Comparison of central corneal thickness measurements using Pentacam and ultrasonic pachymetry in post-LASIK eyes for myopia

Comparison of a New Optical Biometer That Combines Scheimpflug Imaging With Partial Coherence Interferometry With That of an Optical Biometer Based on Swept-Source Optical Coherence Tomography and Placido-Disk Topography

PURPOSE

To evaluate measurement precision and to compare the Pentacam AXL (Oculus Optikgeräte, Wetzlar, German), a new optical biometer based on Scheimpflug imaging and partial coherence interferometry (PCI) with that of the OA-2000 biometer (Tomey, Nagoya, Japan), which combines swept-source optical coherence tomography (SS-OCT) and Placido-disk topography.

METHODS

Axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AQD), mean keratometry (Km), astigmatism vectors J0, J45, and corneal diameter (CD) were measured in triplicate by two technical operators. Within-subject standard deviation (Sw), repeatability and reproducibility (2.77 Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were used to assess the Pentacam AXL intra-observer repeatability and inter-observer reproducibility. Paired t-test and Bland-Altman plots were used to determine the agreement between the two biometers.

RESULTS

The new optical biometer had high intra-observer repeatability [all parameters evaluated had low CoV (<0.71%) and high ICC (>0.88)]. Inter-observer reproducibility was also excellent, with high ICC (>0.95) and low CoV (<0.52%). The 95% LoA between the new biometer and OA-2000 were insignificant for most of the parameters evaluated, especially for AL. However, the measurement agreement was moderate for CCT.

CONCLUSIONS

Intra-observer repeatability and inter-observer reproducibility were excellent for all parameters evaluated using the new optical biometer based on Scheimpflug imaging and PCI. There was a high agreement between the two devices and hence could be clinically interchangeable for the measurement of most ocular parameters.

Comparison of corneal thickness measurements using ultrasound pachymetry, noncontact tonopachy, Pentacam HR, and Fourier-domain OCT

We retrospectively compared the central corneal thickness (CCT) obtained by ultrasound pachymetry (USP; SP-3000, Tomey Corp., Nagoya, Japan), non-contact tonopachy (TP) (NT-530P, Nidek Co., Ltd., Gamagori, Japan), Pentacam HR (OCULUS Inc., Wetzlar, Germany), and RTVue optical coherence tomography (OCT) (Optovue Inc., Fremont, CA, USA) in 78 eyes of 78 healthy subjects with myopia. Agreement between the measurement methods was evaluated using 95% confidence intervals for the limits of agreement (LoA). The mean CCT values were 546.9 ± 34.7, 548.1 ± 33.5, 559.2 ± 34.0, and 547.2 ± 34.8 μm for USP, non-contact TP, Pentacam, and RTVue, respectively. The thickest and the thinnest mean CCT values corresponded to those obtained by Pentacam HR and USP, respectively. Plots of the differences against the means showed the best agreement between USP and RTVue (LoA, 10.14-10.70 μm), while the largest discrepancy was observed between RTVue and Pentacam systems (LoA, -25.47-1.44 μm). Our data showed that CCT measurements using these 4 instruments were well correlated. However, the results from Pentacam differed significantly from those of the other instruments.

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 Measurements by Pentacam and Ultrasound Pachymetry in Normal Myopic Patients

Introduction

Precise measurement of corneal thickness is of crucial importance in corneal refractive procedures. The aim of this work is to compare the central corneal thickness measurements using Scheimpflug imaging (Pentacam) and contact US pachymetry in normal myopic patients.

Methods

This retrospective cohort study was conducted on in 144 eyes of 72 normal myopic patients during 6 months. The study location was the Research Institute of Ophthalmology (Giza, Egypt), and Magrabi Eye Hospital (Dubai, United Arab Emirates). Central corneal thickness was measured with the two devices. Data were analyzed by descriptive statistics, independent-samples t-test, paired-samples t-test, Mann-Whitney U test and Pearson-Product Moment Correlation Coefficient.

Results

The mean age was 25.3±5.6 years (range 18 to 38 years). The median age for our patients is 24 years. The average measurements of CCT were 526.8±35.3 and 529.1±37.9 for the Pentacam pachymetry and US pachymetry values, respectively. Mean difference between both measurements was 2.3±2.6μm which is statistically insignificant (p=0.08). Bland Altman Plot shows border line agreement of the two methods US pachymetry and Pentacam in detection of central corneal thickness.

Conclusion

The results of this study showed no significant differences in CCT readings between the measurements obtained by Pentacam and US pachymetry in normal myopic patients.

Measurement of central corneal thickness by ultrasonic pachymeter and oculus pentacam in patients with well-controlled glaucoma: hospital-based comparative study

Background

The measurement of central corneal thickness (CCT) plays an important role in the diagnosis and treatment of glaucoma and many corneal diseases.

Objective of the study

To compare the measurement of CCT by ultrasonic pachymeter with that measured by oculus pentacam in both normal subjects and patients with well-controlled glaucoma.

Patients and methods

In 173 eyes of both controls and patients with open-angle glaucoma (normal intraocular pressure) attending Ibn Al Haitham Teaching Eye Hospital, CCT was measured by oculus pentacam and then by ultrasound pachymeter at the same morning by the same technicians.

Results

The results showed no significant difference in CCT readings measured by the two devices in both glaucoma and control groups (glaucoma group: 547.29±49.32 µm with pentacam vs 547.66±45.24 µm with ultrasound pachymeter; control group: 551.02±36.28 µm with pentacam vs 541.25±34.96 µm with ultrasound pachymeter). P-values were >0.05 in both groups (statistically not significant).

Conclusion and recommendation

Ultrasonic pachymeter and oculus pentacam can be used interchangeably in measuring CCT, and we recommend a nontouch method (in this study, pentacam Scheimpflug camera) for measuring CCT during assessment of patients with glaucoma or any ocular disease or surgery.

Characterization of the thickness of different corneal zones in glaucoma: effect on dynamic contour, Goldmann and rebound tonometries

PURPOSE

To characterize five models of corneal thickness circular zoning in a sample of healthy controls and a sample of patients with primary open-angle glaucoma (POAG) and to determine their effect on Goldmann (GAT), dynamic contour (DCT) and rebound tonometers (RT).

METHODS

The study participants were 122 controls and 129 cases. Five corneal thickness zoning models (A, B, C, D and E) were constructed. The partitioning pattern consisted of a circle centred at the corneal apex and several concentric rings, until the limbus; the contours of each ring followed the geometry of the corneal contour of each participant. In Model A, the central circle was 1 mm in diameter and five concentric rings were established. Mean was obtained for each zone for both samples and compared between them using a t-test. The effect on the tonometers of central cornel thickness (CCT) and mean thickness of the zones generated was determined through several linear regression models (one per tonometer and per sample).

RESULTS

According to a t-test, cases and controls differ in zones I [mean difference (MD): 17.93 μm], V (MD: 25.52 μm) and VI (MD: 31.78 μm) of model A (higher values in the cases sample). RT was affected by CCT (controls: B = 0.089; cases: B = 0.081). DCT was affected by zone IV of model A (controls: B = -0.029; cases: B = -0.012). GAT was affected by CCT (controls: B = 0.043; cases: B = 0.025) and zone III of model A (controls: B = -0.045; cases: B = -0.033).

CONCLUSION

Our results highlight the importance of the thickness of other regions of the cornea different from its main centre in discriminating between healthy controls and patients with POAG and in IOP measurements made using DCT, GAT and RT.

Meta-analysis of Pentacam vs. ultrasound pachymetry in central corneal thickness measurement in normal, post-LASIK or PRK, and keratoconic or keratoconus-suspect eyes

BACKGROUND

The aim of this meta-analysis is to evaluate the central corneal thickness (CCT) measurement differences between Pentacam (Oculus Inc., Germany) and Ultrasound Pachymetry (USP) in normal (unoperated eyes , myopic and astigmatic eyes without corneal disease or topographic irregularity), after laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK), and keratoconic or keratoconus suspected eyes. We assess whether Pentacam and USP have similar CCT differences in normal, thinner corneas after LASIK or PRK procedures, and kerotoconic or keratoconus suspected eyes.

METHODS

Data sources, including PubMed, Medline, EMBASE, and Cochrane Central Registry of Controlled Trials on the Cochrane Library, were searched to find the relevant studies. Primary outcome measures were CCT measurement between Pentacam and USP. Three groups of eyes were analyzed: normal; LASIK or PRK eyes; and keratoconus suspected or keratoconic eyes.

RESULTS

Nineteen studies describing 1,908 eyes were enrolled in the normal group. Pentacam results were 1.47 μm ,95 % confidence interval (CI) -2.32 to 5.27, higher than USP without statistically significant difference (P = 0.45). Nine studies with total 539 eyes were included in the corneas after LASIK or PRK. The mean difference in the CCT measurement with Pentacam and ultrasound pachymetry was 1.03 μm, with the 95 % CI -3.36 to 5.42, there was no statistically difference (P = 0.64). Four studies with a total of 185 eyes were included in the keratoconic eyes or keratoconus-suspect group, however,the mean difference was -6.33 μm (95 % CI -9.17 to-3.49), which was statistically different between Pentacam and ultrasound pachymetry in the CCT measurement (P < 0.0001).

CONCLUSIONS

Pentacam offers similar CCT results to ultrasound pachymetry in normal eyes, thinner corneas after LASIK or PRK procedures. However, in keratoconic or keratoconus-suspect eyes, Pentacam slightly underestimates the central corneal thickness than does ultrasound pachymetry, which may result from the difficulty in fixation of keratoconic eyes, misalignment of Pentacam and the variation of ultrasonic velocity due to the histological deformation.