Comparison of ICare tonometer with Goldmann applanation tonometer in glaucoma patients

Intraocular Pressure Measurements With the Tono-Vera: A New Handheld Rebound Tonometer

PRCIS

In a cross-sectional study comparing the novel Tono-Vera handheld rebound tonometer with the Ocular Response Analyzer, a strong agreement was found between the intraocular pressure measurements of the 2 devices.

PURPOSE

To compare intraocular pressure (IOP) measurements obtained by the new Tono-Vera (Reichert Technologies), a novel handheld rebound tonometer with a proprietary camera-based positioning system, with those from the Ocular Response Analyzer (ORA, Reichert Technologies) non-contact tonometer.

PATIENTS

Fifty-four eyes of normal individuals and open angle glaucoma subjects.

METHODS

All subjects had at least 6 reliable measurements with the Tono-Vera and 3 with the ORA, acquired by the same technician in the same visit. The sample was randomly split into calibration and validation samples. An ordinary least squares linear regression model generated a calibration formula for Tono-Vera readings using ORA's Goldmann-correlated IOP (IOPg) as a target. Bland-Altman plots evaluated the agreement between Tono-Vera calibrated IOP (IOPtv) and ORA IOPg in the validation sample.

MAIN OUTCOME MEASURES

Agreement between IOPtv and IOPg measurements.

RESULTS

Fifty glaucoma and 4 normal eyes were included, mean age 68.3 ± 9.4 years, mean central corneal thickness 535.0 ± 39.6 μm. In the validation sample, mean IOPtv was 14.6 ± 5.2 mmHg (range, 7.4-28.5 mmHg) versus 15.0 ± 5.3 mmHg (range, 6.6-28.6 mmHg) for ORA IOPg ( R ² = 0.782). Bland-Altman plots showed a mean difference of -0.4 ± 2.5 mmHg (95% limits of agreement: -5.4 to 4.5 mmHg). 58.6%, 79.3%, and 96.5% of IOPtv measurements fell within ± 2, ± 3, and ± 5 mmHg of ORA measurements. No fixed or proportional biases were observed ( P = 0.620).

CONCLUSION

There was a strong correlation and agreement in IOP measurements between calibrated Tono-Vera IOP and ORA IOPg.

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.

The relationship between intraocular pressure and glaucoma: An evolving concept

Intraocular pressure (IOP) is the most important modifiable risk factor for glaucoma and fluctuates considerably within patients over short and long time periods. Our field's understanding of IOP has evolved considerably in recent years, driven by tonometric technologies with increasing accuracy, reproducibility, and temporal resolution that have refined our knowledge regarding the relationship between IOP and glaucoma risk and pathogenesis. The goal of this article is to review the published literature pertinent to the following points: 1) the factors that determine IOP in physiologic and pathologic states; 2) technologies for measuring IOP; 3) scientific and clinical rationale for measuring diverse IOP metrics in patients with glaucoma; 4) the impact and shortcomings of current standard-of-care IOP monitoring approaches; 5) recommendations for approaches to IOP monitoring that could improve patient outcomes; and 6) research questions that must be answered to improve our understanding of how IOP contributes to disease progression. Retrospective and prospective data, including that from landmark clinical trials, document greater IOP fluctuations in glaucomatous than healthy eyes, tendencies for maximal daily IOP to occur outside of office hours, and, in addition to mean and maximal IOP, an association between IOP fluctuation and glaucoma progression that is independent of mean in-office IOP. Ambulatory IOP monitoring, measuring IOP outside of office hours and at different times of day and night, provides clinicians with discrete data that could improve patient outcomes. Eye care clinicians treating glaucoma based on isolated in-office IOP measurements may make treatment decisions without fully capturing the entire IOP profile of an individual. Data linking home blood pressure monitors and home glucose sensors to dramatically improved outcomes for patients with systemic hypertension and diabetes and will be reviewed as they pertain to the question of whether ambulatory tonometry is positioned to do the same for glaucoma management. Prospective randomized controlled studies are warranted to determine whether remote tonometry-based glaucoma management might reduce vision loss and improve patient outcomes.

A Comparative Analysis of Intraocular Pressure Measurement Accuracy With Reused iCare Probes

PURPOSE

To assess the accuracy of reused iCare probes after disinfection with 70% isopropyl alcohol and ethylene oxide gas compared to new iCare probes and Goldmann applanation tonometry (GAT).

DESIGN

Prospective comparative analysis.

PARTICIPANTS

A total of 118 eyes from 59 patients recruited from the Aravind Eye Hospital glaucoma clinic in Tirupati, South India.

METHODS

Intraocular pressure (IOP) was measured on each eye using a new iCare tonometer probe, an iCare probe previously used and disinfected 1 time prior (once used probe) and 5 times prior (multiply used probe), as well as with GAT. Probes were disinfected after each use with 70% isopropyl alcohol swabs and ethylene oxide sterilization.

MAIN OUTCOME MEASURES

Agreement demonstrated with intraclass correlation coefficients (ICCs), mean difference in IOP values with limits of agreement, and Bland-Altman plots among IOP measurement approaches.

RESULTS

Compared to new iCare probes, both once used probes (ICC = 0.989, 95% confidence interval [CI] 0.985-0.993) and multiply used probes (ICC = 0.989, 95% CI 0.984-0.992) showed excellent agreement, and the mean difference in IOP was minimal for both once used probes (0.70 mmHg, 95% CI 0.29-1.11) and multiply used probes (0.75 mmHg, 95% CI 0.66-0.82) compared to new probes. Bland-Altman plots demonstrated minimal differences between new and reused probes across the spectrum of IOP. When comparing multiply used probes to once used probes, there was a high level of agreement (0.993) (95% CI 0.990-0.995) and negligible mean IOP difference 0.04 mmHg (95% CI 0.32-0.40). Additionally, ICC values for new probes (0.966, 95% CI 0.951-0.976), once used probes (0.958, 95% CI 0.940-0.971), and multiply used probes (0.957, 95% CI 0.938-0.970) compared to GAT were similar and all showed excellent agreement. Both new and reused iCare probes underestimated IOP by 2 to 3 mmHg compared to GAT.

CONCLUSIONS

In this prospective comparative analysis, we found that reusing iCare probes up to 5 times does not compromise the accuracy of IOP measurements when disinfected with 70% isopropyl alcohol swabs and ethylene oxide. Reusing iCare probes has the potential to transform care by reducing cost, decreasing environmental waste, and allowing for glaucoma screening camps and increased glaucoma monitoring in low resource settings leading to earlier identification and treatment of glaucoma.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

A comparison of iCare and Goldmann applanation tonometry measurements during the COVID-19 pandemic: a retrospective study

PURPOSE

To evaluate factors associated with differences in intraocular pressure (IOP) readings between iCare and Goldmann applanation tonometry (GAT) in established glaucoma patients.

METHODS

This retrospective comparative study included clinical data of 350 eyes from 350 established glaucoma patients who had iCare and GAT IOP measured by an ophthalmic technician and a glaucoma specialist, respectively. The main outcome measure was the difference in IOP measurements of the right eyes with iCare and GAT.

RESULTS

The intraclass correlation coefficient (ICC) between GAT and iCare was 0.90. The mean IOP difference between tonometers was - 0.18 ± 2.89 mmHg. Bland-Altman plots indicated a 95% limit of agreement of - 5.8 to 5.5 mmHg. Central corneal thickness (CCT) and age were significantly correlated with the difference in IOPs of the iCare and GAT. GAT-IOP and age were significantly associated with the absolute difference in measured IOP of the two tonometers. The difference in measurements was not significantly associated with prior glaucoma surgery, average global index of optical coherence tomography, axial length, technician years of experience and certification, and IOP range.

CONCLUSION

Although there is good agreement between the iCare and GAT mean values, these devices are not interchangeable in glaucoma patients due to the wide range of the limit of agreement.

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.

The effects of traditional Muslim prayer positions on intraocular pressure in subjects with and without glaucoma

PURPOSE

To compare the magnitude and duration of intraocular pressure (IOP) increase during the two principal Islamic prayer positions, Rukū (standing while bowing forward at a 90-degree angle), and Sujud (kneeling with the forehead touching the ground) in healthy subjects and patients with primary open-angle glaucoma (POAG).

METHODS

Prospective, observational case series. Ninety-five eyes of 47 patients (27 with POAG and 68 without POAG) were included. Eligible candidates underwent IOP measurements in the sitting position and in two prayer positions using the Goldmann applanation tonometer and the Icare-Pro tonometer. IOP was measured at set intervals until it returned to baseline.

RESULTS

Mean IOP increased from a sitting baseline value of 16.1  ±  2.9 mmHg (8.6-26) to 19.3  ±  4.2 mmHg (10.2-32.3) following 30 s of Rukū (p ≤ 0.0001) and from 16.1  ±  0.4 mmHg to 22.2  ±  3.1 mmHg (14.9-37) following Sujud (p ≤ 0.0001). IOP increased similarly in the POAG and non-POAG groups in both positions. Twenty-six eyes (27%) failed to normalize within 2mmHg of baseline, but all returned to baseline after another five minutes.

CONCLUSIONS

Performing traditional Muslim prayer positions increases IOP significantly. The increase did not resolve immediately in approximately a quarter of individuals. These findings may have a considerable impact on Muslim patients with glaucoma.

Assessing Agreement and Variability Among Alternative Devices for Intraocular Pressure Measurement: A Comparative Study

Purpose

Intraocular pressure (IOP) measurement is critical in diagnosing and managing eye conditions. This study aims to assess the comparability of three alternative devices for measuring IOP: Noncontact tonometer, Icare rebound tonometer, and Tono-Pen.

Patients and Methods

A cross-sectional study included 172 adult participants (87 males and 85 females) who underwent IOP and central corneal thickness (CCT) assessments. IOP was measured using Noncontact (Canon TX-20), Icare (Icare TA01i), and Tono-Pen (Tonopen XL). CCT was measured with the built-in pachymetry of the Noncontact tonometer. Correlation coefficients and Bland-Altman analyses were conducted to assess the relationships and agreements between these tonometers. Participants were grouped based on IOP and CCT levels. The mean of the standard deviation of the three tonometer results was calculated to evaluate measurement result variability. One-way analysis of variance was conducted for comparing between the groups.

Results

IOP measurements among the three devices were not significantly different, indicating their comparability. Correlation analysis revealed strong correlations between the tonometers. Bland-Altman analysis showed good agreement, with the Icare rebound tonometer and Tono-Pen exhibiting narrower limits of agreement. Furthermore, IOP levels influenced measurement result variability, with higher IOP levels associated with greater variance.

Conclusion

This study demonstrates that the alternative devices examined can provide reliable IOP measurements. It highlights the potential of these alternative devices for IOP measurement. These findings have implications for clinical practice, offering practitioners additional tools for accurate IOP assessment.

Comparison of intraocular pressure measured by iCare tonometers and Goldmann applanation tonometer

OBJECTIVE

To evaluate the relationship between the Goldmann applanation tonometer (GAT) and the iCare PRO and iCare IC200 tonometers in measuring intraocular pressure (IOP) in adult eyes with a diagnosis of glaucoma or glaucoma suspect.

PARTICIPANTS AND METHODS

One hundred and one eyes from 101 participants diagnosed with glaucoma or glaucoma suspect were evaluated in this study. IOP was measured by iCare PRO and iCare IC200 tonometers in a randomized sequence followed by IOP measurements by the GAT tonometer and then central corneal thickness measurements. After the IOP measurements, participants scored their comfort level using a visual analog scale with each tonometer. Intraclass correlation coefficient (ICC) and Bland-Altman analysis were used to investigate the agreement among tonometers. SPSS and Microsoft Excel programs were used for statistical analysis.

RESULTS

Overall, there was good agreement among the 3 tonometers used in this study. The ICC for the iCare PRO and the iCare IC200 was 0.95 (p < 0.001), and the ICC for the iCare PRO and the GAT and the iCare IC200 and the GAT was >0.80 (p < 0.001). However, both iCare tonometers underestimated IOP by approximately 2 mm Hg compared with the GAT. Furthermore, 84% of iCare readings fall within ±5 mm Hg of GAT measurements. Neither body mass index nor central corneal thickness affected the IOP agreement among the tonometers. Participant response on visual analog scale rated IOP measurements by iCare tonometers to be more comfortable than the GAT.

CONCLUSION

Our results demonstrated a good agreement between iCare tonometers and GAT; but iCare tonometers underestimated IOP compared to the GAT.

Performance of home-based self-tonometry (iCare HOME (TA022)) for measuring intraocular pressure among healthy and glaucoma patients

Introduction: The purpose of this study was to compare iCare HOME (TA022) with Goldmann applanation tonometer and to evaluate the self-tonometry measurements among the Indian population. Methods: Eligible patients underwent iCare HOME training through guided demonstration (verbal, pictorial, video) and practised self-tonometry measures using iCare HOME. Certification for independent iCare HOME measure was provided if first iCare HOME intraocular pressure (IOP) measurement fell within ± 5 mmHg of Goldmann applanation tonometer (GAT) measurement which was measured by the trained clinician (principal investigator). Certified participants underwent simulated home self-tonometry measurements using iCare HOME, and agreement with GAT IOP measurements was assessed. Results: Seven of 83 participants (8.43%) failed to complete the study due to difficulty in performing the task, leading to non-certification. Patients who could use the iCare HOME had a mean age of 53 ± 15.55years (53% males; 46% females). Only one in 12 subjects did not qualify to use iCare HOME. The overall mean difference between iCare HOME and GAT was 0.83 mmHg (95%, 3.92 and -2.25). At various pressure ranges, 7-16 mmHg, 17-23 mmHg and >23 mmHg, the mean difference between iCare HOME and GAT was 1.22 mmHg (95%, 4.32 and -1.86), 0.77 mmHg (95%,3.69 and -2.19), -0.11 mmHg (95%, 2.52 and -2.74) respectively. The intra-class correlation coefficient of the iCare HOME device was 0.997(95% CI,0.995-0.998). Conclusions: Patients were able to perform self- tonometry using iCare HOME with good reliability and safety. iCare HOME can be used to address the issue of difficulty in acquiring frequent and diurnal IOP measurements by patients doing self-tonometry from home.

Lateralized Raise in Intraocular Pressure During Electroconvulsive Therapy: A Tonometry Pilot Study

Right unilateral ECT causes an increase in eye pressure that is partially lateralized, higher on the right side.

Objective

The aim of this study was to evaluate intraocular pressure (IOP) changes during and after electroconvulsive therapy.

Methods

In 20 patients, IOP was measured using a handheld iCare tonometer before, during, and up to 15 minutes after the seizure. Electrode placement was either right unilateral (RUL) or bilateral (BL). Statistical analyses were done at baseline, during, and 15 minutes after the seizure.

Results

In the RUL group (n = 14), the IOP in the left eye increased from 14.8 mm Hg before the seizure to 27.8 mm Hg during the seizure (P = 0.0001) and decreased to 14.0 mm Hg after the seizure (P = 0.0002). The IOP in the right eye increased from 15.4 mm Hg before the seizure to 34.4 mm Hg during the seizure (P = 0.0001) and decreased to 16.0 mm Hg after the seizure (P = 0.0002).

In the BL group (n = 6), the IOP in the left eye increased from 13.0 mm Hg before the seizure to 26.3 mm Hg during the seizure (P = 0.1250) and decreased to 14.5 mm Hg after the seizure (P = 0.250). In the right eye, the IOP increased from 13.3 mm Hg before the seizure to 28.4 mm Hg during the seizure (P = 0.1250) and decreased to 13.7 mm Hg after the seizure (P = 0.25).

When the results were compared between the 2 electrode placements, the difference in IOP between the right and left eye was higher in the RUL group during (RUL 6.7 mm Hg vs BL 2.0 mm Hg, P = 0.0231) and after (RUL 2.1 mm Hg vs BL −0.8 mm Hg, P = 0.0492) the seizure.

Conclusions

RUL stimulation with electroconvulsive therapy causes a rise in IOP that is partially lateralized, ipsilateral to the side of stimulation.

Comparison of Icare HOME and non-contact tonometer in intraocular pressure measurement in the early stage after ICL V4c implantation

Purpose

To investigate the characteristics of intraocular pressure (IOP) measurements using the Icare HOME rebound tonometer (RBT) and non-contact tonometer (NCT) during the early stage after implantable collamer lens (ICL) V4c implantation, and to assess the agreement between the two methods.

Methods

This prospective case series study included 104 eyes of 53 patients (mean age 28.77  ±  5.34 years), who underwent ICL V4c implantation. IOP was measured preoperatively, and at 0.5, 1, 2, 4, and 24 h postoperatively by Icare HOME and NCT, respectively.

Results

All surgeries were uneventful. IOP measurements by Icare and NCT preoperatively were 14.03  ±  2.90 mmHg and 14.09  ±  2.87 mmHg, respectively.The corresponding values were 12.56  ±  8.09 mmHg and 14.12  ±  6.52 mmHg (P > 0.05) at postoperative 0.5 h, 19.21  ±  8.74 mmHg and 19.60  ±  7.66 mmHg at postoperative 1 h (P > 0.05), 21.21  ±  8.10 mmHg and 20.31  ±  6.93 mmHg at postoperative 2 h (P > 0.05), 16.11  ±  5.89 mmHg and 17.04  ±  4.84 mmHg at postoperative 4 h (P > 0.05), and 14.04  ±  3.88 mmHg and 14.78  ±  2.80 mmHg at postoperative 24 h, respectively (P > 0.05). There was good agreement based on intraclass correlation coefficients (ICCs) between NCT and Icare HOME (all ICCs > 0.6 at different time points [range, 0.6986–0.956]). The Bland-Altman plot showed a mean percentage of over 95.81% of the points falling within the limits of agreement. There was a significant difference in the low IOP measurements (<10 mmHg) between Icare HOME and NCT (7.28  ±  2.55 vs. 10.65  ±  2.48, P < 0.001).

Conclusion

Icare HOME can be used for IOP measurement after ICL V4c implantation and demonstrated good agreement with NCT, except in cases with low intraocular pressure (<10 mmHg).

How should we measure intraocular pressure in the era of coronavirus disease 2019? Balancing infectious risk, cleaning requirements, and accuracy

PURPOSE OF REVIEW

Accurate and precise measurement of intraocular pressure (IOP) is a vitally important component of the ophthalmic examination. There are multiple methods of tonometry, each of which has considerations in light of the ongoing severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic. This review discusses these considerations and compares various tonometer methods with the gold standard of Goldmann applanation tonometry (GAT).

RECENT FINDINGS

The SARS-CoV-2 virus may spread via droplets, microaerosols, or direct contact in the ophthalmology clinic. Tonometry poses a high risk of contamination. The accuracy and reliability of various methods of tonometry with single-use disposable equipment has been compared with Goldmann applanation tonometry.

SUMMARY

Goldmann applanation tonometry with disposable applanation tips, Tono-pen, and iCare employ single use tips to decrease the risk of cross-contamination of infectious agents. Review of the literature demonstrates good correlation between these devices and GAT, although the published level of agreement between devices varies.

Effect of Body Position on Intraocular Pressure Measured by Rebound Tonometer in Healthy Children

Objectives:

To evaluate the effect of body position on intraocular pressure (IOP) measurement in the pediatric age group.

Materials and Methods:

Children whose general condition was healthy and ophthalmic examination was within normal limits were included. Forty-nine eyes of 49 pediatric patients were included in the study. IOP was measured with an ICARE rebound tonometer (ICARE PRO; ICARE, Helsinki, Finland) while patients were in standing, sitting, and supine positions. Differences between the consecutive measurements were compared statistically.

Results:

Twenty-two of the 49 patients were female, 27 were male. The mean age was 9.61±2.66 (5-15) years. Mean IOP values in the standing, sitting, and supine positions were 18.81±2.97 (11.6-26.2) mmHg, 18.88±3.44, (12-28.2) mmHg, and 19.01±2.8 (13.5-25.9) mmHg, respectively. There were no statistically significant differences in pairwise comparisons of the measurements taken in the different positions (p=0.846, p=0.751, p=0.606). There was a statistically significant correlation between corneal thickness and intraocular pressure values in all measurements (p=0.001, r=0.516).

Conclusion:

IOP values measured with the ICARE rebound tonometer in healthy children are not affected by body position.

Agreement between rebound (Icare ic200) and applanation tonometry (Perkins) in patients with primary congenital glaucoma

PURPOSE

To examine agreement between intraocular pressure (IOP) measurements made using the rebound tonometer Icare ic200 (RT200) and the Perkins handheld applanation tonometer (PAT) in patients with primary congenital glaucoma (PCG). The impacts of several covariables on measurements using the two devices were also assessed.

MATERIALS AND METHODS

Intraocular pressure measurements were made in a single session in 86 eyes of 86 patients with PCG (46 under anaesthesia, 40 in the office). The order was RT200 then PAT. The variables age, central corneal thickness (CCT), corneal state and anaesthesia were recorded in each patient. Data were compared by determining interclass correlation coefficients (ICC) for each tonometer and representing the differences detected as Bland-Altman plots. Effects of covariables were assessed through univariate and multivariate regression.

RESULTS

Mean IOP difference between tonometers (RT200 minus PAT) was 1.26 mmHg (95%: 0.22-2.31). Absolute agreement (ICC) was 0.73 (95% CI: 0.62-0.82). Lower and upper limits of agreement (95%) were -8.06 mmHg (95% CI: -9.87 to -6.25) and 10.59 mmHg (95% CI: 8.77-12.40), respectively. The tonometers showed systematic differences (a = -4.63 mmHg; 95% CI: -9.11 to -1.44) and proportional differences; for each mmHg increase in PAT-IOP, the RT200 reading increased by 1.28 mmHg (b = 1.28; 95% CI: 1.12-1.53). None of the variables tested as predictors were able to explain differences between the tonometers.

CONCLUSIONS

Despite the good overall agreement between both tonometers, caution should be taken in high values of IOP, considering the interchangeability of its readings as systematic and proportional differences appear to exist between both methods.

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.

A Review to Populate A Proposed Cost-Effectiveness Analysis of Glaucoma Screening in Sub-Saharan Africa

To populate a proposed cost-effectiveness analysis of glaucoma screening in Sub-Saharan Africa (SSA).A complete search was conducted on PubMed, Medline and African Journals Online (AJOL) to obtain relevant published articles, which were included in this review. All relevant articles on prevalence of glaucoma in SSA and among other African-derived populations, severity of glaucoma, cost of diagnosis and management, clinical effectiveness of glaucoma screening and treatment and the different glaucoma screening strategies in SSA were reviewed.Population screening interventions for glaucoma may be considered as follows: standalone screening for glaucoma, screening for glaucoma during cataract outreach, and screening incorporated with diabetic retinopathy image review using tele-ophthalmology. Our review suggests that cost of glaucoma treatment is relatively low with cost of medical treatment ranging from USD 273 to USD 480 per year/patient and surgical treatment cost of USD 283 per patient as with other developing countries. Compliance with medication is moderate to good in about 50% of glaucoma patients. Prevalence of glaucoma is much higher in SSA and almost 50% of glaucoma patients are blind in at least one eye at presentation in clinics (without outreach screening). Our review suggests a moderate sensitivity and specificity in identifying glaucoma with basic equipment (direct ophthalmoscope, contact tonometer and frequency doubling technology) during outreach screening although about a third or fewer take up glaucoma services in clinics.Our review provides the necessary information to conduct a cost-effective analysis of glaucoma screening in SSA using the decision Markov model.

Postoperative Changes in Central Corneal Thickness and Intraocular Pressure in a Prospective Cohort of Congenital Cataract Patients

PURPOSE

To evaluate changes in central corneal thickness (CCT) and intraocular pressure (IOP) in children after surgery for congenital cataracts and to investigate the association between CCT and IOP.

METHODS

For this prospective observational cohort study, we recruited patients undergoing surgery for unilateral or bilateral congenital cataracts. CCT and IOP were measured before surgery and 1, 3, 6, 12, and 24 months after surgery.

RESULTS

Seventy-six children (152 eyes) were enrolled; 33 eyes were unaffected by cataracts, 77 were aphakic, and 42 were pseudophakic. In aphakic eyes, mean CCT increased by 31.14 ± 44.32 μm at 12 months postoperation and 33.09 ± 35.42 μm at 24 months postoperation; this increase was significantly higher than that in pseudophakic eyes 12 months after surgery (8.36 ± 19.91 μm; P < 0.001) and 24 months after surgery (0.31 ± 14.19 μm; P = 0.024). However, no significant differences in IOP were found between the different phakic states at 12 and 24 months postoperation (P = 0.672 and P = 0.080, respectively). There were also no significant differences in CCT and IOP before and after surgery in the unaffected eyes.

CONCLUSIONS

Mean CCT peaked at 12 months, and the mean IOP remained normal in both the aphakic and pseudophakic eyes during this study. CCT and IOP were positively correlated, regardless of the phakic status or age, a relationship which suggests that both parameters should be monitored closely in postsurgical patients for up to 12 months and in this time, may impact the ability to diagnose glaucoma.

The Effect of Ocular Perfusion Pressure on Retinal Thickness in Young People with Presumed Systemic Hypotension

Low ocular perfusion pressure (OPP) may increase the risk of optic neuropathy. This study investigated the effects of OPP on the ganglion cell complex (GCC) and optic nerve head-retinal nerve fibre layer (ONH-RNFL) thickness in presumed systemic hypotensives (PSH). Fifteen participants with PSH and 14 controls underwent automated sphygmomanometry and Icare tonometry to calculate OPP: mean OPP (MOPP), systolic OPP (SOPP), and diastolic OPP (DOPP). ONH-RNFL and macula GCC thickness were evaluated using the Optovue iVue optical coherence tomographer. Statistical analysis comprised independent t-tests, the Mann-Whitney U test and binary logistic regression analysis. There was no significant difference when comparing ONH-RNFL and macula GCC thickness between both groups. Increased MOPP (OR = 0.51; 95% CI: 0.27-0.97; p = 0.039) and SOPP (OR = 0.79; 95% CI: 0.64-0.98; p = 0.035) were significantly associated with a decreased risk of reductions in GCC total thickness. Increased SOPP (OR = 0.11; 95% CI: 0.01-0.89; p = 0.027) was significantly associated with a decreased risk of reductions in the average ONH-RNFL thickness. The study found no significant retinal thickness changes in PSH's, in comparison to the controls. The study established that, by increasing MOPP and SOPP, there was a decreased risk of reductions in the total GCC thickness and average ONH-RNFL thickness. Higher SOPP may decrease the possibility of retinal thinning of the GCC and ONH-RNFL. However, higher MOPP may decrease the odds of thinning of the GCC before ONH-RNFL changes.

The Utility of iCare HOME Tonometry for Detection of Therapy-Related Intraocular Pressure Changes in Glaucoma and Ocular Hypertension

PURPOSE

To assess whether iCare HOME rebound tonometry can detect therapy-related changes during self-monitoring of intraocular pressure (IOP).

DESIGN

Prospective clinical trial.

PARTICIPANTS

A total of 43 eyes (n = 27 subjects) with open-angle glaucoma or ocular hypertension were enrolled during standard-of-care clinic visits. Participants were grouped into control eyes managed on stable therapy (n = 18 eyes) or therapy change eyes undergoing selective laser trabeculoplasty (SLT, n = 8 eyes), initiating topical therapy (n = 8 eyes), or adding a second medication to existing monotherapy (n = 9 eyes).

METHODS

Subjects recorded IOP 4 times daily for 1 week using iCare HOME tonometry. Upon tonometer return, subjects underwent SLT or new medication start; an additional week of iCare HOME measurements was collected after 4 to 6 weeks. Control subjects recorded an additional week of measurements after 6 weeks. Measurements were grouped into 4 time periods (5-10 am, 10 am to 3 pm, 3-8 pm, 8 pm to 1 am). Goldmann applanation tonometry (GAT) was performed at each study visit for comparison.

MAIN OUTCOME MEASURES

Detection of therapy response defined as an IOP reduction of ≥20%.

RESULTS

For eyes that demonstrated a therapy response by GAT (n = 11), iCare HOME detected a therapy response in 90.9% of eyes in ≥1 time period and 45.5% of eyes in all 4 time periods. In eyes without a GAT-measured therapy response (n = 14), iCare HOME detected a response for 71.4% (n = 10) of eyes in ≥1 time period and for 7.1% of eyes (n = 1) at all 4 time periods. In treatment eyes, intraday and interday average minimum and maximum IOP, as well as interday IOP range, were significantly reduced after therapy without a significant change in intraday IOP range. Control group eyes did not demonstrate a significant change in average IOP minimum, maximum, or range between study weeks.

CONCLUSIONS

Home tonometry with iCare HOME reliably detects therapy-related IOP changes in patients with glaucoma and ocular hypertension. Treatment responses correlated well with in-office GAT and may detect treatment responses missed by GAT. Intraocular pressure measurements via home tonometry provide additional clinical information regarding intraday and interday IOP fluctuation beyond standard of care in office GAT measurements. The iCare HOME is a valuable tool to monitor therapeutic efficacy in patients with glaucoma.

Agreement of Intraocular Pressure Measurement of Icare ic200 with Goldmann Applanation Tonometer in Adult Eyes with Normal Cornea

PURPOSE

To study the agreement between the Icare ic200 (ICare Finland Oy, Helsinki, Finland) and the Goldmann Applanation Tonometer (GAT) in the measurement of intraocular pressure (IOP) in adult eyes.

DESIGN

Noninterventional, cross-sectional study.

PARTICIPANTS

A total of 156 eyes of 156 adult participants with clear corneas were included.

METHODS

The IOP measurements were obtained with the Icare ic200 by 1 observer followed by GAT readings by a second masked observer. The central corneal thickness (CCT) and biometry of all subjects were recorded.

MAIN OUTCOME MEASURES

The agreement between Icare ic200 and GAT was measured using the Bland-Altman plot.

RESULTS

The mean age ± standard deviation of subjects was 55.3 ± 13.7 years. The GAT IOP ranged from 6 to 50 mmHg with a mean IOP of 19.5 ± 8.8 mmHg. The Icare ic200 IOP ranged from 7.4 to 50 mmHg with a mean IOP of 20.8 ± 9.3 mmHg. The mean difference between the IOP measurement of GAT and Icare ic200 was -1.27 mmHg with the 95% limits of agreement (LoA) ranging from -3.4 to 0.9 mmHg for all ranges of IOP. The mean difference (95% LoA) between the IOP measurement of GAT and Icare ic200 was -1 mmHg (-3 to 1 mmHg) and -1.8 mmHg (-4 to 0.2 mmHg) for a GAT IOP ≤21 mmHg and >21 mmHg, respectively. The CCT, axial length, age, and gender did not significantly affect the difference in measurement of IOP between the 2 tonometers. However, for every 1-mmHg increase in GAT IOP, the difference between the 2 tonometers increased by 0.04 mmHg (P < 0.001).

CONCLUSIONS

In our study, the Icare ic200 overestimated the IOP. The overestimation increased as the baseline IOP increased. The agreement between the IOP measurement by GAT and Icare ic200 was <2 mmHg at all ranges of IOP. The narrow LoA between the tonometers for an IOP <21 mmHg makes it a useful alternative to GAT in this pressure range.

Effect of Electrical Stimulation of Cervical Sympathetic Ganglia on Intraocular Pressure Regulation According to Different Circadian Rhythms in Rats

Purpose

The purpose of this study was to investigate the relationship between circadian rhythm and intraocular pressure (IOP), and to explore whether electrical stimulation of cervical sympathetic ganglia (SCG) can regulate IOP via neurotransmitter distribution around the Schlemm's canal (SC) in rats.

Methods

Sprague Dawley rats were housed under normal (N-normal), constant dark (N-dark), and constant light (N-light) rhythms (n = 6 per group). Electrical stimulation (intermittent wave [20 hertz {Hz}, 2 mA, 10 minutes]) was used to stimulate the SCG. Atropine sulfate eye gel was applied three times a day. DiI was injected into the SCG and anterior chamber. The cross-sectional area and circumference of SC were evaluated using hematoxylin-eosin staining. Immunofluorescence staining was used to evaluate dopamine-β-hydroxylase (DβH) expression in SC endothelial (SCE) cells.

Results

N-Dark increased the IOP, decreased the cross-sectional area of SC, and increased DβH levels in SCE cells. Nerve projection between SC and SCG was detected, and electrical stimulation of SCG upregulated DβH expression in SCE cells. Under normal and constant light rhythms, electrical stimulation of SCG increased DβH and decreased the cross-sectional area and circumference of SC, while simultaneously increasing IOP and decreasing IOP fluctuations. After paralyzing the ciliary muscles, electrical stimulation of SCG decreased the cross-sectional area and circumference of SC under normal and constant light rhythms.

Conclusions

N-Dark increased DβH in SCE cells, reduced the cross-sectional area of SC, and increased IOP. Under the normal and light rhythms, electrical stimulation of SCG increased DβH in SCE cells, reduced the cross-sectional area and circumference of SC, and in turn elevated IOP and decreased IOP fluctuations.

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.

Rebound Tonometry over Soft Contact Lenses

Introduction:

Goldmann applanation tonometry (GAT) is named as a gold standard for intraocular pressure (IOP) measurement.

Aim:

To assess the accuracy of intraocular pressure (IOP) measurements using rebound tonometry over hydrogel and silicone hydrogel contact lenses (CLs) of different powers.

Methods:

This study included 117 eyes of 61 patients (12 male, 49 female), all habitual wearers of hydrogel and silicone hydrogel CLs, and none previously diagnosed with glaucoma, ocular hypertension or anterior surface disease. Five IOP measurements were taken over each eye using a rebound tonometer (Icare): with soft CLs in situ and then repeated without CLs. Lens power ranged from -9.50 to +10.00 spherical diopters and to a maximum of -0.75 cylinder diopters.

Results:

A significant positive correlation was found between IOP measurements with and without CLs. The difference between IOP measurements with (mean 20.74±5.19 mmHg) and without (mean 18.79±4.36 mmHg) CLs was found to be 1.95 mmHg (P <0.01). Statistical analysis was performed using the paired t-test and a correlation coefficient was calculated (r = 0.59; P <0.001). We have observed that increase in central corneal thickness (CCT) correlates positively with increase of measurement error of rebound tonometry (r = 0.43; P <0.001).

Conclusion:

We have shown good reliability of IOP measurements over CLs of different materials and thickness profiles while using rebound tonometer which makes it a feasible and accurate method for clinical purposes.

Variations of Intraocular Pressure Measured by Goldmann Applanation Tonometer, Tono-Pen, iCare Rebound Tonometer, and Pascal Dynamic Contour Tonometer in Patients With Corneal Edema After Phacoemulsification

PRCIS

Edematous corneas had lower Goldmann applanation tonometer (GAT) intraocular pressure (IOP) compared with other tonometers. A significant, mild negative correlation between central corneal thickness (CCT) and GAT IOP was found in a group of significant edematous corneas with CCT increases of >100 µm.

PURPOSE

To compare the IOP that was randomly obtained with the GAT, Tono-Pen, iCare, and Pascal dynamic contour tonometer in patients with corneal edema after phacoemulsification.

MATERIALS AND METHODS

Corneal edema was quantified by CCT measurement. The agreement between IOP measurements assessed by different instruments was evaluated using Bland-Altman plots. The relationship between CCT and IOP was investigated using the coefficient of correlation. The CCT and IOP were compared between the periods of postsurgical edema and after its resolution.

RESULTS

The mean age of 60 patients was 75.9±7.8 years. CCT increased significantly after surgery, by an average of 96.1±39.9 µm (P<0.001). Relative to the IOPs measured with the GAT in edematous eyes: the mean difference in Tono-Pen IOPs was 4.7 mm Hg; 95% limits of agreement (LOA), -0.3 to 9.6 mm Hg. For iCare, was 2.3 mm Hg; 95% LOA, -2.2 to 6.8 mm Hg. For Pascal dynamic contour tonometer, was 3.0 mm Hg; 95% LOA, -0.4 to 6.5 mm Hg. Edematous corneas had significantly lower GAT IOP than Tono-Pen IOP; 12.3±3.2 versus 16.9±3.1 (P=0.02). Pearson correlation coefficients (r) showed a high correlation between the 4 tonometers in eyes without edema. There was a significant, mild negative correlation between CCT and GAT IOP (r=-0.25, P=0.02) in a group of significant edematous corneas with CCT increases of >100 µm: GAT IOP decreased by 3.1 mm Hg for every 10-µm increase in CCT.

CONCLUSIONS

IOP readings with GAT tended to be lower than those obtained with the other tonometers, especially the Tono-Pen. GAT IOP readings in cases of severe corneal edema should be interpreted with caution.

Intraocular pressure measurements using the TONOVET® rebound tonometer: Influence of the probe-cornea distance

PURPOSE

To demonstrate the effect of different probe-cornea distances during intraocular pressure (IOP) data acquisition in dogs and rats.

ANIMALS STUDIED

Twenty-four conscious dogs and 15 anesthetized Wistar rats.

METHODS

Three interchangeable three-dimensional printed polylactide plastic spacer collars were used in place of the original Icare TonoVet® collar piece, which provided different distances (4, 6, and 8 mm) between the instrument's probe and the corneal surface. IOP values were obtained in sequence by a single observer, with the tonometer probe at a 4-, 6-, and 8-mm distance from the corneal surface. The dogs were gently restrained, and the rats were anesthetized with isoflurane.

RESULTS

Intraocular pressure values obtained at 4, 6, and 8 mm from the TonoVet® probe to corneal surface distance in both dogs and rats were significantly different (P < .01). There was a small positive correlation between IOP (mm Hg) and probe-cornea distance (mm) (r_s  = 0.39 for dogs and r_s  = 0.51 for rats). In dogs, the mean IOP (± SD mm Hg) obtained at different distances were 16.2 ± 3.0 at 4 mm; 17.6 ± 3.4 at 6 mm; and 19.8 ± 3.8 at 8 mm. In rats, IOP values were 8.2 ± 1.5 at 4-mm; 9.4 ± 1.8 at 6-mm; and 10.5 ± 1.5 mm Hg at 8-mm distance.

CONCLUSIONS

Probe-cornea distance of the Icare TonoVet® significantly affects IOP readings, even within the 4- to 8-mm range recommended by the manufacturer.

Agreement and repeatability of Icare ic100 tonometer

Purpose

To find the agreement and repeatability of Icare ic100 tonometer.

Methods

We included 150 subjects above the age of 18 years for this cross-sectional, multicenter study with intraocular pressure (IOP) ≥7 mmHg. After the initial ophthalmic examination, two masked examiners took five IOP measurements using three different instruments; Icare ic100, Icare TA01i, and Goldmann applanation tonometer (GAT) in only one eye of the participants. Comparison of agreement of IOP using different instruments was quantified with intraclass correlation coefficient (ICC) using the two-way random effects models of absolute agreement and Cronbach's alpha. The test-retest variability of the instruments was assessed by deriving repeatability coefficient (RC) and coefficient of variation (CV).

Results

Agreement between the tonometers across the different IOP groups had no statistically significant difference in their mean IOP. Icare ic100 was found to have good reliability across all IOP groups (ICC value >0.78) when compared with Icare TA01i. In comparison with GAT, Icare ic100 showed good reliability across all IOP groups (ICC >0.87) except >16 to <23 mmHg group where it showed moderate reliability (ICC = 0.52). Icare ic100 showed good repeatability with RC and CV of 2.67 and 4.89, respectively.

Conclusion

Icare ic100 rebound tonometer can measure IOP with relatively small measurement error and can provide a reliable and repeatable reading in comparison with GAT across a wide pressure range without hampering corneal health.

Comparison of the Icare ic100 Rebound Tonometer and the Goldmann Applanation Tonometer in 1,000 Eyes

BACKGROUND

Measurement of intraocular pressure (IOP) forms a crucial component in the diagnosis and management of glaucoma. Many devices have been developed to measure IOP with Goldmann applanation tonometry (GAT) considered the gold standard for IOP measurement.

OBJECTIVES

The objective was to compare the IOP measured using Icare ic100 and GAT.

METHODS

This cross-sectional study measured IOP in 1,000 eyes (500 left and 500 right) using the Icare ic100 and GAT. Central corneal thickness (CCT) was measured using a hand-held pachymeter. IOP measurements were investigated in all eyes, by IOP substrata, by CCT group, by number of topical glaucoma medications, and diagnosis.

RESULTS

There was moderate agreement between ic100 and GAT IOP measurements (intraclass correlation coefficient 0.73). Mean IOP was significantly lower when measured by ic100 than by GAT (12.1 vs. 16.2 mm Hg, p < 0.0001). Mean ic100 IOPs were also significantly lower than mean GAT IOPs within each IOP strata ≤12 (7.9 vs. 9.7 mm Hg, p < 0.0001), 13-21 (12.1 vs. 16.6 mm Hg, p < 0.0001), and ≥22 (18.4 vs. 25.2 mm Hg, p < 0.0001) and within each subanalysis.

CONCLUSIONS

The Icare tonometer consistently under estimated IOP compared to GAT, irrespective of CCT ranges and other subgroup analyses. The mean difference of 4.2 mm Hg can have significant clinical implications, particularly in the management of glaucoma patients.

Agreement of Intraocular Pressure Measurement of Icare ic200 with Goldmann Applanation Tonometer in Adult Eyes with Normal Cornea

PURPOSE

To study the agreement between the Icare ic200 (ICare Finland Oy, Helsinki, Finland) and the Goldmann Applanation Tonometer (GAT) in the measurement of intraocular pressure (IOP) in adult eyes.

DESIGN

Noninterventional, cross-sectional study.

PARTICIPANTS

A total of 156 eyes of 156 adult participants with clear corneas were included.

METHODS

The IOP measurements were obtained with the Icare ic200 by 1 observer followed by GAT readings by a second masked observer. The central corneal thickness (CCT) and biometry of all subjects were recorded.

MAIN OUTCOME MEASURES

The agreement between Icare ic200 and GAT was measured using the Bland-Altman plot.

RESULTS

The mean age ± standard deviation of subjects was 55.3 ± 13.7 years. The GAT IOP ranged from 6 to 50 mmHg with a mean IOP of 19.5 ± 8.8 mmHg. The Icare ic200 IOP ranged from 7.4 to 50 mmHg with a mean IOP of 20.8 ± 9.3 mmHg. The mean difference between the IOP measurement of GAT and Icare ic200 was -1.27 mmHg with the 95% limits of agreement (LoA) ranging from -3.4 to 0.9 mmHg for all ranges of IOP. The mean difference (95% LoA) between the IOP measurement of GAT and Icare ic200 was -1 mmHg (-3 to 1 mmHg) and -1.8 mmHg (-4 to 0.2 mmHg) for a GAT IOP ≤21 mmHg and >21 mmHg, respectively. The CCT, axial length, age, and gender did not significantly affect the difference in measurement of IOP between the 2 tonometers. However, for every 1-mmHg increase in GAT IOP, the difference between the 2 tonometers increased by 0.04 mmHg (P < 0.001).

CONCLUSIONS

In our study, the Icare ic200 overestimated the IOP. The overestimation increased as the baseline IOP increased. The agreement between the IOP measurement by GAT and Icare ic200 was <2 mmHg at all ranges of IOP. The narrow LoA between the tonometers for an IOP <21 mmHg makes it a useful alternative to GAT in this pressure range.

A Comparison of Applanation and Rebound Tonometers in Young Chicks

PURPOSE

To assess the validity of and compare applanation and rebound tonometry readings of intraocular pressure in alert normal chicks from ages 3 to 45 days.

METHODS

Intraocular pressures (IOPs) were measured weekly in awake White Leghorn chicks, from ages 3-45 days (n = 22-30 per age group), with both applanation Tono-Pen and rebound TonoLab tonometers. Three repeated measurements on individual eyes were used to derive variance data for both instruments at each age. Calibration curves were also derived for each instrument and each age, weekly from ages 10-45 days (n = 3-4 per age group), from in situ manometry data collected over IOP settings of 0 to 100 mmHg in 5 mmHg steps in cannulated eyes.

RESULTS

The TonoLab showed less within measurement variability, but more variability with age, than the Tono-Pen. The coefficient of variation ranged from 3.8-8.3% for the TonoLab, compared to 11.0-19.7% for the Tono-Pen across all ages. For the youngest, 3 day-old chicks, mean IOPs recorded with the Tono-Pen and TonoLab were not significantly different (17.0 ± 5.6 and 15.2 ± 3.7 mmHg, respectively, P = .27). However, with increasing age, IOP readings significantly increased for the TonoLab (P < .001), whereas Tono-Pen readings did not. Compared to manometry settings, the Tono-Pen tended to underestimate IOPs while the TonoLab overestimated IOPs over the range 20-60 mmHg, saturating thereafter; there were also age-dependent differences for the TonoLab.

CONCLUSIONS

Both the Tono-Pen and TonoLab gave IOP readings that differed from manometry settings in normal young chicks over some or all of the ages tested. These results reinforce the importance of calibrating clinical tonometers in animal studies involving IOP as a key variable.

Icare versus Goldmann in a randomised middle-aged population : The influence of central corneal thickness and refractive errors

PURPOSE

The aim of this study was to compare the measurements of intraocular pressure by two tonometers, the Icare rebound tonometer and the Goldmann applanation tonometer, in a randomised screening study. The influence of refraction and central corneal thickness on the measurements was also evaluated.

METHODS

Intraocular pressure was measured with rebound tonometer and Goldmann applanation tonometer in 1266 participants; refraction and central corneal thickness were also determined. One randomised eye of each participant was selected for this report's analysis. A Bland-Altman plot was used to compare the values obtained with the two devices.

RESULTS

The correlation between rebound tonometer and Goldmann applanation tonometer was good: the intraclass correlation coefficient (r) between the two methods was 0.735 (p < 0.001). The mean difference (rebound tonometer-Goldmann applanation tonometer) was 0.11 ± 2.3 mmHg. The difference was not statistically significant (95% confidence interval: 0.11 to 0.13, p = 0.09). With increasing central corneal thickness, not only did intraocular pressure values with both devices increase, but the difference between them also increased. Refraction (spherical equivalent) did not influence intraocular pressure or the rebound tonometer-Goldmann applanation tonometer difference. However, high astigmatism (≥2D) exerted an influence on intraocular pressure values taken with Goldmann applanation tonometer.

CONCLUSION

Measurements with rebound tonometer and Goldmann applanation tonometer are relatively uniform although rebound tonometer slightly overestimated intraocular pressure. Both rebound tonometer and Goldmann applanation tonometer and the difference between these devices were affected by central corneal thickness but not by refraction. Higher astigmatism affected Goldmann applanation tonometer more than rebound tonometer. It is concluded that rebound tonometer is a reliable method for measuring intraocular pressure in a population-based screening study.

ICare Pro: Age Dependent Effect of Central Corneal Thickness on Intraocular Pressure in Glaucoma and Ocular Hypertension Patients

Purpose: Measurement of the exact intraocular pressure (IOP) is essential in glaucoma diagnosis and follow-up, thus all therapeutic options affect IOP in order to win sighted lifetime. As it is known that corneal properties of glaucoma patients differ from normal subjects, the present study aimed to investigate the influence of CCT on rebound tonometry (ICT, ICare Pro) in glaucoma and ocular hypertension patients in dependency of age additionally considering different times of day.Methods: Three hundred sixty-two eyes of 190 subjects were included: 339 open-angle glaucoma and 23 ocular hypertension. IOP was measured at 5 different times of day (6 a.m., 12 a.m., 4 p.m., 9 p.m., and 0 p.m.) by Goldmann applanation tonometry (GAT) and Icare Pro rebound tonometry in a sitting position. Central corneal thickness was measured by central ultrasonic pachymetry (Pachymeter SP-100). Δ ICT was calculated as the difference of GAT, corrected according to age and CCT, and ICT, respectively at each time point.Results: All different GAT time points data correlated significantly (p < .05) with ICT time points. An age effect was observed on overall ICT (p = .02). A decrease of ICT was observed with increasing age. The within differences among ICT repeated measurements were significant as well. Additionally, repeated means of Δ ICT correlated significantly with age and CCT. Intercepts and coefficients were offered for each time point, respectively. GLM model yielded a relation between MD (dependent variable) and age together with CCT (age: p < .0001) and (CCT: p = .043).Conclusions: IOP measurements with ICare Pro were shown to be dependent on age, CCT and time of day in glaucoma and ocular hypertension patients. Thus, aging, corneal biomechanical properties and circadian rhythms should be taken into consideration when adjusting IOP.

Feeling the pressure: a cross-sectional study exploring feasibility of a healthcare Pop-Up for intraocular pressure measurements in shopping centres in England

OBJECTIVES

To test the hypothesis that a shopping centre Pop-Up health check combining an intraocular pressure (IOP) check with a general health check (blood pressure (BP)) is more readily accepted by the general public than an IOP check only. We investigate public awareness of IOP compared with BP and the feasibility of measuring IOP in large numbers in a Pop-Up.

DESIGN

A cross-sectional study using a tailor-made healthcare Pop-Up.

SETTING

The 'Feeling the Pressure' Pop-Up was sited in eight regionally-different shopping centres in England.

PARTICIPANTS

Adult members of the public in shopping centres.

METHODS

On one day we measured IOP only and on another measured BP and IOP. IOP was measured by Icare IC100 tonometer (Helsinki, Finland). Potential participants were asked about their awareness of IOP and BP and when they last visited their optometrist.

RESULTS

More people attended the combined BP + IOP days (461; 60%; 95% CI 56% to 64%) than IOP-only days (307; 40%, 95% CI 37% to 43%) over 16 days of testing. We recorded IOP in 652 participants (median (IQR) age and IOP of 54 (42 to 68) years and 13 (11 to 15) mm Hg, respectively). Fewer people reported awareness about IOP (19%, 95% CI 16% to 23%) compared with BP (71%, 95% CI 66% to 75%). Of 768 participants, 60 (8%) reported no previous optometric eye examination and 185 (24%) reported >2 years since their most recent examination.

CONCLUSIONS

Measuring IOP in large numbers of the public via a shopping centre Pop-Up is feasible. Public engagement was greater when a BP check was offered alongside an IOP check, suggesting unfamiliar health checks can be promoted by aligning them with a more familiar check. Our findings hint at strategies for public health schemes that engage the public with their eye health.

Comparability of three intraocular pressure measurement: iCare pro rebound, non-contact and Goldmann applanation tonometry in different IOP group

Background

Measurement of intraocular pressure (IOP) is essential for glaucoma patients. Many factors such as central corneal thickness (CCT) can affect the accuracy of IOP measurement. The purpose of this study was to evaluate the agreement of IOP measured by non-contact tonometer (NCT), iCare pro rebound tonometer (iCare), and Goldmann applanation tonometer (GAT) in different IOP group.

Methods

This was a Hospital-based cross-sectional study. Two hundred subjects were enrolled in this study. All subjects underwent IOP measurement using an NCT–iCare–GAT sequence. Bland-Altman, Pearson correlation and intraclass correlation analysis were performed using SPSS 17.0 software. The influence of CCT on each IOP measurement methods was evaluated by linear regression analysis.

Results

The mean difference (Δ) of NCT–GAT did not differ from (Δ) iCare–GAT in IOP < 10 and 10–21 mmHg group. However, (Δ) NCT–GAT was significantly higher than (Δ) iCare–GAT in IOP 22–30 and > 30 mmHg group (P < 0.05). Bland–Altman analysis showed significant agreement between the three devices (P < 0.01). IOP measurements of the three methods were significantly correlated with CCT (P < 0.01).

Conclusions

ICare pro shows a higher agreement with GAT over a wide range of IOP compared with NCT. The consistency between the three tonometers was similar in a low and normal IOP range. However, NCT shows a greater overestimate of IOP in moderate and higher IOP group. The variability of IOP measurement affected by CCT is NCT > iCare pro > GAT.

A comparison of Icare PRO and Perkins tonometers in anesthetized children

AIM

To compare intraocular pressure (IOP) measurements obtained with the Perkins applanation tonometer and Icare PRO (ICP) rebound tonometer in anesthetized aphakic or strabismus children. Furthermore, intra-operator correlation and inter-operator correlation have been evaluated, along with the effects of central corneal thickness (CCT) on IOP measurements.

METHODS

Seventy children undergoing examination under anesthesia with sevoflurane for aphakic patients and for surgery for strabismus were included. IOP have been measured twice immediately after anesthesia induction with both Perkins applanation tonometer (PAT) and ICP in one eye and by two different operators with both devices in the fellow eye. Furthermore, CCT was measured with ultrasound pachymetry Pacline (Optikon). Agreement between the device measurements has been evaluated using Bland-Altman analyses. Repeatability and reproducibility of the device have been evaluated with intraclass correlation coefficient (ICC) with a value > 0.75 associated with excellent reliability. The relationship between IOP and CCT has been evaluated with Spearman's correlation coefficient r and determination coefficient r².

RESULTS

Mean difference in IOP measurements between ICP and PAT was 1.97 mmHg ± 1.23 mmHg (p < 0.05). This difference appeared to be higher in aphakic patients (mean difference 2.15 ± 1.35) than in patients undergoing strabismus surgery (mean difference 1.83 mmHg ± 1.12). Intraclass correlation coefficient (ICC) is used to evaluate repeatability and reproducibility, which are both high for PAT (repeatability 0.96, reproducibility 0.76) compared with ICP (repeatability 0.81, reproducibility 0.70). Correlation coefficient between CCT and IOP is 0.66 for both ICP and PAT.

CONCLUSION

ICP tends to overestimate IOP compared to PAT. Repeatability and reproducibility are both high for PAT as compared to ICP. A significant correlation between IOP and CCT for both instruments has been demonstrated.

Comparison of Icare Pro Tonometry and Icare One Tonometry Measurements in Healthy Eyes

Objectives

To compare intraocular pressure (IOP) measurements obtained with the Icare Pro tonometer used in clinical practice and the Icare One self-tonometer.

Materials and Methods

Fifty-two eyes of 52 healthy, right-handed individuals with no prior intraocular surgery or ocular trauma, structural ocular pathology, or systemic disease were evaluated. IOP was first measured using the Icare Pro tonometer. The participants were then told how to use the Icare One tonometer and asked to measure their own IOP. The results were analyzed statistically using SPSS v.24.

Results

Of the 52 healthy participants, 16 (30.7%) were male and 36 (69.3%) were female. Their mean age was 31.6±6.3 (23-47) years. Mean IOP measured with the Icare Pro was 17.10±6.2 (11.5-25.2) mmHg, and the mean self-measured IOP with Icare One was 14.01±3.4 (7-24) mmHg. When the two methods were compared using Levene’s t-test, there was a significant mean difference of -3.08±0.6 (95% confidence interval: -4.39 -1.78; p<0.001).

Conclusion

In this study, there was a significant difference between the IOP measurements we made using the Icare Pro and the participants’ self-measured IOP using the Icare One, with the latter being relatively lower. This may be related to the fact that the participants were unfamiliar with using the Icare One. Although the Icare One is a promising tool for glaucoma patients to self-monitor their IOP, further studies are needed.

Comparison of IOP Measurement by Goldmann Applanation Tonometer, ICare Rebound Tonometer, and Tono-Pen in Keratoconus Patients after MyoRing Implantation

Purpose. To evaluate the different IOP readings by Goldmann applanation tonometer (GAT), ICare rebound tonometer, and Tono-Pen in keratoconus patients after MyoRing implantation. To assess the influence of central corneal thickness (CCT) and thinnest corneal location (TCL) on IOP measurements by different tonometers. Setting. Prospective observational study was conducted in two private centers in Egypt from February 2015 to November 2016. Methods. Seventeen eyes of 10 patients suffering from keratoconus and who underwent MyoRing implantation were recruited. All subjects underwent GAT, ICare, and Tono-Pen IOP measurements in random order. Central corneal thickness and thinnest corneal location were assessed by Pentacam. Difference in mean in IOP readings was assessed by T-test. Correlation between each pair of devices was evaluated by Pearson correlation coefficient. The Bland–Altman analysis was used to assess intertonometer agreement. Results. Seventeen eyes (10 patients) were evaluated. The mean IOP reading was 13.9 ± 3.68, 12.41 ± 2.87, and 14.29 ± 1.31 mmHg in GAT, ICare, and Tono-Pen group, respectively. There was a significant difference between IOP readings by GAT/ICare and Tono-Pen/ICare (p value: 0.032 and 0.002, respectively) with no significant difference between GAT/Tono-Pen (p value: 0.554). Mean difference in IOP measurements between GAT/ICare was 1.49 ± 2.61 mmHg, Tono-Pen/ICare was 1.89 ± 2.15 mmHg, and GAT/Tono-Pen was −0.39 ± 2.59 mmHg. There was no significant correlation between the difference in IOP readings among any pair of devices and CCC or TCL. The Bland–Altman analysis showed a reasonable agreement between any pair of tonometers.

Comparison of rebound tonometry and non-contact airpuff tonometry to Goldmann applanation tonometry

Purpose:

The aim of this study was to compare the intraocular pressure measurements obtained from healthy subjects with the rebound tonometry, non-contact airpuff tonometry, and Goldmann applanation tonometry in different age groups.

Methods:

A total of 180 eyes of 90 healthy subjects were included in the study. According to the subjects’ ages, the eyes were categorized into three groups: group 1 (age: 7–17 years), group 2 (age: 18–40 years), and group 3 (age: 41–75 years). Intraocular pressure was measured on each subject always in the same order: rebound tonometry, non-contact airpuff tonometry, and Goldmann applanation tonometry. Central corneal thickness values were obtained using ultrasonic pachymetry. One-way repeated-measures analysis of variance, Pearson’s correlation coefficient, and Bland–Altman analysis were used for the statistical assessment.

Results:

The mean corneal thickness was found to be 604 ± 13 µm, 546 ± 15 µm, and 547 ± 15 µm in group 1, group 2, and group 3, respectively. Non-contact airpuff tonometry was significantly higher than both Goldmann applanation tonometry and rebound tonometry measurements in all groups (p < 0.001, for all). No statistical difference between Goldmann applanation tonometry and rebound tonometry measurements was found in group 1 (p = 0.248), group 2 (p = 0.63), and group 3 (p = 0.126). There was a significant positive correlation in the meaning of intraocular pressure measurements between rebound tonometry and non-contact airpuff tonometry; non-contact airpuff tonometry and Goldmann applanation tonometry; and Goldmann applanation tonometry and rebound tonometry in all groups.

Conclusion:

As a result, without need for topical anesthesia, fast measurement and ease-of-use rebound tonometry is a reliable alternative to Goldmann applanation tonometry in different age groups.

Intraocular pressure elevation after cataract surgery and its prevention by oral acetazolamide in eyes with pseudoexfoliation syndrome

PURPOSE

To examine whether intraocular pressure (IOP) increases immediately after cataract surgery in eyes with pseudoexfoliation (PXF) syndrome and to assess whether orally administered acetazolamide can prevent the IOP elevation.

SETTING

Hayashi Eye Hospital, Fukuoka, Japan.

DESIGN

Prospective case series.

METHODS

Patients with PXF syndrome scheduled for phacoemulsification were randomly assigned to 1 of 3 groups: (1) oral acetazolamide administered 1 hour preoperatively (preoperative administration group), (2) administered 3 hours postoperatively (postoperative administration group), and (3) not administered (no administration group). The IOP was measured using a rebound tonometer 1 hour preoperatively, upon completion of surgery, and at 1, 3, 5, 7, and 24 hours postoperatively.

RESULTS

The study comprised 96 patients (96 eyes). The mean IOP increased at 3, 5, and 7 hours postoperatively in all groups. At 1 hour and 3 hours postoperatively, the IOP was significantly lower in the preoperative administration group than in the postoperative group and no administration group (P ≤ .001). At 5, 7, and 24 hours postoperatively, the IOP was significantly lower in the preoperative group and postoperative administration group than in the no administration group (P ≤. 045). An IOP spike higher than 25 mm Hg occurred less frequently in the preoperative administration group than in the postoperative administration group and the no administration group (P = .038).

CONCLUSIONS

Intraocular pressure increased at 3, 5, and 7 hours after cataract surgery in eyes with PXF syndrome. Oral acetazolamide administered 1 hour preoperatively reduced the IOP elevation throughout the 24-hour follow-up; acetazolamide administered 3 hours postoperatively reduced the elevation at 5 hours postoperatively and thereafter.

Tonometers-which one should I use?

Although several factors are known to play a role in the development and progression of glaucoma, intraocular pressure (IOP) remains the only modifiable risk factor. Medical and surgical treatments for glaucoma both aim to reduce IOP to minimize disease progression. Tonometry is therefore an essential element of the ophthalmological exam. There are several types of tonometers available currently. These range from well-established instruments that have been in clinical use for decades to new devices, which are the result of recent technological advances. The various instruments have advantages and disadvantages that affect their suitability for a given setting, purpose, and patient population. In this review, we aim to describe the most commonly available tonometers today along with their advantages, disadvantages, and applicability.

Measurement of Intraocular Pressure by Patients With Glaucoma

Importance

The ability of patients to measure their own intraocular pressure (IOP) would allow more frequent measurements and better appreciation of peak IOP and IOP fluctuation.

Objective

To examine whether patients with glaucoma can perform self-tonometry using a rebound tonometer and examine patient acceptability.

Design, Setting, and Participants

An observational study in which IOP was assessed using Goldmann applanation tonometry and a rebound tonometer. Consecutive patients were provided with a patient information sheet and those consenting to take part in the study received standardized self-tonometry training and were then instructed to measure their own IOP under observation. This study was conducted at a glaucoma clinic at a university hospital from March 1, 2016, to December 30, 2016, and included both eyes of 100 patients with glaucoma or ocular hypertension.

Main Outcomes and Measures

The percentage of patients who could successfully perform self-tonometry. Complete success was defined by a good technique and an IOP reading within 5 mm Hg of that obtained by a clinician using the same device. A 3-item questionnaire was used to examine perceptions of self-tonometry among patients.

Results

Among the 100 patients, the mean (SD) age was 67.5 (10.9) years (53% female). A total 73 of 100 patients (73%) met the complete success criteria. An additional 6 patients could use the device but had IOP readings greater than 5 mm Hg different from those obtained by the clinician. On average, IOP by the rebound tonometer was 2.66 mm Hg lower than Goldmann applanation tonometry (95% limits of agreement, -3.48 to 8.80 mm Hg). The IOPs with the rebound tonometer were similar whether obtained by self-tonometry or investigator, with excellent reproducibility with an intraclass correlation coefficient of 0.903 (95% CI, 0.867-0.928). A total of 56 of 79 successful or partially successful patients (71%) felt self-tonometry was easy, with 73 of 79 (92%) reporting self-tonometry to be comfortable, and a similar number happy to perform self-tonometry in the future.

Conclusions and Relevance

Most patients could perform self-tonometry and the method was acceptable to patients. Self-tonometry has the potential to improve patient engagement, while also providing a more complete picture of IOP changes over time.

Glaucoma after corneal replacement

Glaucoma is a well-known complication after corneal transplantation surgery. Traditional corneal transplantation surgery, specifically penetrating keratoplasty, has been slowly replaced by the advent of new corneal transplantation procedures: primarily lamellar keratoplasties. There has also been an emergence of keratoprosthesis implants for eyes that are high risk of failure with penetrating keratoplasty. Consequently, there are different rates of glaucoma, pathogenesis, and potential treatment in the form of medical, laser, or surgical therapy.