Measurement of Central Corneal Thickness Using Ultrasound Pachymetry and Orbscan II in Normal Eyes

Comparison of central corneal thickness measured by automatic and manual analysis of optical coherence tomography

PURPOSE

To compare central corneal thickness (CCT) measured with optical coherence tomography (OCT) using an automatic algorithm (A-OCT) vs. manual measurements (M-OCT) with respect to the gold standard ultrasound pachymetry (USP).

METHODS

CCT measurements were performed on both eyes of 28 healthy subjects at four times of the day. A-OCT used an automatic software analysis of the corneal image, M-OCT was performed by two operators by setting a digital calliper on the corneal borders, and USP was performed after corneal anesthesia. Measurements were compared using a three-way repeated measures ANOVA. Bland-Altman plots were used to evaluate the agreement between OCT measurements and USP.

RESULTS

Both A-OCT and M-OCT significantly underestimated the USP measures, with the mean difference, i.e., the systematic error, being larger for A-OCT (- 19.0 µm) than for M-OCT (- 6.5 µm). Good reproducibility between the two operators was observed. Bland-Altman plots showed that both OCT methods suffered from proportional errors, which were not affected by time and eye.

CONCLUSIONS

Measuring CCT with OCT yielded lower values than USP. Therefore, clinicians should be aware that corneal thickness values may be influenced by the measurement method and that the various devices should not be used interchangeably in following up a given patient. Intriguingly, M-OCT had less systematic error than A-OCT, an important outcome that clinicians should consider when deciding to use an OCT device.

Comparison of corneal measurements in keratoconus eyes with two swept-source-optical coherence tomography devices and a Scheimpflug device

PURPOSE

To assess the feasibility and reliability of biometric measurements taken with the Eyestar 900 device in keratoconus eyes in comparison with those taken with the Pentacam HR and IOLMaster 700.

METHODS

Seventy-five eyes of 75 patients with keratoconus were included. The central corneal thickness (CCT), thinnest point of corneal thickness (TCT), axial length (AL), flat (K1) and steep (K2) anterior and posterior (Kp1, Kp2) keratometry, maximal keratometry (KMax) and anterior chamber depth (ACD) were compared between the Eyestar 900, Pentacam HR and IOLMaster 700. Reliability parameters such as the coefficient of variation (CoV) and intraclass correlation coefficient (ICC) were calculated. Pearson's r was determined to assess the correlation between devices.

RESULTS

A high repeatability (CoV < 1%) and intraclass correlation (ICC > 0.9) was found for all devices, led by AL, TCT, K1 and K2 (CoV 0.01-0.36%; ICC 0.994-1.00). The largest correlation between devices was found for AL (Eyestar vs. IOLMaster, r = 1.0), K1 (Eyestar vs. IOLMaster, r = 0.997) and ACD (Eyestar vs. IOLMaster, r = 0.995; Pentacam vs. IOLMaster, r = 0.987; Eyestar vs. Pentacam, r = 0.983), but there were significant differences in measured values between devices (p < 0.001), whereas the correlation was only slightly lower (r = 0.947 to 0.994) for KMax, CCT, TCT, K2, Kp1 and Kp2.

CONCLUSION

Keratometric and axial length measurements with the Eyestar 900 were feasible and revealed a high repeatability and a good correlation to the other devices in eyes with keratoconus.

Comparison of central corneal thickness in healthy eyes using ultrasound pachymetry, non-contact specular microscopy and a high-resolution Scheimpflug camera

PURPOSE

To compare and analyze the interchangeability in measuring central corneal thickness (CCT) using ultrasonic pachymetry (USP, PACHMATE 2, DGH, Inc, Exton, PA, USA), non-contact specular microscopy (NCSM, CEM-530, Nidek CO, LTD, Gamagori, Japan) and a high-resolution Scheimpflug Camera (Pentacam HR, OCULUS, Wetzlar, Germany).

METHODS

An observational, cross-sectional study was performed recruiting 216 volunteers, for a sample size of 216 eyes with no ocular abnormalities other than refractive errors. All subjects underwent pachymetric measurements obtained by USP, NCSM and Pentacam HR. Examinations were performed by the same examiner with USP always following the noncontact examinations.

RESULTS

The mean CCT (± SD) was 560.30 ± 38.80 μm, 556.76 ± 36.83 μm and 547.31 ± 35.28 μm for USP, NCSM and Pentacam HR, respectively. The Bland-Altman analysis showed that the highest concordance was found between USP and NCSM, with differences between - 13.18 μm and 20.26 μm. For the differences between measurements obtained with Pentacam HR and USP, the differences at Bland-Altman plot were between - 28.25 and 13.57 μm. The lowest concordance was found for the CCT values measured with Pentacam HR and NCSM, with differences between - 25.67 and 6.86 μm. The intraclass correlation coefficient (ICC) between all pairs of measurements was between 0.979 and 0.987, suggesting that the mean measurements were strongly correlated.

CONCLUSION

Measurements obtained with all three devices had high correlation. USP and NCSM were found in good agreement and high concordance, too. The above results indicate that these two devices are interchangeable in clinical practice. Pentacam HR may be a useful alternative for measuring CCT; however, it significantly underestimates CCT and cannot be used interchangeably with the other devices that we studied.

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.

Normal Corneal Thickness and Endothelial Cell Density in Rhesus Macaques (Macaca mulatta)

Purpose

To define the normal range of central corneal thickness (CCT) and corneal endothelial cell density (ECD) in rhesus macaques (Macaca mulatta) and the effects of age, body weight, sex, and intraocular pressure (IOP) on these parameters.

Methods

Ophthalmic examinations were performed on 144 rhesus macaques without anterior segment pathology. The CCT was measured via ultrasound pachymetry (USP) and specular microscopy, and the ECD was semiautomatically and manually counted using specular microscopy. Rebound tonometry was used to measure IOP. Linear regression and mixed-effects linear regression models were used to evaluate the effects of age, body weight, sex, and IOP on CCT and ECD.

Results

We included 98 females and 46 males with an age range of 0.2 to 29.4 years. The mean CCT by USP and specular microscopy were 483 ± 39 and 463 ± 33 µm, respectively, and were statistically different (P < 0.001). The ECDs were 2717 ± 423 and 2747 ± 438 cells/mm2 by semiautomated and manual analysis, respectively. Corneal endothelial degeneration was identified in one aged rhesus macaque.

Conclusions

The mean USP and specular microscopy CCT values differed significantly, whereas the semiautomatic and manual ECD did not. The CCT was associated with the IOP and sex, whereas the ECD was associated with body weight and age (P < 0.05). As in humans, corneal disease in rhesus macaques is uncommon.

Translational Relevance

Establishing reference values is fundamental to use rhesus macaques as a model for corneal disease or to identify toxicity in studies of ocular drugs or devices.

Topical Drug Delivery to the Posterior Segment of the Eye

Topical drug delivery to the posterior segment of the eye is a very complex challenge. However, topical delivery is highly desired, to achieve an easy-to-use treatment option for retinal diseases. In this review, we focus on the drug characteristics that are relevant to succeed in this challenge. An overview on the ocular barriers that need to be overcome and some relevant animal models to study ocular pharmacokinetics are given. Furthermore, a summary of substances that were able to reach the posterior segment after eye drop application is provided, as well as an outline of investigated delivery systems to improve ocular drug delivery. Some promising results of substances delivered to the retina suggest that topical treatment of retinal diseases might be possible in the future, which warrants further research.

The Emerging Role of Topical Ocular Drugs to Target the Posterior Eye

The prevalence of chronic fundus diseases is increasing with the aging of the general population. The treatment of these intraocular diseases relies on invasive drug delivery because of the globular structure and multiple barriers of the eye. Frequent intraocular injections bring heavy burdens to the medical care system and patients. The use of topical drugs to treat retinal diseases has always been an attractive solution. The fast development of new materials and technologies brings the possibility to develop innovative topical formulations. This article reviews anatomical and physiological barriers of the eye which affect the bioavailability of topical drugs. In addition, we summarize innovative topical formulations which enhance the permeability of drugs through the ocular surface and/or extend the drug retention time in the eye. This article also reviews the differences of eyes between different laboratory animals to address the translational challenges of preclinical models. The fast development of in vitro eye models may provide more tools to increase the clinical translationality of topical formulations for intraocular diseases. Clinical successes of topical formulations rely on continuous and collaborative efforts between different disciplines.

Fibril density reduction in keratoconic corneas

This study aims to estimate the reduction in collagen fibril density within the central 6 mm radius of keratoconic corneas through the processing of microstructure and videokeratography data. Collagen fibril distribution maps and topography maps were obtained for seven keratoconic and six healthy corneas, and topographic features were assessed to detect and calculate the area of the cone in each keratoconic eye. The reduction in collagen fibril density within the cone area was estimated with reference to the same region in the characteristic collagen fibril maps of healthy corneas. Together with minimum thickness and mean central corneal refractive power, the cone area was correlated with the reduction in the cone collagen fibrils. For the corneas considered, the mean area of keratoconic cones was 3.30 ± 1.90 mm². Compared with healthy corneas, fibril density in the cones of keratoconic corneas was lower by as much as 35%, and the mean reduction was 17 ± 10%. A linear approximation was developed to relate the magnitude of reduction to the refractive power, minimum corneal thickness and cone area (R² = 0.95, p < 0.001). Outside the cone area, there was no significant difference between fibril arrangement in healthy and keratoconic corneas. The presented method can predict the mean fibril density in the keratoconic eye's cone area. The technique can be applied in microstructure-based finite-element models of the eye to regulate its stiffness level and the stiffness distribution within the areas affected by keratoconus.

Comparison of central corneal thickness measurement by scanning slit topography, infrared, and ultrasound pachymetry in normal and post-LASIK eyes

OBJECTIVES

To compare central corneal thickness (CCT) measurements by scanning slit topography (SST), infrared pachymetry (IRP), and ultrasound pachymetry (USP), and their agreement in normal and post-laser in situ keratomileusis (LASIK) eyes.

METHODS

Sixty normal and 35 post-LASIK subjects were recruited. Only one eye from each subject was analyzed. Non-contact pachymetry was performed first, and the order for SST (Orbscan IIz) and IRP (Tonoref III) was randomized for each patient, to be followed by contact USP (Echoscan US-4000). Pearson's correlation, paired t test, and Bland-Altman plots were used to investigate association, difference, and agreement among different instruments respectively.

RESULTS

The measurements obtained with the instruments were highly correlated. Compared to CCT determined by USP (CCT_USP), CCT determined by SST (after correction with acoustic factor) (CCT_SST^C) was thicker by 7 µm in normal eyes (P < 0.001). There was no significant difference between CCT_SST^C and CCT_USP (P = 0.128), but a thickness-dependent deviation in post-LASIK eyes (P = 0.003). The CCT determined by IRP (CCT_IRP) was thicker than CCT_USP in normal (P < 0.001) and post-LASIK eyes (P < 0.001) and demonstrated proportional overestimation with thinner corneas, with less predictable ultrasonic equivalent corneal thickness in normal eyes. Conversely, CCT_IRP significantly underestimated CCT compared to CCT_SST and showed increasing underestimation with thinner corneas in both normal and post-LASIK eyes (both P < 0.001).

CONCLUSION

Central corneal thickness determined by SST, IRP and USP were not interchangeable or interconvertible, probably attributed to difference in methodologies. Compensation with algorithms may improve agreements amongst instruments.

Measurement of central corneal thickness using Orbscan 3, Pentacam HR and ultrasound pachymetry in normal eyes

PURPOSE

To assess the agreement between Orbscan 3, Pentacam HR and ultrasound pachymetry (Palm Scan AP 2000) in measuring central corneal thickness.

METHODS

Prospective observational cross-sectional study of ninety-two eyes of 48 patients with normal corneas was conducted. Central corneal thickness was measured via Pentacam HR, Orbscan 3 and ultrasound pachymetry. Bland-Altman analysis was used to demonstrate agreement between various methods.

RESULTS

Ninety-two eyes of 46 subjects were enrolled. The mean age was 29.67 years (18-59). The average measurements of central corneal thickness were 545.73 ± 29.35 μm, 549.34 ± 29.14 μm and 545.78 ± 31.48 μm for the Pentacam HR, Orbscan and ultrasound pachymetry, respectively. The three devices measurements are closely correlated, with Pearson correlation coefficient ranging from 0.868 to 0.929. The 95 % limits of agreement were 25.2 to - 18 μm between Orbscan and Pentacam central corneal thickness, 25.2 to - 25.7 μm between Pentacam and pachymetry central corneal thickness and 34.4 to - 27.2 μm between Orbscan and pachymetry central corneal thickness.

CONCLUSION

In spite of advancement of Orbscan 3, still there are wide agreement limits between CCT measurements obtained via Orbscan 3, Pentacam HR and ultrasound pachymetry; thus, interchangeable use in clinical practice is not recommended.

Impact of Patient Interface Diameter and Vacuum Level on Suction Stability Using a Flat Applanating Interface for Femtosecond Laser-Assisted LASIK

PURPOSE

To investigate the impact of different patient interface (PI) diameters and different vacuum levels on the suction stability during vacuum application for femtosecond laser-assisted LASIK.

METHODS

Break-away forces as a marker for suction stability were measured by an automated test bench set-up. The test bench was based on a customized stamp connected to a digital load cell. Three flat applanating PI with different diameters (8.5, 9.5 and 10.0 mm) and four different vacuum levels (500, 600, 700 and 800 mbar) were investigated using the FEMTO LDV Z8 (Ziemer Ophthalmic Systems AG, Switzerland).

RESULTS

Mean break-away force was 5.23N (±0.99N) using the 8.5 mm PI and 500 mbar vacuum, 8.18N (±1.39N) using the 8.5 mm PI and 800 mbar, 3.37N (±0.56N) using the 10.0 mm PI and 500 mbar, and 6.14N (±0.68N) using the 10.0 mm PI and 800 mbar vacuum (p < .001; CI95%). Increasing the PI diameter from 8.5 to 10.0 mm resulted in a 28.89% (+1.97 ± 1.02N) lower break-away force (p < .001) when using default vacuum settings (700 mbar) compared to increasing vacuum from 500 to 800 mbar, which resulted in a 60.37% (+1.95 ± 1.40N) higher mean break away force (p < .001).

CONCLUSION

The vacuum level and the diameter of the PI showed significant impact on suction stability measured as break-away force during flat applanating docking for corneal and refractive surgery. Break-away forces were inversely related to the PI diameter and directly to the vacuum level. Increasing the PI diameter by one step or reducing vacuum by 100 mbar resulted in a comparable decrease of break-away forces. Therefore, the surgeon could potentially maintain stabile suction by increasing vacuum when choosing a larger PI diameter to obtain a larger treatment zone. Furthermore, reduction of the PI diameter and/or increasing vacuum could help improving suction stability in situations of poor suction and in situations with increased risk of suction loss during LASIK.

Reproducibility and reliability of central corneal thickness determination in more and less profound corneal edema using ultrasound pachymetry, a Scheimpflug camera and anterior segment OCT

PURPOSE

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

METHODS

Forty-four patients undergoing ophthalmic surgery were included in this prospective study. All measurements were acquired by two investigators. The Pentacam and AS-OCT measurements were performed in randomized order followed by USP. Two measurements were taken by each investigator with each device. CCT was evaluated by using the apex value provided by the Pentacam, the corneal apex cut in the AS-OCT and averaging 2 cycles of 4 measurements for USP. Coefficients of variation (COV) and intraclass correlation coefficients (ICC) were determined. To investigate the reproducibility in different degrees of corneal edema, patients were subdivided into edema more/less than 10% of CCT, ≥/< 600 μm and > 650 μm CCT.

RESULTS

No significant differences were recorded for each individual investigator and measuring device. However, overall the devices differed significantly in the < 600 μm group (ANOVA p < 0.04). The reproducibility decreased with higher degrees of corneal edema in particular for investigator 1 and USP measurements. No significant overestimation of corneal thickness by the Pentacam was recorded in higher degrees of corneal edema.

CONCLUSION

USP measurements are highly user dependent especially in higher degrees of corneal edema. Nevertheless, all methods were able to reach a high level of agreement in CCT measurement in higher degrees of corneal edema. Interestingly lower degrees of corneal edema revealed the only significant differences in-between the 3 devices.

Distribution of central corneal thickness and intraocular pressure in emmetropic eyes of healthy children of Palestine: a representative cross-sectional study

AIM

To determine the distributions of central corneal thickness (CCT) and intraocular pressure (IOP) in emmetropic eyes of healthy children of Palestine.

METHODS

This representative cross sectional study included a total of 1156 eyes from 578 healthy school children aged 7-15y. Inclusion criteria included emmetropia, no previous history of ocular or systemic diseases, no previous history of contact lens use, and the availability of both eyes. CCT and IOP were measured using ultrasound pachymeter and Goldmann applanation tonometer, respectively. The relationship of the results with age and gender was investigated.

RESULTS

The mean age of school children was 11.13±2.8y. Mean CCT was 542.2±37.4 and 544.3±39.2 µm for right and left eyes, respectively. Mean IOP was 12.5±2.2 and 12.3±2.2 mm Hg for right and left eyes, respectively. A positive correlation was observed between CCT and IOP of the right eye (P<0.001, R=0.358) and CCT and IOP of the left eye (P<0.001, R=0.324). No significant differences were observed in CCT and IOP due to age or gender (P>0.05). There were significant differences in mean CCT and IOP between right and left eyes (P=0.004, P=0.001, respectively).

CONCLUSION

A population profile of CCT and IOP is established in Palestinian children for the first time. Mean CCT is comparable to some studies but differ from others. Mean IOP is considerably lower than that of majority children of other ethnic groups. Intereye difference of more than 36 µm in CCT, and 5 mm Hg in IOP should prompt evaluation for potential ocular disorders.

Intraoperative optical pachymetry in photorefractive keratectomy

PURPOSE

To study the effect of variables on the accuracy and reliability of the optical pachymeter built into the WaveLight EX500 excimer laser during photorefractive keratectomy (PRK).

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, USA.

DESIGN

Retrospective case series.

METHODS

A chart review of 352 eyes (181 patients) that had excimer laser PRK was performed. Programmed excimer laser residual stromal bed (RSB) measurements, optical pachymeter measurements after ablation, and Scheimpflug pachymetry measurements (Pentacam) at the 1-year follow-up were compared. Variables included ablation time, preoperative spherical equivalent (SE), 1-year SE, mitomycin-C use, operating room temperature and humidity, and programmed monovision.

RESULTS

The mean programmed RSB was 27 μm greater than the optical pachymetry post-ablation measurement (P < .001). Of patients with a 1-year follow-up, the 1-year Scheimpflug pachymetry RSB was 24 μm greater than the optical pachymetry post-ablation RSB (P < .001). Comparison of the programmed RSB with the optical pachymetry post-ablation RSB showed that the preoperative SE and ablation time had a Pearson correlation coefficient of -0.36 and 0.30, respectively (P < .001). There was no correlation between operating room temperature, humidity, or programmed monovision with these differences.

CONCLUSIONS

The RSB post-ablation values measured by optical pachymetry during PRK were significantly lower than the programmed excimer laser RSB value and 1-year Scheimpflug pachymetry RSB value. Intraoperative pachymetry during PRK underpredicted the actual long-term RSB thickness. The greater temporary drying effect associated with increased ablation time in higher myopic corrections might have caused this error.

Comparison of ultrasonic pachymetry and Fourier-domain optical coherence tomography for measurement of corneal thickness in dogs with and without corneal disease

Several ultrasonic and Fourier-domain optical coherence tomography (FD-OCT) pachymeters are used to measure corneal thickness in canine patients and research subjects. This study assessed the reliability of and consistency between two ultrasonic pachymetry (USP) devices, Pachette 3 and Accupach VI, as well as automated and manual measurements obtained using FD-OCT in dogs with and without corneal disease. Corneal thickness measurements were compiled from 108 dogs and analyzed using mixed effects linear regression, with Bonferonni adjustments for post-hoc comparisons, to determine the effects of age, weight and disease state. Data are presented as predicted mean±standard error. Canine corneal disease can result in marked increases in thickness that frequently exceed the upper limits of measurement of some pachymetry devices developed for human use. In this study, the corneas of dogs with endothelial disease or injury frequently exceeded the upper limits of quantitation of 999 and 800μm for the Accupach VI and automated FD-OCT pachymeters, respectively. Using values <800μm, the Pachette 3 generated significantly greater values for central corneal thickness (CCT) than the Accupach VI, manual FD-OCT and automated FD-OCT at 625±7.0, 615±7.2, 613±7.2, and 606±7.4μm respectively (P<0.001). Of the two devices where measurements >1000μm were obtained, manual FD-OCT demonstrated less variability than the Pachette 3. Corneal thickness increased linearly with age and weight with an increase of 6.9±1.8μm/year and 1.6±0.8μm/kg body weight (P<0.005 and P=0.038, respectively).

Comparison of central corneal thickness measurements in corneal edema using ultrasound pachymetry, Visante anterior-segment optical coherence tomography, Cirrus optical coherence tomography, and Pentacam Scheimpflug camera tomography

Purpose

To compare the central corneal thickness (CCT) measurements in subjects with corneal edema using ultrasound pachymetry, Visante anterior-segment optical coherence tomography (OCT), Cirrus OCT, and Pentacam Scheimpflug camera tomography.

Methods

This prospective cross-sectional study included 46 eyes of 33 patients with corneal edema and a CCT exceeding 550 μm evaluated by ultrasound pachymetry, Visante OCT, Cirrus OCT, and Pentacam. Two observers measured each eye twice. Intraobserver and interobserver reproducibility were determined and agreement among the devices calculated.

Results

CCT was measured in 40 eyes of 29 patients. Regardless of the CCT, the measurements obtained using Visante OCT, Cirrus CCT, and ultrasound pachymetry were well correlated. Interobserver and intraobserver reproducibility were high among the three devices. Pentacam overestimated the results compared with the other devices, and ultrasound pachymetry was unmeasurable in six (13%) eyes with very thick and opaque corneas. In eyes with mild corneal edema (CCT 551–650 μm), measurements from the four devices were comparable.

Conclusion

All devices reliably measured the CCT <650 μm. In eyes with edema exceeding 650 μm, CCT measurements from the Visante OCT, Cirrus OCT, and ultrasound pachymetry devices showed good reproducibility and were well correlated, while the Pentacam overestimated the values compared to the other devices. Pentacam and ultrasound pachymetry should not be used in eyes with extreme corneal edema and opacity.

Reproducibility of Central Corneal Thickness Measurements in Normal Eyes Using the Zeiss Cirrus 5000 HD-OCT and Pentacam HR

Objectives:

To determine the repeatability and reproducibility of Central Corneal Thickness (CCT) measurements using two different anterior segment imaging modalities, including those obtained with the new anterior segment lens attachments for the Cirrus 5000 HD-OCT.

Methods:

A total of 32 eyes from 16 normal volunteers (8 male, 8 female) were enrolled in this prospective study. CCT was measured by the same examiner using the Cirrus 5000 HD-OCT and Pentacam HR. The results of CCT obtained by each method were averaged and compared using t-test analysis. The agreement between the measurement methods was evaluated. Coefficient of Repeatability (CoR) and Intra-Class Correlation Coefficient (ICC) were computed.

Results:

The mean measurements taken with the Cirrus OCT anterior chamber lens (CCT_AC), HD cornea lens (CCT_HDC) and pachymetry scans (CCT_Pach) were 545.35 ± 31.02, 537.87 ± 26.82, and 532.04 ± 29.82 µm, respectively. The mean CCT obtained with the Pentacam (CCT_Pent) was 545.51 ± 30.71 µm. CCT_Pent were significantly higher than CCT_HDC and CCT_Pach (p< 0.0001). In contrast, the CCT_Pent and CCT_AC were similar (p=0.87). CCT, as evaluated by the two different instruments, showed excellent correlation (r > 0.98, p< 0.0001) with an ICC > 0.99 (95% CI, 0.97 – 0.99). CoR was the highest for CCT_Pach (3.7 ± 1.4, 95% CI (3.0- 4.6)).

Conclusion:

CCT measurements from the Cirrus OCT using the new anterior segment lens attachments and the Pentacam HR are highly correlated. This should allow the use of a standardized correction factor if necessary to inter-relate the measurements between the two 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.

Distribution of corneal thickness and its determinants in 6-12-year-old children in an Iranian general population

Purpose

To determine the central corneal thickness (CCT), apex, and paracentral thicknesses and their determinants in children aged 6-12 years.

Methods

The present study was part of the phase 1 of Shahroud School Children Eye Cohort Study in 2015. Cluster sampling was done in urban areas while all children were invited to participate in the study in rural areas. The Pentacam HR was used for measurements. CCT was measured within the central 3 mm zone of the cornea, and corneal thickness 3 mm further from the center was considered paracentral thickness.

Results

Of 6624 students who were selected, 5620 (84.8%) participated in the study. Among 4956 students, studied in this report, 52.2% were boys, and the mean age of the study participants was 9.75 ± 1.71 years (6-12). The mean CCT and apical thickness was 556.29 ± 34.04 and 557.43 ± 34.03 μm, respectively. The mean paracentral thickness was 657.62 ± 39.11 μm in the superior, 632.65 ± 37.63 μm in the inferior, 648.64 ± 38.75 μm in the nasal, and 617.36 ± 37.19 μm in the temporal region. A multiple regression model showed that CCT decreased by 4.70 μm with every 1 diopter increase in the mean keratometry and increased by 20.06 μm with every 1 mm increase in the anterior chamber depth (ACD) (Both P-Value < 0.001). Age, sex, ethnicity and residence place were also found to be associated with CCT.

Conclusions

This study is the first to describe the distribution of corneal thickness in Iranian children with a large sample size. This study showed that corneal thickness was significantly correlated with younger age, female gender, urban residence, and a number of biometric variables.

Comparison of Central Corneal Thickness Measurements Using Ultrasonic Pachymetry, Anterior Segment OCT and Noncontact Specular Microscopy

PURPOSE

To evaluate and compare central corneal thickness (CCT) values measured with anterior segment optical coherence tomography (AS-OCT), noncontact specular microscopy (NCSM), and ultrasound pachymetry (USP).

MATERIALS AND METHODS

CCT was measured in 182 healthy eyes without ocular abnormalities other than refractive errors. Three consecutive measurements of CCT by the same examiner were obtained during the same session. The testing sequence of AS-OCT and NCSM was randomly selected. The USP always was performed after the noncontact examinations.

RESULTS

The average CCT measured by AS-OCT, NCSM, and USP were 535.8±35.5, 547.7±38.2, and 537.4±37.5 μm, respectively. The mean differences between modalities were 11.8±14.7 μm (P<0.01) between NCSM and AS-OCT, 10.3±17.7 μm (P<0.01) between NCSM and USP and 1.6±8.6 μm (P=0.02) between USP and AS-OCT.

CONCLUSIONS

AS-OCT, NCSM, and USP showed an overall strong agreement in measuring CCT. However, CCT measurements with AS-OCT showed a good correlation to those obtained by USP, NCSM tended to give statistically significant higher CCT readings than either alternative and showed the worse repeatability indices. On the basis of our results, CCT measurement obtained with different instruments cannot be considered directly interchangeable.

Accuracy of Alcon WaveLight® EX500 optical pachymetry during LASIK

Purpose

To study the accuracy and reliability of optical pachymetry using the Alcon WaveLight EX500 during laser-assisted in situ keratomileusis (LASIK).

Materials and methods

This was a retrospective chart review of 90 eyes from 45 patients who had undergone LASIK (mean age 35.2±8.2 years; 19 males, 26 females). The WaveLight FS200 femtosecond laser was programmed to cut LASIK flaps at a desired depth of 120 μm. Optical low-coherence reflectometry (WaveLight EX500) was used to measure central corneal thickness prior to lifting the flap, and the residual stromal bed immediately after excimer ablation. Flap thickness (FT) was calculated using simple subtraction. Optical coherence tomography (OCT) was used to measure central corneal thickness, flap thickness, and residual stromal bed in the postoperative period and the results compared to intraoperative measurements.

Results

Mean programmed FS200 FT was 119 μm. Mean FT using EX500 optical pachymetry was 109 μm. The difference between FS200- programmed and EX500-measured FT was 9 μm (P<0.001). There was also a significant difference between the EX500 and OCT FT (109 μm vs 119 μm, respectively; P<0.001).

Conclusion

FT values calculated using intraoperative EX500 optical pachymetry were significantly lower than programmed FS200 values or OCT measurements.

Repeatability of topographic corneal thickness in keratoconus comparing Visante™ OCT and Oculus Pentacam HR® topographer

PURPOSE

To assess the repeatability and reproducibility of Visante™ OCT and Oculus Pentacam HR® in measuring central (CCT) and topographic corneal thickness (TCT) along the principle meridians in keratoconus (KC) corneae.

METHOD

Twenty participants diagnosed with KC were recruited. There were two study visits. On the first study visit, two repeated corneal thickness measurements were obtained with each instrument. Measurements were repeated at least 48hrs later in the same order. TCT were recorded in the 90, 180, 45 and 135 meridians at 1mm intervals across 8mm chord.

RESULTS

Mean CCT for Visante™ OCT was 484.97±43.14μm (range: 484.84-486.09) and Oculus Pentacam HR® was 478.86±45.31μm (range: 477.20-480.53). No significant difference in TCT between the two visits (p=0.54) and measurements (p=0.63) for Visante™ OCT. For Oculus Pentacam HR®, no significant difference was found for each visit (p=0.18) but differences existed in the measurements outside of the central region (p=0.001). Tukey post-hoc analysis shows the differences (p˂0.05) were found in the +1 and +4 (supero-temporal) locations in the 135 meridian. Significant differences were found comparing the two instruments, (p<0.05). Bland Altman plots were used to demonstrate the differences between the two instruments and indicate their limits of agreement.

CONCLUSION

Both instruments gave repeatable measurements as no significant differences were found in most locations in all meridians. Comparing the two instruments, they were not reproducible in all locations.

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.

Corneal Thickness in Highlanders

Patyal, Sagarika, Amit Arora, Arun Yadav, and Vijay K. Sharma. Corneal thickness in highlanders. High Alt Med Biol. 18:56-60, 2017.

BACKGROUND

Corneal thickness is an important parameter with diagnostic and therapeutic implications. Various studies have highlighted increase in corneal thickness in lowlanders on ascending to high altitude. However, there are no studies in the published literature pertaining to corneal thickness of the highlanders who are inhabitants of such altitudes. Hence, study was carried out with objective to determine the corneal thickness of highlanders living at heights of more than 11,000 feet and compare it with corneal thickness of lowlanders.

MATERIALS AND METHODS

The highlander participants of the study consisted of inhabitants of Ladakh region of India at an altitude of 11,000 feet or more and lowlander participants consisted of inhabitants at an altitude of 1500 feet. A total of 254 highlanders and 212 lowlanders participated. A mean of 25 measurements of central corneal thickness (CCT) of every participant was obtained for each eye using ultrasonic pachymeter.

RESULTS

The mean age of the participants was 41.8 (15.9) and 47.7 (17.7) years among lowlanders and highlanders, respectively. The highlanders had 11.95 μm lower mean CCT reading compared to lowlanders after adjusting for age and sex (p value <0.001). There was no statistically significant difference in mean CCT readings of right eye and left eye in either lowlanders or highlanders. Age also had a significant effect after adjustment for location and gender (p = 0.001). CCT decreased by 0.31 μm with every year increase in the age. Gender had no statistically significant effect.

CONCLUSION

This study found statistically significant difference in CCT measurements between highlanders and lowlanders. The thinner corneas of highlanders may have a bearing on diagnosis and treatment of glaucoma, refractive surgery, contact lens fitting implantation of Intacs, and astigmatic keratectomy done on such patients. The study also opens the scope of further research in the area.

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.