Comparison of dynamic contour tonometry with Goldmann applanation tonometry in glaucoma practice

Purpose: To compare intraocular pressure (IOP) readings taken using dynamic contour tonometry (DCT) with IOP readings taken with Goldmann applanation tonometry (GAT) in eyes with glaucoma or ocular hypertension. Methods: The present study included 100 eyes in 100 patients with glaucoma or ocular hypertension. After pachymetry DCT and GAT were performed. Intraocular pressures as measured with DCT and GAT were compared with one another and with central corneal thickness (CCT). Results: Mean DCT IOP measurements (20.1 ± 4.3 mmHg) were significantly (p < 0.001) higher than GAT IOP values (17.9 ± 4.7 mmHg). The mean difference between DCT and GAT measurements was 2.1 mmHg (range ? 3.4 to 9.7 mmHg). The difference followed a normal distribution. Measurements made with DCT and GAT correlated significantly with one another (Spearman’s rho = 0.761, p < 0.001). Neither GAT nor DCT measurements showed a significant correlation with CCT (537 ± 39 μm, range 458–656 μm). Multivariate regression analysis has shown that the difference between DCT and GAT is influenced significantly by ocular pulse amplitude (r = ? 0.334, p = 0.001) and it is not influenced by CCT (r = ? 0.106, p = 0.292). Conclusions: In eyes with glaucoma or ocular hypertension, DCT facilitates suitable and reliable IOP measurements which are in good concordance with GAT readings. Variation in CCT cannot by itself explain the differences in measurements taken with DCT and GAT in a number of eyes.     

Repeatability and accuracy of applanation resonance tonometry in healthy subjects and patients with glaucoma

Purpose: To evaluate the repeatability and accuracy of the applanation resonance tonometer (ART) used in the automatic servo‐controlled version, and to evaluate the influence of central corneal thickness (CCT) on the ART intraocular pressure (IOP) measurements. Methods: This prospective, randomized, single‐centre study included one eye of 153 subjects (35 healthy volunteers and 118 patients with glaucoma). All participants underwent ultrasonic CCT measurement, followed by IOP evaluation with Goldmann applanation tonometer (GAT) and ART in random order. A single operator measured the IOP with each tonometer three times. Intra‐examiner variability was evaluated using the coefficient of variation (CoV), intraclass correlation coefficient (ICC) and test–retest differences. Intermethod agreement was assessed using the Bland–Altman method. Linear regression analysis was used to evaluate the relationship between IOP measurements and CCT. Results: The mean IOP was 17.7 ± 4.4 mmHg with GAT and 20.6 ± 5.3 mmHg with ART (p < 0.001). CoV and ICC were, respectively, 5 ± 3% and 0.99 for GAT, and 8 ± 4% and 0.96 for ART (intermethods differences, p = 0.001). The ART test–retest differences significantly increased with increasing mean IOP (p = 0.003). The mean IOP difference (ART minus GAT) was 3.0 ± 4.0 mmHg, which increased with increasing mean IOP (p < 0.001). Both GAT IOP and ART IOP readings were significantly directly related to the CCT values (p = 0.03 and p = 0.004, respectively; intermethods difference, p = 0.32). Conclusions: The ART intra‐examiner repeatability was excellent, although significantly lower than that of GAT, and decreased at higher IOP levels. ART significantly overestimated GAT IOP measurements, especially at higher IOP range. Both GAT and ART appeared similarly influenced by CCT value.     

Effect of corneal thickness on intraocular pressure measurements with the Pascal dynamic contour,Canon TX‐10 non‐contact and Goldmann applanation tonometers in healthy subjects

Purpose: To investigate the effects of central corneal thickness (CCT) on intraocular pressure (IOP) measurements of the Pascal dynamic contour tonometry (DCT), Canon TX‐10 non‐contact tonometry (NCT) and Goldmann applanation tonometry measurements (GAT) in healthy subjects. Methods: IOP values of 135 eyes with normal corneas of 135 healthy volunteers were determined by DCT, NCT and by GAT. The CCT was measured using an ultrasonic pachymeter after all IOP determinations had been made. Results: When DCT measurements were compared (IOP = 17.52 ± 2.0 mmHg) with NCT measurements (IOP = 16.54 ± 2.77 mmHg) and GAT measurements (IOP = 15.07 ± 2.35 mmHg), DCT measurements were significantly higher than NCT and GAT (p < 0.001). There was a significant correlation between CCT with both NCT (r = 0.260, p = 0.003) and GAT measurements (r = 0.257, p = 0.005). There was a weak correlation that was not statistically significant between CCT and DCT (r = 0.160, p = 0.079). Conclusion: The IOP measurements with DCT seem to be less dependent on CCT. NCT appears to be more affected by variation in CCT than GAT.     

Can we trust intraocular pressure measurements in eyes with intracameral air?

Purpose

To evaluate the effect of intracameral air on intraocular pressure (IOP) measurements using Goldmann applanation tonometry (GAT) and applanation resonance tonometry (ART) in an in-vitro porcine eye model.

Methods

IOP was measured on thirteen freshly enucleated eyes at three reference pressures: 20, 30, and 40 mmHg. Six measurements/method were performed in a standardized order with GAT and ART respectively. Air was injected intracamerally in the same manner as during Descemet’s stripping endothelial keratoplasty (DSEK) and Descemet’s membrane endothelial keratoplasty (DMEK), and the measurements were repeated.

Results

Measured IOP increased significantly for both tonometry methods after air injection: 0.7?±?2.1 mmHg for GAT and 10.6?±?4.9 mmHg for ART. This difference was significant at each reference pressure for ART but not for GAT.

Conclusions

Although slightly affected, this study suggests that we can trust GAT IOP-measurements in eyes with intracameral air, such as after DSEK/DMEK operations. Ultrasound-based methods such as ART should not be used.     

三种眼压计测量高眼压儿童眼压及其与中央角膜厚度的关系

目的：探讨经Topcon眼压计(non-contact tonometry,NCT)初筛高眼压的屈光不正儿童的中央角膜厚度(central corneal thickness,CCT)分布,以及NCT、Goldmann压平眼压计(Goldmann applanation tonometry,GAT)与OCULUS Corvis ST角膜生物力学分析仪(CST)所测眼压值的差异,并分析眼压和CCT的相关性。

方法：选择经NCT测量单眼或双眼眼压高于21mmHg的非青光眼屈光不正儿童39例78眼,用CST和GAT再次进行眼压测量,两种仪器的测量顺序随机,同时用CST测量CCT并根据CCT进行眼压校正。根据CCT分成正常组和较厚组,分析经NCT初筛高眼压的屈光不正儿童的总体CCT分布情况,探讨三种仪器所测眼压值的不同及其与CCT的相关性。

结果：正常CCT组,CST低于GAT和NCT的眼压测量值,差异有统计学意义(F=5.12,P=0.01); 较厚组,三种眼压测量方式的眼压测量值比较,差异均有统计学意义(F=15.72,P<0.001)。NCT和GAT眼压值与CCT呈明显正相关(r_NCT=0.298,P_NCT=0.04; r_GAT=0.408,P_GAT= 0.01); CST校正眼压值与CCT无明显相关性(r_CST=0.062,P_CST=0.593)。

结论：NCT初筛高眼压的屈光不正儿童的CCT偏厚,CST校正眼压低于NCT和Goldmann眼压,NCT和GAT所测眼压与CCT呈正相关; 对于CCT偏厚的儿童患者,CST校正眼压比NCT和GAT更接近于真实眼压值。     

Deviations between transpalpebral tonometry using TGDc-01 and Goldmann applanation tonometry depending on the IOP level

Background Recent comparisons between transpalpebral tonometry using TGDc-01 and Goldmann applanation tonometry were performed in populations with IOPs between 10 and 20 mmHg. The purpose of this study was to evaluate device deviations depending on different IOP levels (range 5–40 mmHg).Methods A total of 68 eyes of 68 patients were included and assigned to four IOP levels according to an initial applanation tonometry assessment: level I, <10 mmHg (n=8); level II, 10–19 mmHg (n=20); level III, 20–29 mmHg (n=20); and level IV, 30 mmHg (n=20). Two independent and randomized observers performed three replicate measurements per eye—observer 1 using TGDc-01 tonometry, and observer 2 using Goldmann applanation tonometry. Intraindividual deviations between measurement results were investigated concerning clinical relevance by medians and quartiles, concerning statistical significance by pairwise sign tests; p values <0.05 indicate local statistical significance.Results In patients with initial IOP 20 mmHg, TGDc-01–based tonometry significantly underestimated the IOP as based on Goldmann applanation tonometry (p<0.001). This effect increased with increasing IOP: IOP level III median difference (TGDc-01 – Goldmann) –1.3 mmHg (interquartile range, –2.5, –0.4), IOP level IV median difference –2.7 mmHg (–3.7, –1.0). In patients with initial IOP <10 mmHg, an at least gradual underestimation by TGDc-01 tonometry (p=0.219; median difference, –0.6, –1.6, 0) was observed. A total 18% of patients showed device deviations >±3 mmHg, and even 35% of those patients with initial IOP 30 mmHg.Conclusions TGDc-01–based tonometry demonstrated an increasing underestimation of IOP with increasing IOP levels when compared with the current standard method of Goldmann applanation tonometry.     

Comparison of the Proview pressure phosphene tonometer performed by the patient and examiner with the Goldmann applanation tonometer

Objective: To compare the results of Proview pressure phosphene tonometry (PPPT) performed by the patient and an examiner with Goldmann applanation tonometry (GAT). Methods: A comparative case series of 96 (192 eyes) consecutive patients from a glaucoma clinic was conducted. Intraocular pressure (IOP) was measured with GAT by one examiner, PPPT by another examiner, and PPPT by the patient. All examiners were masked to the results from any preceding IOP measurement. Results: The coefficient of repeatability for repeated measurements for the GAT was ±0.48 mmHg. The limits of agreement for self‐measurement of IOP with the PPPT and examiner measured IOP with PPPT were 6.3 mmHg and 4.8 mmHg, respectively. The limits of agreement between GAT and self assessed PPPT were ±11.8 mmHg (mean difference of 0.63 mmHg). When the same comparison was made between GAT and examiner assessed PPPT, the results were limits of agreement of ±10 mmHg (mean difference of 2.86 mmHg). No significant difference was identified in the agreement of the GAT and the PPPT when subanalysed for age of patient or diagnosis (P > 0.05). The limits of agreement between self‐assessed IOP with the PPPT and the GAT were ±8.2 for those with IOP <20 mmHg and ±14.9 mmHg for those with IOP>20 mmHg. Conclusions: Poor agreement exists between IOP measured by GAT and PPPT measured by an examiner or by the patient.     

DCT和GAT对LASIK手术前后眼压的比较性研究

目的 评价动态轮廓眼压计(DCT)和Goldmann压平眼压计(GAT)对在准分子激光原位角膜磨镶术(LASIK)手术前后眼压测量值的变化.方法 取71例141只眼近视患者在LASIK术前和术后一周分别进行角膜厚度(CCT)、GAT、DCT测量.结果 ①LASIK手术前后DCT测得值尤显著性差异(P=0.062),GAT测得值有显著性差异(P＜0.001),CCT测得值有显著性差异(P＜0001).②Bland-Altman分析示LASIK手术前后DCT与GAT两种测量方法均呈现高度一致性.术前DCT测量值高于GAT测量值1.1mmHg,95%可信区间为(-0.6,2.8)mmHg;术后DCT测量值高于GAT测量值8.2mmHg,95%可信区间为(5.3,11.1)mmhg.③△GAT与△CCT呈正相关,△DCT与△CCT无统计相关性.结论 DCT测量值不受LASIK手术切削的影响,更适合于LASIK手术前后眼压的测量.     

The effect of contact lens-induced corneal edema on Goldmann applanation tonometry and dynamic contour tonometry

Purpose  To evaluate the effect of contact lens-induced corneal edema on intraocular pressure (IOP) measurements using Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) in Asian subjects. Participants  The study included 40 eyes of 20 normal volunteers with no evidence of ocular disease. Methods  Forty eyes of 20 healthy volunteers were required to wear soft contact lenses for 2 hours to induce corneal swelling. Central corneal thickness (CCT) and IOP were measured before and immediately after contact lens wear using specular microscope, GAT, and DCT. The IOP measurements by GAT and DCT were compared. The changes in the CCT and the IOP measurements after wearing contact lenses were assessed. Results  The mean CCT of the 40 eyes evaluated was 532.6 ± 31.6 μm. The mean IOP was 11.78 ± 2.04 mmHg for the GAT and 14.46 ± 1.89 mmHg for the DCT, and the difference was statistically significant (P < 0.001). After wearing contact lenses, the mean CCT was 553.2 ± 34.3 μm, which was 20.6 ± 12.9 μm greater than before wearing them (P < 0.001). The mean IOP measurements of the GAT and DCT were decreased after wearing the contact lenses. The mean decrease of the GAT values was 0.43 ± 1.95 mmHg, which was not statistically significant (P = 0.175). However, the mean decrease of the DCT readings, which was 0.75 ± 1.74 mm Hg, was statistically significant (P = 0.010). Conclusion  The IOP measurements with DCT were significantly higher than those with GAT in healthy Asian eyes. Although the mean IOP measurements of both the GAT and the DCT were decreased in the edematous cornea, IOP measurements of the DCT were more affected by corneal edema than were the GAT. The authors have no proprietary, commercial, or financial interests in any of the products described in this study.     

Dynamic contour tonometry versus Goldmann applanation tonometry: a comparative study

Background Various sources of error, including central corneal thickness (CCT) and structural corneal rigidity, have been proposed for Goldmann applanation tonometry (GAT). The Pascal dynamic contour tonometer (DCT) is a novel device designed for intraocular pressure (IOP) measurements assumed to be largely independent of CCT and corneal curvature. We compared DCT with GAT in eyes with normal corneas of various thickness.Methods We prospectively measured IOP using DCT and GAT in random order in 100 eyes of 100 subjects (M:F=46:54; mean age 42±19, range 23–88 years).Results Mean DCT values were about 1mmHg higher than GAT readings (16±3 vs 15±3 mmHg, p=0.001). Bland–Altman analysis of individual pairs of DCT and GAT measurements revealed a bias of –1.0 mmHg [95% confidence interval (CI): ±1.2]. Neither GAT nor DCT showed a significant correlation with CCT (533±48, range 399–641 m).Conclusions In eyes with normal corneas, DCT allows suitable and reliable IOP measurements which are in good concordance with GAT. Comparison of DCT with intracameral manometry is desirable in the future.     

Clinical evaluation of the IOPen® in a glaucomatous population

The aim of this study was to evaluate the level of agreement of measurements of intraocular pressure (IOP) taken by a rebound tonometer (IOPen^®), in comparison to a reference Goldmann applanation tonometer (GAT) in a glaucomatous population. Both eyes from 60 patients were assessed with the two tonometers, the induction tonometry was performed first by an experienced optometrist, and the GAT by an ophthalmologist. In this study, statistically significant differences were found when comparing the IOPen^® tonometer with the GAT tonometer (p < 0.001), mean differences were ?4.81 ± 4.31 and ?4.76 ± 5.76 mmHg (mean ± S.D.) for the right eye and left eye respectively These values represent an underestimation in the present population by the IOPen^® when compared with the GAT. Frequency distribution of differences demonstrated that in more than 71.6% of the measurements the IOP readings differed by more than 3 mmHg between the two tonometers. These results suggest that IOPen^® should be used with great caution in the determination of IOP.     

Performance of the rebound,noncontact and Goldmann applanation tonometers in routine clinical practice

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.     

Poor utility of intraocular pressure correction formulae in individual glaucoma and glaucoma suspect patients

Background: To compare Pascal dynamic contour tonometry (DCT) measurements with Goldmann applanation tonometry (GAT) readings after adjustment with correction formulae in a population of Caucasian glaucoma and glaucoma suspect patients. Design: Retrospective cross‐sectional case series in a specialist glaucoma practice. Participants: Consecutive glaucoma and glaucoma suspect Caucasian patients. Methods: Case notes review of the GAT and DCT intraocular pressure (IOP) measurements from patients who presented on a non‐acute basis over a 30‐month period. The GAT measurement was adjusted with six different correction formulae. Agreement between GAT IOP, adjusted GAT IOP and DCT IOP was evaluated with the Bland‐Altman analysis. Main Outcome Measures: Agreement between GAT IOP (both unadjusted and adjusted) and DCT IOP. Results: Data from 200 patients with a mean age of 58.4 (±12.7) years were analysed. The mean central corneal thickness was 554.8 (±36.9) µm and the mean corneal hysteresis was 9.8 (±1.9) mm Hg. Sixty five (32.5%) had confirmed glaucomatous optic neuropathy. GAT IOP demonstrated poor agreement with DCT IOP. GAT IOP was on average 2.1 mm Hg less than DCT IOP. None of the six correction formulae resulted in improved agreement with DCT IOP. General linear model analysis found no statistically significant measurement differences between the glaucoma and glaucoma suspect groups. Conclusions: GAT demonstrated poor agreement with DCT, and agreement did not improve after adjustment with correction formulae. Our results suggest that correction formulae for GAT IOP are unsuitable to clinically approximate ‘true’ IOP in Caucasian glaucoma and glaucoma suspect patients.     

Introduction and clinical evaluation of servo‐controlled applanation resonance tonometry

Purpose: In recent years, Applanation Resonance Tonometry (ART) has been suggested for intraocular pressure (IOP) measurements. The manual version of ART (ART_manual) has been further developed, and to improve usability, an automatic servo‐controlled prototype (ART_servo) has been proposed. The aim of this study was to assess the limits of agreement (LoA) of ART_manual and ART_servo as compared with the reference method, Goldmann Applanation Tonometry (GAT). Methods: This was a prospective single‐centre study on 152 eyes from 77 subjects. It was designed according to International Standard Organization’s (ISO) requirements for tonometers ( ISO 2001 ). Intraocular pressure was measured six times/method in a standardized order. The ART technique has two available analysis procedures: a dynamic one that measures IOP during the indentation phase and a static one that causes a Goldmann‐like measurement during two seconds of full applanation. The 95% LoA was defined as ±1.96 × standard deviation of difference against GAT. Results: Mean IOP for GAT was 19.1 mmHg (range: 10–37 mmHg). The 95% LoA of ART_manual was ±4.5 mmHg for both dynamic and static analyses. The 95% LoA of ART_servo was ±5.7 mmHg for dynamic and ±4.9 mmHg for static analyses. Conclusions: This study confirms that the ART methodology is feasible. The further developed ART_manual fulfilled the ISO standard with both the dynamic and the static analysis techniques. ART_servo with static analysis was close to fulfilling the standard but failed to do so in the highest IOP range. ART_servo has the potential to greatly improve usability if further development is completed.     

Telemedicine-friendly, portable tonometers: an evaluation for intraocular pressure screening

PURPOSE: To evaluate the intraocular pressure (IOP) readings from two portable, telemedicine-friendly tonometers for suitability in glaucoma screening. METHODS: 213 eyes of 107 consenting patients attending an eye clinic were tested with an I-care tonometer and a Pulsair-Easy Eye puff-air tonometer. Gold standard IOP was measured with a Goldmann applanation tonometer (GAT). Effect of central corneal thickness, anterior chamber depth and refractive errors on IOP measurements were also analysed. RESULTS: The mean difference of IOP by GAT and both the portable tonometers was +/- 2.2 mmHg. The analysis indicates minimal difference between IOP readings of both the portable tonometers. The mean difference between two consecutive readings by I-care was 0.01 mmHg. Using 21 mmHg as a threshold for suspected glaucoma, both the portable digital tonometers reported a sensitivity of 38% and specificity of >95%. In the subjects studied, central corneal thickness had statistically significant influence on IOP measurements while refractive errors and anterior chamber depth had no significant influence on IOP measurements with any tonometry. CONCLUSION: The IOP readings by both portable tonometers are comparable and were within clinically acceptable range from GAT. These portable tonometers are useful tools for IOP screening.     

Physiological diurnal variability and characteristics of the ocular pulse amplitude (OPA) with the dynamic contour tonometer (DCT-Pascal<Superscript>®</Superscript>)

PURPOSE: The Pascal dynamic contour tonometer (DCT) allows measurement of intraocular pressure (IOP) independently of corneal properties. It records, simultaneously, haemodynamic IOP fluctuations and the difference between the systolic and the diastolic IOP corresponding to the ocular pulse amplitude (OPA). The OPA indirectly reflects choroidal perfusion and could be considered as an independent risk factor in glaucoma. We aimed to establish the physiological diurnal variability of the OPA and its correlations with other biophysical parameters because its characteristics remain partly unclear. METHOD: Prospective study including 52 eyes of 28 normal subjects with Goldmann applanation tonometry (GAT) IOPs < 22 mmHg. Subjects treated with systemic medications that could interfere with blood pressure or heart rate were excluded. IOP was measured at 9:00 am, 1:00 pm, and 4:00 pm by GAT and DCT. Two consecutive GAT followed by three consecutive DCT measurements were performed in each session by the same clinician (SP). Only DCT measurements with quality 1 and 2 were taken into account. Blood pressure, pulse rate, and central corneal thickness (CCT) were recorded after the last IOP measurements. Spearman correlation coefficient was used for assessment of correlations. RESULTS: Mean age was 40 +/- 14 years. Mean DCT values were significantly higher than GAT readings (mean = 16.8 +/- 2.0 vs. 15.2 +/- 2.8 mmHg, P < 0.02). The mean OPA was 2.2 +/- 0.7 mmHg (range: 1-3.4 mmHg). The mean amplitude of diurnal OPA fluctuations was 0.4 mmHg. There was no significant difference in the mean OPA values at each time of the diurnal curve. The intraclass correlation (ICC) of only one OPA measurement in relation to part of total variance due to inter-measurement variation was 78%. Averaging over three independent readings of OPA improved ICC to 91%. The OPA was correlated with GAT (r = 0.31, P < 0.0001) and DCT IOP measurements (r = 0.49, P < 0.0001). It was correlated neither with blood pressure nor with age. OPA values of both eyes of the same individual were highly correlated (r = 0.89, P < 0.0001). CONCLUSION: In normal healthy eyes, the ocular pulse amplitude remains stable during normal outpatient office hours and was not correlated with blood pressure or age of patients.     

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: IOP_Pascal and IOP_ICare correlated with IOP_GAT (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 IOP_GAT (r = 0.23) and IOP_ICare (r = 0.43) but not with IOP_Pascal (P = 0.12). CCT was correlated with age. In a subgroup (>50 years), ICare and the difference between IOP_GAT and IOP_Pascal were affected significantly by the CCT, whereas IOP_GAT and IOP_Pascal were not. Corneal curvature was correlated significantly with IOP_GAT (r = ?0.27) and IOP_Pascal (r = ?0.26) but not with IOP_ICare (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.     

Comparison of the ICare® rebound tonometer with the Goldmann tonometer in a normal population

The aim of this study was to evaluate the accuracy of measurement of intraocular pressure (IOP) using a new induction/impact rebound tonometer (ICare) in comparison with the Goldmann applanation tonometer (AT). The left eyes of 46 university students were assessed with the two tonometers, with induction tonometry being performed first. The ICare was handled by an optometrist and the Goldmann tonometer by an ophthalmologist. In this study, statistically significant differences were found when comparing the ICare rebound tonometer with applanation tonometry (AT) (p < 0.05). The mean difference between the two tonometers was 1.34 +/- 2.03 mmHg (mean +/- S.D.) and the 95% limits of agreement were +/-3.98 mmHg. A frequency distribution of the differences demonstrated that in more than 80% of cases the IOP readings differed by <3 mmHg between the ICare and the AT. In the present population the ICare overestimates the IOP value by 1.34 mmHg on average when compared with Goldmann tonometer. Nevertheless, the ICare tonometer may be helpful as a screening tool when Goldmann applanation tonometry is not applicable or not recommended, as it is able to estimate IOP within a range of +/-3.00 mmHg in more than 80% of the population.     

Dynamic contour tonometry (DCT) versus Goldmann applanation tonometry (GAT) - a comparison of agreement and reproducibility

Background

The PASCAL® dynamic contour tonometer (DCT) is a novel device designed for intraocular pressure (IOP) measurements. It is assumed to be largely independent of corneal properties. In a previous study we compared DCT with Goldmann applanation tonometry (GAT) in 100 right eyes with normal corneas. The aim of the present study is to evaluate whether differences DCT-GAT?≥?2.0 mmHg found in the previous study are reproducible and also present in the fellow eye.

Methods

Twenty-three of the 100 patients (M:F?=?8:15, mean age: 36?±?11 SD, range 22–53 years) with a previous difference DCT-GAT?≥?2.0 mmHg were included in the present study. The minimum interval between the initial and the current examination was 3 weeks. The IOP-values of the fellow eyes in this subgroup were assessed in parallel.

Results

The difference DCT-GAT was 2.44?±?0.4 SEM mmHg in the subgroup of the 23 right eyes and 2.03?±?0.5 SEM mmHg for the fellow eyes, compared to 0.94?±?0.5 SEM mmHg in the initial sample of 100 eyes.

Conclusions

In cases with higher difference between DCT-GAT, the difference is reproducible and even present in the fellow eye. We, therefore, assume that the differences are not caused by chance, but by differing biomechanical corneal properties.     

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.