Comparison of ICare tonometer with Goldmann applanation tonometer in glaucoma patients

[Mobile intraocular pressure measurement. From palpation to initial clinical experience with the handheld dynamic contour tonometer]

Goldmann applanation tonometry is still the gold standard of intraocular pressure measurement (IOP) and an essential part in the diagnosis of glaucoma. Applanation tonometry is usually performed on a sitting patient at the slit lamp. However, under certain circumstances it is necessary to measure the IOP outside the office setting. With handheld devices the measuring procedure is brought to bedside and surgery theatres, as well as to patients who are not able to sit behind the slit lamp. The dynamic contour tonometer (DCT) represents a new method of direct IOP measurement. Its physical principle is based on piezo-electronic contour matching tonometry and is claimed to be less dependent on biochemical properties of the cornea. Besides the IOP, the ocular pulse amplitude can also be measured. Until now, the DCT had been available as a slit lamp mounted device. In this report, we present a portable prototype of the device. In comparison with the Perkins tonometer and the TONO-PEN XL, the handheld DCT shows smaller intra- and inter-examiner variability. Additionally, the device offers the unique possibility to display the ocular pulse amplitude while the patient is in a horizontal position.

Minimal cross-infection risk through Icare rebound tonometer probes: a useful tool for IOP-screenings in developing countries

AIMS

Recently, a new rebound tonometer has been introduced into the market, which might be useful for glaucoma screenings in developing countries. Disposable probes, that are potentially reusable, are recommended by the manufacturer. Our study aimed to address the question of microbial transmission risks if the probes are reused.

METHODS

IOP measurements were obtained from 100 healthy eyes. The used probes were inoculated on broth and culture media. In addition, 10 probes were analyzed using environmental scanning electron microscopy in saturated hydrogen-steam atmosphere after usage and wipe disinfection technique with Sekusept 4% solution or Isopropanol 70%.

RESULTS

No bacterial or fungal growth could be detected in any of the inoculated agar plates or broth tubes. No microorganisms, clumps of cells, or single intact epithelium cells were detected in any of the probes using environmental scanning electron microscopy. Cell debris was detected on seven probes; three probes were completely free of any residual cell elements.

CONCLUSION

Transmission of possibly infective material through reused probes is significantly less than for reusable Goldmann probes if the same sterilization protocols are applied. Re-usage of the probes appears safe and is helpful in avoiding unnecessary costs.

The iCare rebound tonometer: comparisons with Goldmann tonometry, and influence of central corneal thickness

PURPOSE

To assess agreement between the iCare rebound tonometer and Goldmann tonometry and to assess the influence of central corneal thickness and the value of scleral rebound tonometer readings.

METHODS

Prospective single-centre cross-sectional study comparing iCare rebound tonometer (RT) intraocular pressure (IOP) readings taken from corneal and scleral locations to Goldmann applanation tonometer (GAT) readings in 100 subjects attending ophthalmology clinics.

RESULTS

There was a significant difference between RT and GAT, with RT tending to overestimate IOP. The mean difference between RT and GAT measurements was 3.36 mmHg. The mean difference between the log of RT and the log of GAT measurements was 0.2356, a ratio of 1.27 (P < 0.0001). A formula derived from a linear regression analysis suggested that a 10% increase in CCT increased the RT IOP reading by 9.9%. Scleral RT readings showed no relationship to GAT readings.

CONCLUSIONS

The rebound tonometer cannot replace the Goldmann tonometer in the office setting given the wide limits of agreement between the two devices. Corneal rebound tonometer readings are influenced by CCT whereas scleral rebound tonometer readings are of no value.

The influence of refractive errors on IOP measurement by rebound tonometry (ICare) and Goldmann applanation tonometry

PURPOSE

To evaluate the effect of refractive errors and central corneal thickness (CCT) on the measurement of intraocular pressure (IOP) by ICare rebound tonometer (RT), and its agreement with measurements by Goldmann applanation tonometer (GAT).

PATIENTS AND METHODS

Two observers measured the IOP by using RT and GAT in four groups of healthy volunteers with emmetropic (n = 78), hyperopic (n = 83), myopic (n = 87) and astigmatic (n = 79) eyes. Refraction was assessed by an autorefractometer. CCT was assessed by ultrasound pachymetry.

RESULTS

In all groups, no significant interobserver difference was seen in IOP values detected by both tonometers (Wilcoxon signed-rank test not significant). In all groups, IOP values were higher as measured by RT than by GAT (paired t-test p = 0.000): mean RT-GAT difference was higher in myopic eyes (+1.6 +/- 1.8 mmHg), and it was less than 1 mmHg in the other groups. RT-GAT difference was correlated to the refraction (p < 0.001), and it was greater when an higher IOP was detected by RT (significant correlation between RT-GAT difference and IOP by RT, p < 0.001). Compared with GAT values, the IOP readings by RT were greater than 2 mmHg in respectively 17.9% (emmetropic), 13.3% (hyperopic), 34.5% (myopic) and 7.6% (astigmatic) of the eyes. With both tonometers, in all groups the IOP values were correlated with CCT (p < 0.05), but the discrepancy between RT and GAT values was not related to CCT.

CONCLUSIONS

In all groups of subjects, higher IOP values were detected by RT; the IOP readings exceed the GAT values usually in a range of less than 1 mmHg, except when RT detects IOP >18 mmHg and generally in myopic eyes; RT-GAT discrepancy is related to the refractive error, but not to CCT.

Effects of corneal thickness on intraocular pressure measured with three different tonometers

PURPOSE

To compare intraocular pressure (IOP) measured by a Goldmann applanation tonometer (GAT), a noncontact tonometer (NCT), and a portable noncontact tonometer (PNCT) in eyes of healthy volunteers, and to determine if a significant correlation exists between the IOP and the central corneal thickness (CCT).

METHODS

A total of 144 healthy participants were randomly assigned to one of two groups; in the first group, IOP was measured first with the NCT and then with the GAT. In the second group, IOP was measured first with the PNCT and then with the GAT. Subsequently, the CCT of all subjects was measured with an ultrasonic pachymeter.

RESULTS

The IOPs determined by the GAT and NCT and were strongly correlated, as were those determined by the GAT and PNCT, in both groups. However, a Bland-Altman plot showed that the correlations between the GAT and NCT and between the GAT and the PNCT measurements were not significant. With all three instruments, the IOP readings varied with the CCT. The mean IOPs obtained with the GAT increased by 0.23 mmHg with each 10-microm increase in CCT (0.23 mmHg/10 microm). The comparable value for the NCT was 0.29 mmHg/10 microm, and that for the PNCT was 0.31 mmHg/10 microm.

CONCLUSIONS

For measurements of IOP in normal eyes, the GAT is the tonometer least affected by the CCT, compared with the PNCT and NCT. A PNCT is more likely to be affected by variations in CCT than the GAT.

Pascal, ICare and Goldmann applanation tonometry--a comparative study

PURPOSE

To compare intraocular pressure (IOP) measurements by Pascal, ICare and Goldmann applanation tonometry (GAT), to evaluate the effects of central corneal thickness (CCT) and curvature on IOP measurement and to estimate the intra-observer variability.

METHODS

A prospective, single-centre study of 150 eyes with a wide range of pressures. Six masked IOP measurements/method; corneal thickness and curvature were studied for each eye. GAT was the reference.

RESULTS

IOPPascal and IOPICare correlated with IOPGAT (r = 0.91, 0.89). Mean ICare measurement exceeded GAT by 2 mmHg. Pascal measured higher than GAT at low IOPs and lower at high IOPs. For every 10 mmHg increase in IOP above 31 mmHg, Pascal measured 2 mmHg lower than GAT and vice versa. CCT was correlated significantly with IOPGAT (r = 0.23) and IOPICare (r = 0.43) but not with IOPPascal (P = 0.12). CCT was correlated with age. In a subgroup (>50 years), ICare and the difference between IOPGAT and IOPPascal were affected significantly by the CCT, whereas IOPGAT and IOPPascal were not. Corneal curvature was correlated significantly with IOPGAT (r = -0.27) and IOPPascal (r = -0.26) but not with IOPICare (P = 0.60). Intra-observer variability within each set of six measurements was approximately 2 mmHg, irrespective of method.

CONCLUSION

This study showed a reasonable overall correlation and concordance between the IOP obtained with the three instruments. None of the methods were completely independent of the biomechanical properties of the cornea. ICare showed a significant dependency upon CCT, whereas GAT and Pascal showed a significant dependency on corneal curvature. All methods showed intra-observer variability, which leaves room for further improvement of methods.

Clinical comparison of the Icare tonometer and Goldmann applanation tonometry

PURPOSE

To compare a new method of intraocular pressure (IOP) measurement, using the Icare tonometer, with Goldmann applanation tonometry (GAT).

PATIENTS AND METHODS

Two observers obtained IOP readings in 292 eyes (143 right and 149 left) of 153 subjects, using the Icare without topical anesthetic. A GAT reading was subsequently obtained by a consultant ophthalmologist, without the knowledge of the Icare readings. Central corneal thickness (CCT) was obtained on all eyes with ultrasound pachymetry. Patient comfort after IOP measurement was assessed in a consecutive subset of patients.

RESULTS

The intraclass correlation coefficient between the 2 modalities of IOP measurement was r=0.95 for the right and r=0.93 for the left eye. The mean difference (Icare-GAT) between the IOP measured by the 2 methods was 0.4 mm Hg in the right eye (SD 3.0, 95% confidence interval -5.5 to 6.3), and 0.8 mm Hg in the left eye (SD 3.0, confidence interval -4.7 to 6.2). GAT measurements did not vary with CCT [correlation coefficient=0.09 (P=0.25) right and 0.14 (P=0.09) left eyes]. However, IOP measured with Icare tonometry increased with increasing CCT [correlation coefficient=0.16 (P=0.05) right and 0.21 (P=0.01) left eyes]. For every 100-microm increase in CCT, the difference (Icare-GAT) increased by 1 mm Hg. Of the 38 consecutive patients surveyed, 28 (73.7%) rated the Icare more comfortable than GAT, with only 2 (5.3%) rating it less comfortable (P<0.001).

CONCLUSIONS

There is good correlation between the 2 methods of IOP measurement, even at extremes of IOP. The Icare instrument was easy to use and recorded rapid and consistent readings with minimal training. It seems to be more comfortable than GAT and obviates the need for topical anesthesia.

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

BACKGROUND

The aim of this study was to compare the intraocular pressure (IOP) results measured by the iCare rebound tonometer with those obtained by the Goldmann applanation tonometer (GAT) over a wide range of IOP values. Furthermore, the comfort level of the iCare measurement was evaluated.

METHOD

The study included 75 eyes of 75 patients. The patients were divided into three groups (7-15 mmHg n = 25, 16-22 mmHg n = 25, 23-60 mmHg n = 25). The measurements were taken by two independent observers in a masked fashion. All patients were asked about discomfort during the iCare measurement. To establish the agreement between the two devices, a Bland-Altman analysis was performed.

RESULTS

Overall, the 95% confidence interval of the differences between the two devices was -8.67 to 10.25 mmHg and in 62.7%, the iCare measurement was within +/-3 mmHg of the GAT measurements. The distribution of the differences in IOP was similar, from 7-22 mmHg. In the higher IOP range (23-60 mmHg), however, the deviation was almost twice as large. The measurement with the iCare tonometer was well tolerated; 100% of the patients denied any discomfort.

CONCLUSIONS

The iCare tonometer is a mobile alternative to GAT in a low to moderate IOP range, but our findings show a greater deviation than previously reported. In high IOP values, measurements with the iCare tonometer do not correlate well with GAT.

The influence of corneal properties on rebound tonometry

PURPOSE

To determine the influence of corneal thickness, corneal hysteresis (CH), and corneal resistance factor (CRF) on intraocular pressure (IOP) measurements obtained using the iCARE rebound tonometer.

DESIGN

Cross-sectional study.

PARTICIPANTS

One hundred twenty-five eyes of 125 normal healthy subjects.

METHODS

Intraocular pressure was determined in all subjects using the iCARE at both central and temporal corneal regions. Corneal thickness at these 2 regions was determined by ultrasonic pachymetry. Corneal hysteresis and corneal resistance factor were measured using an ocular response analyzer. Goldmann applanation tonometry (GAT) was also performed on all eyes.

MAIN OUTCOME MEASURES

Intraocular pressure, corneal thickness, corneal hysteresis, and corneal resistance factor.

RESULTS

Although the peripheral cornea was significantly thicker than the central cornea, IOPs obtained by the iCARE at the 2 regions were similar and significantly higher than GAT measurements. There were an overestimation at higher IOPs and an underestimation at lower IOPs relative to GAT measurements. Multiple regression analysis showed a significant correlation between the iCARE and CH (partial correlation r = -0.67, P<0.01) and CRF (partial correlation r = 0.82, P<0.01). The correlation between the iCARE and central corneal thickness was not significant.

CONCLUSIONS

Rebound tonometry is affected by corneal properties including CH and CRF but not corneal thickness.

Comparison of the rebound tonometer with the Goldmann applanation tonometer in glaucoma patients

PURPOSE

To determine the agreement between the measurement of intraocular pressure (IOP) by the rebound tonometer (RBT) and by the Goldmann applanation tonometer (GAT) and to find out the effect of central corneal thickness (CCT) values on IOP measurements in glaucoma patients.

METHODS

IOP was measured with the RBT and GAT, respectively, in 61 eyes of 61 glaucoma patients. CCT was measured using an ultrasonic pachymeter after all IOP determinations had been made. The mean IOP measurement by the RBT was compared with the measurement by the GAT, by Student's t-test. Bland-Altman analysis was performed to assess the clinical agreement between the two methods. The effect of CCT on measured IOP was explored by linear regression analysis.

RESULTS

The mean patient age was 56.7+/-21.1 years (range: 30-80 years). There were 32 (52.46%) women and 29 (47.54%) men in the study group. The mean IOP readings were 18.70+/-4.76 mmHg using the RBT, and 18.27+/-3.49 mmHg using the GAT. The difference was not statistically significant (mean difference 0.43+/-2.55, P=0.2). A frequency distribution of the differences demonstrated that in more than 80% of cases the IOP readings differed by <2.3 mmHg between the RBT and GAT. There was a strong correlation between the RBT and GAT readings (r=0.852, P<0.0001). The IOP measurements with the two methods were correlated with CCT (r=0.40, P=0.02 for the RBT and r=0.48, P<0.0001 for the GAT). The IOP increased 1.1 mmHg and 8 mmHg for every 100-microm increase in CCT for the GAT and RBT, respectively.

CONCLUSION

The RBT slightly overestimated the IOP value by 0.43 mmHg on average when compared with the GAT. Nevertheless, the RBT readings appeared to be more affected by the various thicknesses of different corneas when compared with those obtained using the GAT.

Rebound Tonometer Compared With Goldmann Tonometer in Normal and Pathologic Corneas

PURPOSE

To compare the intraocular pressure (IOP) measurements obtained with the rebound tonometer (RT) and the Goldmann handheld tonometer (GT) in normal and altered corneas.

METHODS

A total of 208 normal corneas and 50 corneas with pathologies were included in this prospective study. All measurements were randomly obtained by 1 observer. The medians and interquartile range (IR) for both tonometers were compared. The median differences were assessed in IOP groups. Agreement between the tonometers was calculated using the Bland-Altman method.

RESULTS

The median IOP in all eyes was 17 mm Hg (IR, 13-22 mm Hg) with the RT and 16 mm Hg (IR, 13-21 mm Hg) with the GT (P < 0.001). The correlation was excellent between tonometers (r2 = 0.86; P < 0.001). The minimal differences between the two were obtained from 10 to 20 mm Hg (GT). The Bland-Altman scatterplot obtained good agreement between the instruments. In normal corneas, the median difference was < or =2 mm Hg in 77.4% of cases. In the altered corneas, the median difference was < or =2 mm Hg in 73% of cases (P = 0.21 compared with the normal group). In 10% and 2% of cases, the IOP could not be measured using the GT and RT, respectively.

CONCLUSIONS

The results were similar for both tonometers. In the altered corneas, the IOP could be difficult to obtain with the GT because of distorted half-circles. The 1-mm-diameter disposable RT tip facilitated obtaining measurements without anesthetic drops, which avoids infections. The RT could be useful in routine clinical settings when measuring IOP in corneas with pathologies.

Reproducibility and Tolerability of the ICare Rebound Tonometer in School Children

PURPOSE

To establish the intraobserver and interobserver reliability of the rebound tonometer (RBT) in healthy schoolchildren and to test patient tolerance in an unanesthetized eye.

SUBJECTS AND METHODS

To examine the reproducibility of the RBT, 2 experienced ophthalmologists undertook 3 consecutive intraocular pressure (IOP) measurements with the RBT without an anesthetic in 304 eyes of 152 healthy schoolchildren. Any pain or discomfort experienced by the children was recorded. Intraobserver and interobserver reliabilities were established by calculating correlation coefficients (r).

RESULTS

Of the 152 patients, 78 (51.3%) were males and 74 (48.7%) were females. The mean patient age was 11.2+/-2.6 years (range: 7 to 15 y). Mean IOP values obtained by examiners 1 and 2 were 16.48+/-2.82 mm Hg and 17.27+/-3.27 mm Hg for the right eyes and 17.15+/-3.36 mm Hg and 17.06+/-3.21 mm Hg for the left eyes. Intraobserver correlation coefficients for examiner 1 were 0.970 for the right eyes and 0.974 for the left eyes. For examiner 2, intraobserver correlation coefficients were 0.963 for the right eyes and 0.970 for the left eyes. The interobserver correlation coefficients were 0.798 for the right eyes and 0.858 for the left eyes (all P<0.0001). With the RBT, 98.6% of the subjects felt no pain and/or discomfort.

CONCLUSIONS

Measurement of IOP with the RBT is a highly reproducible method in schoolchildren showing high intraobserver and interobserver correlation and it seems to be very comfortable when performing IOP measurements in schoolchildren without an anesthetic.

Évaluation clinique du tonomètre dynamique Icare®

PURPOSE

The Icare dynamic tonometer (impact or Rebound tonometry) is a new tonometer based on making a moving object collide with an eye and on monitoring the motion parameters of this object following contact. The purpose of this study was to assess intra- and interobserver variability of IOP measurements with the Icare and their correlations with Goldmann applanation tonometry (GAT) and central corneal thickness (CCT).

MATERIAL AND METHODS

A prospective study including three groups of patients: group 1 (50 normal subjects), group 2 (50 patients with OHT or POAG and GAT IOP>22 mmHg), and group 3 (38 glaucomatous patients with GAT IOP< or =22 mmHg). In group 1, three consecutive IOP measurements were taken by three distinct observers with Icare followed by three GAT measurements by the same clinician. In group 2, the same procedure was followed from patients 1 to 25 and the reverse sequence from patients 25 to 50 after a 10-min break. In group 3, only one clinician took three GAT measurements followed by three Icare measurements after a 10-min break to exclude a tonographic effect in eyes with statistically normal-range IOPs.

RESULTS

: In group 1, intraobserver variability was about 6% for each observer (NS). There was no learning curve effect. The interobserver variation coefficient was 6.4%. Icare overestimated IOP compared to GAT (mean difference, 1.5-2.2 mmHg) (p<0.001). Icare IOP was 23.4 mmHg for observer 1 when GAT was 22 mmHg (95% individual CI, 18-28.9 mmHg). In group 2, intraobserver variation coefficients of the IOP ranged from 5% to 5.4% (NS). Icare overestimated IOP by mean 0.84 mmHg compared with GAT. In group 3, mean IOP was not different between Icare and GAT. Icare IOP of 20.7 mmHg corresponded to a value of 22 mmHg using GAT. In this group, correlations between CCT and IOP measurements were higher for Icare than for GAT (p=0.062).

CONCLUSION

Icare measures IOP in an unanesthetized sitting patient in a very brief time. Patient's minimal cooperation is needed. As long as the device is correctly positioned, the learning curve is short. Icare gives reproducible IOP measurements. Intra- and interobserver variability of IOP measurements are close to those of GAT. Icare overestimates IOP measurements an average 1.5 mmHg compared with GAT. Whatever the IOP level, Icare IOP measurements are well correlated with GAT. To a greater extent than for GAT, the reliability of IOP measurements is influenced by CCT. This tonometer can be used as a screening device for ocular hypertension as long as CCT measurements can be taken.