the longitudinal effect of the systemic factors on the change of IOP was investigated.

Results

IOP significantly decreased by −0.084 mm Hg/year. BMI, SBP, DBP, smoking habits, total triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and glycosylated hemoglobin A1c were not significantly associated with the change of IOP. Higher values of age, aspartate aminotransferase, hemoglobin, platelet, and calcium were suggested to be significantly associated with the decrease of IOP, whereas higher alanine aminotransferase, guanosine triphosphate, white blood cell count, red blood cell count, and female gender were significantly associated with the increase of IOP.

Conclusions

Age, aspartate aminotransferase, hemoglobin, platelet, calcium, alanine aminotransferase, guanosine triphosphate, white blood cell count, red blood cell count, and gender were the systemic variables significantly associated with the change of IOP.

Normal Corneal Thickness and Endothelial Cell Density in Rhesus Macaques (Macaca mulatta)

Purpose

To define the normal range of central corneal thickness (CCT) and corneal endothelial cell density (ECD) in rhesus macaques (Macaca mulatta) and the effects of age, body weight, sex, and intraocular pressure (IOP) on these parameters.

Methods

Ophthalmic examinations were performed on 144 rhesus macaques without anterior segment pathology. The CCT was measured via ultrasound pachymetry (USP) and specular microscopy, and the ECD was semiautomatically and manually counted using specular microscopy. Rebound tonometry was used to measure IOP. Linear regression and mixed-effects linear regression models were used to evaluate the effects of age, body weight, sex, and IOP on CCT and ECD.

Results

We included 98 females and 46 males with an age range of 0.2 to 29.4 years. The mean CCT by USP and specular microscopy were 483 ± 39 and 463 ± 33 µm, respectively, and were statistically different (P < 0.001). The ECDs were 2717 ± 423 and 2747 ± 438 cells/mm2 by semiautomated and manual analysis, respectively. Corneal endothelial degeneration was identified in one aged rhesus macaque.

Conclusions

The mean USP and specular microscopy CCT values differed significantly, whereas the semiautomatic and manual ECD did not. The CCT was associated with the IOP and sex, whereas the ECD was associated with body weight and age (P < 0.05). As in humans, corneal disease in rhesus macaques is uncommon.

Translational Relevance

Establishing reference values is fundamental to use rhesus macaques as a model for corneal disease or to identify toxicity in studies of ocular drugs or devices.

Correction methods for noncontact intraocular pressure measurement in patients with keratoconus and healthy individuals

PURPOSE

The objective of this study was to investigate the usefulness of four different algorithms to correct noncontact intraocular pressure measurement errors in keratoconus patients and normal individuals.

METHODS

Noncorrected intraocular pressure and corrected intraocular pressures were measured in one eye of 34 patients with keratoconus and 34 age- and gender-matched healthy controls using Corvis Scheimpflug Technology. The correlation of noncorrected intraocular pressure and corrected intraocular pressures with age, axial length, corneal shape, thickness, and biomechanics was calculated. Corrected intraocular pressures were compared with noncorrected intraocular pressure using paired t test and Bland-Altman plots (95% limits of agreement).

RESULTS

The noncorrected intraocular pressure correlated with corneal thickness and biomechanical parameters in both groups (all p≤0.047), and front and back mean keratometry in the keratoconus group (r=-0.39, p=0.02, and r=0.39, p=0.02, respectively). After adjustment with different intraocular pressure correction algorithms, biomechanically corrected intraocular pressure showed a minimal correlation with corneal features and a nonsignificant difference with noncorrected intraocular pressure in the healthy group (-0.1 ± 1.1 mmHg, p=0.58; 95% limits of agreement: -2.3 to 2.1 mmHg).

CONCLUSIONS

Measuring intraocular pressure using noncontact tonometry and its corrected forms with a corneal thickness-based simple linear formula in patients with keratoconus is associated with many errors. Using more complex formulas that take into consideration more corneal stiffness parameters in addition to corneal thickness, such as biomechanically corrected intraocular pressure formula, may be more reliable and beneficial in this group of patients.

Evaluation of the impact of subepithelial corneal infiltrates on corneal biomechanics after epidemic keratoconjunctivitis

PURPOSE

To examine the effect of subepithelial corneal infiltrates on corneal biomechanical properties after epidemic keratoconjunctivitis compared to that in healthy controls.

METHODS

The cross-sectional study included consecutive patients with bilateral subepithelial corneal infiltrates after epidemic keratoconjunctivitis and healthy controls. Best corrected visual acuity corneal subepithelial infiltrate scoring Fantes grading scale, and central corneal thickness were measured. Corneal hysteresis corneal resistance factor Goldmann correlated intraocular pressure and corneal compensated intraocular pressure were assessed using an ocular response analyzer.

RESULTS

This study included 66 eyes of 33 patients with subepithelial corneal infiltrates following epidemic keratoconjunctivitis and randomly selected 37 eyes of 37 healthy volunteers. The mean Fantes and CSIS scores were 1.8 ± 0.8 and 2.9 ± 1.3, respectively, in the first involved eyes and 1.3 ± 1.1 and 1.9 ± 1.7, respectively, in the fellow eyes (p=0.009 and p=0.002, respectively). The first (526.1 ± 28.1 µm; p=0.005) and second involved eyes (523.4 ± 38.1 µm; p=0.044) had significantly thinner corneas compared to that in healthy controls (557.0 ± 38.1 µm). While best-corrected visual acuity showed a positive correlation with corneal resistance factor (r=0.363, p=0.045) and corneal hysteresis (r=0.414, p=0.021), corneal subepithelial infiltrate scoring showed a negative correlation with Goldmann correlated intraocular pressure (r=-0.479, p=0.006) and corneal compensated intraocular pressure (r=-0.413, p=0.021).

CONCLUSION

Eyes with subepithelial corneal infiltrates had significantly thinner corneas compared to that in healthy controls. A positive correlation of the corneal resistance factor and corneal hysteresis with best-corrected visual acuity and a negative correlation of the Goldmann correlated intraocular pressure and corneal compensated intraocular pressure with corneal subepithelial infiltrate scoring should be taken into account when measuring intraocular pressure values in patients with subepithelial corneal infiltrates.

Comparison of Non-contact Tonometry and Goldmann Applanation Tonometry Measurements in Non-pathologic High Myopia

Purpose

To compare intraocular pressure (IOP) values obtained using Goldmann applanation tonometry (IOPGAT) and non-contact tonometry (IOPNCT) in a non-pathologic high myopia population.

Methods

A total of 720 eyes from 720 Chinese adults with non-pathologic high myopia were enrolled in this cross-sectional study. Demographic and ocular characteristics, including axial length, refractive error, central corneal thickness (CCT), and corneal curvature (CC) were recorded. Each patient was successively treated with IOPNCT and IOPGAT. Univariate and multivariable linear regression analyses were conducted to detect factors associated with IOPNCT and IOPGAT, as well as the measurement difference between the two devices (IOPNCT−GAT).

Results

In this non-pathologic high myopia population, the mean IOPNCT and IOPGAT values were 17.60 ± 2.76 mmHg and 13.85 ± 2.43 mmHg, respectively. The IOP measurements of the two devices were significantly correlated (r = 0.681, P &lt; 0.001), however, IOPNCT overestimated IOPGAT with a mean difference of 3.75 mmHg (95% confidence interval: 3.60–3.91 mmHg). In multivariate regression, IOPNCT was significantly associated with body mass index (standardized β = 0.075, p = 0.033), systolic blood pressure (SBP) (standardized β = 0.170, p &lt; 0.001), and CCT (standardized β = 0.526, p &lt; 0.001). As for IOPGAT, only SBP (standardized β = 0.162, p &lt; 0.001), CCT (standardized β = 0.259, p &lt; 0.001), and CC (standardized β = 0.156, p &lt; 0.001) were significantly correlated. The mean IOPNCT−GAT difference increased with younger age (standardized β = −0.134, p &lt; 0.001), higher body mass index (standardized β = 0.091, p = 0.009), higher SBP (standardized β = 0.074, p = 0.027), thicker CCT (standardized β = 0.506, p &lt; 0.001), and lower IOPGAT (standardized β = −0.409, p &lt; 0.001).

Conclusion

In the non-pathologic high myopia population, IOPNCT overestimated IOPGAT at 3.75 ± 2.10 mmHg. This study suggests that the difference between the values obtained by the two devices, and their respective influencing factors, should be considered in the clinical evaluation and management of highly myopic populations.

Possibilities of monitoring intraocular pressure in children using EASYTON transpalpebral tonometer

Purpose

To compare the effectiveness of transpalpebral scleral tonometry (TPST) and corneal pneumotonometry in children, and assess the discomfort level when measuring intraocular pressure (IOP) by these methods.

Methods

TPST using EASYTON tonometer (Russia) and pneumotonometry using Reichert 7 Non-contact AutoTonometer (USA) have been sequentially performed on 84 eyes (42 children aged 5–14, ave. 9.3 ± 2.7), including 64 myopic eyes (-0.5 to 6.75D), 18 hyperopic eyes (+ 0.75 to + 3.75D), and 2 emmetropic eyes. We assessed tolerance to the procedure on a five-point scale using a questionnaire which listed several criteria: discomfort, presence of pain, fear or anxiety during the procedure, the child's resistance to measurement.

Results

EASYTON tonometry demonstrated repeatability of IOP indicators when measuring the same eye three times sequentially and almost the same IOP level in paired eyes of isometropic children. Pneumotonometry reveals a greater individual data variability and a more pronounced asymmetry of the paired eyes’ indicators. IOP measured using the TPST was 18.3 ± 2.3 mmHg across the whole group, 18.2 ± 2.3 mmHg in myopic, and 18.5 ± 2.3 mmHg in hyperopic children. With pneumotonometry, the corresponding indicators were 17.1 ± 3.9 mmHg, 16.9 ± 3.8 mmHg, and 18.2 ± 4.0 mmHg. The average score for the TPST (4.64 ± 0.60 points) was significantly higher than that for pneumotonometry (3.85 ± 0.90 points) (p < 0.05).

Conclusions

TPST provides broader possibilities for IOP control in pediatric practice, yielding more reliable and accurate results than pneumotonometry, eliminating the influence of corneal thickness and irregularity on the measurement result, and ensuring a calmer behavior and more comfort of children during the procedure.

How to Measure Intraocular Pressure: An Updated Review of Various Tonometers

Intraocular pressure (IOP) is an important measurement that needs to be taken during ophthalmic examinations, especially in ocular hypertension subjects, glaucoma patients and in patients with risk factors for developing glaucoma. The gold standard technique in measuring IOP is still Goldmann applanation tonometry (GAT); however, this procedure requires local anesthetics, can be difficult in patients with scarce compliance, surgical patients and children, and is influenced by several corneal parameters. Numerous tonometers have been proposed in the past to address the problems related to GAT. The authors review the various devices currently in use for the measurement of intraocular pressure (IOP), highlighting the main advantages and limits of the various tools. The continuous monitoring of IOP, which is still under evaluation, will be an important step for a more complete and reliable management of patients affected by glaucoma.

Telehealth and Screening Strategies in the Diagnosis and Management of Glaucoma

Telehealth has become a viable option for glaucoma screening and glaucoma monitoring due to advances in technology. The ability to measure intraocular pressure without an anesthetic and to take optic nerve photographs without pharmacologic pupillary dilation using portable equipment have allowed glaucoma screening programs to generate enough data for assessment. At home, patients can perform visual acuity testing, web-based visual field testing, rebound tonometry, and video visits with the physician to monitor for glaucomatous progression. Artificial intelligence will enhance the accuracy of data interpretation and inspire confidence in popularizing telehealth for glaucoma.

Goldmann Tonometry and Corneal Biomechanics

Glaucoma is the second cause of irreversible blindness in the world. Intraocular pressure (IOP) is a recognized major risk factor for the development and progression of glaucomatous damage. Goldmann applanation tonometry (GAT) is internationally accepted as the gold standard for the measurement of IOP. The purpose of this study was to search for correlations between Goldmann tonometry and corneal mechanical properties and thickness by means of in vitro tests. IOP was measured by the Goldmann applanation tonometer (GIOP), and by a pressure transducer inserted in the anterior chamber of the eye (TIOP), at increasing pressure levels by addition of saline solution in the anterior chamber of enucleated pig eyes (n = 49). Mechanical properties were also determined by inflation tests. The GAT underestimated the real measurements made by the pressure transducer, with most common differences in the range 15–28 mmHg. The difference between the two instruments, highlighted by the Bland–Altman test, was confirmed by ANOVA, normality tests, and Mann–Whitney’s tests, both on the data arranged for infusions and for the data organized by pressure ranges. Pearson correlation tests revealed a negative correlation between (TIOP-GIOP) and both corneal stiffness and corneal thickness. In conclusion, data obtained showed a discrepancy between GIOP and TIOP more evident for softer and thinner corneas, that is very important for glaucoma detection.

Evaluation of some factors affecting the agreement between the Proview Eye Pressure Monitor and the Goldmann applanation tonometer measurements

BACKGROUND

Our aim was to examine whether training level and ocular factors could account for part of the difference in intraocular pressure (IOP) measured using the Goldmann applanation tonometer (GAT) and Proview Eye Pressure Monitor (PPT).

METHODS

One hundred and nineteen individuals (238 eyes) were enrolled in the study. The mean age was 35.8 years (range 21 to 79). All study participants obtained IOP measurements using the PPT after hearing instructions on how to perform PPT. Glaucoma patients obtained additional IOP measurements using PPT after viewing an instructional video and after 30 days of home use. IOP was also measured using the GAT at each experimental session.

RESULTS

The difference in IOP measured by the GAT and the PPT was 0.55 +/- 3.38 mmHg, 0.17 +/- 3.79 mmHg and -1.30 +/- 3.79 mmHg for myopic, emmetropic and hypermetropic groups, respectively, which were statistically significant (ANCOVA; p = 0.014). The difference in IOP between GAT and PPT was not significantly different for measurements obtained after verbal instructions, instructional video or after 30 days of home use (Repeated-ANCOVA; p = 0.30). The overall agreement between the GAT and the PPT was poor. Intra-class correlation coefficient was 0.575, and the 95% confidence interval (CI) of agreement was -6.93 to +6.73 mmHg.

CONCLUSION

There was a small systematic difference in IOP measured by the GAT and PPT when comparing the different refraction groups; however, this level of difference between the groups is unlikely to be of clinical significance. The level of training in using the PPT did not influence its measurements. The limits of agreement between the PPT and the GAT were wide and long-term use of PPT did not improve its agreement.

An Intraocular Pressure Measurement Technique Based on Acoustic Radiation Force Using an Ultrasound Transducer: A Feasibility Study

High intraocular pressure (IOP) is one of the major risk factors for glaucoma, and thus accurate IOP measurements should be performed to diagnose and treat glaucoma early. In this study, a novel technique for measuring the IOP based on acoustic radiation force was proposed, and its potential was experimentally demonstrated. The proposed technique uses the acoustic radiation force to generate axial displacement on the ocular surface while simultaneously measuring the degree of deformation. In order to verify that the ocular displacement induced by the acoustic radiation force is related to the IOP, the experiment was conducted by fabricating a 5 MHz single element transducer and gelatin phantoms with different stiffness values. Our experimental results show that there is a close relationship between the ocular displacement by the acoustic radiation force and the IOP obtained by a commercial tonometer. Therefore, the proposed acoustic radiation force technique can be a promising candidate for measuring the IOP.

Real-world comparison between the Tonopen and Goldmann applanation tonometry in a university glaucoma clinic

PURPOSE

To determine whether Tonopen intraocular pressure (IOP) measurements by Ophthalmic technicians are interchangeable with Goldmann applanation tonometry (GAT) by a specialist in our glaucoma clinic.

METHODS

Ophthalmic technician Tonopen and glaucoma specialist GAT IOP measurements were performed on both undilated eyes of 300 consecutive patients during the same visit to our glaucoma clinic.

RESULTS

Among all 600 eyes of 300 patients (age 65.4, range: 23-92 years, male: 44.3%), Tonopen and GAT IOPs were similar (15.5 ± 0.6 vs. 15.4 ± 0.7 mmHg, respectively, p = 0.63) and directly correlated (r² = 0.58, p < 0.0001). However, among 120 patients with bilateral primary open-angle glaucoma GAT IOP was significantly higher than Tonopen in the right eyes (17.1 ± 1.1 vs. 16.2 ± 0.9 mmHg, p = 0.024) and in the left eyes (17.0 ± 1.0 vs. 16.3 ± 1.0 mmHg, p = 0.029). In all 300 right eyes, Tonopen underestimated IOP in 48.3% of eyes and overestimated in 39% (difference range: ( - )14 to ( + )12 mmHg), with IOP difference >  ± 3 mmHg in 34% of eyes. In eyes with GAT IOP ≥ 22 mmHg, Tonopen IOP was significantly lower (24.7 ± 2.6, range: 11-43 mmHg vs. 28.2 ± 2.2, range: 22-43 mmHg, p = 0.0002, mean difference: - 3.6 ± 1.7 mmHg), and the Tonopen measured IOP ≤ 21 mmHg in 33.3% of eyes. In eyes with Tonopen IOP ≤ 10 mmHg GAT measured IOP of 11-17 mmHg in 65.7% of eyes.

CONCLUSIONS

Tonopen may mask a third of eyes with elevated IOP and two third of eyes with potentially above-goal IOP. The Tonopen may not be interchangeable with GAT or sufficiently reliable for patient management or screening in our glaucoma clinic. However, further study is recommended to assess the limitations of the Tonopen IOP measurements in eyes with higher or lower GAT IOPs.

CLINICAL TRIALS REGISTRATION

The Institutional review board, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY does not require this retrospective study to register.

Adaptive finite element eye model for the compensation of biometric influences on acoustic tonometry

BACKGROUND AND OBJECTIVE

Glaucoma is currently a major cause for irreversible blindness worldwide. A risk factor and the only therapeutic control parameter is the intraocular pressure (IOP). The IOP is determined with tonometers, whose measurements are inevitably influenced by the geometry of the eye. Even though the corneal mechanics have been investigated to improve accuracy of Goldmann and air pulse tonometry, influences of geometric properties of the eye on an acoustic self-tonometer approach are still unresolved.

METHODS

In order to understand and compensate for measurement deviations resulting from the geometric uniqueness of eyes, a finite element eye model is designed that considers all relevant eye components and is adjustable to all physiological shapes of the human eye.

RESULTS

The general IOP-dependent behavior of the eye model is validated by laboratory measurements on porcine eyes. The difference between simulation and measurement is below 8 µm for IOP levels from 5 to 40 mmHg. The adaptive eye model is then used to quantify systematic uncertainty contributions of a variation of eye length and central corneal thickness based on input statistics of a clinical trial series. The adaptive eye model provides the required relation between biometric eye parameters and the corneal deflection amplitude, which here is the measured quantity to trace back to the IOP. Implementing the relations provided by the eye model in a Gaussian uncertainty propagation calculation now allows the quantification of the uncertainty contributions of the biometric parameters on the overall measurement uncertainty of the acoustic self-tonometer. As a result, a systematic uncertainty contribution resulting from deviations in eye length dominate stochastic deviations of the sensor equipment by a factor of 3.5.

CONCLUSION

As perspective, the proposed adaptive eye model provides the basis to compensate for systematic deviations of (but not only) the acoustic self-tonometer.

Comparison of the iCare, Tono-Pen, non-contact airpuff, and Goldmann applanation tonometers in eyes with corneal edema after penetrating keratoplasty

BACKGROUND

To compare the utility of the iCare, Tono-Pen, and non-contact airpuff (NCT) tonometers with the Goldmann applanation tonometer (GAT) for measuring intraocular pressure (IOP) in patients with corneal edema after penetrating keratoplasty (PKP) and to assess the effects of central corneal thickness (CCT) and corneal curvature (CC) on IOP measurements.

METHODS

Thirty-two eyes of 27 patients with corneal edema after PKP due to corneal abnormalities and 43 control eyes of 30 patients with normal corneas were recruited. Before IOP measurements, all patients underwent a baseline examination, including auto-refraction, keratometry, slit lamp biomicroscopy, and CCT measurement. IOP was measured using the devices in the same order: first the NCT, followed by the iCare, Tono-Pen, and GAT. The differences between the iCare, Tono-Pen, NCT, and GAT were calculated with repeated-measures analysis of variance. The Bland-Altman method was used to assess the agreement between the iCare, Tono-Pen, and NCT versus the GAT. The influences of CCT and CC on IOP measurement were evaluated by correlation analysis using Pearson's correlation coefficient.

RESULTS

Mean IOP measurements were significantly higher with the NCT and Tono-Pen than with the GAT in the PKP and control groups. When compared with GAT, iCare showed significantly higher IOP readings in the control group, but the IOP readings did not differ between the iCare and GAT in the PKP group. Poor agreement was noted between the NCT and GAT in both groups. The Tono-Pen showed clinically acceptable agreement with GAT in control eyes and poor agreement in PKP eyes. The agreement between the iCare and GAT appeared to be clinically acceptable in both groups. Correlation analysis of the results from control eyes showed that the IOP measurements with the GAT and NCT were weakly related to CCT and moderately correlated with CC. The iCare IOP readings were weakly correlated with CCT and CC.

CONCLUSION

In the PKP group, the NCT and Tono-Pen significantly overestimated IOP, whereas the iCare IOP readings were similar to those obtained using the GAT. Poor agreement was noted between the NCT and GAT as well as between the Tono-Pen and GAT, but the iCare showed clinically acceptable agreement with GAT. In normal corneas, the GAT, NCT, and iCare were affected by CCT and CC. The iCare tonometer was less affected by corneal edema than were the NCT and the Tono-Pen. The iCare appears to be a useful device for IOP measurement in eyes with corneal edema after PKP.

Wearable and Implantable Intraocular Pressure Biosensors: Recent Progress and Future Prospects

Biosensors worn on or implanted in eyes have been garnering substantial attention since being proven to be an effective means to acquire critical biomarkers for monitoring the states of ophthalmic disease, diabetes. Among these disorders, glaucoma, the second leading cause of blindness globally, usually results in irreversible blindness. Continuous intraocular pressure (IOP) monitoring is considered as an effective measure, which provides a comprehensive view of IOP changes that is beyond reach for the "snapshots" measurements by clinical tonometry. However, to satisfy the applications in ophthalmology, the development of IOP sensors are required to be prepared with biocompatible, miniature, transparent, wireless and battery-free features, which are still challenging with many current fabrication processes. In this work, the recent advances in this field are reviewed by categorizing these devices into wearable and implantable IOP sensors. The materials and structures exploited for engineering these IOP devices are presented. Additionally, their working principle, performance, and the potential risk that materials and device architectures may pose to ocular tissue are discussed. This review should be valuable for preferable structure design, device fabrication, performance optimization, and reducing potential risk of these devices. It is significant for the development of future practical IOP sensors.

Predicting intraocular pressure using systemic variables or fundus photography with deep learning in a health examination cohort

The purpose of the current study was to predict intraocular pressure (IOP) using color fundus photography with a deep learning (DL) model, or, systemic variables with a multivariate linear regression model (MLM), along with least absolute shrinkage and selection operator regression (LASSO), support vector machine (SVM), and Random Forest: (RF). Training dataset included 3883 examinations from 3883 eyes of 1945 subjects and testing dataset 289 examinations from 289 eyes from 146 subjects. With the training dataset, MLM was constructed to predict IOP using 35 systemic variables and 25 blood measurements. A DL model was developed to predict IOP from color fundus photographs. The prediction accuracy of each model was evaluated through the absolute error and the marginal R-squared (mR2), using the testing dataset. The mean absolute error with MLM was 2.29 mmHg, which was significantly smaller than that with DL (2.70 dB). The mR2 with MLM was 0.15, whereas that with DL was 0.0066. The mean absolute error (between 2.24 and 2.30 mmHg) and mR2 (between 0.11 and 0.15) with LASSO, SVM and RF were similar to or poorer than MLM. A DL model to predict IOP using color fundus photography proved far less accurate than MLM using systemic variables.

The Relationship Between Corneal Hysteresis and Progression of Glaucoma After Trabeculectomy

PURPOSE

The purpose of this study was to investigate the association of corneal hysteresis (CH) measured with Ocular Response Analyzer on the progression of glaucoma after trabeculectomy.

MATERIALS AND METHODS

Twenty-four eyes of 19 patients with primary open-angle glaucoma underwent trabeculectomy. A series of visual fields (Humphery Field Analyzer 24-2 SITA-standard) were measured starting after 6 months after trabeculectomy (4.2±5.0 y, mean±SD). The mean total deviation (mTD) of the 52 test points were calculated. In addition, the mTD was divided into the following areas: central area (within central 10 degrees), superior area and inferior area: mTDcentre, mTDsuperior, and mTDinferior, respectively. The relationship between each area's progression rate of mTD and the 7 variables of baseline age, central corneal thickness, baseline mTD, mean intraocular pressure (IOP), SD of IOP divided by the mean IOP, the difference between baseline IOP obtained before the initiation of any treatment, mean IOP, and CH were analyzed using the linear mixed model, and the optimal model was selected using the model selection method with the second ordered Akaike Information Criterion.

RESULTS

In the optimal model for mTD progression rate, only CH was selected with the coefficient of 0.11. The optimal model for the mTDcentre progression rate included mean IOP with the coefficient of -0.043 and CH with the coefficient of 0.12, and that for mTDinferior included only CH with the coefficient of 0.089. There was no variable selected in the optimal model for the mTDsuperior progression rate.

CONCLUSION

CH is a useful measure in the management of glaucoma after trabeculectomy.

Icare Home Tonometer: A Review of Characteristics and Clinical Utility

The Icare HOME (TA022, Icare Oy, Vanda, Finland) is rebound tonometer recently approved by the US Food and Drug Administration in March 2017 designed for self-measurement of intraocular pressure (IOP). IOP remains a major modifiable risk factor for glaucoma progression; however, IOP measurements typically occur through single office measurements on Goldmann applanation tonometry (GAT) and do not always reveal the complete picture of patient’s IOP patterns and daily fluctuations, which are important for accurate diagnosis and evaluation. Numerous studies have now compared the efficacy of the Icare HOME to that of GAT. The objective of this article is to review the existing literature surrounding the Icare HOME tonometer and its efficacy as a self-tonometer in comparison to GAT. The available literature has shown promising results in its accuracy of measuring IOP but suggests cautious usage in patients with central corneal thicknesses or IOP ranges that are outside of a certain range. This article will also provide details and example cases for when the Icare HOME may be most clinically useful.

Evaluation of biomechanically corrected intraocular pressure using Corvis ST and comparison of the Corvis ST, noncontact tonometer, and Goldmann applanation tonometer in patients with glaucoma

Purpose

The aim of the study was to investigate the effects of various anatomical structures on intraocular pressure (IOP) measurements obtained by the Corneal Visualization Scheimpflug Technology (Corvis ST), Goldmann applanation tonometer (GAT), and noncontact tonometer (NCT), as well as to assess the interchangeability among the four types of IOP measurement: IOP-GAT, IOP-NCT, IOP-Corvis, and biomechanically corrected IOP (bIOP-Corvis), with a particular focus on bIOP-Corvis.

Materials and methods

We included 71 patients with primary open-angle glaucoma and assessed their IOP measurements obtained with the GAT, NCT, and Corvis ST using a repeated measures ANOVA, a paired t-test with Bonferroni correction, stepwise multiple regression analyses and Bland–Altman plots.

Results

IOP-GAT showed the highest values (13.5 ± 2.1 mmHg [mean ± standard deviation]), followed by IOP-NCT (13.2 ± 2.7 mmHg), IOP-Corvis (10.6 ± 2.8 mmHg), and bIOP-Corvis (10.0 ± 2.3 mmHg). With exceptions of bIOP-Corvis and IOP-GAT, all IOP variations were explained by regression coefficients involving the central corneal thickness. Bland–Altman plots showed a mean difference between IOP-GAT and the other IOP measurements (IOP-Corvis, bIOP-Corvis, and IOP-NCT), which were -2.90, -3.48, and -0.29 mmHg, respectively. The widths of the 95% limits of agreement between all pairs of IOP measurements were greater than 3 mmHg.

Conclusion

IOP values obtained with the Corvis ST, NCT, and GAT were not interchangeable. The bIOP-Corvis measurement corrected for the ocular structure.

Results of First In Vivo Trial of an Acoustic Self-Tonometer

Purpose

Glaucoma is the world's most common cause of irreversible blindness, which makes early diagnosis, with the goal of preserving vision, essential. The current medical intervention is to reduce intraocular pressure (IOP) to slow down progression of the disease. The main goal of this study was to test a novel handheld acoustic self-tonometer on humans.

Methods

A sound pressure pulse generated by a loudspeaker causes the eye to vibrate. A pressure chamber is placed on the human orbit to form a coupled system comprised of the patient's eye, the enclosed air, and the loudspeaker. A displacement sensor in front of the loudspeaker membrane allows the dynamic behavior of the entire system to be detected.

Results

For this clinical trial series, a prototype of the acoustic self-tonometer principle was applied. The resulting membrane oscillation data showed sensitivity of patient IOP, but direct allocation of the measured damping and frequency to the IOP was not significant. For this reason, an artificial neural network was used to find relationships among the subjects’ biometric eye parameters in combination with the self-tonometer data for the IOP reference. An expanded measurement uncertainty (k_p = 2) equal to 6.53 mm Hg was determined for the self-tonometer in a Bland–Altman analysis using Goldmann applanation tonometer reference measurements.

Conclusions

The usability and success rate of producing valid measurement values with the device during self-measurements by test subjects was nearly 92%. The cross-sensitivities observed require compensation in a possible redesign phase to reduce the measurement uncertainty by at least 25% to the maximum of 5 mm Hg required to seek medical device approval.

Translational Relevance

Building on successful laboratory experiments with pig eyes, this article reports the results of testing the acoustic tonometer on humans.

Effectiveness of 4 tonometers in measuring IOP after femtosecond laser-assisted LASIK, SMILE, and transepithelial photorefractive keratectomy

PURPOSE

To test the performance of 4 tonometers in estimating intraocular pressure (IOP) after 3 forms of refractive surgery.

SETTING

Eye Hospital, Wenzhou Medical University, China.

DESIGN

Prospective case series.

METHODS

Patients matched for preoperative age, corneal thickness, and myopic correction enrolled for femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK), small-incision lenticule extraction (SMILE), or transepithelial photorefractive keratectomy (tPRK) were included in the study. For each patient, 4 measurements of IOP were obtained preoperatively and 3 months postoperatively, using the Goldmann applanation tonometer (GAT-IOP), the Dynamic Contour Tonometer (DCT-IOP), corneal-compensated IOP (IOPcc) from the Ocular Response Analyzer, and biomechanically corrected IOP (bIOP) from the Corvis ST. Overall corneal stiffness was also estimated based on the stiffness parameter (SP-A1) provided by the Corvis ST.

RESULTS

The study included 144 eyes of 144 patients. Among the 3 procedures, the smallest variances between preoperative and postoperative IOP estimates and SP-A1 values were observed with the tPRK, followed by SMILE and FS-LASIK. In the tPRK group, no significant differences were observed in both bIOP (-0.18 ± 1.63 mm Hg) and DCT-IOP (-.64 ± 2.34 mm Hg), whereas they were larger and significant in GAT-IOP (-1.78 ± 2.29 mm Hg) and IOPcc (-2.77 ± 1.84 mm Hg). In FS-LASIK and SMILE groups, although there were similar significant reductions in IOP postoperatively, these reductions were still lower in bIOP and DCT-IOP than those in GAT-IOP and IOPcc.

CONCLUSIONS

The bIOP and DCT-IOP were the least affected IOP estimates between the 3 refractive surgery procedures considered. It was evident that tPRK produced significantly smaller reductions in IOP readings than did FS-LASIK and SMILE.

Evaluation of Biomechanically Corrected Intraocular Pressure Measurements in Keratoconus and Forme Fruste Keratoconus

INTRODUCTION

Although biomechanically corrected intraocular pressure (bIOP) is available, the effectiveness of intraocular pressure (IOP) correction in keratoconus and forme fruste keratoconus (FFK) eyes has not been investigated.

OBJECTIVE

Evaluation of bIOP measurements in eyes with keratoconus and FFK.

METHODS

Forty-two eyes in 21 patients with keratoconus in one eye and FFK in the fellow eye were examined (KC/FFK group; mean age 24.62 ± 8.6 years; 16 males and 5 females). The control group consisted of 62 eyes in 31 unaffected subjects (mean age 26.26 ± 3.64 years; 15 males and 16 females). The bIOP was determined using a Scheimpflug-based tonometer (Corvis Scheimpflug Technology [Corvis ST®]) after measuring the IOP with a conventional non-contact tonometer (NIOP). The agreement between NIOP and bIOP values was examined using the Bland-Altman plot. The difference between NIOP and bIOP (bIOP correction amount) was compared between keratoconus and FFK eyes.

RESULTS

In the control group, there were no significant differences between right and left eyes in both NIOP and bIOP values (p = 0.975 and p = 0.224, respectively). In the KC/FFK group, NIOP values were significantly lower in the keratoconus eyes (9.93 ± 1.96 mm Hg) than in the FFK eyes (12.23 ± 3.03 mm Hg; p = 0.0003). There was no significant difference in bIOP values between the right and left eyes of the KC/FFK group (p = 0.168). The bIOP correction amount was significantly increased in keratoconus eyes (3.58 ± 2.12 mm Hg) compared to in FFK eyes (1.80 ± 3.32 mm Hg; p = 0.011).

CONCLUSIONS

For eyes with keratoconus and FFK, the bIOP method is effective to adjust IOP measurements based on corneal biomechanical properties.

Prevalence of Unknown Ocular Hypertension, Glaucoma Suspects, and Glaucoma in Patients Seen in an Ophthalmology Center in France

INTRODUCTION

The rate of unknown glaucoma is around 50% in industrialized countries. The purpose of our study was to estimate the prevalence of unknown cases of ocular hypertension, glaucoma suspects, and glaucoma in patients consulting for refractive disorders in France.

METHODS

A retrospective study in the Point Vision ophthalmology center was led in Toulouse, France. All participants consulting for refractive disorders between June 2015 and June 2017 in the ophthalmology center were included. The cases were identified by the assessment of intraocular pressure, optic nerve head structure, and visual field. Ocular hypertension was defined as an intraocular pressure >21 mm Hg. Glaucoma was defined as the association of a glaucomatous papilla and two successive pathological visual fields. Glaucoma suspect was defined as the association of a glaucomatous papilla without visual field defect. The primary endpoint was the prevalence of unknown ocular hypertension, glaucoma suspects, and glaucoma in patients seen in an ophthalmology center.

RESULTS

A total of 66,068 patients (mean age = 37 years) consulted for a refraction visual assessment during the study period. Among them, 234 had a visual field and a retinal nerve fiber layer assessment for ocular hypertension and/or suspicious papilla. The prevalence of unknown cases of ocular hypertension, glaucoma suspect, and glaucoma was 2.6, 0.8, and 0.5 per 1,000 consultants, respectively. Median age at diagnosis of ocular hypertension, glaucoma suspect, and glaucoma was 52, 53, and 65 years, respectively.

CONCLUSION

The present study highlights the importance of glaucoma screening in people over 40 years old with the measurement of intraocular pressure and an optic nerve head assessment.

Intraocular Pressure Calculation in Myopic Patients After Laser-Assisted In Situ Keratomileusis

Background

Corneal refractive surgery is widely used worldwide. Myopia is the most common reason for laser-assisted corneal refractive surgery (LASIK) and one of the risk factors for glaucoma. Intraocular pressure (IOP) measurement becomes variable postoperatively as the results are affected by the decrease in corneal thickness and biomechanics. This prospective clinical case study attempted to establish a simple correction formula for the calculation of IOP in post-LASIK myopic patients.

Methods

This study included 300 eyes of 150 patients with myopia and myopic astigmatism as a refractive error who underwent LASIK. IOP was measured preoperatively and 6 months postoperatively. Preoperative and postoperative corneal thickness as well as ablation depth were measured. Statistical analysis was performed to detect the relationship between ablation depth and change in IOP. An attempt was made to construct a correction formula for the calculation of post-LASIK IOP.

Results

The age of the patients ranged between 18 and 50 (mean ± SD 34.78±8.8) years. The spherical equivalent of refractive error ranged between -1.5 and -10 diopters. The mean IOP decreased significantly from 15.72±2.37 mmHg preoperatively to 11.71±2.24 mmHg postoperatively, with a mean difference of 4±1.75 mmHg (p˂0.001). A positive correlation was detected between corneal thickness and IOP difference among patients both preoperatively and postoperatively (p˂0.001). A positive correlation was identified between ablation depth and IOP change (p˂0.001). The correction formula for IOP was established: Real IOP=4+0.7(preoperative IOP)-0.3(ablation depth).

Conclusion

IOP measurements change after corneal refractive surgery with LASIK. A corrected formula may be a good option for the proper calculation of post-LASIK IOP.

Acute effects of posture on intraocular pressure

Many experiments have documented the response of intraocular pressure (IOP) to postural change. External forces caused by gravitational orientation change produce a dynamic response that is encountered every day during normal activities. Tilting the body at a small downward angle is also relevant to studying the effects of hypogravity (spaceflight), including ocular changes. We examined data from 36 independent datasets from 30 articles on IOP response to postural change, representing a total population of 821 subjects (≥1173 eyes) with widely varying initial and final postures. We confirmed that IOP was well predicted by a simple quantity, namely the hydrostatic pressure at the level of the eye, although the dependence was complex (nonlinear). Our results show that posturally induced IOP change can be explained by hydrostatic forcing plus an autoregulatory contribution that is dependent on hydrostatic effects. This study represents data from thousands of IOP measurements and provides insight for future studies that consider postural change in relation to ocular physiology, intraocular pressure, ocular blood flow and aqueous humor dynamics.

Conceptual design considerations for a wireless intraocular pressure sensor system for effective glaucoma management

As a leading form of preventable visual impairment, it is imperative to assess glaucoma treatment as a function of intraocular pressure (IOP). IOP can spike throughout the day. This necessitates a device that can (1) monitor IOP outside of clinical visits by providing a memory when IOP exceeds a set threshold indicating the possibility for glaucomatous damage to occur; and (2) accurately assess IOP. Both requirements point ultimately towards the development of an implantable device. The Wireless Intraocular Pressure Sensor System (WIPSS) devised by our team uses optical technologies and may assist an overseeing clinician with assessing glaucoma treatment efficacy and avoiding irreversible glaucomatous visual field loss downstream.