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Purpose: To examine agreement between intraocular pressure (IOP) measurements made using the rebound tonometer Icare ic200 (RT200) and the Perkins handheld applanation tonometer (PAT) in patients with primary congenital glaucoma (PCG). The impacts of several covariables on measurements using the two devices were also assessed., Materials and Methods: Intraocular pressure measurements were made in a single session in 86 eyes of 86 patients with PCG (46 under anaesthesia, 40 in the office). The order was RT200 then PAT. The variables age, central corneal thickness (CCT), corneal state and anaesthesia were recorded in each patient. Data were compared by determining interclass correlation coefficients (ICC) for each tonometer and representing the differences detected as Bland-Altman plots. Effects of covariables were assessed through univariate and multivariate regression., Results: Mean IOP difference between tonometers (RT200 minus PAT) was 1.26 mmHg (95%: 0.22-2.31). Absolute agreement (ICC) was 0.73 (95% CI: 0.62-0.82). Lower and upper limits of agreement (95%) were -8.06 mmHg (95% CI: -9.87 to -6.25) and 10.59 mmHg (95% CI: 8.77-12.40), respectively. The tonometers showed systematic differences (a = -4.63 mmHg; 95% CI: -9.11 to -1.44) and proportional differences; for each mmHg increase in PAT-IOP, the RT200 reading increased by 1.28 mmHg (b = 1.28; 95% CI: 1.12-1.53). None of the variables tested as predictors were able to explain differences between the tonometers., Conclusions: Despite the good overall agreement between both tonometers, caution should be taken in high values of IOP, considering the interchangeability of its readings as systematic and proportional differences appear to exist between both methods., (© 2020 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)

Objective: This study was designed to assess changes in corneal topography and biomechanics after intraocular pressure (IOP) monitoring using the Triggerfish contact lens sensor (CLS)., Methods: For this prospective study, 30 eyes of 30 subjects: 14 healthy subjects (G1) and 6 glaucoma patients (G2), were recruited for 24 hours of continuous IOP monitoring using the CLS. The following measurements were taken before CLS fitting and after lens removal: maximum keratometry (Kmax), mean keratometry (MK), and corneal astigmatism (Cyl) measured through Pentacam corneal topography, and the corneal biomechanical variables corneal hysteresis (CH) and corneal resistance factor (CRF) measured with the Ocular Response Analyzer (ORA)., Results: Pentacam data revealed significant changes after CLS removal in Kmax (+3.14 ± 2.46 D, p = 0.002), MK (+0.52 ± 0.63 D, p = 0.02), and Cyl (+0.48 ± 0.53 D, p = 0.019) in G1; and Kmax (+1.38 ± 1.43 D, p = 0.002) in G2. The changes observed were more pronounced in G1 than in G2 but differences were not significant. The ORA results indicated higher CH (11.35 ± 2.42 vs 8.17 ± 2.09) and CRF (10.3 ± 2.03 vs 9.1 ± 1.81) before lens fitting in G1 than G2, while no significant changes were produced after CLS removal in either group., Conclusions: The use of CLS for IOP monitoring over 24 hours caused topographic changes in both healthy subjects and glaucoma patients. No changes were produced in corneal biomechanics., (Copyright © 2018. Published by Elsevier Inc.)

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.

The level of intraocular pressure (IOP) is the main known risk factor for the development and progression of glaucomatous optic neuropathy. Despite Goldmann applanation tonometry (GAT) being the gold standard for determining IOP since the last century, its limitations were obvious from the start and include substantial effects of several eye variables such as axial length, curvature, rigidity, and corneal thickness. These limitations have prompted the development of numerous formulas and nomograms designed to compensate for the ocular characteristics effect on GAT, but none of these methods has been entirely satisfactory. Similarly, as a result of efforts to mitigate some of the limitations of conventional tonometry, several new tonometers have appeared on the scene., (© 2015 Elsevier B.V. All rights reserved.)

Purpose: To characterize five models of corneal thickness circular zoning in a sample of healthy controls and a sample of patients with primary open-angle glaucoma (POAG) and to determine their effect on Goldmann (GAT), dynamic contour (DCT) and rebound tonometers (RT)., Methods: The study participants were 122 controls and 129 cases. Five corneal thickness zoning models (A, B, C, D and E) were constructed. The partitioning pattern consisted of a circle centred at the corneal apex and several concentric rings, until the limbus; the contours of each ring followed the geometry of the corneal contour of each participant. In Model A, the central circle was 1 mm in diameter and five concentric rings were established. Mean was obtained for each zone for both samples and compared between them using a t-test. The effect on the tonometers of central cornel thickness (CCT) and mean thickness of the zones generated was determined through several linear regression models (one per tonometer and per sample)., Results: According to a t-test, cases and controls differ in zones I [mean difference (MD): 17.93 μm], V (MD: 25.52 μm) and VI (MD: 31.78 μm) of model A (higher values in the cases sample). RT was affected by CCT (controls: B = 0.089; cases: B = 0.081). DCT was affected by zone IV of model A (controls: B = -0.029; cases: B = -0.012). GAT was affected by CCT (controls: B = 0.043; cases: B = 0.025) and zone III of model A (controls: B = -0.045; cases: B = -0.033)., Conclusion: Our results highlight the importance of the thickness of other regions of the cornea different from its main centre in discriminating between healthy controls and patients with POAG and in IOP measurements made using DCT, GAT and RT., (© 2013 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.)

Objectives: To determine the effects on dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) of the power of the flattest and steepest corneal meridians, their orientation, central corneal thickness (CCT), mean overall corneal thickness, and the mean thickness of a circular zone centered at the corneal apex of 1 mm radius (zone I) and the mean thicknesses of several concentric rings also centered at the apex of width 1 mm (zones II to VI, respectively)., Methods: A total of 136 consecutive healthy eyes were examined. Two multivariate linear regression models were constructed, 1 for each tonometry system. In both models, the predictive variables were: keratometric power of the flattest and steepest axes, flattest axis (as one of the categories 0 to 30, 30 to 60, 60 to 90, 90 to 120, 120 to 150, and 150 to 180 degrees), CCT, mean overall corneal thickness (determined using the Pentacam), and mean thicknesses of corneal zones I, II, III, IV, V, and VI (determined using the Pentacam)., Results: The multivariate regression analysis (adjusted R=0.11; P=0.04) revealed that GAT was influenced by CCT [B=0.042; 95% confidence interval (CI), 0.002-0.085] and the mean thicknesses of zones I (B=0.996; 95% CI, 0.105-1.729), II (B=-1.688; 95% CI, -3.171 to -0.204), and III (B=0.718; 95% CI, 0.028-1.407), whereas DCT was solely affected by the mean thickness of zone II (B=-0.372; 95% CI, -0.728 to -0.016) (adjusted R2=0.13; P=0.02)., Conclusions: Although DCT is only affected by the mean thickness of zone II, GAT is influenced by CCT and the mean thickness of zones I, II, and III.

Purpose: To examine the reproducibility of the new digital Goldmann applanation tonometer AT 900D (DGT) for measuring intraocular pressure and to compare its readings with those provided by the conventional analog Goldmann tonometer (AGT)., Methods: In 3 different sessions (S1, S2, and S3), 3 intraocular pressure measurements were made in 15 eyes of 15 healthy subjects using both the DGT and AGT. The order of use of the tonometers was random and the data were collected by a different examiner to the one taking the measurements. Data were compared by determining coefficients of variation for each session and representing the differences detected as Bland-Altman plots., Results: The mean differences recorded (AGT-DGT) were 0.1, 0.3, and -0.1 for S1, S2, and S3, respectively. None of the differences were significant and none were ≥3 mm Hg. Coefficients of variation were lower in the 3 sessions for the DGT, the difference being significant for S2 and S3 (4.87% vs. 3.99%, P=0.400; 4.84% vs. 3.55%, P=0.028; and 5.04% vs. 3.50%, P=0.025 in S1, S2, and S3 respectively)., Conclusions: The new digital Goldmann tonometer shows a high reproducibility and excellent correlation of measures with those of the AGT.

Purpose: To compare rebound tonometry (RBT) and noncontact tonometry (NCT) using Goldmann applanation tonometry (GAT) as reference., Methods: The study sample was comprised of 108 eyes of 108 subjects consecutively examined at a general ophthalmology clinic. The order of use of the three tonometers was randomized at the study outset. The difference between the methods was plotted against the mean to compare the tonometers. The hypothesis of zero bias was examined by a paired t-test and 95% limits of agreement (LoA) were also calculated. Differences with respect to GAT were assessed according to the international standard for ocular tonometers (ISO 8612)., Results: Mean intraocular pressures (IOPs ± SD) obtained using the three instruments were GAT 17.5 ± 3.8 mmHg; RBT 18.5 ± 5.5 mmHg and NCT 17.4 ± 5.6 mmHg. The 95% LoA were from -7.9 to +7.7 mmHg for NCT-GAT and from -6.8 mmHg to +8.7 mmHg for RBT-GAT. A difference with respect to GAT under ± 1 mmHg was observed in 11.1% of the eyes measured by NCT and 18.5% of eyes measured by RBT. According to the IOP ranges established by the ISO 8612, differences from GAT measurements greater than ± 5 mmHg were always above the accepted level of 5%. Correlations between IOP and central corneal thickness (CCT) were significant for all three tonometers., Conclusions: The rebound and noncontact tonometer behaved similarly when used to measure IOP taking GAT measurements as the reference standard. Neither tonometer fulfilled ISO 8612 requirements. Both were similarly influenced by CCT., (© 2009 The Authors. Journal compilation © 2009 Acta Ophthalmol.)

Purpose: To compare intraocular pressure (IOP) measurements obtained using the rebound tonometer (RBT) and the handheld Goldmann applanation tonometer (Perkins) in children with congenital glaucoma., Methods: Using both tonometers, the IOP was prospectively determined in 68 eyes of 68 patients with congenital glaucoma aged 3 to 13 years. Corneal curvature, central corneal thickness (CCT), and axial length were also measured in each patient. The ease of the use of each tonometer was scored using a visual analog scale., Results: IOP readings obtained using the RBT and Perkins tonometer showed good correlation (r=0.869, P<0.001) although RBT readings were consistently higher (mean difference: 3.1 +/-4.0 mm Hg). According to the Bland-Altman plot, the 95% limits of agreement between the 2 methods were -4.8 to 10.9 mm Hg (slope=0.589, P<0.001). When estimating CCT, the 2 tonometers behaved similarly and correlation was observed between IOP measurements and CCT, with higher IOPs obtained as the CCT increased. In contrast, no correlation was detected between corneal curvature or axial length and the IOPs recorded using either tonometer. Ease of use scores awarded by the examiner was higher for the RBT., Conclusions: The RBT overestimates the IOP compared with the Perkins tonometer in patients with congenital glaucoma. Differences in readings between the 2 tonometers become larger as the CCT increases.