Clinical use of a new position-independent rebound tonometer

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.

[Tonometry and pachymetry to evaluate fluctuations of intraocular pressure in the context of SCUBA diving]

BACKGROUND

It is currently still not clarified whether diving using a self-contained breathing apparatus (SCUBA) is associated with intraocular pressure (IOP) fluctuations of clinical relevance and whether intensive diving could exacerbate the damage in glaucoma patients.

OBJECTIVE

This study aimed to evaluate the effect of SCUBA diving on IOP in healthy volunteers without prior eye injuries or surgery.

HYPOTHESIS

recreational diving does not lead to significant increases or fluctuations of the IOP.

MATERIAL AND METHODS

The study included 16 divers (5 female) who performed a total of 96 dives with air or nitrox32 to a depth of 20-30 m for an average of 50 min. The central cornea thickness was measured using ultrasonic pachymetry Pocket IITM (Quantel Medical Pocket II™, Quantel Medical, Clermont-Ferrand, France), and the IOP was measured using an Icare® PRO (Icare® PRO, Icare Finland Oy, Espoo, Finland) directly before the dive and 10 min after surfacing.

RESULTS

All data refer to the right eye. Average IOP values ranged from 15.6 to 19.2 mm Hg pre-dive and 16.8 to 18.2 mm Hg post-dive. The range of IOP values was 2.2-11.5 mm Hg pre-dive (∆ = 9.3 mm Hg) and 2.7-14.8 mm Hg post-dive (∆ = 12.1 mm Hg). Of the divers 11.5% vs. 18.8% had increased IOP values > 21 mm Hg (pre-dive vs. post-dive).

CONCLUSION

This study found no significant differences in IOP values between pre-dive and post-dive measurements in healthy SCUBA divers. Therefore, recreational SCUBA diving is unlikely to affect the IOP in healthy individuals.

Comparison of the iCare rebound tonometer and the Perkins applanation tonometer in children under general anesthesia

INTRODUCTION

The goal of the study was to compare Perkins applanation tonometry and iCare rebound tonometry, evaluating their correlation and agreement in a diverse pediatric population under general anaesthesia (GA).

MATERIALS AND METHODS

Children undergoing an eye examination under GA between November 2019 and March 2020 were included. Intraocular pressure (IOP) was measured successively using the Perkins applanation tonometer and the iCare IC200 rebound tonometer. Ultrasonic central pachymetry and axial length were measured.

RESULTS

One hundred and thirty-eight eyes of 72 children were included. The mean age was 2.87years. IOP measurements obtained with the two tonometers were statistically and significantly highly correlated (r=0.8, P<0.001), although the iCare overestimated IOP by an average of 3.37mmHg (SD±4.48). The agreement between the two methods was moderate; the 95% agreement limits ranged from -5.41 to +12.15mmHg (r=0.5, P<0.001). The IOP difference between the two tonometers was weakly but significantly correlated with mean IOP (r=0.52; P=0.006). No correlation was found with axial length and pachymetry.

CONCLUSION

In this study, the IOP values obtained using the Perkins applanation tonometer and the iCare IC200 rebound tonometer were well correlated. The iCare tended to overestimate the IOP, especially for high IOP values. However, no underestimation of IOP was found with this device, hence its potential for glaucoma screening in children.

Evaluation of rebound tonometer iCare IC200 as compared with IcarePRO and Goldmann applanation tonometer in patients with glaucoma

Background

This study investigated the agreement between a new rebound tonometer, IC200, and IcarePRO and Goldmann applanation tonometry (GAT).

Methods

This was a prospective cross-sectional study. We measured the intraocular pressure (IOP) in 145 eyes of 145 glaucoma patients in the sitting position using GAT, IcarePRO, and IC200. IcarePRO and IC200 measurements were also obtained in the supine position. IC200 measurement was performed using two modes: single six (IC200-single) and automatic (IC200-continuous) six-measurements mode.

Results

All tonometers provided high reproducibility in both positions (all intraclass correlation coefficients > 0.90), although it was highest with GAT, followed by IC200-continuous and IC200-single and then IcarePRO. In the sitting position, the mean (± SD) IOPs of GAT, IcarePRO, IC200-single, and IC200-continuous were 14.5 ± 2.9 mmHg, 13.3 ± 3.2 mmHg, 11.6 ± 3.2 mmHg, and 11.5 ± 3.2 mmHg, respectively. IOPs measured with IcarePRO or IC200 were significantly lower than those with GAT, particularly in patients with low IOP. IOPs measured with all tonometers were significantly elevated in the supine position as compared with the sitting position, but this difference was significantly greater with IC200-single and IC200-continuous compared with IcarePRO. IOP elevation was significant in eyes without bleb versus those with bleb, but this finding was not observed when IOP was measured with IcarePRO. The IOPs of the single and continuous modes of IC200 were interchangeable in both positions.

Conclusions

GAT, IcarePRO, and IC200 had sufficiently high reproducibility, but measurements with IcarePRO may not be accurate in the supine position. Elevation of IOP in the supine position, especially in eyes with bleb, was more sensitively captured with IC200 than with IcarePRO.

Trial registration

Japan Clinical Trials Register, No. UMIN000039982.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40662-021-00249-z.

Changes in intraocular pressures associated with inhalational and mixed anesthetic agents currently used in ophthalmic surgery

Purpose:

The aim of this study was to measure changes in intraocular pressures (IOPs) associated with inhalational and mixed anesthetic agents currently used for general anesthesia (GA) in ophthalmic surgery.

Methods:

In a cross-sectional study, 48 eyes from 48 consecutive subjects that underwent ophthalmic surgery under GA were included. Mixed anesthetics were used in 26 eyes and sevoflurane in 22 eyes. IOPs of the nonsurgery eyes were recorded at T1 (5 min before induction of anesthesia), T2 (5 min after intubation), and T3 (at the conclusion of surgery before extudation) using ICare PRO and Perkins tonometers. Linear mixed-effects models were used to compare differences in IOPs at various time points. Outcome measures were changes in IOP after induction of GA, intubation, and just before extubation and comparisons of decreases in IOPs induced by sevoflurane and mixed anesthetics.

Results:

Mean preanesthesia IOP for patients in this study (mean age ± standard deviation = 26.9 ± 18.3 years; range: 5–70 years) was 17.9 ± 4.9 (range: 10–30) mm Hg. There was a significant decrease in the mean IOP (standard error (SE) (in mm Hg) at T2 (Perkins: –4.65 (0.57); ICare PRO: –5.16 (0.56) and T3 (Perkins: –5.63; ICare PRO: –5.36) as compared to the IOP at T1 (P < 0.001). The decreases in IOPs at T2 and T3 were similar in both anesthetic groups (T2:P = 0.60; T3: P = 0.33).

Conclusion:

Significant decreases in IOPs after GA were observed and the differences were not significantly different between sevoflurane and mixed anesthetic agents. For management decisions in pediatric glaucoma, the IOP measurements under GA are crucial, the underestimation of IOP as noted with currently used anesthetic agents has to be accounted for and decisions are taken appropriately.

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.

Correlation of iCare ic100 tonometry with iCare TA01i in screening of unselected population in Northern Finland Birth Cohort Eye study

PURPOSE

iCare tonometers are easy-to-use and portable devices for measuring the intraocular pressure (IOP). Purpose was to evaluate the IOP values measured by both novel iCare ic100 and conventional model TA01i devices in unselected population.

METHODS

IOP was measured with iCare ic100 and TA01i tonometers in 149 participants aged 32-33 years (born in 1985 or 1986) of the Northern Finland Birth Cohort Eye 2 study. The right eye of each participant was selected for analysis. We also collected data on axial length, corneal curvature and central corneal thickness (CCT). Bland-Altman plot was used for comparing the values obtained by these devices.

RESULTS

Mean IOP measured with the ic100 device was 13.8 (3.4) mmHg, with TA01i it was 12.5 (3.0) mmHg. The mean difference between these devices was 1.30 mmHg (p < 0.001) and R2 was 0.694. In Bland-Altman analysis, the agreement between the two tonometers ic100 and TA01i was constantly good (mean difference -1.30, ic100 device showing higher measures). There was a correlation between IOP and CCT (r = 0.269, p < 0.001 for ic100 and r = 0.255, p = 0.002 for TA01i), but not with IOP and corneal curvature or IOP and axial length.

CONCLUSION

In summary, we found ic100 rebound tonometry to be both reliable and effective, although CCT may influence IOP measurements with ic100 and TA01i. Therefore, iCare ic100 is suitable for IOP measurement in large cohort studies.

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.

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.

Error in measurement of intraocular pressure with the Icare and IcarePRO

PURPOSE

We sought to determine whether changes in the measurement angle of the Icare TA01i and IcarePRO tonometers led to errors in the measurement of intraocular pressure (IOP).

METHODS

In this prospective, single-facility study, we analyzed 77 patients from November 2017 to September 2019. We measured IOP with the Icare TA01i and IcarePRO while changing the angle of the device with the cornea center and analyzed the associated changes in the measurement.

RESULTS

IOP measured with the Icare tilted - 30°, - 15° vertically was significantly higher than that measured with the Icare tilted horizontally (p < 0.0001, p < 0.0001). The IOP measured with a + 10° vertical tilt was significantly lower than that measured horizontally (p < 0.0001). When the IcarePRO was tilted + 90° vertically, the IOP was significantly lower with the patient in the supine position than in the lateral position (p = 0.00058).

CONCLUSIONS

IOP measured with the Icare and IcarePRO is affected by the measurement angle. The study results will direct the clinicians to exercise extra precautions in determining the measurement angle while measuring IOP.

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.

Analysis of reproducibility, evaluation, and preference of the new iC100 rebound tonometer versus iCare PRO and Perkins portable applanation tonometry

Objectives:

To analyze the reproducibility of the new iC100 rebound tonometer, to compare its results with the applanation tonometry and iCare PRO and to evaluate the preference between them.

Materials and methods:

For the study of reproducibility, 15 eyes of 15 healthy Caucasian subjects were included. Three measurements were taken each day in three separate sessions. For the comparative study, 150 eyes of 150 Caucasian subjects were included (75 normal subjects and 75 patients with glaucoma). Three consecutive measurements were collected with each tonometer, randomizing the order of use. The discomfort caused by each tonometer was evaluated using the visual analogue scale.

Results:

No statistically significant differences were detected between sessions. In the comparison between tonometers, the measurements with iC100 were statistically lower than those of Perkins (−1.35 ± 0.417, p = 0.004) and that iCare PRO (−1.41 ± 0.417, p = 0.002). The difference between PRO and Perkins was not statistically significant ( p = 0.990). The mean time of measurement (in seconds) with iC100 was significantly lower than with Perkins (6.74 ± 1.46 vs 15.53 ± 2.01, p < 0.001) and that PRO (6.74 ± 1.46 vs 11.53 ± 1.85, p < 0.001). Visual analogue scale score with iC100 was lower than Perkins (1.33 ± 0.99 vs 1.73 ± 1.10, p < 0.05). In total, 61.7% preferred iC100 against Perkins.

Conclusion:

The reproducibility of this instrument has been proven good. iC100 underestimates intraocular pressure compared to applanation tonometry at normal values and tends to overestimate it in high intraocular pressure values. Most of the subjects preferred iC100 tonometer.

Effect of Topical Hypotensive Medications for Preventing Intraocular Pressure Increase after Cataract Surgery in Eyes with Glaucoma

PURPOSE

To compare the effects of a topical intraocular pressure (IOP)-lowering medication for preventing an IOP increase after cataract surgery in eyes with glaucoma.

DESIGN

Randomized clinical study.

METHODS

A total of 165 eyes of 165 patients with primary open-angle glaucoma or pseudoexfoliation glaucoma scheduled for phacoemulsification were randomly assigned to 1 of 3 groups to receive each medication immediately postoperatively: 1) prostaglandin F_2α analog (travoprost), 2) β-blocker (timolol maleate), or 3) carbonic anhydrase inhibitor (brinzolamide). Intraocular pressure (IOP) was measured using a rebound tonometer at 1 hour preoperatively, at the end of surgery, and at 2, 4, 6, 8, and 24 hours postoperatively. The incidence of eyes exhibiting a marked IOP increase to greater than 25 mm Hg was compared among the groups.

RESULTS

At 1 hour preoperatively and at the end of surgery, mean IOP did not differ significantly among the groups. Mean IOP increased significantly between 4 and 8 hours postoperatively and then decreased at 24 hours postoperatively in all groups (P < .0001). Mean IOP was significantly lower in the brinzolamide group than in the travoprost or timolol group at 4, 6, and 8 hours postoperatively (P ≤ .0374) and did not differ significantly among groups at 2 and 24 hours postoperatively. The incidence of an IOP spike was significantly lower in the brinzolamide group than in the travoprost and timolol groups (P = .0029).

CONCLUSIONS

Brinzolamide reduces the short-term IOP increase after cataract surgery more effectively than travoprost or timolol in eyes with glaucoma, suggesting that brinzolamide is preferable for preventing an IOP spike.

Meta-analysis of the concordance of Icare® PRO–based rebound and Goldmann applanation tonometry in glaucoma patients

Background:

The Icare® PRO rebound tonometer is being promoted as a patient-friendly device for glaucoma detection and monitoring, allowing rapid and accurate intraocular pressure measurement avoiding anaesthesia. The aim of this systematic review was to examine the concordance of Icare® PRO and Goldmann applanation tonometry in glaucoma patients.

Methods:

The German and English literature research was carried out using PubMed and Cochrane Library between January 2010 and March 2018. Method comparison trials in a paired sample study design were identified. Search criteria were ‘Icare PRO’, ‘Rebound’, ‘Goldmann’ and ‘Applanation’. Adult patients with glaucoma of any aetiology were included. The intraindividual intraocular pressure deviation between Icare® PRO and Goldmann applanation tonometry (mm Hg) served as primary endpoint, parameterized by the reported mean differences. For each study, an asymptotic 95% confidence interval was derived. The overall intraocular pressure meta-difference (Icare® PRO-Goldmann applanation tonometry) and 95% confidence interval were estimated using the random effect model.

Result:

Of 147 publications, 6 studies (672 eyes) were included after reviewing. Four studies showed an intraocular pressure underestimation by the Icare® PRO, two an overestimation. The meta-difference (Icare® PRO-Goldmann applanation tonometry = −0.14 mm Hg; 95% confidence interval: (−0.43 mm Hg; 0.15 mm Hg)) indicated a non-significant, clinically irrelevant mean deviation (p = 0.335). The devices showed good agreement, but there was a strong heterogeneity between the studies (I² = 77%): two studies presented a significant difference (Icare® PRO-Goldmann applanation tonometry), however, with deviations in opposite directions.

Conclusion:

Although the manufacturer advertises the Icare® PRO as a ‘tonometer with superior accuracy’, the present review could neither confirm nor deny considerable agreement between Goldmann applanation tonometry and Icare® PRO in glaucomatous patients.

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.

[Application of rebound self-tonometry for measurements in a supine position]

BACKGROUND

Diurnal or nocturnal fluctuations of intraocular pressure (IOP), which are especially common in glaucoma patients, often require hospitalization of the patient in order to be detected. This is often inconvenient for the patient. Therefore, this study evaluated the usefulness of a rebound tonometer (RT) designed for IOP self-tonometry (RT-Home) in an outpatient department, especially in the supine position and out of office hours.

METHODS

Over a period of 6 months unselected open-angle glaucoma patients were equipped with a RT-home device for one night each. At the beginning IOP values measured by medical personnel (RT-Home(o)) were compared with IOP measured by the patient (RT-Home(p)), as well as measured by applanation tonometry according to Goldmann (GAT). Patients also completed a questionnaire regarding subjective comfort during use of the RT-Home.

RESULTS

The RT-Home(o) showed a bias of -1.1 mm Hg (-7.9 to 5.7 mm Hg) compared to GAT and RT-Home(p) showed a bias of -1.6 mm Hg (-8.9 to 5.9 mm Hg) compared to GAT. The measurement differences between GAT and RT-Home(o) as well as RT-Home(p) showed a stong correlation with the IOP and the central corneal thickness (IOP: r = 0.481, P > 0.0001, RT-Home(o) vs. GAT; corneal thickness: r = 0.612, P < 0.0001, RT-Home(o) vs. GAT). The RT-Home(p) in a supine position showed significantly elevated IOP levels than during the day (P < 0.0001). The RT-Home showed no qualitative differences between measurements in supine and sitting positions.

DISCUSSION

The RT-Home is effective and precise for use in an outpatient department to gain a general overview over patients' IOP out of office hours and also in the supine position. In the long term it seems possible that RT-Home can avoid hospitalization for diurnal and nocturnal IOP evaluation especially of young, mobile patients; however, interpretation of the data always requires professional knowledge.

Icare® rebound tonometers: review of their characteristics and ease of use

The rebound tonometer has a unique mechanism for measuring intraocular pressure (IOP) and has become popular worldwide due to its ease of use. The most notable advantages are the lack of an air-puff and need for topical anesthesia, ease of operation and transport, and the ability to use it with children. Four rebound tonometers (Icare® TA01i, Icare PRO, Icare HOME, and Icare ic100) are currently available for clinical examination. It is important to understand the characteristics of each tonometer and select the most appropriate one because the IOP values and the purpose of measurement are different. In this review, with the goal of improving the understanding of a range of tonometers, the issues with each device are discussed.

Effect of anesthesia on intraocular pressure measurement in children

Measurement of the intraocular pressure (IOP) is central to the diagnosis and management of pediatric glaucoma. An examination under anesthesia is often necessary in pediatric patients. Different agents used for sedation or general anesthesia have varied effects on IOP. Hemodynamic factors, methods of airway management, tonometry technique, and body positioning can all affect IOP measurements. The most accurate technique is one that reflects the awake IOP. We review factors affecting IOP measurements in the pediatric population and provide recommendations on the most accurate means to measure IOP under anesthesia based on the present literature.

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.

Rebound tonometry over an air-filled anterior chamber in the supine child after intraocular surgery

BACKGROUND

Intracameral air is a critical component of multiple ophthalmic surgical procedures and is frequently used in pediatric intraocular surgery. Among other benefits, it helps to facilitate postoperative examination in uncooperative children by allowing quick confirmation of a formed anterior chamber. The purpose of this study was to evaluate the usefulness and accuracy of a position-independent rebound tonometer (Icare PRO) in measuring intraocular pressure (IOP) intraoperatively in pediatric eyes with intracameral air compared to a commonly used handheld applanation tonometer (Tono-Pen XL).

METHODS

In this prospective study of sequential children undergoing intraocular surgery, IOP was measured immediately following general anesthesia induction using both Icare PRO rebound tonometry and Tono-Pen XL tonometry, with instrument order randomized, in the supine child's eye(s). At completion of surgery after standard placement of intracameral air IOP was again measured using both instruments.

RESULTS

A total of 42 eyes of 30 children were included. Surgeries included glaucoma (25), cataract-related (16), and both (1). Mean preoperative IOP by Tono-Pen XL was 23.52 ± 9.76 mm Hg; by Icare PRO, 20.94 ± 10.01 mm Hg (P = 0.0012). Mean IOP over intracameral air at surgery conclusion by Tono-Pen XL (n = 41) was 12.66 ± 4.90; by Icare PRO (n = 42), 12.96 ± 5.10 mm Hg (P = 0.46). One eye had postoperative IOP unrecordable by Tono-Pen XL but 7.9 mm Hg by Icare PRO. Bland-Altman analysis, which included only paired measurements, showed a preoperative mean difference in IOP (ΔIOPT-I) of 2.58 mm Hg (95% CI, -6.86 to 12.02); postoperative mean ΔIOPT-I of -0.42 mm Hg [95% CI, -7.57 to 6.73].

CONCLUSIONS

Position-independent rebound tonometry (Icare PRO) accurately measured IOP in supine children's eyes postoperatively in the presence of intracameral air.

Comparison of Intraocular Pressure Measurements Obtained by Icare PRO Rebound Tonometer, Tomey FT-1000 Noncontact Tonometer, and Goldmann Applanation Tonometer in Healthy Subjects

PURPOSE

To compare intraocular pressure (IOP) measurements obtained by Icare PRO rebound tonometer (RT), Tomey FT-1000 noncontact tonometer (NCT), and Goldmann applanation tonometer (GAT) in healthy subjects, and to investigate the influence of central corneal thickness (CCT) on IOP measurements.

METHODS

A total of 132 eyes of 66 healthy subjects were included in the study. All IOP measurements were applied in a sitting position and always in the same order (RT, NCT, and GAT). CCT was measured by noncontact anterior segment optical coherence tomography.

RESULTS

The mean CCT was 523.5±31.2 μm. The mean IOPs with GAT, NCT, and RT measurements were 14.56±2.77, 13.42±2.99, 14.18±2.55 mm Hg, respectively. A significantly good agreement was found between RT and GAT measurements (P=0.515). The mean difference between RT and GAT measurements was -0.38 mm Hg. An underestimation was found in NCT measurements compared with GAT ones as defined from paired comparisons (P=0.003). The mean difference between NCT and GAT measurements was -1.14 mm Hg. There was no significant difference between NCT and RT readings (P=0.069). The mean difference between NCT and RT measurements was -0.76 mm Hg. There was a significant correlation between GAT-NCT (r=0.740, P<0.001), GAT-RT (r=0.743, P<0.001), NCT-RT (r=0.729, P<0.001) measurement methods. The increment in measured IOP for a 10 μm increase in CCT was 0.16, 0.33, and 0.18 mm Hg for the GAT, NCT, and RT, respectively.

CONCLUSIONS

The IOP readings with the new Icare PRO RT showed good correlation with those obtained by GAT. Tomey FT-1000 NCT underestimated the IOP compared with GAT.

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.

The effect of nocturnal CPAP therapy on the intraocular pressure of patients with sleep apnea syndrome

PURPOSE

Few studies have documented that nocturnal continuous positive airway pressure (CPAP) therapy is associated with an increase in intraocular pressure (IOP) in patients with severe obstructive sleep apnea syndrome (OSAS). We re-examined the effect of CPAP therapy on the IOP of OSAS patients.

METHODS

The IOP of two different groups of newly diagnosed OSAS patients was compared at their first sleep lab exam without CPAP treatment (non-CPAP treated group; n = 20) and at the second sleep lab exam with CPAP treatment (CPAP treated group; n = 31). The sleep lab exam (sleep period: from 11:00 p.m. until 6:00 a.m.) included IOP measurements, a complete ophthalmologic exam, and nocturnal hemodynamic recordings. The IOP was measured serially using rebound tonometer (IOP; ICARE® PRO) performed while in sitting and supine positions before, during, and after the sleep period. We compared the difference in IOP of CPAP and non-CPAP groups.

RESULTS

The mean IOP of the CPAP and non-CPAP groups measured in sitting position before the sleep period was 13.33 ± 2.04 mmHg and 14.02 ± 2.44 mmHg, respectively (p = 0.9). Assuming a supine position for 1 minute significantly increased the IOP by 1.93 mmHg and 2.13 mmHg for both the non-CPAP and CPAP groups (paired t-test; p = 0.02, p = 0.001 respectively), but this IOP rise showed no difference between the two groups. The IOP increased significantly further after 7 hours of sleep in the supine position, and the mean IOP of the CPAP and non-CPAP groups was 19.2 ± 5.68 mmHg and 19.69 ± 5.61 mmHg respectively (independent t-test; p = 0.74). The rise in IOP for both groups was not correlated with any hemodynamic parameters. Three OSAS patients with glaucoma treated with CPAP had mean IOP of 23.75 mmHg after 7 hours of sleep.

CONCLUSIONS

OSAS patients have a significant rise in IOP during the sleep period when comparing measurements before and after the sleep period; however, CPAP therapy did not affect the measured IOP. The presented findings suggest that in terms of IOP, CPAP is safe for non-glaucomatous patients, but this may not hold true for glaucomatous patients.

Intraocular pressure in children: the effect of body position as assessed by Icare and Tono-Pen tonometers

PURPOSE

To explore the effect of body position (sitting vs supine) on intraocular pressure (IOP) in children, as assessed by the Icare PRO and the Tono-Pen.

DESIGN

Prospective clinical study.

METHODS

Children with known or suspected glaucoma and those without glaucoma were recruited from the Duke Eye Center pediatric clinic. Subjects underwent tonometry in both eyes while upright (sitting), after instillation of topical anesthetic, with either the Icare PRO or the Tono-Pen first, and then the second instrument (order randomized). Goldmann applanation tonometry (GAT) was then performed by a clinician masked to the previous measurements. The subjects were then placed in the supine position for 5 minutes, and tonometry using the Icare PRO and the Tono-Pen was obtained, in the same order used when they were the sitting position.

RESULTS

Enrolled were 47 children (94 eyes). Mean seated IOP for GAT, Icare PRO and Tono-Pen were 16.4 ± 4.2, 17.5 ± 3.5, and 18.0 ± 3.9 mm Hg, respectively. The mean supine IOP for the Icare PRO and Tono-Pen were 18.4 ± 4.5 and 18.8 ± 4.2 mm Hg, respectively. This rise was +0.9 ± 2.3 mm Hg for Icare PRO (P = 0.01) and +0.7 ± 1.8 mm Hg for Tono-Pen (P = 0.009), respectively.

CONCLUSION

In children, Icare PRO tonometry correlates well with GAT in the sitting position, and with the Tono-Pen in both the sitting and supine positions. IOP rises when a child changes position from sitting to supine when measured by the Icare PRO or the Tono-Pen. However, the increase, which is less than 1 mm Hg, seems clinically insignificant and is unlikely to alter glaucoma management in children.

Comparative measurement of intraocular pressure by Icare tonometry and Airpuff tonometry in healthy subjects and patients wearing therapeutic soft contact lenses

BACKGROUND

The aim of the present study was to compare the measurement of intraocular pressure (IOP) through a therapeutic soft contact lens with the "native" measurement. We additionally investigate whether a rebound tonometer (RT) or non-contact tonometer (NCT) is more suitable to measure IOP through a bandage contact lens.

METHODS

The IOP was determined using each of the two methods, three times successively with (lens measurement) and without (native measurement) a soft contact lens. The Icare tonometer (Icare® TA01i, Icare Finland Oy, 23 subjects) and the Airpuff tonometer (Nidek NT 53OP, Nidek CO., LTD, Hiroishi Gamagori, Aichi, Japan, 16 subjects) were used. We compared the mean values (validity parameter) and standard deviation (precision parameter) of the three individual measurements in each case using the paired t-test. In addition, we conducted a power analysis to estimate the maximum error in the measurement caused by the contact lens (power level set to 0.8).

RESULTS

With the Airpuff tonometer we detected no statistically significant between the lens and the native measurement (15.6 ± 2.6 vs. 15.3 ± 2.6 mmHg; p = 0.42). The power analysis revealed that the maximum error caused by the contact lens was 1.2 mmHg. The Icare tonometry, however, trended toward higher values in the contact lens measurements (17.5 ± 4.3 vs. 16.4 ± 3.5 mmHg in the native measurements; p = 0.05). Interestingly, this difference exhibited a statistically significant correlation with the corneal thickness (0.03 mmHg per μm corneal thickness; p = 0.04).

CONCLUSION

The use of NCT and RT for IOP measurement over a soft contact lens is feasible. The accuracy appears to be sufficient for the most common clinical applications.