Rebound, Applanation, and Dynamic Contour Tonometry in Pathologic Corneas

Twenty-four hours intraocular pressure in keratoconic eyes assessed by applanation tonometry and Tono-Pen AVIA

AIM

To assess intraocular pressure (IOP) during the daily curve of intraocular pressure (DCPo) in keratoconic eyes and compare Goldmann applanation tonometer (GAT), without and with astigmatism correction (nGAT and cGAT) and Tono-Pen AVIA (TPA) assessment methods.

METHODS

Thirty-nine keratoconic eyes of 24 patients were assessed. DCPo was evaluated with five IOP measurements; four were performed with a GAT (nGAT and cGAT), and a Tono-Pen AVIA (TPA) at various times throughout the day.

RESULTS

Mean IOP DCPo values (mm Hg) were: nGAT, 9.9±2.6; cGAT, 11.3±2.6; TPA 12.3±3.1. Mean IOP DCPo differences (mm Hg) and Spearman's correlation coefficients were as follows: cGATc-nGAT, 1.32±1.31, r _s=0.879 (P<0.01); cGAT-TPA, -1.02±2.08, r _s=0.723 (P<0.01); and nGAT-TPA, -2.35±2.23, r _s=0.730 (P<0.01). Bland-Altman analysis for agreement between cGAT-TPA and nGAT-TPA mean IOP DCPo measurements revealed a mean difference of 1.02 (95%CI, 0.35-1.70) and 2.35 (95%CI, 1.62-3.07) mm Hg, respectively. Regression analysis yielded the following equation: TPA IOP=5.49+0.775×cGAT-0.015×ACD-0.299×corneal astig matism, which allowed us to infer TPA IOP values from other parameters.

CONCLUSION

In keratoconic eyes, IOP peaks of DCPo measurements are identified at 6 a.m., independent of the tonometer. The mean DCPo values are: TPA>cGAT>nGAT. IOP TPA measures are predictive of cGAT values, adjusted according to anterior chamber depth and corneal astigmatism.

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

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

Reliability of iCare ic100 Rebound Tonometry and Agreement With Goldmann Applanation Tonometry in Healthy and Post-myopic LASIK Patients

PRECIS

Rebound tonometry offers excellent reliability for obtaining intraocular pressure (IOP) measurements in healthy and post-myopic laser-assisted in situ keratomileusis (LASIK) patients regardless of corneal parameters and axial length and regardless of the instillation of ocular topical anesthesia.

PURPOSE

The purpose of this study was to assess the reliability of rebound tonometry, its agreement with Goldmann applanation tonometry (GAT) and its concordance after topical anesthesia in a group of nonoperated healthy patients and a group of post-myopic LASIK patients.

PATIENTS AND METHODS

Fifty-four patients were included in this prospective observational, case-control study. Patients were divided into 2 groups: control (n=32, 26.7±6.1 y) and LASIK (n=22, 35.8±7.6 y). Measurements of IOP were carried out using the iCare ic100 tonometer and GAT. The repeatability, intersession and interobserver reproducibility, GAT interchangeability and concordance after topical anesthesia of the iCare ic100 tonometer were assessed.

RESULTS

Clinical reliability of the iCare ic100 was excellent in terms of repeatability [intraclass correlation coefficient (ICC)=0.909 and 0.951 in control and ICC=0.938 and 0.961 in LASIK] as well as interobserver reproducibility (ICC=0.896 in control and 0.916 in LASIK) and concordance after anesthesia (ICC=0.910 in control and 0.972 in LASIK) in both groups. Intersession reproducibility was clinically good in nonoperated patients (ICC=0.758 and 0.849) and excellent in LASIK patients (ICC=0.878 and 0.904), although statistically significant differences were obtained in the control group for both examiners (P=0.003 for examiner 1 and P=0.04 for examiner 2). Agreement with GAT was good in both groups (ICC=0.805 in control and 0.790 in LASIK), although statistically different (P<0.001 and P=0.02, respectively). Finally, the iCare ic100 reliability was independent of corneal parameters and axial length in both groups (P>0.05 for all parameters).

CONCLUSIONS

Rebound tonometry offers good or excellent clinical reliability in both healthy and post-myopic LASIK patients. This article highlights the efficacy of iCare ic100 rebound tonometry as a reliable tool for the measurement of IOP and the management of glaucoma in healthy patients and patients undergoing myopic LASIK surgery.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Comparison of two rebound tonometers in healthy horses

Objective

To obtain a reference range for evaluation of intraocular pressure (IOP) in horses using Tonovet Plus^®, to compare the IOP readings obtained with Tonovet^® and Tonovet Plus^®, and to evaluate the repeatability of readings.

Animals studied and Procedures

Intraocular pressure of 30 client‐owned horses (60 eyes) with no signs of illness or ocular disease was evaluated using Tonovet^® and Tonovet Plus^® rebound tonometers. Horses’ mean age was 10.7 (range 6‐17) years. Triplicate measurements were performed without using sedatives or local anesthetics, with minimal restraint.

Results

Calculated reference intervals (the CLSI robust method) were 14.4‐27.2 mmHg for Tonovet^® and 16.0‐26.1 mmHg for Tonovet Plus^®. Mean values (± standard deviation, SD [± coefficient of variation, CV]) obtained with Tonovet Plus^® (21.6 ± 2.45 mmHg [11.3%]) were on average 0.6 mmHg higher than with Tonovet^® (21.0 ± 3.14 mmHg [15.0%]), and a negligible statistical difference between the devices was found using the paired sample t test (P = .049). The correlation coefficient for the averaged triplicate measurements was 0.73. The average CV was 4.6% and 4.4% for Tonovet^® and Tonovet Plus^®, respectively.

Conclusions

The repeatability of measurements was very good with both devices. The readings between the two devices differed statistically significantly, but the correlation was considered good and the variation was numerically small, and thus, the difference was considered clinically irrelevant. When monitoring disease process or treatment response in an individual patient, repeated readings are best performed using a similar device to avoid false interpretation of results.

Impact of corneal parameters on intraocular pressure measurements in different tonometry methods

AIM

To evaluate the impact of central corneal thickness (CCT) and corneal curvature on intraocular pressure (IOP) measurements performed by three different tonometers.

METHODS

IOP in 132 healthy eyes of 66 participants was measured using three different tonometry techniques: Goldmann applanation tonometer (GAT), Pascal dynamic contour tonometer (DCT), and ICare rebound tonometer (RT). CCT and corneal curvature were assessed.

RESULTS

In healthy eyes, DCT presents significantly higher values of IOP than GAT (17.34±3.69 and 15.27±4.06 mm Hg, P<0.0001). RT measurements are significantly lower than GAT (13.56±4.33 mm Hg, P<0.0001). Compared with GAT, DCT presented on average 2.51 mm Hg higher values in eyes with CCT<600 µm and 0.99 mm Hg higher results in eyes with CCT≥600 µm. The RT results were lower on average by 1.61 and 1.95 mm Hg than those obtained by GAT, respectively. Positive correlations between CCT in eyes with CCT<600 µm were detected for all IOP measurement techniques, whereas a similar relationship was not observed in eyes with thicker corneas. A correlation between IOP values and keratometry in the group with CCT<600 µm was not detected with any of the tonometry methods. In thicker corneas, a positive correlation was found for GAT and mean keratometry values (R=0.369, P=0.005).

CONCLUSION

The same method should always be chosen for routine IOP control, and measurements obtained by different methods cannot be compared. All analysed tonometry methods are dependent on CCT; thus, CCT should be taken into consideration for both diagnostics and monitoring.

The influence of corneal geometrical and biomechanical properties on tonometry readings in keratoconic eyes

PURPOSE

To identify the effect of corneal geometrical and biomechanical parameters on the intraocular pressure (IOP) measurements obtained by Goldmann Applanation Tonometer (GAT), non-contact tonometer, iCare Pro Rebound Tonometer (IRT), Tonopen and Ocular Response Analyzer (ORA, Goldmann-correlated IOP: IOPg, corneal compensated IOP: IOPcc).

METHODS

We prospectively recruited patients with a tomographically confirmed diagnosis of keratoconus. IOP measurements were performed in the following order: non-contact tonometry, ORA, IRT, GAT and Tonopen. The means of the three IOP measurements were used for the analysis. Correlation analyses were performed to assess the association between tonometer readings and the corneal geometrical and biomechanical parameters including ORA waveform parameters. Tonometer variability was assessed using a stepwise linear regression analysis.

RESULTS

Fifty-one patients with keratoconus (27 females, mean age 30.8 ± 8.7 years) were evaluated. The highest mean IOP was measured by IOPcc (14.6 ± 2.3 mmHg) followed by IRT IOP (13.0 ± 3.2 mmHg), Tonopen IOP 12.0 ± 2.6 mmHg), GAT IOP (11.7 ± 3.1 mmHg), NCT IOP (10.2 ± 3.2 mmHg) and IOPg (10.2 ± 3.6 mmHg). NCT and IOPg were affected from all corneal parameters including thickness, curvature and biomechanical parameters. While GAT and IRT had significant correlations with corneal resistance factor (CRF) and corneal hysteresis, IOPcc only had a significant correlation with CRF. None of the corneal factors had any statistically significant correlation with Tonopen. CRF predicted tonometer measurement variability in 7 of the 15 inter-device variability assessments.

CONCLUSION

Tonopen was the least affected from the corneal parameters followed by IOPcc and GAT. CRF was a strong determinant of tonometer variability.

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

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

Tonometry after Intrastromal Corneal Ring Segments for Keratoconus

SIGNIFICANCE

Reliable intraocular pressure (IOP) measurement after intrastromal corneal ring segments (ICRS) implantation is a challenge because of altered corneal morphology. In this study, IOP is measured with four tonometers, compared with Goldmann applanation tonometry (GAT) values and the influence of corneal parameters is established.

PURPOSE

This study compares IOP measurements made using different tonometers in patients implanted with ICRS and assesses the effects of central corneal thickness (CCT), corneal curvature, and corneal astigmatism on the IOP measurements obtained.

METHODS

In this cross-sectional study, IOP was measured using three different tonometers in 91 eyes of 91 patients with corneal ectasia implanted at least 6 months previously with ICRS. The tonometers tested were the TonoPen XL, Pascal dynamic contour tonometer (DCT), and iCare Pro rebound tonometer. GAT measurements were used as reference. Agreement among the IOPs provided by the different tonometers and the influence of corneal variables on the IOP measurements obtained were assessed using the Bland-Altman method, intraclass correlation coefficients, and multiple linear regression analysis.

RESULTS

Mean IOP differences were GAT versus TonoPen XL -0.8 ± 3.07 mm Hg, GAT versus DCT -1.0 ± 3.26 mm Hg, and GAT versus iCare Pro 0.8 ± 2.92 mm Hg. Our multiple linear regression analysis identified CCT as a confounding factor affecting all the tonometer readings but DCT-IOP.

CONCLUSIONS

In patients fitted with ICRS, IOP measurements made using the iCare Pro and TonoPen XL showed most agreement with GAT. Intraocular pressure measurements made by DCT were unaffected by corneal topographic factors though this procedure slightly overestimated GAT readings.

Comparison of intraocular pressure measurements using Goldmann tonometer, I-care pro, Tonopen XL, and Schiotz tonometer in patients after Descemet stripping endothelial keratoplasty

PURPOSE

Post-Descemet stripping endothelial keratoplasty (DSEK) patients are prone for intraocular pressure (IOP) elevations and glaucoma. Corneal characteristics influence various IOP measuring devices in various ways. The aim of this study was to evaluate the agreement between four different IOP measuring devices: Goldmann applanation tonometer (GAT), I-care pro, Tonopen XL, and Schiotz tonometr in patients who underwent DSEK.

METHODS

This was a prospective comparative study using a convenience cohort of post-DSEK patients with compact grafts. Post-DSEK patients had IOP measured using GAT, I-care Pro, Tonopen XL, and Schiotz tonometer. Measurements were compared and agreement assessed. Wilcoxon signed-rank test was used for comparison of means as variables did not show a normal distribution. Bland-Altman plots were used for assessing agreement.

RESULTS

Thirty eyes of 24 patients were included in the study. Mean time from DSEK surgery was 25.31 ± 13.05 months. Mean IOP with GAT, I-care pro, Tonopen XL, and Schiotz tonometer was 13.99 ± 3.76, 13.92 ± 3.36, 13.31 ± 3.89, and 12.83 ± 4.07, respectively. GAT, I-care pro, and Tonopen XL had similar mean IOP measurements (P = 0.135 and P = 0.551, respectively), while Schiotz tonometry measurements were higher (P = 0.046). Bland-Altman plots show good agreement between GAT, Tonopen XL, and I-care pro. GAT and Schiotz tonometry show less agreement, with large variations in the differences of measured IOP.

CONCLUSIONS

IOP measurements in post-DSEK patients showed good agreement between GAT and either Tonopen XL or I-care pro. Schiotz tonometer has large variations in this patient group. IOP measurements and IOP difference between devices were not dependent on central corneal thickness.

Evaluation of Goldmann applanation tonometry, rebound tonometry and dynamic contour tonometry in keratoconus

PURPOSE

To compare the intraocular pressure (IOP) measurements obtained with the rebound tonometry (RT), dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in keratoconic corneas and to investigate the effects of central corneal thickness (CCT) and corneal radius of curvature (CR) on IOP measurements.

METHODS

Sixty-three eyes of 63 keratoconus patients were enrolled in this cross-sectional study. IOP was measured on each subject always in the same order, ICare RT-Pascal DCT-GAT, after a minimum interval of 10min between measurements. CCT and CR were measured using a rotating Scheimpflug camera before the IOP measurements in all subjects. One way repeated measures ANOVA and Pearson correlation coefficient analysis was used for the statistical assessment.

RESULTS

Mean IOP for all enrolled eyes was 11.72±2.59mmHg for GAT, 9.34±3.29mmHg for RT, and 15.42±3.31mmHg for DCT. There were statistically significant differences among the three tonometers; GAT and RT (P<0.001), GAT and DCT (P<0.001), and RT and DCT (P<0.001). GAT and RT were significantly positively correlated with CCT (r=0.288, P=0.025 and r=0.483, P<0.001, respectively). RT was also significantly positively correlated with CR (r=0.550, P<0.001). DCT was not significantly correlated with CCT (r=0.115, P=0.377) nor CR (r=-0.179, P=0.168).

CONCLUSIONS

DCT has overestimated but RT has underestimated IOP readings according to GAT measurements in keratoconic corneas. DCT may be the most appropriate tonometer to use in keratoconus for the measurements of IOP, because DCT do not appear to be dependent upon CCT and CR.

A cross-sectional study to compare intraocular pressure measurement by sequential use of Goldman applanation tonometry, dynamic contour tonometry, ocular response analyzer, and Corvis ST

OBJECTIVE

To study the correlation and effect of sequential measurement of intraocular pressure (IOP) with Goldmann applanation tonometer (GAT), ocular response analyzer (ORA), dynamic contour tonometer (DCT), and Corvis ST.

SETTING AND DESIGN

Observational cross-sectional series from the comprehensive clinic of a tertiary eye care center seen during December 2012.

METHODS

One hundred and twenty-five study eyes of 125 patients with normal IOP and biomechanical properties underwent IOP measurement on GAT, DCT, ORA, and Corvis ST; in four different sequences. Patients with high refractive errors, recent surgeries, glaucoma, and corneal disorders were excluded so as to rule out patients with evident altered corneal biomechanics.

STATISTICAL ANALYSIS

Linear regression and Bland-Altman using MedCalc software.

RESULTS

Multivariate analysis of variance with repeated measures showed no influence of sequence of device use on IOP (P = 0.85). Linear regression r2 between GAT and Corvis ST, Corvis ST and Goldmann-correlated IOP (IOPg), and DCT and Corvis ST were 0.37 (P = 0.675), 0.63 (P = 0.607), and 0.19 (P = 0.708), respectively. The Bland-Altman agreement of Corvis ST with GAT, corneal compensated IOP, and IOPg was 2 mmHg (-5.0 to + 10.3), -0.5 mmHg (-8.1 to 7.1), and 0.5 mmHg (-6.2 to 7.1), respectively. Intraclass correlation coefficient for repeatability ranged from 0.81 to 0.96.

CONCLUSIONS

Correlation between Corvis ST and ORA was found to be good and not so with GAT. However, agreement between the devices was statistically insignificant, and no influence of sequence was observed.

Intraocular pressure measurement after DSAEK by iCare, Goldmann applanation and dynamic contour tonometry: A comparative study

PURPOSE

Corneal thickness inevitably increases following Descemet's stripping automated endothelial keratoplasty (DSAEK), owing to the addition of a donor graft. The current study compares different devices in assessing post-DSAEK intraocular pressure (IOP).

METHODS

We compared IOP values measured by the Goldmann tonometry (GAT), iCare rebound tonometry (iCare) and Pascal dynamic contour tonometry (PDCT) in eyes following DSAEK. Agreement between measurements was calculated with correlation analysis and Bland-Altman plots. Effects of keratometry, central, thickness (CCT), endothelial cell density (ECD) and axial length on IOP measurements were assessed with Pearson's correlation.

RESULTS

Twenty eyes of 20 patients (mean age 74.3±14.4, 14 females) post-DSAEK were included in this study. There was a high concordance between the IOP readings obtained by the three devices: a strong and significant correlation was found between GAT and PDCT (r=0.94, P<0.001) GAT and iCare (r=0.86, P<0.001) and iCare with PDCT (r=0.81, P<0.001). However, the iCare measurements were significantly and consistently lower than that obtained with GAT (ΔIOP=1.68±2.0, P=0.002, 95% CI: 0.7-2.6) and with PDCT (ΔIOP=1.61±2.5, P=0.01, 95% CI: 0.4-2.8). CCT, ECD, CCT, AXL, corneal curvature or astigmatism did not influence IOP measurement by any instrument.

CONCLUSIONS

IOP measurement with three different techniques (applanation, rebound and dynamic contour) showed good correlations, despite an increased corneal thickness following DSAEK. However, the iCare, which is based on a rebound tonometry showed significant lower IOP then the two other methods. This should be taken into account when evaluating patients post DSAEK.

Measuring Intraocular Pressure in Patients With Keratoconus With and Without Intrastromal Corneal Ring Segments

PURPOSE

To compare intraocular pressure (IOP) measurements made using 5 tonometers in keratoconic eyes with and without intrastromal corneal ring segments.

METHODS AND PATIENTS

This was an observational case series study. A total of 147 eyes of 147 patients with keratoconus, 74 of which had undergone corneal ring segment placement, were prospectively evaluated. IOP was measured using the tonometers Tonopen XL, Pascal dynamic contour tonometer, iCare Pro, ocular response analyzer (ORA), and Goldmann applanation (GAT) in random order. The Bland-Altman method was used to examine interinstrument agreement. Effects on readings of central corneal thickness, corneal curvature, and corneal astigmatism were assessed by multivariate regression analysis.

RESULTS

Smallest mean IOP differences with GAT measurements in eyes without and with ring segments, respectively, were detected for iCare Pro [0.2 (2.9) mm Hg and 0.4 (3.0) mm Hg, P=0.914] and greatest differences for ORA Goldmann-correlated IOP [5.8 (3.3) mm Hg and 6.0 (3.1) mm Hg, P=0.363]. Best agreement with GAT was shown by iCare Pro (ICC=0.829; 95% CI, 0.721-0.896) and worse agreement by ORA corneal-compensated IOP (ICC=-0.145; 95% CI, -0.826 to 0.283). All but the dynamic contour tonometer readings were influenced by central corneal thickness, yet these measurements were affected by the presence of ring segments (P=0.017) and corneal astigmatism (P=0.030). Corneal curvature only affected ORA Goldmann-correlated IOP (P=0.029).

CONCLUSIONS

All 5 tonometers provided reliable IOP readings in the keratoconic eyes regardless of the presence of corneal ring segments. iCare Pro readings were most consistent with GAT, whereas ORA readings were least consistent with this reference standard.

Comparison of Diaton transpalpebral tonometer with applanation tonometry in keratoconus

AIM

To investigate the added value of using a Diaton transpalpebral tonometer (DT) to measure IOP in keratoconus. Most type of tonometers use corneal applanation or biomechanical resistance to measure intraocular pressure (IOP); however, these factors can be altered by keratoconus. Specifically, we examined whether DT can detect false-negative low Goldmann applanation tonometry (AT) measurements.

METHODS

Patients with keratoconus were recruited from our tertiary academic treatment center. Measurements included AT and DT (in random order) and Scheimpflug imaging. An age- and gender-matched group of control subjects with no history of corneal disease or glaucoma was also recruited.

RESULTS

In total, 130 eyes from 66 participants were assessed. In the keratoconus group, mean AT was 11.0 ± 2.6, mean DT 11.2±5.5 (P=0.729), and the two measures were correlated significantly (P=0.006, R=0.323). However, a Bland-Altman plot revealed a wide distribution and poor agreement between both measurements. Previous corneal crosslinking, corneal pachymetry, and Krumeich classification had no effect on measured IOP.

CONCLUSION

Measurements obtained using a Diaton tonometer are not affected by corneal biomechanics; however, its poor agreement with Goldmann AT values calls into question the added value of using a Diaton tonometer to measure IOP in keratoconus.

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.

[Ease of handling of first and second generation rebound tonometers]

PURPOSE

To evaluate the ease of handling of two rebound tonometers, which are designed for self-measurement of intraocular pressure (IOP) in a clinical setting by untrained patients.

METHODS

After self-measurement of the IOP with the rebound tonometers iCare ONE and iCare HOME, participants were asked to complete a questionnaire containing different subitems concerning ease of operation using a visual analog scale (1 = very good to 5 = very poor). Moreover, the feasibility and duration of measurement were tested.

RESULTS

A total of 147 subjects participated in this study. The mean score for general handling ability was 2.79 ± 1.01 for the iCare ONE and 1.85 ± 0.87 for the iCare HOME (p < 0.001). The evaluation of the subitems sense of safety (iCare ONE: 2.71 ± 1.03 and iCare HOME: 1.87 ± 0.81, p < 0.001) and comfort of measurement (iCare ONE: 2.07 ± 1.01 and iCare HOME: 1.66 ± 0.72, p < 0.001) also showed a significant discrepancy between the two tonometers. Participants needed significantly less time for a single valid measurement when using the iCare HOME tonometer (mean 66.14 ± 61.54 s) compared to the iCare ONE tonometer (mean 81.54 ± 69.51 s, p < 0.001).

CONCLUSIONS

A better handling of the iCare HOME rebound tonometer in comparison to the iCare ONE tonometer can be deduced on the basis of the subjective assessments of patients and the shorter duration of measurements. Moreover, the iCare HOME received a significantly better evaluation for all subitems. The accuracy of measurements using the iCare HOME still needs to be clarified.

Comprasion of ICare rebound tonometer and Goldmann applanation tonometer in high myopia

Purpose. To compare intraocular pressure (IOP) measurements with the Goldmann applanation tonometer (GAT) and the ICare rebound tonometer (RBT) in high myopic eyes. Patients and Methods. This randomized prospective study included 40 eyes of 40 patients with high myopia. All patients' central corneal thickness (CCT), anterior chamber depth (ACD), axial length (AXL), keratometry, and refractive measurements were recorded and followed by IOP measurement with RBT and GAT. Results. The average CCT, AXL, and ACD were determined to be 514.65 ± 32 μm, 27.65 ± 2.22 mm, and 3.25 ± 0.51 mm, respectively. Mean K was 43.27 ± 1.4 D and mean spherical equivalent was −11.31 ± 4.30 D. The mean IOP values obtained by RBT and GAT were 17.18 ± 3.72 mmHg and 16.48 ± 3.19 mmHg, respectively. The deviations of RBT readings from corrected GAT values were highly correlated with CCT values (r = 0.588, P = 0.0001). The mean corrected GAT reading was 17.49 ± 3.01 mmHg. Linear regression analysis showed that a CCT change of 10 μm resulted in an RBT reading deviation of 0.57 mmHg. The Bland-Altman scatter-plot and McNemar test showed a clinically good level of agreement between the two tonometers. Conclusion. This study found a good agreement level between the two tonometers in high myopic patients and that RBT measurements are influenced by CCT variations.