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1.  Correlation of Intraocular Pressure Measured With Goldmann and Dynamic Contour Tonometry in Normal and Glaucomatous Eyes 
Journal of glaucoma  2009;18(2):119-123.
To compare intraocular pressure (IOP) values measured by both Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) in both normal and glaucomatous eyes, and to determine the relationship between these parameters and central corneal thickness (CCT).
Patients and Methods
Forty-seven subjects with primary open-angle glaucoma and 38 normal subjects attended a 12-hour session during which IOP was assessed at 7 time points, every 2 hours, by both GAT and DCT. CCT was also assessed at the same visit. Mean IOP was calculated for each eye of each subject by each method from the 7 diurnal IOP measurements obtained.
Mean IOP was higher when measured by DCT than by GAT in both normal (by 1.1 mm Hg, P<0.0001) and glaucomatous (by 1.6 mm Hg, P<0.0001) eyes. IOP measurements by GAT and DCT were moderately correlated in both normal (r2=0.354, P<0.0001) and glaucomatous (r2=0.552, P<0.0001) eyes. In normal eyes, there was a weak positive correlation between GAT IOP and CCT (r2=0.088, slope=0.022 mm Hg/µm, P=0.009) and no correlation between DCT IOP and CCT (r2=0.007, slope=0.005 mm Hg/µm, P=0.468). In glaucomatous eyes, there was no correlation between GAT IOP and CCT (r2=0.006, slope=0.007 mm Hg/µm, P=0.473) and a weak inverse correlation between DCT IOP and CCT (r2=0.075, slope= −0.021 mm Hg/µm, P=0.008).
Both GAT and DCT are affected by CCT, albeit in different ways. Normal and glaucomatous eyes exhibit different relationships between CCT and IOP measured by either GAT or DCT. The relationships between CCT and transcorneal IOP measurements are complex and incompletely characterized, which limits the clinical interpretation of GAT and DCT measurements of IOP in both normal and glaucomatous eyes.
PMCID: PMC2704612  PMID: 19225347
intraocular pressure; diurnal; tonometry; glaucoma
2.  The relative effects of corneal thickness and age on Goldmann applanation tonometry and dynamic contour tonometry 
The British Journal of Ophthalmology  2005;89(12):1572-1575.
Aims: To establish the effects of central corneal thickness (CCT) on intraocular pressure (IOP) measured with a prototype Pascal dynamic contour tonometer (DCT), to evaluate the effect of CCT and age on the agreement between IOP measured with the Pascal DCT and Goldmann applanation tonometer (GAT), and to compare the interobserver and intraobserver variation of the DCT with the GAT.
Methods: GAT and DCT IOP measurements were made on 130 eyes of 130 patients and agreement was assessed by means of Bland-Altman plots. The effect of CCT and age on GAT/DCT IOP differences was assessed by linear regression analysis. Interobserver and intraobserver variations for GAT and DCT were assessed in 100 eyes of 100 patients.
Results: The mean difference (95% limits of agreement) between GAT and DCT was −0.7 (−6.3 to 4.9) mm Hg. GAT/DCT IOP differences increased with thicker CCT (slope 0.017 mm Hg/μm, 95% CI 0.004 to 0.03, r2 = 0.05, p = 0.01), and with greater age, slope 0.05 mm Hg/year (95% CI 0.012 to 0.084, r2 = 0.05, p = 0.01). The intraobserver variability of GAT and DCT was 1.7 mm Hg and 3.2 mm Hg, respectively. The interobserver variability was (mean difference (95% limits of agreement)) 0.4 (−3.5 to 4.2) mm Hg for GAT and 0.2 (−4.9 to 5.3) mm Hg for DCT.
Conclusions: GAT is significantly more affected than DCT by both CCT and subject age. The effect of age suggests an age related corneal biomechanical change that may induce measurement error additional to that of CCT. The prototype DCT has greater measurement variability than the GAT.
PMCID: PMC1772992  PMID: 16299132
dynamic contour tonometry; central corneal thickness; age; intraobserver variability; interobserver variability
3.  Comparison of iCare tonometer and Goldmann applanation tonometry in normal corneas and in eyes with automated lamellar and penetrating keratoplasty 
Eye  2011;25(5):642-650.
To compare intraocular pressure (IOP) measurements with Goldmann applanation tonometry (GAT) and iCare tonometry in normal and post-keratoplasty corneas and to assess the influence of central corneal thickness (CCT), corneal curvature (CC), and corneal astigmatism (CA) on IOP.
This prospective cross-sectional study included one eye of 101 subjects with normal corneas (58 healthy subjects, 43 glaucoma); and 90 post-keratoplasty patients: 34 penetrating keratoplasties (PK); 20 automated-lamellar-therapeutic keratoplasties (ALTK); 19 Descemet-stripping-automated-endothelial keratoplasties (DSAEK); 17 edematous grafts. All subjects underwent GAT and iCare IOP measurements in random order, and CCT, CC, and CA evaluation. The Bland–Altman method and multivariate regression analysis were used to assess inter-tonometer agreement and the influence of CCT, CC, and CA on IOP.
iCare significantly underestimated IOP in all groups compared with GAT (GAT minus iCare of 3.5±3.5 mm Hg, P<0.001), but overestimated IOP in the edematous grafts (GAT minus iCare of −6.5±1.9 mm Hg, P<0.001). In normal corneas, both tonometer measurements were directly related to CCT values; iCare readings appeared inversely related to CC. There was no significant relationship between IOP and CCT, CC and CA in post-keratoplasty eyes, except between CC and iCare measurements for PK eyes.
The agreement between GAT and iCare was clinically acceptable in control, ALTK and DSAEK groups, and poor in PK and edematous grafts eyes. In normal corneas, GAT was significantly affected by CCT; iCare was influenced by CCT and CC. The iCare appeared less influenced by corneal edema when compared with GAT. High IOP readings taken with both tonometers in grafts should raise suspicion of true elevated IOP.
PMCID: PMC3171271  PMID: 21436848
intraocular pressure; Goldmann applanation tonometer; iCare tonometer; corneal thickness; corneal curvature; keratoplasty
4.  Tonometry in corneal edema after cataract surgery: dynamic contour tonometry versus Goldmann applanation tonometry 
Intraocular pressure (IOP) determination using dynamic contour tonometry (DCT) has been considered to be independent of central corneal thickness (CCT), while Goldmann applanation tonometry (GAT) is known to be influenced by various corneal properties. In this study, IOP was measured before and 1 day after cataract surgery using GAT and DCT to investigate the possible effects of corneal edema on IOP measurements.
Thirty patients with advanced cataracts were included in a pilot study. IOP was measured using GAT and DCT before and 1 day after phacoemulsification. CCT was determined before and after surgery to quantify postsurgical corneal edema.
CCT increased significantly (by 89.7 ± 107.4 μm, P < 0.0001) 1 day after surgery. No significant difference was found for IOP measurements using GAT and DCT before surgery (mean IOP GAT: 17.5 ± 5.7 mmHg; mean IOP DCT: 17.9 ± 6.4 mmHg; P = 0.67) and 1 day after surgery (mean IOP GAT: 16.1 ± 6.6 mmHg; mean IOP DCT: 16.8 ± 8.3 mmHg; P = 0.69). IOP values using GAT and DCT were significantly correlated before as well as 1 day after surgery (before surgery: r = 0.82, P < 0.0001; after surgery r = 0.83, P < 0.0001). Bland–Altman plots showed a high variability in the difference in IOP measurements between methods before and 1 day after surgery.
GAT and DCT seem to be equally valuable in IOP determination in postsurgical central corneal edema, although large differences between both methods are present in individual patients. IOP evaluation in corneal edema remains a difficult clinical challenge.
PMCID: PMC3647600  PMID: 23662041
Goldmann applanation tonometry; dynamic contour tonometry; corneal edema; cataract surgery; intraocular pressure
5.  Measuring accurate IOPs: Does correction factor help or hurt? 
To evaluate if using the Ehlers correction factor on the intraocular pressure (IOP) measured using the Goldmann applanation tonometer (GAT) improves its agreement with the PASCAL dynamic contour tonometer (DCT).
Patients and methods:
A total of 120 eyes of 120 individuals were examined. Participants underwent IOP measurement with both the DCT and the GAT and central corneal thickness measurement. The Ehlers correction factor was applied on the GAT IOP measurements to calculate Ehlers-corrected GAT IOP. The agreement between the DCT and GAT, and DCT and Ehlers-corrected GAT IOP was analyzed. The analyses were repeated by stratifying the data by race.
The mean IOP of the GAT, DCT, and the Ehlers-corrected GAT was 15.30, 16.78, and 14.68 mmHg, respectively. The agreement as assessed by Bland–Altman plot for the GAT with the DCT and DCT and Ehlers-corrected GAT IOP was +4.1 to −6.9 and +4.15 to −8.25 mmHg, respectively. The results were similar even when stratifying the data by race.
Using Ehlers correction factor to account for the effect of corneal parameters on the IOP measured by the GAT worsens the agreement with the DCT. This effect remains even when stratifying the data by race.
PMCID: PMC2909890  PMID: 20668723
dynamic contour tonometer; Goldmann applanation tonometer; tonometric correction factors; central corneal thickness; intraocular pressure
6.  Correlation between ocular perfusion pressure and ocular pulse amplitude in glaucoma, ocular hypertension, and normal eyes 
The purpose of this study was to investigate the correlation between ocular perfusion pressure and ocular pulse amplitude in glaucoma, ocular hypertension, and normal eyes.
Ninety eyes from 90 patients were included. Thirty patients had been recently diagnosed with glaucoma and had no previous history of treatment for ocular hypotension, 30 had elevated intraocular pressure (IOP) without evidence of glaucoma, and 30 had normal IOP (<21 mmHg) with no detectable glaucomatous damage. Goldmann applanation tonometry (GAT), dynamic contour tonometry (DCT), blood pressure measurement, pachymetry, Humphrey visual field, and routine ophthalmic examination was performed in each patient. Ocular perfusion pressure was calculated as the difference between mean arterial pressure and IOP. The ocular pulse amplitude was given by DCT. The Pearson correlation coefficient was used to compare the glaucomatous and ocular hypertensive groups, and comparisons with the normal IOP group were done using the Spearman’s rank correlation coefficient.
Mean IOP by DCT was 22.7 ± 4.3 mmHg in the glaucoma group, 22.3 ± 2.8 mmHg in the ocular hypertension group, and 14.3 ± 1.6 mmHg in the control group. Mean IOP by GAT was 19.0 ± 5.1 mmHg for glaucoma, 22.4 ± 2.1 mmHg for ocular hypertension, and 12.9 ± 2.2 mmHg for controls. Mean ocular pulse amplitude was 3.4 ± 1.2 mmHg in the glaucoma group, 3.5 ± 1.2 mmHg in the ocular hypertension group, and 2.6 ± 0.9 mmHg in the control group. Mean ocular perfusion pressure was 46.3 ± 7.9 mmHg in the glaucoma group, 46.3 ± 7.9 mmHg in the ocular hypertension group, and 50.2 ± 7.0 mmHg in controls. No significant correlation between ocular perfusion pressure and ocular pulse amplitude was found in any of the groups (P = 0.865 and r = −0.032, P = 0.403 and r = −0.156, P = 0.082 and ρ = −0.307 for glaucoma, ocular hypertension, and normal eyes, respectively).
There is no significant correlation between ocular perfusion pressure and ocular pulse amplitude values in glaucoma, ocular hypertension, or normal eyes. IOP values measured by GAT correlate with those measured by DCT.
PMCID: PMC3745293  PMID: 23966769
glaucoma; ocular pulse amplitude; ocular perfusion pressure; dynamic contour tonometry; vascular factors
7.  Assessment of intraocular pressure measured by Reichert Ocular Response Analyzer, Goldmann Applanation Tonometry, and Dynamic Contour Tonometry in healthy individuals 
To investigate the accuracy of intraocular pressure (IOP) as measured by a Reichert Ocular Response Analyzer (ORA), as well as the relationship between central corneal thickness (CCT) and IOP as measured by ORA, Goldmann applanation tonometry (GAT), and dynamic contour tonometry (DCT).
A total of 158 healthy individuals (296 eyes) were chosen randomly for measurement of IOP. After CCT was measured using A-ultrasound (A-US), IOP was measured by ORA, GAT, and DCT devices in a randomized order. The IOP values acquired using each of the three tonometries were compared, and the relationship between CCT and IOP values were analyzed separately. Two IOP values, Goldmann-correlated IOP value (IOPg) and corneal-compensated intraocular pressure (IOPcc), were got using ORA. Three groups were defined according to CCT: 1) thin cornea (CCT<520µm); 2) normal-thickness cornea (CCT: 520–580µm); and 3) thick cornea (CCT>580µm) groups.
In normal subjects, IOP measurements were 14.95±2.99mmHg with ORA (IOPg), 15.21±2.77mmHg with ORA (IOPcc), 15.22±2.77mmHg with GAT, and 15.49±2.56mmHg with DCT. Mean differences were 0.01±2.29mmHg between IOPcc and GAT (P>0.05) and 0.28±2.20mmHg between IOPcc and DCT (P>0.05). There was a greater correlation between IOPcc and DCT (r=0.946, P=0.000) than that between IOPcc and GAT (r=0.845, P=0.000). DCT had a significant correlation with GAT (r=0.854, P=0.000). GAT was moderately correlated with CCT (r=0.296, P<0.001), while IOPcc showed a weak but significant correlation with CCT (r=−0.155, P=0.007). There was a strong negative correlation between CCT and the difference between IOPcc and GAT(r=-0.803, P=0.000), with every 10µm increase in CCT resulting in an increase in this difference of 0.35mmHg. The thick cornea group (CCT>580µm) showed the least significant correlation between IOPcc and GAT (r=0.859, P=0.000); while the thin cornea group (CCT<520µm) had the most significant correlation between IOPcc and GAT (r=0.926, P=0.000). The correlated differences between IOPcc and DCT were not significant in any of the three groups (P>0.05).
Measurement of IOP by ORA has high repeatability and is largely consistent with GAT measurements. Moreover, the ORA measurements are affected only to a small extent by CCT, and are likely to be much closer to the real IOP value than GAT.
PMCID: PMC3340849  PMID: 22553765
intraocular pressure; tonometry; central corneal thickness
8.  The influence of soft contact lenses on the intraocular pressure measurement 
Eye  2011;26(2):278-282.
To evaluate the influence of silicone hydrogel contact lenses on the intraocular pressure (IOP) measurement using Goldmann applanation tonometry (GAT), non-contact tonometry (NCT), and Pascal dynamic contour tonometry (DCT).
We included in the study 40 eyes of 40 patients who did not have any ocular or systemic diseases or contraindications to contact lens use. We measured and recorded the IOP values of each patient using NCT without and with contact lenses (groups 1 and 2, respectively), using DCT without and with contact lenses (groups 3 and 4, respectively), and using GAT without contact lenses (group 5).
The mean IOP value of group 1 was 14.55±2.95 mm Hg and 13.92±2.58 mm Hg in group 2. We detected no statistically significant difference between group 1 and group 2 (P=0.053). The mean IOP values for group 3 and group 4 were 16.26±2.33 mm Hg and 15.19±2.40 mm Hg, respectively. We detected a statistically significant difference between groups 3 and 4 (P=0.005). Group 5's mean IOP value was 12.97±2.65 mm Hg. IOP values measured with DCT were statistically significantly higher compared with IOP values measured with NCT and GAT (P<0.0001 and P<0.0001, respectively). Additionally, IOP values measured with NCT were statistically significantly higher compared with IOP values measured with GAT (P<0.0001).
According to the results of our study, silicone hydrogel soft contact lens use does not significantly affect IOP values measured with NCT, but it affects IOP values measured with DCT.
PMCID: PMC3272185  PMID: 22079968
dynamic contour tonometry; non-contact tonometry; goldmann applanation tonometry; contact lens
9.  Dynamic Contour Tonometry in Primary Open Angle Glaucoma and Pseudoexfoliation Glaucoma: Factors Associated with Intraocular Pressure and Ocular Pulse Amplitude 
To compare the intraocular pressures (IOP) and ocular pulse amplitudes (OPAs) in patients with primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PXG), and to evaluate ocular and systemic factors associated with the OPA.
Materials and Methods:
In this prospective study, on 28 POAG and 30 PXG patients, IOP was measured with the Goldmann applanation tonometry (GAT) and the Pascal dynamic contour tonometry (DCT). Other measurements included central corneal thickness (CCT), vertical cup-to-disc ratio (CDR), and systolic and diastolic blood pressure. Statistical significance was defined as P < 0.05.
In each of the POAG and PXG groups, GAT IOP was correlated with CCT (r = 0.40, P = 0.03 and r = 0.35, P = 0.05, respectively), whereas DCT IOP and CCT were not correlated. In all patients and in the POAG group, OPA was positively correlated with DCT IOP (r = 0.39, P = 0.002). OPA was not correlated with CCT in the POAG (P = 0.80), nor in the PXG (P = 0.20) group, after adjusting for DCT IOP. When corrected for DCT IOP and CCT, there was a significant negative correlation between OPA and vertical CDR in all patients (r = −0.41, P = 0.002). There was no significant difference in OPA between groups (P = 0.55), even when OPA was adjusted for IOP and systolic and diastolic pressure (P = 0.40), in a linear regression model.
DCT IOP and OPA are not correlated with CCT. There is no significant difference between the OPA of PXG and POAG eyes. OPA is correlated with DCT IOP, and is lower in eyes with more advanced glaucomatous cupping.
PMCID: PMC3669493  PMID: 23741135
Dynamic Contour Tonometry; Ocular Pulse Amplitude; Primary Open-Angle Glaucoma; Pseudoexfoliation Glaucoma
10.  Comparison of Goldmann and Pascal tonometry in relation to corneal hysteresis and central corneal thickness in nonglaucomatous eyes 
To compare measurements obtained by Goldmann applanation tonometry (GAT) and Pascal dynamic contour tonometry (DCT), and to study their relationship to corneal thickness and biomechanical properties in nonglaucomatous eyes.
This is a prospective and randomized study of 200 eyes from 200 non-glaucomatous subjects who underwent intraocular pressure (IOP) measurements by GAT and DCT. The two methods were compared and assessed for agreement by means of the Bland–Altman plot. Central corneal thickness (CCT) and corneal hysteresis (CH) were obtained by ultrasound pachymeter and Ocular Response Analyzer, respectively. The effect of CH and CCT was correlated with the DCT/GAT IOP differences.
Mean age was 57.4 ± 14.7 years (range 24–82 years). Mean IOP measurements obtained were 16.7 ± 3.2 mmHg by GAT and 19.4 ± 3.3 mmHg by DCT. DCT showed a statistically significant higher mean IOP (2.7 ± 1.9 mmHg, P < 0.001) compared with GAT. Mean CCT and CH were 546.5 ± 40 μm and 10.85 ± 2.0 mmHg, respectively. The differences in IOP (DCT – GAT) were significantly correlated with CCT and CH (Pearson’s correlation coefficient r = −0.517 and −0.355, P < 0.0001, respectively). The difference between the two correlation coefficients was statistically significant (P < 0.05, Z-statistic). According to the Bland–Altman plot, the results of the two methods were clinically different.
Significantly higher IOP readings were obtained by DCT than by GAT in nonglaucomatous subjects. The IOP differences between the two methods were associated with CCT and CH, suggesting that DCT was less dependent on corneal parameters. Each method provides clinically different IOP values, indicating that DCT and GAT should not be used interchangeably.
PMCID: PMC3155272  PMID: 21847339
Pascal dynamic contour tonometry; Goldmann applanation tonometry; glaucoma; central corneal thickness; corneal hysteresis
11.  Comparison Between Dynamic Contour Tonometry and Goldmann Applanation Tonometry 
To compare the intraocular pressures (IOPs) measured by dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT), and to investigate the association of IOPs on eyes of varying central corneal thickness (CCT).
In this prospective study, 451 eyes of 233 subjects were enrolled. IOPs were measured by GAT and DCT. CCT was measured three times and the average was calculated. Each eye was classified into one of three groups according to CCT: low CCT (group A, CCT<520 µm, n=146); normal CCT (group B, 520 µm ≤ CT ≤ 550 µm, n=163); and high CCT (group C, CCT>550 µm, n=142). In each group, we investigated the association of CCT with IOP measurement by GAT and DCT.
The IOPs measured by GAT and DCT were significantly associated for all eyes (R=0.853, p<0.001, Pearson correlation). CCT was related with both IOP measurement by GAT and DCT with statistical significance (mixed effect model, p<0.001). However, subgroup analysis showed that CCT affected IOP measured by GAT for groups B and C, whereas it affected IOP measured by DCT only for group C.
IOP measured by DCT was not affected by CCT in eyes with low to normal CCT, whereas this measurement was affected in eyes of high CCT range. CCT may have less effect on IOP measurements using DCT than those obtained by GAT, within a specified range of CCT.
PMCID: PMC2655749  PMID: 19337476
Central corneal thickness; Dynamic contour tonometry; Goldmann applanation tonometry
12.  Clinical utility of spectral analysis of intraocular pressure pulse wave 
BMC Ophthalmology  2014;14:30.
To evaluate the clinical utility of spectral analysis of intraocular pressure pulse wave in healthy eyes of a control group (CG), patients having glaucomatous optic disc appearance or ocular hypertension, and patients with primary open angle glaucoma or primary angle closure glaucoma.
This is a prospective study that enrolled 296 patients from a single glaucoma clinic. Age matched CG consisted of 62 individuals. Subjects underwent comprehensive clinical diagnostic procedures including intraocular pressure (IOP) measurement with dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT). DCT time series were analyzed with custom written software that included signal preprocessing, filtering and spectral analysis. An amplitude and energy content analysis, which takes into account non-stationarity of signals but also provides methodology that is independent of IOP and ocular pulse amplitude (OPA) levels, was applied. Spectral content up to the 6th harmonic of the pressure pulse wave was considered. Statistical analyses included descriptive statistics, normality test, and a multicomparison of medians for independent groups using Kruskal-Wallis test.
GAT IOP showed statistical significance (Kruskal-Willis test p < 0.05) for three out of 10 considered multiple comparisons, DCT IOP and OPA showed statistically significant results in five and seven cases, respectively. Changes in heart rate and central corneal thickness between the groups were statistically significant in two cases. None of the above parameters showed statistically significant differences between CG and the suspects with glaucomatous optic disc appearance (GODA). On the other hand, spectral analysis showed statistically significant differences for that case.
Spectral analysis of the DCT signals was the only method showing statistically significant differences between healthy eyes and those of GODA suspects.
PMCID: PMC3975190  PMID: 24620786
Glaucoma; Intraocular pressure; Dynamic contour tonometry; Ocular pulse wave
13.  Intraocular pressure profile during the modified diurnal tension curve using Goldman applanation tonometry and dynamic contour tonometry 
The aim of this study was to compare the intraocular pressure (IOP) profile during the modified diurnal tension curve (mDTC) using Goldman applanation tonometry (GAT) and dynamic contour tonometry (DCT) in treated glaucomatous eyes. Eligible subjects were submitted to the mDTC using GAT and DCT in this sequence. IOP measurements were performed at 8 a.m., 10 a.m., 2 p.m., and 4 p.m.. Central corneal thickness was measured using ultrasound pachymetry in the morning. Statistical analysis was performed using paired Student’s t test and Bland–Altman plot. The mean difference between DCT and GAT measurements was 0.9 mmHg. The mean ± SD IOP measurements during the mDTC were 19.68 ± 4.68, 17.63 ± 4.44, 17.25 ± 5.41, and 17.32 ± 4.25 mmHg using GAT and 19.97 ± 4.75, 18.79 ± 4.61, 19.53 ± 5.30, and 19.43 ± 5.45 mmHg using DCT. IOP measurements were higher in the morning (8 a.m.) and decreased throughout the day using both tonometers. The difference between IOP measurements using GAT and DCT was smaller in the morning and increased throughout the day. The IOP variability using GAT was higher than using DCT. Corneal biomechanical properties might help explain our findings.
PMCID: PMC2802501  PMID: 20072644
Glaucoma; Corneal biomechanics; Intraocular pressure; Dynamic contour tonometry; Tension curves
14.  Repeatability and Reproducibility of Goldmann Applanation, Dynamic Contour and Ocular Response Analyzer Tonometry 
Journal of glaucoma  2013;22(2):127-132.
To evaluate the repeatability and inter-operator reproducibility of the Pascal dynamic contour tonometry (DCT), Ocular Response Analyzer (ORA) and Goldmann applanation tonometer(GAT) in a single population of normal subjects.
The study included fifty-two eyes from 26 normal subjects. One operator measured the intraocular pressure (IOP) with each tonometer three times while two additional operators each measured the IOP with each tonometer once. Repeatability and reproducibility were assessed by the coefficient of Variation (CV) and Intraclass Correlation Coefficient (ICC). Agreement among tonometers was also assessed using Bland-Altman plots.
The mean age of included subjects was 31.5 ±8.8 years and 15 (58%) were female. In general, both intra-operator repeatability and inter-operator reproducibility were significantly higher for DCT compared to the other tonometers. Intra-operator DCT (CV = 3.7, ICC = 0.89), GAT (CV = 9.7, ICC = 0.79), IOPg (CV = 7.0, ICC = 0.79) and IOPcc (CV = 9.8, ICC = 0.57). Inter-operator DCT (CV=6.1, ICC = 0.73), GAT (CV=9.0, ICC=0.82) and IOPg (CV=10.8, ICC = 0.63), IOPcc (CV=11.7, ICC = 0.49)
Overall, DCT was significantly more repeatable and reproducible than GAT, IOPg and IOPcc. The better reproducibility of the DCT may result in more precise measurements for monitoring intraocular pressure changes over time compared to GAT and ORA.
PMCID: PMC3194063  PMID: 21701395
Intraocular pressure; Repeatability; Reproducibility; Goldmann applanation tonometry; dynamic contour tonometry; ocular response analyzer; waveform score
15.  Evaluation of the New Digital Goldmann Applanation Tonometer for Measuring Intraocular Pressure 
Journal of Ophthalmology  2014;2014:461681.
Purpose. To compare a new digital Goldmann applanation tonometer (dGAT) that measures intraocular pressure (IOP) in 0.1 mmHg increments to a standard Goldmann applanation tonometer (sGAT). Methods. This study included 116 eyes of 60 subjects. A single examiner first measured IOP in triplicate using either sGAT or dGAT, which was randomly chosen. After a 5-minute interval, the next set of three consecutive IOP was measured using the other GAT. Results. The mean IOP measured with sGAT was 16.27 ± 6.68 mmHg and 16.35 ± 6.69 mmHg with dGAT. Pearson's correlation coefficient was 0.998 (P < 0.01). The subjects were divided into three groups based on the mean IOP: IOP < 14 mmHg, 14–20 mmHg, or >20 mmHg. The Pearson's correlation coefficient within each group was 0.935, 0.972, and 0.997 (P < 0.01), respectively. The difference within the three consecutive IOP measurements (maximum–minimum) for dGAT (0.72 ± 0.34 mmHg) was significantly smaller than those with sGAT (0.92 ± 0.42 mmHg, P < 0.01). Even in patients with equal IOP (zero left-right difference) with sGAT (n = 30), dGAT detected IOP differences between the left and right eyes (0.47 ± 0.31 mmHg). Conclusion. Compared to sGAT, dGAT measurements are highly reproducible and less variable.
PMCID: PMC4121251  PMID: 25126423
16.  A comparison of four methods of tonometry: method agreement and interobserver variability 
Aim: To compare the inter-method agreement in intraocular pressure (IOP) measurements made with four different tonometric methods.
Methods: IOP was measured with the Goldmann applanation tonometer (GAT), Tono-Pen XL, ocular blood flow tonograph (OBF), and Canon TX-10 non-contact tonometer (NCT) in a randomised order in one eye of each of 105 patients with ocular hypertension or glaucoma. Three measurements were made with each method, and by each of two independent GAT observers. GAT interobserver and tonometer inter-method agreement was assessed by the Bland-Altman method. The outcome measures were 95% limits of agreement for IOP measurements between GAT observers and between tonometric methods, and 95% confidence intervals for intra-session repeated measurements.
Results: The mean differences (bias) in IOP measurements were 0.4 mm Hg between GAT observers, and 0.6 mm Hg, 0.1 mm Hg, and 0.7 mm Hg between GAT and Tono-Pen, OBF, and NCT, respectively. The 95% limits of agreement were smallest (bias ±2.6 mm Hg) between GAT observers, and larger for agreement between the GAT and the Tono-Pen, OBF, and NCT (bias ±6.7, ±5.5, and ±4.8 mm Hg, respectively). The OBF and NCT significantly underestimated GAT measurements at lower IOP and overestimated these at higher IOP. The repeatability coefficients for intra-session repeated measurement for each method were ±2.2 mm Hg and ±2.5 mm Hg for the GAT, ±4.3 mm Hg for the Tono-Pen, ±3.7 mm Hg for the OBF, and ±3.2 mm Hg for the NCT.
Conclusions: There was good interobserver agreement with the GAT and moderate agreement between the NCT and GAT. The differences between the GAT and OBF and between the GAT and Tono-Pen probably preclude the OBF and Tono-Pen from routine clinical use as objective methods to measure IOP in normal adult eyes.
PMCID: PMC1772716  PMID: 15965164
tonometry; intraocular pressure; comparative study; repeatability
17.  Comparison of IOPen rebound tonometer with Goldmann applanation tonometer at different IOP levels 
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.
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.
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%.
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.
PMCID: PMC3808911  PMID: 24195039
rebound tonometry; IOPen; Goldmann applanation tonometry; intraocular pressure
18.  Retrobulbar hemodynamic parameters in open-angle and angle-closure glaucoma patients 
Eye  2012;26(4):523-528.
The purpose of this study is to compare the retrobulbar hemodynamic parameters in the ophthalmic artery (OA), central retinal artery (CRA), and posterior cilliary arteries (PCA), in open-angle glaucoma (OAG) and angle-closure glaucoma (ACG) patients.
Patients and methods
A total of 52 eyes from 52 patients with OAG and 25 eyes from 25 ACG patients who met the inclusion/exclusion criteria were included in this cross-sectional study. Peak-systolic velocity, end-diastolic velocity, and Pourcelot resistivity index (RI) were assessed in the OA, CRA, and PCA. Intraocular pressure (IOP) was measured both with the Goldmann applanation tonometer (GAT) and with the Dynamic Contour tonometer (DCT) three times, respectively. Ocular pulse amplitude was measured using DCT.
The RI was significantly higher in both the ophthalmic and short PCA in the OAG patients as compared with that in those ACG patients, P=0.003 and 0.048, respectively. There was no correlation between the IOP measured with GAT and the retrobulbar hemodynamic parameters in either OAG or ACG.
There was an increased resistance to blood flow in the OA of OAG as compared with ACG patients. Additionally, the degree of circulatory disturbance was not related to either the IOP or the visual-field damage.
PMCID: PMC3325581  PMID: 22241021
open-angle glaucoma; angle-closure glaucoma; color Doppler imaging; ocular blood flow
19.  Diurnal Tension Curves for Assessing the Development or Progression of Glaucoma 
Executive Summary
Clinical Need: Condition and Target Population
There are two main types of glaucoma, primary open angle (POAG) and angle closure glaucoma, of which POAG is the more common type. POAG is diagnosed by assessing degenerative changes in the optic disc and loss of visual field (VF). Risk factors for glaucoma include an increase in intraocular pressure (IOP), a family history of glaucoma, older age and being of African descent. The prevalence of POAG ranges from 1.1% to 3.0% in Western populations and from 4.2% to 8.8% in populations of African descent.
Usually the IOP associated with POAG is elevated above the normal distribution (10-20 mmHg), but when IOP is not elevated it is often referred to as normal-tension glaucoma (NTG). In population based studies, approximately one-third to half of the patients with glaucomatous VF loss have normal IOP on initial examination.
People with elevated IOP (>21 mmHg), but with no evidence of optic disc or VF damage have ocular hypertension. It has been estimated that 3 to 6 million people in the United States including 4% to 7% of those older than 40 years have elevated IOP without detectable glaucomatous damage on standard clinical tests. An Italian study found the overall prevalence of ocular hypertension, POAG, and NTG in 4,297 people over 40 years of age to be 2.1%, 1.4% and 0.6% respectively.
Diurnal Curves for Intraocular Pressure Measurement
Diurnal Curve
In normal individuals, IOP fluctuates 2 to 6 mmHg over a 24 hour period. IOP is influenced by body position with higher readings found in the supine relative to the upright position. As most individuals sleep in the supine position and are upright during the day, IOP is higher on average in people, both with and without glaucoma, in the nocturnal period. IOP is generally higher in the morning compared to the afternoon.
Multiple IOP measurements over the course of a day can be used to generate a diurnal curve and may have clinical importance in terms of diagnosis and management of patients with IOP related conditions since a solitary reading in the office may not reveal the peak IOP and fluctuation that a patient experiences. Furthermore, because of diurnal and nocturnal variation in IOP, 24-hour monitoring may reveal higher peaks and wider fluctuations than those found during office-hours and may better determine risk of glaucoma progression than single or office-hour diurnal curve measurements.
There is discrepancy in the literature regarding which parameter of IOP measurement (e.g., mean IOP or fluctuation/range of IOP) is most important as an independent risk factor for progression or development of glaucoma. The potential for increased rates or likelihood of worsening glaucoma among those with larger IOP swings within defined time periods has received increasing attention in the literature.
According to an expert consultant:
The role of a diurnal tension curves is to assess IOP in relationship to either a risk factor for the development or progression of glaucoma or achievement of a target pressure which may direct a therapeutic change.
Candidates for a diurnal curve are usually limited to glaucoma suspects (based on optic disc changes or less commonly visual field changes) to assess the risk for development of glaucoma or in patients with progressive glaucoma despite normal single office IOP measurements.
Clinically diurnal tension curves are used to determine the peak IOP and range.
Single IOP Measurements
Intraocular pressure fluctuation as a risk factor for progression of glaucoma has also been examined without the use of diurnal curves. In these cases, single IOP measurements were made every 3-6 months over several months/years. The standard deviation (SD) of the mean IOP was used as a surrogate for fluctuation since no diurnal tension curves were obtained.
To determine whether the use of a diurnal tension curve (multiple IOP measurements over a minimum 8 hour duration) is more effective than not using a diurnal tension curve (single IOP measurements) to assess IOP fluctuation as a risk factor for the development or progression of glaucoma.
To determine whether the use of a diurnal tension curve is beneficial for glaucoma suspects or patients with progressive glaucoma despite normal single office IOP measurements and leads to a more effective disease management strategy.
Research Methods
Literature Search
Search Strategy
A literature search was performed on July 22, 2010 using OVID MEDLINE, MEDLINE In-Process and Other Non-Indexed Citations, EMBASE, the Cumulative Index to Nursing & Allied Health Literature (CINAHL), the Cochrane Library, and the International Agency for Health Technology Assessment (INAHTA) for studies published from January 1, 2006 until July 14, 2010. Abstracts were reviewed by a single reviewer and, for those studies meeting the eligibility criteria, full-text articles were obtained. Reference lists were also examined for any additional relevant studies not identified through the search. Articles with unknown eligibility were reviewed with a second clinical epidemiologist, then a group of epidemiologists until consensus was established. The quality of evidence was assessed as high, moderate, low or very low according to GRADE methodology.
Inclusion Criteria
Open angle glaucoma (established or OHT high risk) in an adult population
IOP measurement by Goldmann applanation tonometry (the gold standard)
Number and timing of IOP measurements explicitly reported (e.g., 5 measurements a day for 5 visits to generate a diurnal curve or 1 measurement a day [no diurnal curve] every 3 months for 2 years)
IOP parameters include fluctuation (range [peak minus trough] or standard deviation) and mean
Outcome measure = progression or development of glaucoma
Study reports results for ≥ 20 eyes
Most recent publication if there are multiple publications based on the same study
Exclusion Criteria
Angle closure glaucoma or pediatric glaucoma
Case reports
IOP measured by a technique other than GAT (the gold standard)
Number and timing of IOP measurements not explicitly reported
Outcomes of Interest
Progression or development of glaucoma
There is very low quality evidence (retrospective studies, patients on different treatments) for the use of a diurnal tension curve or single measurements to assess short or long-term IOP fluctuation or mean as a risk factor for the development or progression of glaucoma.
There is very low quality evidence (expert opinion) whether the use of a diurnal tension curve is beneficial for glaucoma suspects or patients with progressive glaucoma, despite normal single office IOP measurements, and leads to a more effective disease management strategy.
PMCID: PMC3377558  PMID: 23074414
20.  Comparative evaluation of intraocular pressure with an air-puff tonometer versus a Goldmann applanation tonometer 
Tonometry, or measurement of intraocular pressure (IOP), is one of the most important examination procedures in ophthalmic clinics, and IOP is an important parameter in the diagnosis of glaucoma. Because there are numerous types of tonometer available, it is important to evaluate the differences in readings between different tonometers. Goldmann applanation tonometers (GATs) and noncontact air-puff tonometers (APTs) are largely available in ophthalmic clinics. The purpose of this study was to evaluate the role of AP tonometer by comparing the measurements of IOP made using this device with those made using a GAT.
Patients and methods
This study involved 196 eyes from 98 study participants, all of whom were patients attending an ophthalmic outpatient clinic. Each patient’s IOP was measured using both Goldmann applanation tonometry and AP tonometry, and the difference in readings between the two methods was calculated.
The mean IOP as measured by GAT was 13.06 ± 4.774 mmHg, while that as measured by AP tonometer was 15.91 ± 6.955 mmHg. The mean difference between the two methods of measurement was 2.72 ± 2.34 mmHg. The readings obtained by AP tonometer were higher than those obtained by GAT in 74% of patients, and this difference was most obvious when the GAT measurement of IOP exceeded 24 mmHg. No statistically significant variation in IOP was noted between the devices when the patients’ age, sex, and laterality (right and left eyes) were considered.
There is a significant difference in the measurement of IOP between GATs and AP tonometers. Goldmann applanation tonometry remains the most suitable and reliable method for measuring IOP. Because measurements of IOP by AP tonometer are usually higher than those obtained by GAT regardless of the patient’s age, sex, or laterality of eyes, AP tonometry is a suitable method for community or mass screenings of IOP.
PMCID: PMC3534293  PMID: 23293511
tonometry; comparison; glaucoma; noncontact tonometry; goldmann applanation tonometer
21.  Performance of the PT100 noncontact tonometer in healthy eyes 
The purpose of this study was to assess the repeatability and reproducibility of the PT100 noncontact tonometer and to compare its consistency with the Goldmann applanation tonometer (GAT) in measuring intraocular pressure (IOP).
Triplicate IOP measurements were obtained on two separate occasions using the PT100 and GAT from randomly selected eyes in 66 healthy volunteers aged 22 ± 1 years. The repeatability and reproducibility of each techniques was assessed. Agreement between the techniques was statistically quantified using intrasession repeatability for each technique as the basis for comparison.
Both techniques returned equal IOP values in the first measurement session (15 ± 3 mmHg). The second session showed a mean difference in average IOP (1 ± 0.71). The 95% limits of agreement between the techniques were −5.2 to 5.5 mmHg and −4.0 to 4.7 mmHg (sessions 1 and 2, respectively). These mean differences were not statistically significant (P > 0.05, paired t-test), with the PT100 underestimating IOP measurement by 1.00 mmHg. The mean intrasession IOP for GAT sessions 1 and 2 was 0 ± 0.90 mmHg and 0.04 ± 1.06 mmHg, respectively, and the corresponding mean IOP measurement difference for the PT100 was −0.06 ± 0.96 and −0.39 ± 0.94 mmHg (sessions 1 and 2, respectively; P > 0.05, paired t-test). Repeatability coefficients for the GAT IOP measurements were 1.8 mmHg and 2.1 mmHg for sessions 1 and 2, while the PT100 repeatability coefficient was 1.9 mmHg and 1.8 mmHg for sessions 1 and 2, respectively. The intrasession repeatability coefficient of both techniques for test–retest differences were within ±5 mmHg.
The PT100 noncontact tonometer produced greater repeatability than the GAT in assessment of IOP, whereas GAT resulted in more reproducible results. Both techniques showed a close level of agreement on comparison, with the PT100 underestimating IOP measurement by 1.0 mmHg only, although this was not clinically or statistically significant. Of importance is that the IOP measurements using these techniques could be interchangeable in the IOP range studied here.
PMCID: PMC3104795  PMID: 21629572
Goldmann applanation tonometer; intraocular pressure; Reichert PT100; noncontact tonometer; repeatability; reproducibility
22.  The influence of central corneal thickness and age on intraocular pressure measured by pneumotonometry, non-contact tonometry, the Tono-Pen XL, and Goldmann applanation tonometry 
Aims: To evaluate the influence of central corneal thickness (CCT) on intraocular pressure (IOP) measurements made with the Goldmann applanation tonometer (GAT), Tono-Pen XL, ocular blood flow tonograph (OBF), and Canon TX-10 non-contact tonometer (NCT).
Methods: CCT was recorded for either eye (randomly selected) of each of 105 untreated patients with ocular hypertension and glaucoma attending the glaucoma research unit at Moorfields Eye Hospital. For each of the selected eyes, IOP was measured with the GAT (two observers), Tono-Pen, OBF, and NCT in a randomised order. The relation of measured IOP and of inter-tonometer differences with CCT and subject age was explored by linear regression analysis.
Results: A significant association between measured IOP and CCT was found with each instrument. The change in measured IOP for a 10 μm increase in CCT was 0.28, 0.31, 0.38, and 0.46 for the GAT, Tono-Pen, OBF, and NCT, respectively (all p⩽0.05). There was a significant association between the NCT/GAT differences and CCT, with a tendency of NCT to overestimate GAT in eyes with thicker corneas. There was a significant association between GAT/Tono-Pen and OBF/Tono-Pen differences and age, with a tendency of GAT and OBF to overestimate the Tono-Pen in eyes of older subjects.
Conclusion: IOP measurement by all four methods is affected by CCT. The NCT is affected by CCT significantly more than the GAT. Subject age has a differential effect on the IOP measurements made by the GAT and OBF compared to the Tono-Pen.
PMCID: PMC1772720  PMID: 15965165
tonometry; intraocular pressure; cornea; age; measurement error
23.  Repeated Measures of Intraocular Pressure Result in Higher Heritability and Greater Power in Genetic Linkage Studies 
To analyze the effect of using one reading, the mean of two readings (from the same eye), or the mean of four readings (two from each eye) on the heritability estimates of intraocular pressure (IOP). This was a cohort study in which 344 pairs of twins, 163 monozygotic (MZ) and 181 dizygotic (DZ), were enrolled.
IOP was measured using three tonometers: the gold standard Goldmann applanation tonometer (GAT), the Ocular Response Analyzer (ORA; Reichert Buffalo, NY), and the Dynamic Contour Tonometer (DCT, Pascal; Swiss Microtechnology AG, Port, Switzerland). The main outcome measure was the heritability of IOP correlated with the number of measurements.
The mean IOPs of all four readings with the three tonometers were: 14.1 ± 2.9 mm Hg for GAT, 15.9 ± 3.2 mm Hg for ORA, and 16.9 ± 2.7 mm Hg for DCT. As the number of readings increased, the calculated heritability (h2) of IOP measured using the GAT readings increased from 0.56 for one reading (95% confidence interval [CI], 0.44–0.65) to 0.58 for the mean of two readings (95% CI, 0.46–0.67) to 0.64 for the mean of all four readings (two right and two left; 95% CI, 0.55–0.72). Similar results were seen with the other two instruments.
The results demonstrated that the use of the mean of several readings from both eyes reduced measurement error, yielding a higher heritability estimate. The higher heritability would increase the power to detect linkage in a genome-wide analysis.
PMCID: PMC4145813  PMID: 19420339
24.  Differences between Goldmann Applanation Tonometry and Dynamic Contour Tonometry following Trabeculectomy 
Journal of Ophthalmology  2010;2010:357387.
Background. To evaluate differences between Goldmann Applanation Tonometry (GAT) and Dynamic Controur Tonometry (DCT) following trabeculectomy. Methods. Thirty eight glaucomatous eyes with a history of trabeculectomy (Trabeculectomy group, TG), 20 eyes without a history of trabeculectomy but with a history of latanoprost use (Latanoprost group, LG), and 19 nonglaucomatous eyes (Control group, CG) were included. GAT-IOP, DCT-IOP, the difference between them (dIOP), the central corneal thickness (CCT), the axial length (AL), and the depth of the anterior chamber (ACD) were measured. Results. dIOP was significantly higher in TG (5.19 mmHg) than in LG (4.01 mmHg) and CG (1.98 mmHg). Correlations between AL and dIOP were statistically significant in both TG and LG but not in CG whereas correlations between dIOP and other clinical parameters examined were statistically not significant in all groups. Conclusions. The significantly higher dIOP in TG implies that the bio-mechanical properties of the ocular walls are altered following trabeculectomy.
PMCID: PMC2913849  PMID: 20706652
25.  Reliability of tonosafe disposable tonometer prisms: clinical implications from the Veterans Affairs Boston Healthcare System Quality Assurance Study 
Eye  2011;25(5):651-656.
Given the Veterans Affairs Boston Healthcare System's recent introduction of single-use Tonosafe disposable tonometer prisms as an alternative to Goldmann applanation tonometers (GATs), this study had two aims: to conduct a large-scale quality assurance trial to assess the reliability of intraocular pressure (IOP) measurements of the Tonosafe disposable tonometer compared with GAT, particularly at extremes of pressure; to evaluate the suitability of Tonosafe disposable tonometer prisms as an acceptable substitute for GATs and for clinic-wide implementation in an academic tertiary referral setting.
Ophthalmology resident physicians measured the IOPs of patients in general and specialty eye clinics with the Tonosafe disposable tonometer and GAT. Tonosafe test–retest reliability data were also collected. A retrospective review of patient charts and data analysis were performed to determine the reliability of measurements.
The IOPs of 652 eyes (326 patients) were measured with both GAT and Tonosafe, with a range of 3–34 mm Hg. Linear regression analysis showed R=0.93, slope=0.91, both of which supported the proposed hypothesis, and the y-intercept=−1.05 was significantly different from the hypothesized value. The Tonosafe test–retest repeatability (40 eyes of 40 patients), r=0.977, was very high, which was further supported by linear regression slope=0.993, y-intercept=0.118, and a Tonosafe repeatability coefficient of 2.06, similar to GAT repeatability.
The IOP measurements by Tonosafe disposable prisms correlated closely with Goldmann measurements, with similar repeated measurement variability to GAT. This suggests that the Tonosafe is an acceptable substitute for GAT to measure IOP in ophthalmology clinic settings.
PMCID: PMC3171273  PMID: 21455241
intraocular pressure; disposable prisms; cross-infection; tonometry

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