Comparison of the iCare rebound tonometer and the Goldmann applanation tonometer over a wide IOP range

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.

A comparison of intraocular pressure measurement using SUOER SW-500 rebound tonometer and conventional reusable Goldmann prisms

Introduction

To determine the agreement between intraocular pressure (IOP) measurements using conventional Goldmann applanation tonometry (GA1,2T) and SUOER SW-500 Rebound Tonometer.

Methods

This was a retrospective observational study where 205 eyes of 106 glaucoma patients had their IOPs measured by 2 fellowship trained ophthalmologists. Data were analyzed using the Bland-Altman method of differences. Correlation was measured using the Pearson coefficient.

Results

Most of our patients were Chinese (88.7%) and female (51.9%). The average age was 66.9 years. The range of IOPs as measured by GAT was 2 to 58 mm Hg. Using the Bland-Altman method to compare GAT and SUOER SW-500 Rebound Tonometer. The tonometer overestimated the IOP by 0.5 mm Hg in the right eye and underestimated it by 0.1 mm Hg in the left eye. Overall, the tonometer overestimated the IOP by 0.2 mmHg. The Tonometer IOP correlated well with GAT, with a Pearson coefficient of correlation(r) of 0.89 (p < 0.001) for the right eye and 0.86 (p < 0.001) for the left eye, respectively. In patients with GAT IOP ≥ 21 mm Hg (n = 25), the Tonometer underestimated the IOP by 2.96 mm Hg.

Discussion

The IOP measurements from the SUOER SW-500 Rebound Tonometer correlates well with the conventional GAT in measuring the IOP within normal ranges of IOP. SUOER SW-500 Rebound Tonometer may be of use, especially if the risk of transmission of infection is high considering that the probes are disposable. It is easy to use and its small size and portability makes it useful in situations where the patient is unable to be examined at the slit lamp.

Comparison of first, second, and third versus the average of six probe-corneal touches for intraocular measurement of two rebound tonometers in healthy horses

The aim of this study was to evaluate the intraocular pressure (IOP) measurements obtained from first, second, and third probe-cornea touch (PCT) and compare them with the average of six PCTs using two rebound tonometers in horses. This study enrolled a total of thirty-eight stallions, comprising of 24 Arabian horses and 14 cross-breeds (with an average age of 8 ± 3 years). The IOP measurements of first, second, and third, as well as the average of six PCTs were obtained using either Tonovet (TV) or Tonovet Plus (TV+) rebound tonometers. The mean differences (95% limits of agreement) between the average of six PCTs and the first, second, and third PCTs were 0.1 (-4.8 to 5), 0.2 (-4.8 to 4.5), and 0.2 (-3.6 to 4.0) mmHg with TV, respectively. With TV+, the differences were 0.3 (-6.6 to 7.2), 1.1 (-8.6 to 10.8), and -0.2 (-3.6 to 4.0) mmHg, respectively. Compared to the average of six PCTs, only 89.5%, 92.1%, and 97.4% of IOP measurements obtained from TV and 78.9%, 73.3%, and 65.8% of IOP measurements obtained from TV+ were within 4 mmHg of the average of six PCTs for first, second, and third PCTs, respectively. In conclusion, the measurement of IOP in the first PCT achieved best agreement with the IOP measurement of six average PCTs. Therefore, the first PCT could be considered as an alternative option for measuring IOP in horses when obtaining an average of six PCTs is not feasible.

Intraocular pressure variation from ocular compression in low and high myopia

CLINICAL RELEVANCE

Change in intraocular pressure during acute ocular compression is related to aqueous humour dynamics. Monitoring intraocular pressure (IOP) change throughout ocular compression has potential to evaluate aqueous outflow facilities.

BACKGROUND

Recent studies have monitored lamina cribrosa deformation using optical coherence tomography during ocular compression. IOP was measured only once immediately after ocular compression. This study aimed to evaluate IOP changes during and after ocular compression and compare the differences between low and high myopia.

METHODS

Two groups of young, healthy adults were age-matched and underwent ocular compression. IOP was measured at baseline and monitored during a 2-min ocular compression followed by a 10-min recovery phase. Rebound tonometry was used and applied at 30-s intervals.

RESULTS

Thirty low and 30 high myopes (60 right eyes) were included in the study. They had similar baseline IOP at 14.9 mmHg. IOP was elevated to 21.7 ± 3.8 mmHg and 22.3 ± 4.2 mmHg for the low and high myopic group, respectively (p = 0.877). Low myopes had faster IOP decay during ocular compression at -3.24 mmHg/min than high myopes at -2.58 mmHg/min (p = 0.0528). The IOP dropped below the baseline level after the release of the compressive force. Low myopes had IOP that returned to baseline levels faster (at 360 s) than high myopes (at 510 s).

CONCLUSION

Measuring IOP once immediately after ocular compression could under-estimate the effect of IOP elevation during ocular compression. Further studies are required regarding IOP changes from ocular compression in aqueous humour dynamics.

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.

Intraocular pressure measurement using ICare rebound tonometer in different positions of eye and different locations on cornea

Intraocular pressure (IOP) is one of the most crucial aspects for diagnosis and treatment plan among patients with glaucoma. Although the gold standard for IOP measurement is Goldmann applanation tonometer (GAT)[1], it must be mounted to a slit lamp biomicroscope. However, rebound tonometer has become popular due to its ease of operation and portable design, does not require topical anesthesia, and results do not differ significantly from those of GAT[2]. The purpose of this cross-sectional study is to investigate the difference in IOP measurement with iCare IC200 in different angles of the eye and different corneal locations. All participants underwent IOP measurement by GAT twice. Then, IOP was measured with iCare by a single physician. IOP was measured in a straight manner in the upright patient position; then participants were asked to look at fixation targets, which located in four different points. IOP was measured in upgaze, downgaze, medial gaze, and lateral gaze. Then, IOP was measured at 2 mm from limbus in superior, inferior, nasal, and temporal cornea. All methods were measured twice, and the mean was used for calculation. The physician who measured IOP by iCare was masked from GAT results. A total of 168 eyes were tested with a mean age of 62.15 ± 12.34 years. Mean IOP measured by GAT and iCare at the central cornea was 15.53 ± 5.57 and 14.78 ± 6.14 mmHg, respectively. The standardized mean difference (SMD) between iCare and GAT was 0.13 (-0.09-0.34), which is insignificant. The average IOP was 0.6, 0.47, 0.91, and 0.44 mmHg lower than the primary position in upgaze, downgaze, medial gaze, and lateral gaze 15 degrees angulated positions respectively (p<.01). IOPs at 2 mm from limbus in the inferior, nasal, and temporal cornea were 0.5, 0.69, and 0.57 mmHg lower than IOP measured at the central cornea (p=<.01). IOP measurements with iCare in different angles of eye were statistically significantly lower than in the primary position. Similarly, IOPs at different locations on cornea were lower than at the central cornea. However, the difference in IOP measurements with iCare in different angles of the eye and different corneal locations was in the trivial range and might be clinically insignificant.

Finite element method for estimation of applanation force and to study the influence of intraocular pressure of eye on tonometry

PURPOSE

Discover the associations of force of applanation on the eye with the plunging depth of the cornea and quantify them. The results will be utilized as the feedback parameter in the new prototype development of eye care instruments as additional force may damage the internal structure of the eye or may result in erroneous output.

METHOD

A finite element-based eye model is designed utilizing the actual dimensions of the human eye. A standardized tonometer is designed and the simulation is carried out at predetermined deformation of the cornea to find the force of applanation on the cornea during tonometry. Adding on, the influence of IOP during tonometry is analyzed for a range of plunging depths of the cornea.

RESULTS

The graphical results inferred the linear relation between the force of applanation with the deformation of the cornea and the results are quantified. The resulting deformation and stress plot of FEM based simulation approach is analyzed and observations regarding deformations and stress are made.

CONCLUSION

The human eye is successfully developed and also computed force on the cornea during tonometry is validated. The inference drawn from the deformation plot and stress plot is that the junction of cornea-sclera along with cornea-tonometer periphery undergo maximum deformation and experiences the highest stress compared to other areas of the eye while during tonometry.

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).

Effect of wearing different types of face masks during dynamic and isometric resistance training on intraocular pressure

CLINICAL RELEVANCE

The use of face masks has demonstrated to be an effective strategy to prevent transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Wearing face masks, mainly Filtering Face Piece 2 (FFP2) masks, during exercise practice has demonstrated to affect several physiological measures.

BACKGROUND

This study was aimed at assessing the intraocular pressure (IOP) behaviour during the execution of the dynamic and isometric biceps-curl exercise with a surgical and FFP2 face mask.

METHODS

Twenty two physically active young adults performed sets of 10 repetitions against the 10-RM (repetition maximum) load and 1-minute isometric effort against a load 15% lower than the 10-RM load with the FFP2 and surgical mask and without any mask. A total of six exercise sets (3 experimental conditions [FFP2, surgical and control] × 2 exercise modalities) were performed. A rebound tonometer was used to measure IOP before, during (10 measurements), and after (30-seconds of passive recovery) each training set.

RESULTS

At rest, there were not statistically significant IOP differences (p = 0.222). During dynamic exercise, there was a progressive IOP rise (p < 0.001), and a higher IOP response with the FFP2 than without the mask (corrected p-value = 0.003). For the isometric exercise, there was a greater IOP response as a function of accumulated effort (p < 0.001), which was dependent of the face mask used (FFP2> surgical>control; corrected p-values< 0.01).

CONCLUSIONS

The FFP2 masks cause a heightened IOP response during the execution of dynamic and isometric biceps-curl exercise, suggesting that, when possible, glaucoma patients should limit the use of FFP2 masks during resistance training.

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.

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.

Falsely high rebound tonometry

BACKGROUND

Rebound tonometry (RBT) can be used to measure intraocular pressure (IOP) in children unable to tolerate measurement with applanation tonometry (AT) while awake. RBT readings are often 2-3 mm Hg higher than AT. We have experienced children with a repeatedly higher difference between RBT and AT measurements (≥6 mm Hg). The purpose of this study was to identify demographic and ocular characteristics that contribute to this artifactuous discrepancy.

METHODS

The medical records of pediatric patients with IOP measured by RBT followed by AT within 6 months without intervening surgery or change in medical management were retrospectively reviewed to identify potential predictors of greater difference between RBT and AT readings.

RESULTS

A total of 123 eyes of 65 patients were included. In patients with normal IOP (≤24 mm Hg), 18.5% had a ≥6 mm Hg difference between RBT and AT, with RBT being higher. Risk factors for this included presence of persistent fetal vasculature (PFV), increased corneal diameter, and higher initial RBT value (>20). In patients with elevated IOP (>24 mm Hg), 77% had ≥6 mm Hg difference, with larger corneal diameter being the sole predictor. Eyes were less likely to have significant RBT-AT difference if there was corneal opacity or iris abnormalities in eyes with elevated IOP (>24 mm Hg).

CONCLUSIONS

In some children, RBT readings are ≥ 6 mm Hg higher than AT readings. Caution should be taken when interpreting RBT values in patients with PFV, increased corneal diameter, and higher initial RBT values.

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.

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.

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.

Accuracy of Tonopen Versus iCare in Human Cadaveric Eyes With Edematous Corneas Over a Wide Range of Intraocular Pressures

PURPOSE

The purpose of this study was to compare the accuracy of 2 portable tonometers, Tonopen and iCare, in extreme corneal edema, while also accounting for the location of pressure measurement over a wide range of intraocular pressure (IOP).

METHODS

Utilizing an experimental laboratory investigation, IOP measurements were obtained with iCare and Tonopen against an internal digital manometer in 2 enucleated human cadaveric eyes with edematous corneas. Pachymetry was used to measure central corneal thickness in each eye. Each eye was then mounted on an upright-positioned mannequin, and a 30-G needle connected to a digital manometer was introduced into the anterior chamber at the limbus. Pressures were maintained at 0, 10, 20, 30, 40, and 50 mmHg using the digital manometer. Three measurements were taken with the tonometers at the central cornea, limbal cornea, and sclera, for a total of 9 measurements per device per eye at each manometric pressure reading.

RESULTS

Comparing the mean absolute error of Tonopen versus iCare measurements at the central cornea for each manometric pressure reading, both devices underestimated the control at pressures >10 mmHg, with mean error increasing as IOP increased [mean absolute error (MAE) ranged from 1.67 to 13.33 with Tonopen and 3.67 to 21.00 with iCare]. Tonopen more accurately estimated pressure with an average MAE of 5.72 at the central cornea, compared with MAE of 10.83 at the central cornea for iCare (P<0.03). Comparing MAE between the devices at the limbus, there was no significant difference between the 2 (P=0.91), with average MAE for the Tonopen 5.47 and average MAE for the iCare 5.22. There was no significant difference between average MAE for Tonopen measurements at the central cornea versus the limbus (P=0.89), while the iCare was more accurate at the limbus with average MAE of 5.22 than the central cornea with average MAE of 10.83 (P<0.03). When measuring at the sclera, there was no statistically significant difference between average MAE for Tonopen (18.03) versus iCare (10.39) (P=0.24).

DISCUSSION

Tonopen was more accurate than iCare when measuring at the central cornea, but consistently underestimated the control. MAE for both devices increased linearly with increasing true IOP. With limbus measurements in an edematous cornea, Tonopen and iCare performed similarly. The iCare performed better at the limbus than at the central cornea. Scleral measurements for both Tonopen and iCare were poor. In this experimental model, Tonopen performed superiorly to iCare with central cornea measurements in a grossly edematous cornea. Both devices underestimated true IOP.

Comparative intraocular pressure measurements using three different rebound tonometers through in an ex vivo analysis and clinical trials in canine eyes

Objective

To evaluate the clinical relevance of intraocular pressure (IOP) measured with three different rebound tonometers in an ex vivo analysis and clinical trials in dogs.

Animals and procedures

Ex vivo analysis and clinical trials were performed separately. For the ex vivo analysis, eight enucleated eyes were obtained from four Beagle dogs. IOP values measured with TONOVET^® (TV‐IOP), TONOVET‐Plus^® (TVP‐IOP), and SW‐500^® (SW‐IOP) were compared with manometric IOPs. For clinical trials, each tonometer was evaluated separately, depending on whether TVP‐IOP was higher or lower than 14 mm Hg. One‐way repeatedmeasures analysis of variance, simple linear regression analysis, and Bland‐Altman plots were used for statistical analyses.

Results

In ex vivo analysis, TV‐IOP and TVP‐IOP were not significantly different from manometric IOP. However, SW‐IOP underestimated IOP compared to manometry. Higher discrepancy was observed in TV‐IOP and SW‐IOP with an increase in manometric IOP. In clinical trials, no significant difference was observed between TV‐IOP (9.73 ± 2.92) and TVP‐IOP (11.36 ± 2.23) when TVP‐IOP was lower than 14 mm Hg, but SW‐IOP (8.70 ± 3.03) was significantly lower than TVP‐IOP. TV‐IOP (15.96 ± 6.47) and SW‐IOP (13.09 ± 3.72) were significantly lower than TVP‐IOP (20.08 ± 6.60) when the IOP was higher than 14 mm Hg of TVP‐IOP.

Conclusions

This study demonstrates that the TONOVET^® and TONOVET‐Plus^® provide a useful approach for ex vivo analysis. In clinical trials, results of TV‐IOP and SW‐IOP were significantly lower than of TVP‐IOP when IOP was higher than 14 mm Hg of TVP‐IOP. The characteristics of rebound tonometers should be considered in clinical settings.

In vivo measures of anterior scleral resistance in humans with rebound tonometry

PURPOSE

To measure regional variations in anterior scleral resistance (ASR) using a ballistic rebound tonometer (RBT) and examine whether the variations are significantly affected by ethnicity and refractive error (RE).

METHODS

ASR was measured using a RBT (iCare TA01) following calibration against the biomechanical properties of agarose biogels. Eight scleral regions (nasal, temporal, superior, inferior, inferior-nasal, inferior-temporal, superior-nasal and superior-temporal) were measured at locations 4mm from the limbus. Subjects were 130 young adults comprising three ethnic groups whose RE distributions [MSE (D) ± S.D.] incorporated individuals categorised as without-myopia (NM; MSE ≥ -0.50) and with-myopia (WM; MSE < -0.50); British-White (BW): 26 NM + 0.52 ± 1.15D; 22 WM -3.83 ± 2.89D]; British-South-Asian (BSA): [9 NM + 0.49 ± 1.06D; 11 WM -5.07 ± 3.76D; Hong-Kong-Chinese (HKC): [11 NM + 0.39 ± 0.66D; 49 WM -4.46 ± 2.70D]. Biometric data were compiled using cycloplegic open-field autorefraction and the Zeiss IOLMaster. Two- and three-way repeated measures analysis of variances (anovas) tested regional differences for RBT values across both refractive status and ethnicity whilst stepwise forward multiple linear regression was used as an exploratory test.

RESULTS

Significant regional variations in ASR were identified for the BW, BSA and HKC (p < 0.001) individuals; superior-temporal region showed the lowest levels of resistance whilst the inferior-nasal region the highest. Compared to the BW and BSA groups, the HKC subjects displayed a significant increase in mean resistance for each respective region (p < 0.001). With the exception of the inferior region, ethnicity was found to be the chief predictor for variation in the scleral RBT values for all other regions. Mean RE group differences were insignificant.

CONCLUSIONS

The novel application of RBT to the anterior sclera confirm regional variation in ASR. Greater ASR amongst the HKC group than the BW and BSA individuals suggests that ethnic differences in anterior scleral biomechanics may exist.

Initial experience in self-monitoring of intraocular pressure

Background/aims

Diurnal variation in intraocular pressure (IOP) is a routine assessment in glaucoma management. Providing patients the opportunity to perform self-tonometry might empower them and free hospital resource. We previously demonstrated that 74% of patients can use the Icare® HOME tonometer. This study further explores Icare® HOME patient self-monitoring.

Methods

Patients were trained by standard protocol to use the Icare® HOME rebound tonometer. Patient self-tonometry was compared to Goldmann applanation tonometry (GAT) over one clinical day. Following this, each patient was instructed to undertake further data collection that evening and over the subsequent two days.

Results

Eighteen patients (35 eyes) participated. Good agreement was demonstrated between GAT and Icare® HOME for IOPs up to 15 mm Hg. Above this IOP the Icare® tended to over-read, largely explained by 2 patients with corneal thickness >600 um. The mean peak IOP during ‘clinic hours’ phasing was 16.7 mm Hg and 18.5 mm Hg (p = 0.24) over three days. An average range of 5.0, 7.0 and 9.8 mm Hg was shown during single day clinic, single day home and three day home phasing respectively (p =<0.001). The range of IOP was lower in eyes with prior trabeculectomy (6.1 mm Hg vs 12.2 mm Hg). All patients undertook one reading in the early morning at home with an average of 4.8 readings during, and 3.1 readings after office hours.

Conclusions

This small study shows that self-tonometry is feasible. The findings from home phasing demonstrated higher peak and trough IOPs, providing additional clinical information. Home phasing is a viable alternative. The cost-effectiveness of this approach has yet to be addressed.

Comparison of Three Different Tonometers in Eyes with Angle Closure

SIGNIFICANCE

Precise measurement of intraocular pressure (IOP) is essential when diagnosing and managing glaucoma. We compared the IOP readings of three different tonometers and analyzed agreement among tonometers in eyes with high IOPs.

PURPOSE

The purpose of this study was to compare the IOP readings obtained using a Goldmann applanation tonometer (GAT), a rebound tonometer (RT), and a Tono-Pen (TP) in angle-closure eyes with elevated IOP before and after medical IOP-lowering therapy.

METHODS

Twenty-five eyes of 25 patients with angle closure and IOPs of greater than 30 mmHg were enrolled. Intraocular pressure was measured using RT (iCare Pro), TP (Tono-Pen XL), and GAT before and after medical treatment. The mean IOP readings of the tonometers were compared before and after treatment. The agreement among the tonometers was assessed via Bland-Altman analysis.

RESULTS

The measurements from 22 eyes of 22 patients were suitable for statistical analyses. Before medical treatment, the mean TP-IOP was significantly lower than the mean GAT-IOP (44.0 ± 10.3 vs. 50.4 ± 8.9 mmHg, respectively; P < .001), but no significant difference was evident between the RT-IOP and the GAT-IOP (50.8 ± 10.9 vs. 50.4 ± 8.9 mmHg, respectively; P = .79). After IOP-lowering treatment, the mean GAT-IOP (14.9 ± 4.7 mmHg) did not differ from either the mean RT-IOP (15.6 ± 4.4 mmHg) or the mean TP-IOP (15.4 ± 5.0 mmHg; P = .05 and P = .18, respectively). The random measurement error among tonometers was greater for high IOP readings.

CONCLUSIONS

Compared with RT or GAT, TP underestimated IOP in angle-closure eyes with a GAT-IOP of greater than 30 mmHg. Intraocular pressure reading agreement among the three tonometers was lower in eyes with high IOP.

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.

Cataract surgery reduces intraocular pressure but not posture-induced intraocular pressure changes in patients with angle-closure glaucoma

Cataract surgery leads to a sustained decrease in sitting intraocular pressure (IOP) in patients with angle-closure glaucoma (ACG). The purpose of this study is to evaluate whether cataract surgery can also reduce postural IOP changes. We prospectively examined 106 eyes from 53 patients with narrow angles scheduled for phacoemulsification. IOP was measured in the sitting, supine, and lateral decubitus positions using an ICare rebound tonometer before and 1 week, 1 month, and 3 months postoperatively. The mean baseline IOP in the sitting and lateral decubitus positions was 17.9 ± 4.8 mmHg and 21.43 ± 6.44 mmHg, which significantly reduced to 13.52 ± 3.8 and 17.46 ± 3.62, respectively, 3 month postoperatively (p < 0.001). However, postural IOP change (lateral decubitus minus sitting) at 3 months postoperatively was not significantly different from that at the baseline (3.17 ± 2.63 vs. 3.53 ± 3.38 mmHg, p = 0.85). Postural IOP change was not associated with preoperative sitting IOP, anterior chamber depth, axial length, fixed pupil, or presence of glaucomatous optic neuropathy. Patients with higher preoperative IOP exhibited greater IOP reduction after cataract surgery in every posture (p < 0.0001). In conclusion, cataract surgery reduces IOP in all postures among patients with ACG; however, it does not reduce the magnitude of postural IOP change.

Prophylactic treatment of intraocular pressure elevation after uncomplicated cataract surgery in nonglaucomatous eyes - a systematic review

The purpose of this systematic review was to evaluate the literature regarding prophylactic treatment of intraocular pressure (IOP) elevation after uncomplicated cataract surgery to provide an evidence-based guideline for cataract surgeons. The relevant literature was identified in EMBASE and PubMed. The risk of bias was assessed according to the 'Cochrane Handbook for Systematic Reviews of Interventions' and the ROBINS-I tool. The Grading of Recommendation, Assessment, Development and Evaluation (GRADE) criteria were used to rate the quality of evidence, and relevant data were systematically extracted to evaluate the pressure-lowering effect of the active substances. The primary outcomes for this systematic review were the absolute and relative pressure-lowering effect of the different drugs after 3-8 hr and 1 day after surgery. In total, 23 randomized controlled trials and one nonrandomized controlled study consisting of 45 treatment arms with 14 different active substances were included in the qualitative synthesis. According to the GRADE criteria, nine trials were graded as 'high' quality of evidence, 12 trials as 'moderate', while three trials were given the grade 'low' quality of evidence. The primary outcomes showed most consistency between the trials, which studied the effect of timolol, and presented a relative effect from 18.6% to 29.6% at 3-8 hr and 9.8% to 23.6% at day 1. This systematic review indicates that timolol, latanoprost and travoprost alone or medications containing timolol as an additive active substance, such as dorzolamide + timolol, brinzolamide + timolol and brimonidine + timolol, are characterized by a good relative IOP-lowering effect, which can be gained by a single dose postoperatively.

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.

Intraocular pressure (IOP) measurements in keratoconic patients: Do variations in IOP respect variations in corneal thickness and corneal curvature?

PURPOSE

To explore the relationship between intraocular pressure (IOP) measurements and topographical variations in corneal curvature and corneal thickness in a cohort of keratoconic patients presenting to a newly-established regional Keratoconic diagnostic and monitoring clinic in Northern Ireland.

METHODS

IOP was recorded, using a hand held ICARE tonometer, at central, nasal and temporal locations on keratoconic corneae of 27 consecutive patients attending clinic. Pachymetry and sagittal keratometry were recorded in matched locations using the Pentacam Topographer. Eyes with history of corneal surgery or anterior surface pathology were excluded.

RESULTS

The median (interquartile range) central keratometry, pachymetry (CCT) and IOP measurements for 49 eyes were 44.1D (42.2D-48.1D); 495 μm (460 μm-526 μm); 10 mmHg (8 mmHg-13 mmHg) respectively. Temporal and nasal keratometry, pachymetry, and IOP values, recorded on midline, were temporal 41.9D (40.7D-42.8D); 621 μm (579 μm-650 μm); 14 mmHg (11 mmHg-16 mmHg); nasal 40.8D (39.5D-42.5D); 641 μm (599 μm-698 μm); 13 mmHg (12 mmHg-17 mmHg). A moderate correlation was shown between reduction in CCT and increase in mean central keratometry (Spearman's Coefficient (ρ) -0.72 P = 0.00). A moderate correlation was found between reduction in CCT and reduction in IOP, as recorded centrally (ρ = 0.37 P = 0.01). Mid-peripheral values demonstrated similar trends in the relationship between keratometry and IOP (nasal ρ = -0.47 P = 0.00; temporal ρ = -0.38 P = 0.00) and pachymetry and IOP (nasal ρ = 0.29 P = 0.05; temporal ρ = 0.33 p = 0.02).

CONCLUSION

In this pilot study, a positive correlation exists between pachymetry, keratometry and IOP. Topographically variations in intraocular pressure mimic changes in keratometry and pachymetry.

Effect of manual eyelid manipulation on intraocular pressure measurement by rebound tonometry

BACKGROUND/AIMS

To investigate the effect of eyelid manipulation on the measurement of intraocular pressure (IOP) using two different tonometries (rebound tonometry (RT) vs Goldmann applanation tonometry (GAT)).

METHODS

103 patients with primary open-angle glaucoma were prospectively enrolled. For all of the patients, IOP measurements were performed in three different ways: (1) RT with lid manipulation (LM), (2) RT without LM and (3) GAT. The order of the three measurements was randomly selected. Additionally, the palpebral fissure height (PFH; elliptical space between upper and lower eyelids) was measured.

RESULTS

The mean value of IOP measured by GAT was 13.97±2.80 mm Hg, which was not significantly different from that by RT without LM (13.75±2.44 mm Hg; P=0.096), but which was significantly lower than that by RT with LM (15.21±2.91 mm Hg; P<0.001). On a Bland-Altman plot, RT with LM was overestimated relative to GAT (mean: -1.5) and RT without LM (mean: -1.2). Among the high IOPs (>20 mm Hg), interestingly, those measured by RT without LM were significantly lower than those measured by GAT (P<0.001). In the subgroup analysis of PFH, the smaller the PFH, the more exaggerated the IOP difference between GAT (P=0.014) and RT with LM (P<0.001).

CONCLUSION

RT-measured IOP was significantly exaggerated when manipulation was applied to the eyelid. This overall trend was more pronounced when PFH was small. GAT-measured IOP, meanwhile, showed a good correlation with IOP measured using RT without LM.

Muscular Strength Is Associated with Higher Intraocular Pressure in Physically Active Males

SIGNIFICANCE

The positive association between intraocular pressure (IOP) and relative maximum force may have relevance for exercise recommendations when IOP is a concern.

PURPOSE

The relationship between exercise and IOP has been approached in several studies. However, the influence of muscle function on IOP remains underexplored. This study aimed to determine the relationship between the maximal mechanical capabilities of muscles to generate force, velocity, and power with IOP.

METHODS

Sixty-five physically active males participated in this cross-sectional study. Baseline IOP measures were obtained by rebound tonometry, and participants performed an incremental loading test in the ballistic bench press.

RESULTS

Baseline IOP showed a strong positive correlation with relative maximum force (r65 = 0.85, P < .001) relative maximum power (r65 = 0.85, P < .001), and relative one-repetition maximum (r65 = 0.91, P < .001). Also, a moderate positive association was obtained between baseline IOP and maximum force (r65 = 0.74, P < .001), maximum power (r65 = 0.72, P < .001), and maximum dynamic strength (r65 = 0.80, P < .001). No significant correlations between IOP and maximal velocity were obtained (all P > .05).

CONCLUSIONS

There is a positive association between greater upper-body power and strength with higher baseline IOP, which might have important implications in the management of ocular health and especially in individuals constantly involved in resistance training programs (e.g., military personnel, weightlifters). The possible protective effect of high fitness level on the acute IOP response to strength exercise needs to be addressed in future studies.

Wound stability and surgically induced corneal astigmatism after transconjunctival single-plane sclerocorneal incision cataract surgery

PURPOSE

To compare intraocular pressure (IOP) immediately after cataract surgery, and surgically induced corneal astigmatism (SIA) and corneal shape changes between eyes with transconjunctival single-plane sclerocorneal incisions (TSSIs) and eyes with clear corneal incisions (CCIs).

METHODS

Bilateral eyes of 64 patients undergoing phacoemulsification were randomized to undergo 2.4-mm temporal TSSI or CCI. IOP was measured preoperatively, and in the immediate postoperative periods. SIA was determined using vector analysis, and corneal shape changes and irregular astigmatism were evaluated using a videokeratography preoperatively, and in the early postoperative periods.

RESULTS

Wound hydration was performed in 23 eyes (35.9 %) of the TSSI group and in 60 (93.8 %) of the CCI group (P < 0.0001). Mean IOP was significantly higher in the TSSI group than in the CCI group at 30, 60, and 120 min postoperatively (P ≤ 0.0179). SIA tended to be smaller in the TSSI group than the CCI group, but the difference was not significant. The higher order irregular astigmatism was smaller in the TSSI group than in the CCI group at 2 days (P = 0.0312). The videokeratography revealed a wound-related flattening postoperatively in both groups; this change disappeared within 4 weeks in the TSSI group, whereas it persisted until 12 weeks in the CCI group.

CONCLUSION

IOP was significantly higher immediately after TSSI than after CCI and required less wound hydration, suggesting better stability with TSSI. Higher order irregular astigmatism and wound-related corneal flattening were smaller after TSSI than after CCI in the early periods, suggesting that fewer corneal shape changes with TSSI.

The Icare HOME (TA022) Study: Performance of an Intraocular Pressure Measuring Device for Self-Tonometry by Glaucoma Patients

PURPOSE

To evaluate the Icare HOME (TA022) device (Icare Oy, Vanda, Finland) for use by glaucoma patients for self-tonometry.

DESIGN

Prospective performance evaluation of a medical device.

PARTICIPANTS

One hundred eighty-nine participants with glaucoma or suspected glaucoma were recruited from the Wilmer Eye Institute, Baltimore, Maryland, between July 2014 and April 2015.

METHODS

Participants had standardized training and had to be able use the Icare HOME device independently. Subjects also had to be able to obtain the first intraocular pressure (IOP) measurement within 5 mmHg of Goldmann applanation tonometry (GAT). Those certified obtained 3 IOP measures using the HOME device, and these were compared with Icare TA01i and GAT IOP measurements.

MAIN OUTCOME MEASURES

The agreement between Icare HOME and reference tonometers was used to assess precision. The intraclass correlation coefficient was used to assess within-patient reliability for the HOME device.

RESULTS

Eighteen of 189 recruited patients were ineligible to take part in the study. Forty-four of 171 patients (25.7%) started but failed to complete the study: 7 stopped because of time concerns, 10 of 171 patients (6%) stopped because of difficulty using the device during certification, and 27 of 171 patients (16%) failed to be certified based on IOP. The HOME and GAT measurements agreed within 5 mmHg in 116 of 127 participants (91.3%); 2 participants (1.6%) had a difference of more than 7 mmHg. The mean difference between the Icare HOME and GAT measurements was -0.33 mmHg (standard deviation, 3.11 mmHg). The overall intraclass correlation coefficient for the HOME device was 0.92 (95% confidence interval, 0.89-0.95).

CONCLUSIONS

Not all participants could learn how to use the Icare HOME device, but for those who could, most were able to obtain measurements similar to those obtained by GAT. The Icare HOME device is safe and reliable for self-tonometry, but nearly 1 in 6 individuals may fail to certify in use of the device based on large differences in IOP when comparing GAT with the Icare HOME measurements. The device has the potential to address an unmet need by providing more frequent IOP measurements in a patient's day to day life.

Can higher end tonometers be used interchangeably in routine clinical practice?

Context:

Precise intraocular pressure (IOP) measurement is important in glaucoma practise. Various instruments are available today to accurately measure IOP. Thus, the question arises about which instrument to use and whether all of them can be used interchangeably.

Aims:

To assess the agreement between noncontact tonometer (NCT), rebound tonometer (RBT), Goldmann applanation tonometer (GAT), and dynamic contour tonometer (DCT) in measuring IOP.

Subjects and Methods:

499 eyes of 250 patients were evaluated during a period of 24 months from September 2010 to August 2012 and measurement of IOP by NCT, RBT, GAT, and DCT was done in the given sequence. The agreement was assessed by use of the Bland–Altman plot keeping GAT as a gold standard technique.

Results:

The mean IOP value of NCT, RBT, GAT, and DCT was 15.9 ± 5.5, 15.9 ± 5.8, 15.9 ± 4.9, and 16.0 ± 4.7 mm of Hg, respectively. The limits of agreement of GAT with DCT, NCT, and RBT were found to be +5.4 to −5.2, −4.7 to +4.6, and −5.2 to +5.1 mm of Hg, respectively.

Conclusions:

A positive and strong correlation was found between newer tonometers and GAT, but the limit of agreement was clinically unacceptable. The use of a single tonometer should be practised at a glaucoma clinic for a patient at each follow-up.

Comparison of intraocular pressure measurements with different contact tonometers in young healthy persons

AIM

To analyze the correlation of Goldmann applanation tonometer (GAT), I-Care tonometer and Tono-Pen tonometer results in young healthy persons, and to investigate the influence of central corneal thickness (CCT) on intraocular pressure (IOP) measurements recorded with these tonometers.

METHODS

We conducted a pilot clinical study in 78 eyes of 78 subjects aged 22-28 years old (44 women and 34 men; mean age 23.8±1.19y). IOP was measured using GAT, I-Care and Tono-Pen tonometers, followed by measurements of CCT. Statistical analysis was performed using SPSS 20.0.

RESULTS

The mean IOPs and standard deviation (±SD) for GAT, I-Care and Tono-Pen were 15.62±2.281 mm Hg, 16.29±2.726 mm Hg and 16.32±2.393 mm Hg, respectively. The mean CCT was 555.15±29.648 µm. Clear positive correlations between GAT and I-Care, GAT and Tono-Pen, and I-Care and Tono-Pen tonometers were found (r=0.867, P<0.001; r=0.861, P<0.001; r=0.915, P<0.001, respectively). In comparison between devices, Bland-Altman analysis showed a significant mean difference (MD) in the measurements by GAT and I-Care of -0.679 mm Hg and by GAT and Tono-Pen of -0.705 mm Hg ( P<0.001), but there was no significant difference between I-Care and Tono-Pen ( P>0.05). Both non-gold standard tonometers were affected by CCT; that is, both I-Care and Tono-Pen tonometer values were significantly higher with higher CCT means (>555 µm; MD=-1.282, P<0.001; MD=-0.949, P<0.001, respectively) compared with GAT.

CONCLUSION

Both I-Care and Tono-Pen tonometers overestimated IOP compared with the GAT values. Either the I-Care or Tono-Pen tonometer could be used instead of GAT because there was no significant difference between their results. Higher CCT values (>555 µm) were associated with overestimated IOP values.

A Comparative Study of Rebound Tonometry With Tonopen and Goldmann Applanation Tonometry Following Vitreoretinal Surgery

PURPOSE

To investigate agreement in intraocular pressure (IOP) measurements among Icare rebound tonometry, Tonopen tonometry, and Goldmann applanation tonometry following vitreoretinal surgery.

DESIGN

Reliability analysis of tonometers.

METHODS

Fifty-eyes of 50 adults undergoing vitreoretinal surgery were enrolled. IOP was measured on first postoperative day using Icare (Tiolat, Helsinki, Finland), followed by Tonopen (Reichert, Depew, New York, USA) and Goldmann (Haag-Streit USA, Mason, Ohio, USA) in randomized order. Intraclass correlation coefficients (ICC) and Bland-Altman plots were calculated for all subcategories.

RESULTS

Icare successfully measured IOP in all eyes, while Goldmann was unmeasurable in 6 eyes (12%) and Tonopen in 1 eye (2%). Mean IOP by Icare, Tonopen, and Goldmann was 15.9 ± 8.9, 16.9 ± 6.2, and 16.0 ± 7.3 mm Hg, respectively (P = .76). Type of intraocular tamponade, status of lens, status of cornea, gauge of instrumentation, and history of prior vitrectomy did not result in significant differences among the 3 tonometers. ICC was excellent (>0.75) in all subgroups, except at IOP <10 and ≥ 23 mm Hg (based on Icare). In eyes with IOP <10 mm Hg, Icare underestimated IOP (mm Hg; P = .01) compared to Goldmann (2.0 ± 2.1) and Tonopen (3.5 ± 2.4), whereas at IOP ≥ 23 mm Hg Icare was overestimated (P = .01) compared to Goldmann (3.77 ± 3.49) and Tonopen (4.97 ± 3.33). Overall, differences in IOP were ≤ 3 mm Hg in 58% of eyes for Icare-Tonopen, 72% for Tonopen-Goldmann, and 62% for Icare-Goldmann.

CONCLUSION

IOP measurements using Icare rebound tonometry, Tonopen, and Goldmann tonometry are in excellent agreement following vitreoretinal surgery. However, Icare overestimates at IOP ≥ 23 and underestimates at IOP <10 mm Hg.

Does patient comfort influence the choice of tonometer for the measurement of intraocular pressure?

The purpose of this study was to compare patient comfort and preference between the use of Icare tonometer and Goldmann applanation tonometer for the measurement of intraocular pressure (IOP). This was a prospective study carried out at the Eye clinic of the University College Hospital, Ibadan on volunteers aged 18 years and above. Demographic information of the participants was collected using a proforma. All participants had Icare tonometry and Goldmann applanation tonometry (GAT) performed on them in sequence within a 15-min period. After the measurements, participants were asked to report their assessment of the level of comfort with each method and to state their preferred choice for IOP measurement. One hundred subjects participated in the study; 45 (45 %) were males, and the mean age was 47.1 (± 17.4) years. Forty-three subjects (43 %) reported that Icare was either much more comfortable or more comfortable than GAT, while 31 (31 %) stated that Goldmann applanation was either much more or more comfortable. Twenty-six participants (26 %) reported that the level of comfort was the same with the two instruments. With regard to which of the instruments will be preferred for IOP check at another clinic visit, 53 (53 %) of the respondents preferred the Goldmann applanation tonometer. Some of the participants preferred GAT because they believed it was more sophisticated, while the main reported reason for preferring Icare was the stinging sensation of the anesthetic eye drop when using GAT. Although more participants reported the Icare tonometer to be more comfortable, the Goldmann tonometer was preferred by majority of the respondents.

[Rebound tonometry after vitreoretinal surgery]

PURPOSE

The aim of this study was to analyze the practicability and comparability of the Icare rebound tonometer (RT) versus the Schiötz indentation tonometer (SIT) and the Goldmann applanation tonometer (GAT) for measuring intraocular pressure (IOP) in patients after pars plana vitrectomy (PPV).

METHODS

A total of 100 eyes from 100 patients who underwent vitreoretinal surgery in the Department of Ophthalmology, University of Cologne were included in this prospective analysis. The IOP was measured using RT preoperatively, on the day of surgery and 2 days after surgery, using SIT on the day of surgery and GAT preoperatively and 2 days after surgery. For the evaluation eyes were divided into subgroups with respect to the endotamponade selected and the IOP level.

RESULTS

The mean preoperative IOP for all enrolled eyes was 15.4 ± 8.0 mmHg for RT and 16.1 ± 7.9 mmHg for GAT. Bland-Altman analysis revealed a bias between RT and GAT of - 0.6 mmHg. Bland-Altman analysis for the postoperative course of all eyes revealed a bias of 3.0 mmHg between RT and SIT on the day of surgery and no bias between RT and GAT in the further postoperative follow-up.

CONCLUSION

Rebound tonometry seems to provide precise IOP values after vitreoretinal surgery. Divergence from SIT values on the day of surgery is presumably due to a general tendency of SIT to underestimate IOP values. Therefore, RT can be used in the clinical routine after vitreoretinal surgery as an alternative to GAT.

Intra-ocular pressure measurements using the Ocular Response Analyser and ICare tonometer: A comparison

The accurate measurement of intra-ocular pressure (IOP) is an important procedure in the detection and treatment of glaucoma. The Ocular Response Analyser (ORA) and the ICare rebound tonometer are two recent additions to the instruments available to eye care practitioners for the measurement of IOP. The present study investigated whether the ORA and the ICare tonometer can be used interchangeably. Twenty-eight subjects had three measures of IOP taken using the two instruments. The ORA provides two different measures of IOP – Goldmann and cornea compensated IOP – whilst the ICare tonometer provides IOP only. The results of this study suggest that only the ORA Goldmann and ICare IOP measures are comparable. In general, it is advisable not to use the ORA and ICare tonometers interchangeably.

Immediate effect of intravitreal injection of bevacizumab on intraocular pressure

Purpose

To investigate the immediate effect of intravitreal injection of bevacizumab on intraocular pressure (IOP).

Methods

This was a prospective and nonrandomized study. A total of 291 eyes with macular edema or active choroidal neovascularization were submitted to a single 1.25 mg (0.05 mL) bevacizumab intravitreal injection. Intraocular pressure was measured with an Icare^® tonometer immediately before and after injection in a seated position. The presence of subconjunctival reflux was recorded. The fellow eye served as the control.

Results

Mean preoperative IOP was 18.0±5.9 mmHg in the treated eye versus 16.9±6.0 mmHg in the fellow eye. Mean postoperative IOP was 42.1±14.5 mmHg in the treated eye versus 17.5±6.0 mmHg in the fellow eye. The IOP variation was statistically significant in both cases and controls (P<0.001 and P=0.003, respectively), and this increase was higher in cases than in controls (P<0.001). Postoperative IOPs higher than 50 mmHg were achieved in 32.0% of the eyes. Subconjunctival reflux was present in 21.3% and determined a lower IOP rise (P<0.001). Tested variables (glaucoma, phakic status, and sex) did not have a statistically significant effect on IOP rise or subconjunctival reflux.

Conclusion

IOP increases with intravitreal bevacizumab injection, reaching 50 mmHg or more in about one third of patients. A higher IOP is expected if no subconjunctival reflux occurs. The baseline IOP does not influence the incidence of subconjunctival reflux. The clinical relevance of these facts has yet to be clarified.

Test-retest reliability of retinal oxygen saturation measurement

PURPOSE

To determine intrasession and intersession repeatability of retinal vessel oxygen saturation from the Oxymap Retinal Oximeter using a whole image-based analysis technique and so determine optimal analysis parameters to reduce variability.

METHODS

Ten fundus oximetry images were acquired through dilated pupils from 18 healthy participants (aged 22 to 38) using the Oxymap Retinal Oximeter T1. A further 10 images were obtained 1 to 2 weeks later from each individual. Analysis was undertaken for subsets of images to determine the number of images needed to return a stable coefficient of variation (CoV). Intrasession and intersession variability were quantified by evaluating the CoV and establishing the 95% limits of agreement using Bland and Altman analysis. Retinal oxygenation was derived from the distribution of oxygenation values from all vessels of a given width in an image or set of images, as described by Paul et al. in 2013.

RESULTS

Grouped in 10-μm-wide bins, oxygen saturation varied significantly for both arteries and veins (p < 0.01). Between 110 and 150 μm, arteries had the least variability between individuals, with average CoVs less than 5% whose confidence intervals did not overlap with the greater than 10% average CoVs for veins across the same range. Bland and Altman analysis showed that there was no bias within or between recording sessions and that the 95% limits of agreement were generally lower in arteries.

CONCLUSIONS

Retinal vessel oxygen saturation measurements show variability within and between clinical sessions when the whole image is used, which we believe more accurately reflects the true variability in Oxymap images than previous studies on select image segments. Averaging data from vessels 100 to 150 μm in width may help to minimize such variability.

Short-term effect of standard automated perimetry testing on intraocular pressure in patients with open-angle glaucoma

Purpose. To evaluate the short-term effect of standard automated perimetry (SAP) testing on intraocular pressure (IOP) in patients with open-angle glaucoma (OAG). Methods. We tested 45 patients (71 eyes) with OAG that had stable IOP under medical treatment. IOP was measured four times using an iCare rebound tonometer (RBT) immediately before, immediately after, 10 minutes after, and 20 minutes after SAP testing. Logistic regression analyses were performed to determine the relationships among SAP test duration, mean deviation of the SAP result, type of glaucoma medications, patient age, and significant IOP change (exceeding 2 mmHg) from baseline IOP. Results. The mean baseline IOP was 13.29 ± 3.06 mmHg. Although IOP changes immediately and 20 minutes after SAP testing were not statistically significant, the IOP change 10 minutes after SAP testing (-0.57 ± 1.84 mmHg) was statistically significant. However, the changes were within the margin of error of the RBT. Test duration, mean deviation, patient age, and type of glaucoma medications did not have a significant influence on IOP change (all P > 0.14). Conclusions. IOP measured by RBT did not vary significantly after SAP testing in patients with OAG. It may be not necessary to reject IOP measured after SAP testing in patients with OAG.