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

Comparison of Central Corneal Thickness Measurements with Four Different New Devices and Ultrasound Pachymetry

Objectives:

To assess the central corneal thickness (CCT) with 5 different devices, evaluate the repeatability of the devices, and determine the possible relationship between thickness values and sex.

Materials and Methods:

The study included 308 eyes of 154 patients (76 women, 78 men) between the ages of 18-30 who presented to the Ophthalmology Clinic of Muğla Sıtkı Koçman University Training and Research Hospital. Autorefractor (Topcon, Japan), ultrasound pachymetry (UP) (Ceniscan, USA), high-resolution Pentacam (Oculus, USA), anterior segment-optical coherence tomography (AS-OCT) (Optovue, USA), and Spectralis AS-OCT (Heidelberg, Germany) measurements were assessed.

Results:

The mean age of the study participants was 23.2±0.2 years and the mean CCT was 540±14.1 μm, with no statistically significant difference in CCT between sexes (p>0.05). Mean CCT values were 557.0±26.7 μm with the autorefractor, 543.6±32.9 μm with UP, 533.8±30.2 μm with the Oculus Pentacam, 519.8±30.1 μm with Optovue AS-OCT, and 547.5±31.6 μm with Heidelberg AS-OCT. Pairwise comparisons between devices showed that the Optovue AS-OCT gave significantly lower CCT measurements than the autorefractor and Heidelberg AS-OCT device (p=0.027 and p=0.033, respectively). The coefficient of repeatability for autorefractor, UP, high-resolution Pentacam, Optovue AS-OCT, and Heidelberg AS-OCT CCT measurements were 1.51%, 2.46%, 3.72%, 2.57%, and 3.34%, respectively.

Conclusion:

Measurements made with five different devices showed that CCT was comparable and clinically usable. However, it was determined that the Optovue AS-OCT showed lower CCT values compare to other devices. When compared in terms of repeatability, it was found to be lower in the Pentacam than other devices.

The effect of central corneal thickness on intraocular pressure values using various tonometers in the dog

OBJECTIVE

To compare intraocular pressure readings from three different tonometers, the Tono-Pen AVIA® (TP), TonoVet® (TV) and TonoVet Plus® (TV+) and to determine how measurements from each tonometer are affected by central corneal thickness (CCT).

ANIMALS

Ninety dogs.

PROCEDURES

Normal dogs and dogs with ocular disease were selected for study inclusion. Central corneal thickness measurements were gathered with the Pachette 4 ultrasonic pachymeter, and IOP measurements were gathered with the three tonometers in random order. ANOVA or Wilcoxon tests were utilized for overall group comparisons. Linear regression analyses were utilized to determine the association between IOP and CCT.

RESULTS

When comparing tonometers to each other, for all dogs, readings from the TV+were significantly different compared to the TV (p = <.0001) and TP (p = <.0001); however, there was no significant difference between the TV and the TP (p = .999). Linear regression did not find any significant correlation between corneal thickness and IOP readings with any tonometer when looking at normal dogs or when including dogs with ocular abnormalities.

DISCUSSION

This study did not find a significant correlation between an increase in CCT and increase in IOP reading in any tonometer comparison amongst normal and dogs with ocular abnormalities. The TV+produced consistently and significantly higher readings, but measurements did not exceed the expected IOP range in normal dogs. For consistency, the same tonometer should be used when monitoring IOP over time.

Comparison of Central Corneal Thickness Measurements by Contact and Non-contact Pachymetry Devices

Aim and objective

To compare central corneal thickness (CCT) measurements obtained by handheld contact ultrasound pachymetry (HCUP) and non-contact pachymetry devices.

Materials and methods

Ninety eyes of 90 patients (52 male and 38 female) were included in the study. Measurements from two non-contact devices, -specular microscopy (SM, Konan Medical, CA, USA) and Oculus Pentacam (Oculus Inc., Germany)-were compared against HCUP (Pachmate 2, DGH Technology, Inc, PA, USA). Ultrasound measurements were obtained 3 times by the same user and averaged. The differences were calculated by one-way ANOVA. Agreement between measurements were assessed by Bland-Altman plots and intraclass correlation coefficient tests. Coefficient of repeatability (%, CR) was defined as 1.96*standard deviations of the differences between pairs of measurements divided by the average of the means.

Results

The mean age was 34.31 ± 14.39 (14-74) years, and the mean intraocular pressure was 16.48 ± 2.63 mm Hg (12-21). Mean CCT measured by HCUP, SM, and Pentacam was 557.76 ± 36.76 μm, 550.29 ± 43.74 μm, and 541.41 ± 35.7 μm, respectively (p < 0.05). In the Bland-Altman plot, 95% limit of agreements were 19.5 and 14.18 μm among HCUP measurements, 34.55 μm between HCUP and Pentacam, 41.49 μm between SM and Pentacam, and 46.98 μm between HCUP and SM. CR values (%) were 3.49, 2.54, 6.28, 7.68, and 8.47, respectively.

Conclusion

There were significant differences between the mean CCT values of the measurement devices.

Clinical significance

Contact and non-contact devices may not interchangeable in the clinical assessment of CCT.

How to cite this article

Mayali H, Altinisik M, Diri I, et al. Comparison of Central Corneal Thickness Measurements by Contact and Non-contact Pachymetry Devices. J Curr Glaucoma Pract 2021;15(1):28-31.

Comparison of central corneal thickness in dogs measured by ultrasound pachymetry and ultrasound biomicroscopy

Ultrasound pachymetry (UP) is currently the most common technique used to evaluate central corneal thickness (CCT). New devices which allow assessment of CCT without corneal contact have been compared, but there are discrepancies among instruments. The aim of this study was to compare CCT measurements obtained by UP and ultrasound biomicroscopy (UBM) in 28 eyes of 14 healthy Beagles dogs. Mean CCT±standard deviation (SD) were 552±63μm for UP and 551±55μm for UBM. UBM showed both a fixed and proportional bias when compared to ultrasound pachymetry, but this was not considered to be clinically important. Measured CCT did not differ between UP and UBM (P=0.796). The intra-class correlation coefficient indicated a strong agreement between methods (0.990). The CCT measurements between left (548±61μm) and right (555±59μm) eyes did not differ (P=0.760). Male dogs had higher CCT measurements than female dogs (P=0.038).

Distortion Correction of Visante Optical Coherence Tomography Cornea Images

PURPOSE

Quantitative biometry measurements from uncorrected anterior segment optical coherence tomography (AS-OCT) images are inaccurate because of spatial and optical distortions. Prior reported distortion correction equations for the Visante AS-OCT were not reproducible. The goal was to calculate the distortions and provide equations to correct corneal parameters for the Visante AS-OCT to get a central corneal radius of curvature from young and older subjects.

METHODS

Five contact lenses (CLs) of known front and back radii of curvature and central thickness were imaged using the Visante AS-OCT (Carl Zeiss, Dublin, CA). Contact lens surface coordinates from Visante images were identified and fitted with a circle using custom Matlab image analysis software. Spatial and optical distortions of the Visante image of the CL radii of curvature and thickness were calculated and corrected. Visante images were also captured from 24 younger (aged 21 to 36 years) and 30 older (aged 36 to 48 years) human subjects. Corneal radii of curvature and thickness measurements from these subjects were corrected, and intrasession and intersession repeatabilities of the corneal parameters were calculated.

RESULTS

Root mean square error of radius and power of the CL surfaces after distortion correction were 0.02 mm and 0.18D for the front and 0.011 mm and 0.11D for the back, respectively. Intraclass correlation coefficient for intrasession and intersession repeatability for all the corneal parameters from the human subjects was greater than 0.88 in both age groups.

CONCLUSIONS

A distortion correction algorithm was developed for the Visante AS-OCT and applied to extract human corneal radius of curvature measurements.

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

Background

Central corneal thickness (CCT) can be measured by using contact and non-contact methods. Ultrasound pachymetry (US pachymetry) is a contact method for measuring CCT and is perhaps the most commonly used method. However, non-contact methods like scanning slit topography (Orbscan II), slit-lamp optical coherence tomography (SL-OCT), and specular microscopy are also used. Not many studies have correlated the measurement of CCT with all four modalities. The purpose of this study was to compare and correlate the CCT measurements obtained by US pachymetry with SL-OCT, specular microscopy, and Orbscan.

Method

This is a prospective, comparative study done in an institutional setting. Thirty-two eyes of 32 subjects with no known ocular disease and best-corrected visual acuity of 20/20 were enrolled. CCT measurements were obtained using SL-OCT, specular microscopy, scanning slit topography (Orbscan), and US pachymetry. Three measurements were made with each instrument by the same operator. Mean, standard deviation, and coefficient of variation were calculated for CCT measurements acquired by the four measurement devices. Bland–Altman plot was constructed to determine the agreements between the CCT measurements obtained by different equipment.

Results

The mean CCT was 548.16±48.68 μm by US pachymetry. In comparison, CCT averaged 546.36±44.17 μm by SL-OCT, 557.61±49.92 μm by specular microscopy, and 551.03±48.96 μm by Orbscan for all subjects. Measurements by the various modalities were strongly correlated. Correlations (r²) of CCT, as measured by US pachymetry compared with other modalities, were: SL-OCT (r²=0.98, P<0.0001), specular microscopy (r²=0.98, P<0.0001), and Orbscan (r²=0.96, P<0.0001). All modalities had a linear correlation with US pachymetry measurements.

Conclusion

In subjects with healthy corneas, SL-OCT, specular microscopy, and Orbscan (with correction factor) can be used interchangeably with US pachymetry in certain clinical settings. The four modalities showed significant linear correlations with one another.

Central corneal thickness determination in corneal edema using ultrasound pachymetry, a Scheimpflug camera, and anterior segment OCT

PURPOSE

The purpose of this study is to determine the influence of post-surgical corneal edema on the reliability and reproducibility of central corneal thickness (CCT) measurements by a Scheimpflug camera (Pentacam), ultrasound pachymetry (USP), and anterior-segment spectral-domain optical coherence tomography (AS-OCT).

METHODS

Thirty-two patients planned for cataract surgery (n = 16) or vitrectomy (n =  6) were included in a prospective study. The non-surgery eye was used as control. Two investigators acquired two measurements each, with the Pentacam (Oculus, Germany) and the AS-OCT (Heidelberg Engineering, Germany) in a randomized order, followed by USP (Tomey SP-100, Germany). CCT was evaluated using the apex value for Pentacam, the corneal apex cut in AS-OCT and averaging eight single measurements for USP. Coefficients of variation (COV) and intra-class correlation coefficients (ICC) were determined.

RESULTS

Post-surgery corneas showed a thickness of (investigators 1 and 2): Pentacam (615.9 ± 58.02 μm and 615.1 ± 60.17 μm), USP (601.4 ± 63.77 μm and 614.5 ± 70.91 μm), AS-OCT (608.8 ± 65.67 μm and 606.9 ± 64.41 μm) ,with no significant difference (ANOVA p > 0.99). The COVs (investigators 1 and 2) for control eyes were: Pentacam (0.78 ± 0.52 and 0.70 ± 0.76), USP (0.66 ± 0.29 and 0.98 ± 0.44), AS-OCT (0.59 ± 0.61 and 0.59 ± 0.40). The COVs (investigators 1 and 2) for post-surgical eyes were: Pentacam (0.98 ± 1.25 and 0.97 ± 0.73), USP (0.73 ± 0.64 and 1.35 ± 0.85), AS-OCT (1.34 ± 1.57 and 1.19 ± 1.18).The ICC was determined in post-surgery corneas (ICC > 0.96) and control corneas (ICC > 0.95).

CONCLUSION

USP measurements have the highest user dependence. Post-surgical corneal edema leads to higher intraobserver variability. All methods reached a high level of agreement in CCT determination in edematous as well as healthy corneas.

Difference in normal corneal thickness and curvature between Mongolian and Han nationalities

AIM

To investigate the differences in central corneal thickness (CCT) and curvature in myopic patients with different genders between Mongolian and Han nationalities in the Inner Mongolia region.

METHODS

Patients with myopia, among whom 122 cases (244 eyes) were Mongolian and 150 cases (300 eyes) were Han, were selected. Pentacam was used to measure the corneal curvature, whereas CCT was determined by Pentacam, Orbscan and ultrasound pachymetry.

RESULTS

Comparisons of the curvature of men and women in Mongolia showed a significant difference (P<0.05) by comparing of the CCT values measured by three methods in Han and Mongolian in Inner Mongolia, we can draw a conclusion that the CCT values measured by Pentacam are less than the values by Orbscan and ultrasound pachymetry, and there are statistically significant difference in CCT measurement among the instruments except between the Orbscan and ultrasound pachymetry. The CCT values of Mongolians are more than Han people, and the analysis exhibited statistical significance. The CCT values measured by Orbscan in Mongolia of women are more than men, the difference showed statistical significance.

CONCLUSION

Corneal curvature in Mongolian females was significantly higher than that in males. However, no significant difference was observed among Han males and females. The CCT values of Mongolian females were higher than those of males. The normal CCT values measured by Pentacam in Mongolian myopic patients were smaller than those obtained by Orbscan or ultrasound. The normal CCT values of Mongolian patients with myopia were higher than those reported for domestic people.

Central corneal thickness measurements in premature infants

AIM

To evaluate the central corneal thickness (CCT) measurements of premature infants.

METHODS

The premature infants who were born between 25-34wk of gestational age (GA) were retrieved for the study. All CCT measurements were performed within the first 2d of their life under topical anesthesia by using an ultrasonic pachymeter.

RESULTS

The mean CCT of 200 eyes was 647.79±63.94 µm. The mean CCT of the right and left eyes were similar (647.30±64.72 µm and 648.29±63.47 µm consecutively). The mean CCT of the girls was 642.08±54.89 µm and the boys was 653.07±71.14 µm, with no statistically significant difference (P>0.05). But there was a negative correlation of the CCT with GA and birth weight (BW) (P<0.01).

CONCLUSION

The CCT values of premature babies were negatively correlated with GA and BW.

Agreement between Orbscan II, VuMAX UBM and Artemis-2 very-high frequency ultrasound scanner for measurement of anterior chamber depth

Background

The aim was to compare the anterior chamber depth (ACD) measurements taken with Orbscan II, ultrasound biomicroscopy (UBM) and the Artemis-2 VHF (very-high-frequency) ultrasound scanner in normal subjects.

Methods

In this prospective study, one eye from each of 60 normal subjects was randomly selected. Three subjects dropped out of the study because they were apprehensive about the UBM examination; their data were excluded entirely. Measurements of ACD were taken with the Orbscan II, UBM and Artemis-2 VHFUS. Results were obtained for coefficient of variance (CV) and intra-class correlation coefficient (ICC), and statistical analysis was by repeated-measures analysis of variance (ANOVA) for intra-observer repeatability. ANOVA and Bland–Altman analyses were used to determine limits of agreement (LOA) between the three instruments.

Results

The average ACD (± standard deviation) was 3.13 ± 0.34 mm, 2.96 ± 0.27 mm and 2.87 ± 0.31 mm for the Orbscan II, UBM and Artemis-2 VHFUS, respectively. The repeatability scores were 0.015 ± 0.014%, 0.08 ± 0.09% and 0.07 ± 0.06% for the Orbscan II, UBM and Artemis-2 VHFUS, respectively. The ICC for repeatability of Orbscan II, UBM and Artemis-2 VHFUS measurements was high and equal to 0.99%. The intra-observer repeatability scores of the ACD measurement p-values using Orbscan II, UBM and Artemis-2 VHFUS were 0.12, 0.70 and 0.10, respectively. The mean difference and standard deviations for ACD measurements using Orbscan II vs UBM, Orbscan II vs Artemis-2 VHFUS and UBM vs Artemis-2 VHFUS were 0.17 ± 0.31 mm, 0.27 ± 0.34 mm and 0.10 ± 0.18 mm, respectively. LOAs were 0.78 to -0.44 mm, 0.93 to -0.39 mm and 0.45 to -0.26 mm. ANOVA revealed a statistically significant difference between the Orbscan II, UBM and Artemis-2 VHFUS (p < 0.0001).

Conclusions

Measurements by the three instruments show high repeatability. UBM and the Artemis-2 VHFUS can be used interchangeably, but the Orbscan II cannot be used interchangeably with UBM or the Artemis-2 VHFUS.

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.

Laser in situ keratomileusis in 2012: a review

Laser in situ keratomileusis (LASIK) is a safe and effective treatment for refractive error. A combination of technological advances and increasing surgeon experience has served to further refine refractive outcomes and reduce complication rates. In this article, we review LASIK as it stands in late 2012: the procedure, indications, technology, complications and refractive outcomes.

Comparison of artemis 2 ultrasound and Visante optical coherence tomography corneal thickness profiles

PURPOSE

To compare corneal thickness profiles of cross-sections of cornea determined by arc-scanned immersion ultrasound and optical coherence tomography (OCT).

METHODS

Corneas of 28 eyes from 14 participants were scanned in triplicate using the Artemis 2 high-frequency arc-scanned ultrasound system (ArcScan Inc) and the Visante OCT system (Carl Zeiss Meditec). Corneal thickness and reproducibility were compared within 3.5 mm of central cornea in the horizontal plane.

RESULTS

Although highly correlated, Visante central and peripheral corneal thickness values were systematically thinner than Artemis 2 values. Within the central 0.5 mm, the difference was approximately 8 μm, but the difference increased with distance from the center. Reproducibility for each instrument was comparable, measuring <4 μm centrally and increasing peripherally.

CONCLUSIONS

Visante OCT measurements of corneal thickness are thinner than Artemis 2 ultrasound values centrally with an increasing difference with peripheral position. Measurement reproducibility was comparable for the two techniques.