Comparison of ICare and IOPen vs Goldmann applanation tonometry according to international standards 8612 in glaucoma patients

AIM： To compare IOPen and ICare rebound tonometry to Goldmann applanation tonometry（GAT） according to International Standards Organization（ISO） 8612 criteria.METHODS： Totally 191 eyes（n =107 individuals） were included. Criteria of ISO 8612 were fulfilled： 3 clusters of IOP, measured by GAT, were formed. The GAT results were given as mean±standard deviation.RESULTS： GAT（19.7±0.5 mm Hg） showed a significant correlation to ICare（19.8±0.5 mm Hg）（r =0.547, P 〈0.001）and IOPen（19.5 ±0.5 mm Hg）（r =0.526, P 〈0.001）.According to ISO 8612 criteria in all 3 IOP groups the number of outliers（of the 95% limits of agreement）exceeded 5% for ICare and IOPen vs GAT： No.1（n =68）29.4% and 22.1%, No.2（n =62） 35.5% and 37.1%, No.3（n =61） 26.2% and 42.6%, respectively.CONCLUSION： The strict requirements of the ISO 8612 are not fulfilled in a glaucoma collective by ICare and IOPen at present. As long as the Goldmann tonometry is applicable it should be used first of all for reproducible IOP readings. ICare and IOPen tonometry should be considered as an alternative tool, if application of Goldmann tonometry is not possible.

Dynamic Contour Tonometry,Tono-Pen XL^(■),and Goldmann Applanation Tonometry in Comparison to Intracameral Intraocular Pressure(IOP)Measurements in Patients with Corneal Pathologies

Purpose: The accuracy of Goldmann applanation tonometry (GAT) has been shown to depend on several biomechanical properties of the cornea. Newer tonometry devices (e.g., the Dynamic Contour Tonometer PASCAL? [DCT] and the Tono-Pen? XL [TP]) have been designed to accurately measure intraocular pressure (IOP) independent of corneal thickness (CCT) and pathology. This study investigates the influence of corneal pathologies on the accuracy of these IOP measuring devices, and compares this accuracy to that of direct intracameral IOP measurement. Methods: 8 eyes of 8 patients suffering from corneal pathologies scheduled for penetrating keratoplasty, and 10 eyes of 10 patients scheduled for cataract surgery (control group) were examined. Before surgery, the anterior chamber was cannulated at the temporal corneal limbus. In a closed system, the intraocular pressure (IOP) was directly set to 10, 20, and 30 mmHg with a manometric water column. Intraocular pressure measurements taken by GAT, DCT, and TP were compared to intracameral measurements obtained by a precision reference pressure sensor. Results: Control group: All three methods showed good agreement with the intracameral readings (mean deviation of all three devices, -0.9 mmHg). Group with corneal pathologies: The TP yielded the most exact IOP values in the group with corneal pathologies when taking all diagnoses into account. The mean deviations from the intracameral IOP measurements were -0.9 mmHg ± 3.2 mmHg (mean ± SD) for TP, -2.9 mmHg ± 3.3 mmHg for GAT, and -5.0 mmHg ± 7.9 mmHg for DCT. For bullous keratopathy, the most exact IOP readings were obtained by the TP (mean deviation -0.2 mmHg ± 3.5 mmHg). The TP and GAT devices underestimated IOP in the patients with Fuchs’ endothelial dystrophy;all 3 devices underestimated adjusted IOP after keratoplasty. DCT showed the greatest deviations from adjusted IOP in the case of non-herpetic scars. In the control group, none of the devices showed a statistically relevant dependency on CCT. Nevertheless, in the group with corneal pathologies, only TP showed no dependency on CCT. Conclusion: Our results suggest that the Tono-Pen XL? is the most accurate measurement device to determine IOP in patients with corneal pathologies, especially in patients suffering from corneal edema (bullous keratopathy). GAT yielded surprisingly exact IOP values in patients suffering from irregular corneal surface. DCT showed a high degree of deviation from the adjusted IOP, and should not be used to determine IOP in corneas with the disorders listed here.

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 lOP in keretoconus. Most type of tonometers use corneal applanation or biomechanical resistance to measure intraocular pressure （lOP）; 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±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 lOP in keratoconus.

Comparison of IOPen rebound tonometer with Goldmann applanation tonometer at different IOP levels

AIM:To compare the accuracy of IOPen rebound tonometer with Goldmann applanation tonometer(GAT) in individuals with low,normal and high intraocular pressure(IOP) and to evaluate the effect of central corneal thickness(CCT) on IOP measurements.METHODS:This cross-sectional study consisted of 159 participants.IOP of one eye of each subject was measured consecutively with IOPen and GAT.Then CCT was measured using an ultrasonic pachymeter.Based on GAT IOP readings,participants were divided into low,normal and high IOP groups.Correlation between tonometers and CCT was calculated by spearman’s correlation coefficient.Agreement between tonometers was evaluated using Bland-Altman method.RESULTS:Non-significant underestimation of IOP by IOPen was observed in low IOP group(Mean difference:0.20mmHg;P=0.454) and also in normal IOP group(Mean difference:0.56mmHg;P=0.065).However,IOPen significantly overestimated IOP in high IOP group(Mean difference:1.06mmHg;P=0.038).The 95% limits of agreement(LoA) width between IOPen and GAT IOPs were 7.84,8.57 and 14.27mmHg in low,normal and high IOP groups,respectively.Low IOP group had thinner corneas compared to high IOP group(P=0.034).IOP measurements taken by IOPen were not influenced by CCT(P=0.099) while poor correlation between CCT and GAT was found(R=0.17,P=0.032).Using receiver operating characteristic(ROC) curve,cutoff value of 18.75mmHg was determined for IOPen with sensitivity of 98.1 and specificity of 97.2%.CONCLUSION:Accuracy of IOPen is comparable to GAT in patients with low or normal IOP but IOPen overestimates IOP at high IOP levels.CCT does not affect IOP readings with IOPen.

Dependence of dynamic contour and Goldmann applanation tonometries on peripheral corneal thickness

AIM：To determine the effects of peripheral corneal thickness（PCT）on dynamic contour tonometry（DCT）and Goldmann applanation tonometry（GAT）.METHODS：A cross-sectional study.We created a software which calculates the corneal contour（CC）as a function of the radius from the corneal apex to each pixel of the contour.The software generates a central circumference with a radius of 1 mm and the remainder of the cornea is segmented in 5 rings concentric with corneal apex being its diameter not constant around the corneal circumference as a consequence of the irregular CC but keeping constant the diameter of each ring in each direction of the contour.PCT was determined as the mean thickness of the most eccentric ring.Locally weighted scatterplot smoothing（LOWESS）regression was used to determine the pattern of the relationship between PCT and both DCT and GAT respectively.Thereafter,two multivariable linear regression models were constructed.In each of them,the dependant variable was intraocular pressure（IOP）as determined using GAT and DCT respectively.In both of the models the predictive variable was PCT though LOWESS regression pattern was used to model the relationship between the dependant variables and the predictor one.Age and sex were also introduced control variables along with their first-degree interactions with PCT.Main outcome measures include amount of IOP variation explained through regression models（R2）and regression coefficients（B）.RESULTS：Subjects included 109 eyes of 109 healthy individuals.LOWESS regression suggested that a 2nd-degree polynomial would be suitable to model the relationshipbetween both DCT and GAT with PCT.Hence PCT was introduced in both models as a linear and quadratic term.Neither age nor sex nor interactions were statistically significant in both models.For GAT model,R2was 17.14%（F=9.02;P=0.0002）,PCT linear term B was-1.163（95%CI：-1.163,-0.617）.PCT quadratic term B was 0.00081（95%CI：0.00043,0.00118）.For DCT model R2was 14.28%（F=9.29;P=0.0002）,PCT linear term B was-0.712（95%CI：-1.052,-0.372）,PCT quadratic term was B=0.0005（95%CI：0.0003,0.0007）.CONCLUSION：DCT and GAT measurements are conditioned by PCT though this effect,rather than linear,follows a2nd-degree polynomial pattern.

Measurement of Intraocular Pressure after LASIK by Dynamic Contour Tonometry

Changes of corneal properties induced by laser in situ keratomileusis （LASIK） results in low inaccurate intraocular pressure （IOP） readings by Goldmann applanation tonometry （GAT）. Before and after LASIK, the applied value of IOP, measured by dynamic contour tonometry （DCT） in comparison to GAT, was evaluated. Before and 1, 4 weeks after LASIK, the IOP in 30 cases （60 eyes） was measured by GAT and DCT respectively. The obtained results were statistically processed by SPSSll. 5 statistical software. The results showed that central corneal thickness （CCT） could affect GAT measurements but not DCT measurements. The comparison of IOP one and 4 weeks after LASIK revealed that the readings from GAT was separately decreased by 5.00±1.12 and 5.45±1.13 mmHg as compared with those before LASIK, while those from DCT had no significant difference. It was concluded that LASIK-induced changes of CCT could influence the accuracy of GAT measurements, but had no influence on those from DCT. DCT was more beneficial to the measurements of IOP in normal eyes and those subject to LASIK surgery.