Comparison of central corneal thickness measurements with a new optical device and a standard ultrasonic pachymeter

Reproducibility, Repeatability, and Correlation of Central Corneal Thickness Measurement with the Pentacam Scheimpflug System and Ultrasound Pachymetry

BACKGROUND/AIM

The importance of an accurate determination of central corneal thickness (CCT) relies on its diagnostic and therapeutic implications in glaucoma, corneal ectasias, corneal edema and endothelial function monitoring, and refractive surgery suitability, among others. We aimed to analyze the repeatability, reproducibility, correlation, and laterality variations of CCT measurements performed with the Pentacam HR and the standard of care ultrasound A-scan (USP).

METHODS

A cross-sectional study including CCT measurements of healthy individuals was performed by three independent examiners with the Pentacam HR and USP. Intra-observer and inter-observer variations were calculated with intra-class correlation coefficients (ICCs). Bland-Altman plots and 95% limits of agreement (95% LoA) were used to assess the agreement between devices. Linear correlation was calculated with Pearson's coefficient.

RESULTS

Thirty individuals (60 eyes), including 10 (33.3%) men and 20 (66.6%) women, with a mean age of 30.0 ± 9.1 years, were studied. No statistical differences were found in CCT measurements between Pentacam HR (range 500 - 609 µm) and USP (range 498 - 628 µm). There was a high degree of correlation in repeatability and reproducibility of each independent device (ICC > 0.90). Pearson's correlation between 1 vs. 2, 2 vs. 3, and 3 vs. 1 Pentacam HR attempts were 0.914, 0.958, and 0.925, respectively (p < 0.001). Corresponding results for USP were 0.957, 0.957, and 0.943 (p < 0.001). The Pentacam HR tended to overestimate CCT by a mean difference of 3.77 µm (95% LoA, - 24.9 - 18.4). Right eyes were also overestimated (- 3.6 ± 14.1 µm) with the Pentacam HR device, whereas left eyes were underestimated (1.3 ± 11.1 µm).

CONCLUSIONS

The Pentacam HR device provides reliable operator-independent estimates of CCT. Right eyes exhibited a tendency to overestimate with the Pentacam HR. We suspect this difference is due to USP underestimation related to patients' position while performing the study. In clinically relevant scenarios, performing a third measurement and cautiously measuring right eyes can provide higher accuracy.

Comparison of central corneal thickness measurements with three different optical devices

Purpose:

The purpose of this study was to compare and evaluate the agreement of central corneal thickness (CCT) values obtained with three different devices working according to optical principle in healthy eyes.

Methods:

60 eyes of 60 individuals (30 men and 30 women) were enrolled in this study. CCT measurements performed with Scheimpflug–Placido topographer (Sirius), spectral-domain optical coherence tomography (RTVue) with an anterior segment module, and optical biometer (AL-Scan) were compared. Bland–Altman analysis was used to demonstrate agreement between methods.

Results:

The mean age was 30.07 ± 7.313 years (range, 18–47 years). The mean CCT values obtained by RTVue, Sirius, and AL-Scan were 518.25 ± 36.38 µm, 526.08 ± 36.33 µm, and 513.50 ± 39.09 µm, respectively. The mean differences in CCT were 7.83 ± 14.15 µm between Sirius and RTVue, 12.58 ± 11.87 µm between Sirius and AL-Scan, and 4.75 ± 4.50 µm between RTVue and AL-Scan. The mean CCT was statistically different among the three groups (p < 0.05). All three modalities of CCT measurements correlated closely with each other, with Pearson’s correlation coefficients ranging from 0.924 to 0.961. The 95% limits of agreement were −19.90 to 35.56 µm between Sirius and RTVue, −10.69 to 35.85 µm between Sirius and AL-Scan, and −4.07 to 13.58 µm between RTVue and AL-Scan.

Conclusion:

Different results could be obtained through different noncontact devices in CCT measurements. Although the measurement values obtained by these devices show a high level of correlation, it would be a more correct approach to not use them directly interchangeably in clinical practice. Evaluation and follow-up of CCT should be performed using the same device.

Comparison of central corneal thickness and intraocular pressure measured with two different tono/pachymeter devices in non-glaucomatouse children

PURPOSE

The goal of this research is to compare the intraocular pressure (IOP) and the mean central corneal thickness (CCT) values obtained from the measurements with Nidek NT-530P and Canon TX-20P devices with the values obtained by ultrasound pachymetry (UP) and Goldmann applanation tonometry (GAT) in children.

METHODS

This prospective study was conducted with 119 healthy children. The measurements were repeated three times for each eye. The intraclass correlation coefficient (ICC) was used to assess the correlation between the measurements obtained from different devices. The Bland-Altman plot was used to analyze the agreement between two different devices graphically. The measurements were taken in the same order in all subjects: TX-20P, NT-530P, UP, and GAT.

RESULTS

The mean age of the children was 10.1 ± 3.2 (6-17) years. The mean CCT values for the eyes were 568.90 and 569.68 (TX-20P), 571.44 and 566.37 (NT-530P), 564.77 and 564.67 μm UP, (right and left, respectively). The highest correspondence observed for CCT was between UP and NT-530P devices (ICC, 0.982, the left eye). The mean IOP measurements for Canon TX-20P, NT-530P, and GAT were 16.5 ± 3.2, 16.3 ± 3.2, and 16.8 ± 3.6 mmHg for the right eyes, respectively, while those for the left eyes were 16.6 ± 3.1, 16.2 ± 3.3, and 16.8 ± 3.7 mmHg. The highest correspondence was noted between measurements obtained using GAT and Nidek NT-530P devices (ICC, 0.945, in the left eye).

CONCLUSION

Tono/pachymetry devices in the healthy children are provides significant agreements with the gold standard methods for IOP and CCT measurements.Clinical Trial Registration number: 2016-94.

Measurement of corneal thickness using Pentacam HR versus Nidek CEM-530 specular microscopy

Objective

To compare corneal thickness (CT) measurements using the CEM-530 (Nidal, Gamagori, Japan) and Pentacam HR (Oculus, Wetzlar, Germany).

Methods

The CT of 209 healthy subjects (209 right eyes) aged 24 to 89 years (71.35 ± 10.72 years) was measured at the corneal apex (CA), pupil center (PC), and thinnest point (TP) with the Pentacam HR and at the corneal center with the CEM-530 in random order at the same time of day.

Results

A good correlation but statistically significant difference was found between the CEM-530 and Pentacam HR measurements at the CA (6.10 ± 8.12 µm, R² = 0.8947), PC (7.46 ± 8.57 µm, R² = 0.8826), and TP (12.44 ± 10.04 µm, R² = 0.8392). Comparison of the two devices produced the following regression formulas: y = 0.8859x + 57.644 for the CA, y = 0.8852x +56.657 for the PC, and y = 0.8557x + 68.148 for the TP, where x is the CT obtained with the CEM-530 and y is that obtained with the Pentacam HR.

Conclusions

These findings indicate that the CEM-530 produces a thicker corneal measurement than the Pentacam HR. The herein-proposed correcting factors are needed to reliably compare these devices.

Comparison of Central Corneal Thickness Measured by Standard Ultrasound Pachymetry, Corneal Topography, Tono-Pachymetry and Anterior Segment Optical Coherence Tomography

PURPOSE

To compare central corneal thickness (CCT) measured by standard ultrasound pachymetry (USP), and three non-contact devices in healthy eyes.

METHODS

A cross-sectional study of CCT measurement in 52 eyes of 52 healthy volunteers was done by a single examiner at Ocular Surface and Contact Lens Laboratory. Three consecutive measurements were done by standard USP, non-contact tono-pachymeter, Pentacam corneal topographer, and Anterior Segment Optical Coherence Tomography (AS-OCT). The mean values were used for assessment. The results were compared using multivariate ANOVA, linear regression, and Pearson correlation. Agreement among the devices was analyzed using mean differences and Bland-Altman analysis with 95% limits of agreement (LoA). Finally, reliability was analyzed using intraclass correlation coefficient (ICC).

RESULTS

Mean CCT by ultrasound pachymeter, tono-pachymeter, corneal topographer and AS-OCT were 558.9 ± 31.2 µm, 525.8 ± 43.1 µm, 550.4 ± 30.5 µm, and 545.9 ± 30.5 µm respectively. There was a significant positive correlation between AS-OCT and USP (Pearson correlation = 0.957, p < 0.001), corneal topography and USP (Pearson correlation = 0.965, p < 0.001), and corneal topography and AS-OCT (Pearson correlation = 0.965, p < 0.001). There was a lower correlation between CT-1P tono-pachymeter and the other three modalities. Intraclass correlation coefficients show an excellent reliability between pairs except for CT-1P against the other three instruments that were found moderate.

CONCLUSIONS

CT-1P tono-pachymeter underestimates CCT measurements compared to Scheimpflug system, AS-OCT device, and USP. Mean CCT among USP, Pentacam and AS-OCT were comparable and had significant linear correlations. In clinical practice, these three modalities could be interchangeable in healthy patients.

Comparison of central corneal thickness with four different optical devices

BACKGROUND

To compare the consistency between the average scores of the contact central corneal thickness measurements from ultrasound pachymetry devices still gold standard, such as iPac^® and Echoscan US-500, and noncontact measurements via Pentacam HR and Sirius topography.

METHODS

This prospective study, subsequently admitted to the ophthalmology department, 76 healthy individuals were performed. The measurements were repeated three times for each eye, and average scores were statistically analyzed on the same day and almost at the same time. While measuring the eyes, Pentacam HR, Sirius topography, iPac^®, and Echoscan US-500 were used, respectively. The inter-rater agreement of measurements from the devices was assessed with intraclass correlation coefficient, and 95% Confidence Interval and p values demonstrating statistically significance were also presented. In the graphical assessment of the agreement, the Bland-Altman graph was used.

RESULTS

Among 76 study participants, 43 (56.6%) were composed of women, and age level was 38.6 ± 12.5 years, ranging between 18 and 69. It was observed that the highest agreement was between the measurements obtained from Echoscan US-500 and iPac^® devices, but the agreement between the measurements of different devices was higher than 0.90. Bland-Altman graphics were also investigated; the results of four different devices were seen to be consistent with one another.

CONCLUSIONS

Therefore, the devices we compared in the study can be used as alternatives to one another due to the higher consistency between CCT measurements provided with through UP devices of Echoscan US-500 and iPac^®, and Pentacam HR and Sirius topography devices.

CLINICAL TRIAL REGISTRATION NUMBER

2016/112.

Pentacam vs SP3000P specular microscopy in measuring corneal thickness

PURPOSE

To compare corneal thickness (CT) measurements obtained with SP3000P specular microscope and Pentacam in eyes screened to undergo refractive surgery (RS).

METHODS

In this prospective study, a non-randomized consecutive series of 73 healthy eyes (age range: 14-78 years; mean=38.4±14.9) underwent CT measurement with both Oculus Pentacam and Topcon SP3000P specular microscope to assess their suitability to undergo corneal RS.

RESULTS

CT measurements with SP3000P ranged from 451 to 609 μs (mean 523.1±34.4 μs). The measurements obtained with Pentacam ranged at the corneal apex from 477 to 672 μs (mean 558.9±38.9 μs), at the pupil center from 477 to 672 μs (mean 557.9±38.9 μs) and at the thinnest point from 474 to 669 μs (mean 551.1±39.4 μs). CT measurements showed a good correlation but a statistically significant difference at the pupil center (mean -34.9±14.6 μs, R(2)=0.860, p<0.001), at the apex (mean -35.9±14.9 μs, R(2)=0.856, p<0.001) and at the thinnest point (mean -32±14.8 μs, R(2)=0.862, p<0.001). The calculated regression formulas were: y=0.816x+66.94 for the apex, y=0.819x+66.07 for the pupil center and y=0.810x+73.13 for the thinnest point; where y is the CT measured with the SP3000P and x is the measurement obtained with the Oculus Pentacam.

CONCLUSIONS

Our results suggest that SP3000P measures thinner corneas compared to the Pentacam and that the correcting factor we identified should be applied to make comparisons between these two devices.

Intraoperative corneal thickness measurement by optical coherence tomography in keratoconic patients undergoing corneal collagen cross-linking

PURPOSE

To assess intraoperative variation of corneal thinnest point in keratoconic patients undergoing riboflavin/ultraviolet type A (UV-A) cross-linking treatment using noncontact time-domain optical pachymetry.

DESIGN

Prospective, noncomparative interventional study.

METHODS

Ten patients underwent epithelium-off riboflavin/UV-A corneal cross-linking at Siena University Hospital; corneal thickness was measured using optical coherence tomography at the following times: preoperatively with epithelium on; after removal of a 9-mm-diameter disc of epithelium; immediately after instillation of 2 drops of riboflavin 0.1%-dextran T 500 20% solution; after repeated instillation of riboflavin 0.1%-dextran T 500 20% solution every 2.5 minutes, at 10, 20, and 30 minutes of soaking time; at the end of the treatment after 30 minutes of UV-A exposure with the riboflavin biofilm in situ; and finally after washing the riboflavin biofilm.

RESULTS

The most significant decrease in thinnest point measurement was detected meanly in the first 10 minutes of corneal soaking. In this interval, the minimum recommended in various studies, a mean reduction of -79.28 μm (-17.61% of initial thinnest point value after removal of the epithelium) was recorded. No adverse events were recorded.

CONCLUSIONS

The study demonstrates a statistically significant intraoperative reduction in corneal thinnest point value during epithelium-off cross-linking procedure using standard riboflavin 0.1%-dextran 20% solutions. Intraoperative optical pachymetry evaluation during cross-linking should be recommended before starting UV-A irradiation, and if a thickness under 380 μm is detected, the stroma should be reexpanded with hypotonic dextran-free riboflavin solutions.

Assessment of central corneal thickness and corneal endothelial morphology using ultrasound pachymetry, non-contact specular microscopy, and Confoscan 4 confocal microscopy

BACKGROUND

The aim was to compare the repeatability, reproducibility and inherent precision of ultrasound pachymetry (USP), noncontact specular microscopy (SP-2000P) and the Confoscan 4 confocal microscope (z-ring CS4) in measuring endothelial cell density (ECD), coefficient of variation of cell size (CV), and central corneal thickness (CCT) in normal eyes.

METHODS

In this prospective study, one eye was selected from each of 30 subjects for the measurements of ECD, CV and CCT, which were taken by two observers. Results were analyzed statistically by repeated-measures analysis of variance (ANOVA) for intra-observer repeatability, inter-observer reproducibility, unpaired t-test, paired t-test, and Bland-Altman analyses to determine limits of agreement (LOA) between the three instruments.

RESULTS

Mean ECD, measured by SP-2000P and z-ring CS4, were 3115.50 ± 279.70 cells/mm(2) and 3167.50 ± 264.75 cells/mm(2), respectively (observer 1), and 3192.63 ± 249.42 cells/mm(2) (z-ring, observer 2). Mean CV measurements were 27.12 ± 2.51 and 27.10 ± 2.41 (SP-2000P and z-ring CS4, respectively; observer 1), and 27.17 ± 2.25 (z-ring, observer 2). Mean CCT values were 555.11 ± 35.83 μm (USP), 535.82 ± 41.10 μm (SP-2000P) and 552.57 ± 36.83 μm (z-ring CS4), and 554.97 ± 36.34 μm (z-ring CS4, observer 2). However, pairwise tests in all cases there was good repeatability and reproducibility as shown by inter-observer and intra-observer analysis of variance for each of the instruments.

CONCLUSIONS

The SP-2000P and the z-ring CS4 can be used interchangeably to measure ECD and CV. For CCT, the sample size was too small to test for differences of the CCT measurements between the three instruments.

A comprehensive comparison of central corneal thickness measurement

PURPOSE

To assess the repeatability and reproducibility of central corneal thickness (CCT) measurements by high-resolution rotating Scheimpflug imaging (Pentacam, Oculus) and Fourier-domain optical coherence tomography (RTvue-100, Optovue) after laser in situ keratomileusis (LASIK) and to compare the agreement with ultrasound pachymetry (USP).

METHODS

Forty-seven eyes of 47 patients after LASIK were included in the study. The first examiner took two successive Pentacam and RTvue CCT measurements, and this was repeated once again by the second examiner to assess intraobserver and interobserver repeatability and reproducibility. After performing non-contact examinations, the corneas were measured by USP to compare the level of agreement among the three devices.

RESULTS

All Pentacamcenter, Pentacamapex, Pentacamthinnest, and RTvue CCT measurements demonstrated high intraobserver repeatability, with respective precision (1.96 within-subject standard deviation) and intraclass correlation coefficients of 7.52, 7.43, 7.55, and 3.81 μm and 0.985, 0.986, 0.986, and 0.997; interobserver repeatability results were similar. All coefficients of variation were low: <1% for all measures. Compared with Pentacam and USP measurements, the RTvue measurement significantly underestimated CCT by a mean of 10.52 to 15.28 μm (p < 0.001) and 9.17 μm (p < 0.001), respectively. The agreement of USP with Pentacam and RTvue by Bland-Altman analysis spanned over 30 μm. The agreement of Pentacam with RTvue spanned approximate 20 μm.

CONCLUSIONS

Both Pentacam imaging and RTvue Fourier-domain optical coherence tomography provide reliable and interchangeable measurement of CCT in post-LASIK corneas. However, they cannot be considered to be clinically interchangeable with USP.

Measurement of central corneal thickness by high-resolution Scheimpflug imaging, Fourier-domain optical coherence tomography and ultrasound pachymetry

PURPOSE

To compare the repeatability and reproducibility of central corneal thickness (CCT) measurements by high-resolution (HR) rotating Scheimpflug imaging and Fourier-domain optical coherence tomography (FD-OCT). CCT measurements were compared to those determined by ultrasound pachymetry (UP).

METHODS

In 35 healthy eyes, intra-observer repeatability for HR Scheimpflug (Pentacam) and FD-OCT (RTVue) systems was determined in consecutive images taken by an observer in the shortest time possible. Imaging was repeated again by a second observer to evaluate inter-observer reproducibility. The CCT measurements were compared among Scheimpflug, FD-OCT and UP images.

RESULTS

Mean coefficients of repeatability were 0.48% for Scheimpflug and 0.26% for FD-OCT. For Scheimpflug, the coefficient of inter-operator reproducibility was 0.87%. For FD-OCT, the coefficient of inter-operator reproducibility was 0.45%. The CCT measurements by Scheimpflug, OCT and UP images were (mean ± standard deviation) 521.7 ± 27.6 μm, 510.8 ± 28.6 μm and 516.5 ± 27.6 μm, respectively. The differences between instruments were statistically significant. The 95% limits of agreement in CCT were -0.7 to 22.5 μm for Pentacam-OCT, -13.4 to 24.0 μm for Pentacam-UP and -26.7 to 15.4 μm for OCT-UP. There was a high degree of correlation between CCT measured by all 3 methods.

CONCLUSION

Noncontact measurements of CCT with HR Scheimpflug and FD-OCT systems yielded excellent repeatability and reproducibility and can be used interchangeably. Although both devices were comparable with UP; in clinical practice, the measurements acquired by optical modalities are not directly interchangeable with UP measurements.

Comparison of central corneal thickness measurements using ultrasound pachymetry, ultrasound biomicroscopy, and the Artemis-2 VHF scanner in normal eyes

Purpose

To compare the precision of central corneal thickness (CCT) measurements taken with the handheld ultrasound pachymeter (USP), ultrasound biomicroscopy (UBM), and the Artemis-2 very high frequency ultrasound scanner (VHFUS) on normal subjects.

Design

Prospective study.

Methods

One eye from each of 61 normal subjects was randomly selected for this study. The measurements of the CCT were taken with the USP, VHFUS, and UBM. Results were compared statistically using repeated-measures analysis of variance (ANOVA), Pearson’s correlation coefficient, and limits of agreement.

Results

The average CCT (± standard deviation) was 530.1 ± 30.5 μm, 554.9 ± 31.7 μm, and 559.5 ± 30.7 μm for UBM, VHFUS, and USP respectively. The intraobserver repeatability analyses of variance are not significant for USP, UBM, and VHFUS. P-values were 0.17, 0.19, and 0.37 respectively. Repeated-measures ANOVA showed a significant difference between the three different methods of measuring CCT (P = 0.0001). The ANOVA test revealed no statistically significant difference between USP and VHFUS (P > 0.05), yet statistical significant differences with UBM versus USP and UBM versus VHFUS (P < 0.001). There were high correlations between the three instruments (P < 0.0001). The mean differences (and upper/lower limits of agreement) for CCT measurements were 29.4 ± 14.3 (2.7/56), 4.6 ± 8.6 (−14.7/23.8), and −24.8 ± 13.1 (−50.4/0.8) for USP versus UBM, USP versus VHFUS, and UBM versus VHFUS, respectively.

Conclusion

The UBM produces CCT measurements that vary significantly from those returned by the USP and the VHFUS, suggesting that the UBM may not be used interchangeably with either equipment for monitoring the CCT in the clinical setting.

Comparison of two partial coherence interferometers for corneal pachymetry in high myopia and after LASIK

PURPOSE

We aimed to compare the Haag-Streit optical low-coherence reflectometry (OLCR) pachymeter and the Zeiss Anterior Chamber Master (ACMaster) for measuring central corneal thickness (CCT) in high myopes and after laser in situ keratomileusis (LASIK) for myopia.

METHODS

Central corneal thickness was measured in 55 eyes of 30 myopic subjects (spherical equivalent refraction of - 5.25 D to - 10.75 D, maximal astigmatism of - 2 D), and in 37 eyes of 21 patients 3 months after LASIK for myopia (preoperative spherical equivalent refraction of - 6.0 D to - 10.75 D, maximal astigmatism of - 2 D). All measurements were performed with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster, using group refractive indices of 1.376 and 1.3851, respectively. Thickness measurements were compared using paired t-tests, Pearson's correlation, linear regression and Bland-Altman plots.

RESULTS

In myopic subjects, CCT measured 531 +/- 28 microm and 533 +/- 27 microm with the OLCR pachymeter and the ACMaster, respectively (p < 0.01); all measurements correlated closely (r = 0.99, p < 0.01). In LASIK-treated eyes, CCT measured 472 +/- 24 microm using the OLCR pachymeter and 475 +/- 23 microm using the ACMaster (p < 0.01), again with close correlation between the two instruments (r = 0.99, p < 0.01).

CONCLUSIONS

Measurements of CCT in high myopes and after myopic LASIK were very similar with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster. Using the current group refractive indices, the observed difference between the two instruments of < 3 microm is of little clinical importance. Thus, it would seem safe to use the OLCR pachymeter and the ACMaster interchangeably for CCT measurements in myopia as well as after myopic LASIK.

Central corneal thickness measured by the Orbscan II system, contact ultrasound pachymetry, and the Artemis 2 system

PURPOSE

To compare central corneal thickness (CCT) measurements by the Orbscan II device, contact ultrasound (US) pachymetry, and the noncontact Artemis 2 scanning US system.

SETTING

Department of Ophthalmology, Weill Cornell Medical College, New York, New York, USA.

METHODS

The CCT in 40 eyes (20 normal subjects) was measured by the Orbscan II followed by contact US pachymetry and then the Artemis 2. Results were compared using analysis of variance (ANOVA), paired t tests, and Bland-Altman plots.

RESULTS

There was a significant difference in CCT measurements between the 3 modes (F = 32.84, P = .0001, 1-way ANOVA). Artemis 2 and US pachymetry measurements were highly correlated (r2 = 0.963, P < .0001), although Artemis 2 values were a mean of 11.2 microm +/- 6.6 (SD) thinner than pachymetry values. Artemis 2 and Orbscan II measurements were less well correlated (r2 = 0.851, P < .001); Orbscan II values were a mean of 7.5 +/- 15.7 microm thinner than Artemis 2 values. Orbscan II values showed a trend toward increasing underestimation of CCT in thinner corneas.

CONCLUSIONS

Ultrasound pachymetry and Artemis 2 CCT measurements were highly correlated; the 11 microm mean difference in measurements may be attributed to decentration, oblique incidence of the probe to the cornea, or possibly the effect of topical anesthesia with contact pachymetry. Although the mean difference between Orbscan II and Artemis 2 values was 7.5 microm, Orbscan values were less correlated than Artemis 2 values with contact US pachymetry and were prone to underestimation of the CCT in thinner corneas.

Comparative study of central corneal thickness measurement with slit-lamp optical coherence tomography and visante optical coherence tomography

PURPOSE

To evaluate the repeatability and reproducibility of central corneal thickness (CCT) measurements obtained by 2 anterior segment optical coherence tomography (OCT) imaging systems and to examine their agreements with ultrasound pachymetry.

DESIGN

Observational cross-sectional study.

PARTICIPANTS

Fifty eyes from 50 healthy normal subjects were recruited.

METHODS

In one randomly selected eye in each subject, CCT was measured by slit-lamp OCT (SLOCT), Visante OCT, and ultrasound pachymetry. For anterior segment OCT measurements, both automatic and manual CCTs were obtained. Twenty-five of the 50 subjects were invited for 2 more visits within a week to evaluate repeatability and reproducibility of CCT measurement.

MAIN OUTCOME MEASURES

Central corneal thickness measurement obtained by the 3 methods and their agreements. Intrasession and intersession within-subject standard deviation (S(w)), precision (1.96xS(w)), coefficient of variation (CV(w)) (100xS(w)/overall mean), and intraclass correlation coefficient (ICC) were calculated to evaluate repeatability and reproducibility.

RESULTS

Good repeatability and reproducibility were found for both automatic and manual CCT measurements obtained by SLOCT and Visante OCT. For intrasession repeatability, CV(w) and ICC values ranged between 0.9% and 1.2% and 0.96 and 0.98, respectively. For intersession reproducibility, the respective CV(w) and ICC values ranged between 1.2% and 1.4% and 0.94 and 0.96. Although no significant difference was found between automatic/manual SLOCT measurements and ultrasound pachymetry, automatic Visante OCT CCT (535.7+/-30.2 microm) was significantly less than CCT with ultrasound pachymetry (550.3+/-31.14 microm) (P<0.001). In contrast, manual Visante OCT measurement (558.8+/-32.8 microm) was slightly higher than ultrasound pachymetry (P<0.001). Nevertheless, SLOCT and Visante OCT measurement of CCT had 95% limits of agreement comparable to that of ultrasound pachymetry. The best agreement was observed in the manual SLOCT measurement (95% limits of agreement between -15.5 and 11.7 microm).

CONCLUSIONS

Both SLOCT and Visante OCT automatic and manual CCT measurements were reliable and showed comparable agreement with ultrasound pachymetry. Although the 2 anterior segment OCT imaging systems have similar design and working principles, clinicians should be aware of the differences in CCT measurement between the 2 anterior segment OCTs.