Compare Central Corneal Thickness Measurements Research Articles

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

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). 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. 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 (- 19.0µm) than for M-OCT (- 6.5µm). 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. 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 central corneal thickness measurements using three different imaging devices

The purpose of this study was to compare central corneal thickness (CCT) values and evaluate the agreement obtained with three different devices in healthy eyes. A total of 120 eyes of 60 healthy individuals (36 men and 24 women) were enrolled in this retrospective study. CCT measurements were performed using an optical biometer (AL-Scan), spectral-domain optical coherence tomography (SD-OCT) (Topcon 3D) and ultrasonic pachymetry (UP) (Accupach VI), and the results were compared. Bland-Altman analysis was used to quantify the agreement between methods. The mean patient age was 28±5.73years (18-40years). The mean CCT values obtained by AL-Scan, UP, and SD-OCT were 532.4μm±29.7, 549μm±30.4, and 547μm±30.6, respectively. The mean differences in CCT were 15.30±9.52μm between AL-Scan and OCT (P<0.01), 17.15±8.42μm between AL-Scan and UP (P<0.01), and 1.85± 8.78μm between UP and OCT (P=0.067). All three methods of CCT measurement were closely correlated with each other. The present study results suggest that, despite good agreement between the three devices, AL-Scan significantly underestimated CCT compared to UP and OCT. Therefore, clinicians should be aware that different results can be obtained using different devices for CCT measurements. It would be a better approach not to use them as interchangeable in clinical practice. CCT examination and follow-up should be performed using the same device, especially for patients who will undergo refractive surgery.

Blind spot in ultrasound central corneal thickness measurement – Central corneal thickness of apex versus central corneal thickness of vertex

Aims: This study aimed to compare central corneal thickness (CCT) using ultrasound pachymetry (USP) (CCT apex) and specular microscopy (CCT vertex) and also to find out the intra-reading variability from the two instruments. Settings and Design: A prospective, observational study was conducted in a tertiary eye care center in southern India. Materials and Methods: This study was conducted on 12 patients (24 eyes, 96 data set eyes, 768 data points in total) aged 20–50, in non-pathological corneas. Eight CCT measurements by specular microscopy and eight measurements by USP were taken by two different experienced observers on day 1, followed by repeating the same on day 2. Statistical Analysis: The readings were averaged and compared by paired t-test. SPSS software was used for statistical analysis. Variability between the eight readings produced by the same instrument was calculated and coefficient of variation was plotted. Inter-examiner variability and intra-examiner variability of the two modalities were studied, and it was considered statistically significant if P &lt; 0.05. Results: The mean CCT by USP was 522.71 µm and the mean CCT by specular microscopy was 519.43 µm. The coefficient of variation of the eight readings varied significantly between the machines. On an average, the coefficient of variation was 0.4% compared to 0.8% in specular microscopy and USP, respectively. Conclusion: The intra-reading variability of ultrasound CCT is twice as that compared to specular microscopy. The clinical relevance of this spread is relevant and important in modern-day practice. Hence, it is better advisable that CCT readings from both the modalities, not be used interchangeably.

The relationship of central corneal thickness with the status of diabetic retinopathy

BackgroundTo compare central corneal thickness (CCT) values measured by three different devices: slit-scanning topography (SST), ultrasonic pachymetry (UP), and optical coherence tomography (OCT) in diabetic eyes and compare the CCT values in patients with and without diabetic retinopathy.MethodsNinety-six patients with diabetes mellitus were included in this prospective study and divided into two groups according to the presence of diabetic retinopathy, as Group I with retinopathy and Group II without. The CCT of 96 eyes was measured by three different devices; SST (Orbscan II), UP and OCT. The results of CCT measurements with three different devices were compared. Also, the intergroup differences in CCT measurements were evaluated.ResultsThe CCT was statistically insignificantly different between the two groups. Although the three methods of CCT measurements correlated well with each other, SST showed significantly (p < 0,0001) higher CCT results compared to both UP and OCT.ConclusionsAccording to our results, neither the duration of DM nor the presence of diabetic retinopathy did have a significant effect on the CCT. The CCT values obtained with three devices were all in correlation. However, the results of SST were significantly higher compared to the other two. Our findings emphasize the value anterior segment OCT in CCT measurements, since it is a non-contact method and correlate very well with UP.

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

ABSTRACTPurpose: 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 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).

Comparison of Central Corneal Thickness Measurements Obtained by RTVue OCT, Lenstar, Sirius Topography, and Ultrasound Pachymetry in Healthy Subjects

ABSTRACTPurpose: To compare central corneal thickness (CCT) measurement results obtained by RTVue OCT, Lenstar, Sirius topography, and ultrasound pachymetry (UP) (OcuScan RxP Ophthalmic Ultrasound System, Alcon Laboratories) in healthy subjects. Materials and Methods: 256 eyes of 128 healthy subjects were included in the study. CCT measurements were obtained from the eyes for each subject using the UP, Lenstar, Sirius topography, and RTVue OCT instruments. Ultrasound pachymetry measurements were performed after the eyes were anesthetized with one drop of 0.5% proparacaine hydrochloride and were performed at the same day after 15 minutes after previous measurements. Results: Of 128 participants, 84 were male and 44 were female with a mean age of 33.15 ± 12.95 years (ranging from 18 to 75 years). The mean CCTs for UP, Lenstar, Sirius topography, and RTVue OCT were 535.60 ± 35.15 (440,00–668,00); 532.63 ± 34.44 (449,00–650,00); 526.05 ± 36.45 (314,00–640,00); 525.89 ± 33.21 (437,00–646,00) µm, respectively. The mean CCT measurements were statistically different among the three groups (p = 0.002). CCT measurements obtained using RTVue-OCT were significantly thinner than those obtained using UP (p = 0.009). Sirius CCT measurements were also thinner than UP (p = 0.011). Mean CCT measurements between UP and Lenstar were similar (p = 0.769). Measurements with Lenstar (r = 0.849), Sirius topography (r = 0.883), and RTVue OCT (0.949) were highly correlated with UP measurements. Conclusion: RTVue OCT and Sirius topography significantly underestimated the CCT compared with UP. Although highly correlated, the measurement values with these devices are not directly interchangeable in clinical practice.

Effect of the eyelid speculum on pachymetry during corneal collagen crosslinking in keratoconus patients

To compare central corneal thickness (CCT) with and without using an eyelid speculum during corneal collagen crosslinking (CXL). University Medical Center Utrecht, Utrecht, the Netherlands. Prospective nonrandomized comparative study. Eyes with progressive keratoconus were treated by CXL and consecutively divided into 2 groups. In Group A, an eyelid speculum remained in place throughout the entire CXL procedure. In Group B, the eyelids remained closed during the 30-minute riboflavin instillation. Intraoperative ultrasound pachymetry measurements were performed at different timepoints. The visual acuity, refraction, keratometry, pachymetry, and endothelium were evaluated 6 months after CXL. The main outcome measures were intraoperative CCT measurements and the clinical CXL effect after 6 months. Fifty-two eyes (50 patients) were treated. After riboflavin instillation, a statistically significant difference in CCT reduction was found between the 2 groups (P<.001), with a mean CCT decrease of 62 μm±53 (SD) (13%±11%) in Group A and 11±35 μm (2%±8%) in Group B. No statistically significant between-group differences were found after epithelial removal or ultraviolet-A (UVA) irradiation. Six months after CXL, no statistically significant between-group difference was found in the visual acuity, refraction, keratometry, pachymetry, or endothelium. Avoidance of an eyelid speculum during riboflavin instillation resulted in less CCT reduction during CXL. This finding could increase the chance of attaining the required pachymetry safety margin for applying UVA and thus decrease the chance of premature CXL treatment termination. No author has a financial or proprietary interest in any material or method mentioned.

Comparative measurement of central corneal thickness using Pentacam, ocular response analyzer, and ultrasound pachymetry devices for normal, glaucomatous, and keratoconic eyes

Purpose The aim of the study was to compare central corneal thickness (CCT) measurements using Scheimpflug imaging (Pentacam), ocular response analyzer (ORA), and ultrasound pachymetry (USP) devices for normal, glaucomatous, and keratoconic eyes. Patients and methods This was a prospective study that enrolled 170 eyes of 85 patients: 86 normal eyes, 50 eyes diagnosed as primary open angle glaucoma (POAG), and 34 eyes with keratoconus (KC). The CCT was measured using three machines - USP, Pentacam, and ORA - at the same time by two expert operators. Microsoft Excel, the Student t -test, and analysis of variance test were used for statistical analyses. Results The mean age of the three groups, normal, POAG and KC patients were 45 ± 17.7, 48 ± 7.8 and 26 ± 15.6 years respectively. CCT measurements using USP, Pentacam, ORA revealed: 552 ± 26.2 μ, 562 ± 23.3 μ and 569 ± 29.7 μ for normal eyes, 559 ± 13.4 μ, 570 ± 22.6 μ, and 587 ± 27.6 μ for POAG eyes, and 482 ± 17.7 μ, 505 ± 7.8 μ and 516 ± 8.5 μ for KC eyes respectively. It was noticed that, readings using USP shows reduced values in comparison to two other machines. USP and Pentacam were relatively comparable machines. Conclusion The measurements of CCT using ultrasound and Pentacam instruments had significant linear correlations with one another. Both methods had highly satisfactory measurement repeatability. Reading using ORA gives higher values.

Comparison of Central Corneal Thickness Measurements with a Rotating Scheimpflug Camera, a Specular Microscope, Optical Low-Coherence Reflectometry, and Ultrasound Pachymetry in Keratoconic Eyes

Objective: To compare central corneal thickness (CCT) measurements with a rotating Scheimpflug camera (RSC), noncontact specular microscopy (SM), optical low-coherence reflectometry (OLCR), and ultrasonic pachymetry (UP) in keratoconus (KC) patients. Method: In this prospective study, four CCT measurements taken with an RSC, SM, OLCR, and UP were compared in 81 eyes of 44 consecutive KC patients. The KC patients were divided into four subgroups according to Amsler-Krumeich’s KC classification. Results: The RSC and UP measurements of the CCT were not statistically significant in all the groups. Comparison of the SM vs. the OLCR measurements yielded statistically significant differences in all the KC patients and in all KC stages. In all the KC patients, RSC and OLCR showed a high correlation coefficient factor (r = 0.87, p = 0.000). Conclusion: CCT measurements with RSC are comparable to those achieved with UP. Compared with the other devices, according to SM measurements, the central cornea is thicker in all keratoconic eyes and in all KC grades, and it is thinner according to OLCR. RSC, UP, SM, and OLCR should not be used interchangeably in keratoconic eyes.

Comparison of anterior segment measurements using rotating Scheimpflug imaging and partial coherence interferometry.

To compare central corneal thickness (CCT) and anterior chamber depth (ACD) measurements using rotating Scheimpflug imaging and partial coherence interferometry. As part of the first phase of Shahroud Eye Cohort Study with 5 190 subjects of 40 to 64 years of age, CCT and ACD were measured using Scheimpflug imaging with the Pentacam (Oculus, Inc., Lynnwood, WA, USA) and partial coherence interferometry with the Allegro BioGraph (Wavelight, Erlangen, Germany). After applying exclusion criteria, we had data of 4 387 subjects with a mean age of 50.7±6.2 years. Mean CCT with Pentacam and BioGraph were 528.6±33.2µm and 525.6±32µm respectively; the difference was statistically significant (P<0.001), but the correlation was high (R=0.920). Mean ACD measurements using Pentacam and BioGraph were 2.68±0.35mm and 2.62±0.33mm respectively; the inter-device difference was significant (P<0.001) with high correlation (R=0.944). The 95% limits of agreements between devices were -22.65µm to 28.61µm and -0.16mm to 0.29mm for CCT and ACD measurements, respectively. For both CCT and ACD, the BioGraph gave significantly lower values than the Pentacam (P<0.05). Despite the high inter-device correlation, the 95% limits of agreements were wide, and this may limit their interchangeability in measuring the CCT and ACD.

Central corneal thickness measurements in normal dogs: a comparison between ultrasound pachymetry and optical coherence tomography

To compare central corneal thickness (CCT) measurements obtained from normal canines using a spectral-domain optical coherence tomography device (SD-OCT) and an ultrasonic pachymeter. Fifteen clinically normal dogs. Dogs were briefly anesthetized with propofol. Central corneal thickness measurements were obtained from both eyes of each animal four times by one operator using a SD-OCT system. The CCT was automatically calculated using the pachymetry software generated from eight radial scans, 6 mm in length. Ultrasonic pachymetry was then performed in both eyes of each animal by one operator five times in succession. The CCT was recorded for each modality and compared statistically for agreement and bias. Fifteen dogs (seven castrated male, eight spayed female) with a mean age of 2.3 ± 1.3 years were examined. The mean CCT for all eyes examined via SD-OCT and ultrasonic pachymetry (velocity set at 1636 m/s) was 587.72 ± 32.44 μm and 598.54 ± 32.28 μm, respectively. Ultrasonic pachymetry consistently overestimated CCT as compared to OCT by a mean value of 10.82 μm (P < 0.0001). No significant difference in CCT was found based on the age or sex of the animal. There was no significant difference in CCT measurements between replicates performed by the same operator for each modality. The coefficient of variation within and between imaging modalities was low (range 0.63-2.5%). The intraclass correlation coefficient comparing methods was 0.92. Correlation between modalities was excellent; however, ultrasonic pachymetry set at a standard velocity of 1636 m/s overestimates CCT as compared to OCT.

Evaluation of central corneal thickness after cataract surgery, penetrating keratoplasty and long-term soft contact lens wear

The aim of this study was to compare central corneal thickness (CCT) between corneas of normal healthy eyes (cNHE), corneas of eyes that had undergone cataract surgery by clear corneal phacoemulsification with implantation of an intracapsular intraocular lens (cIOL), corneal grafts after penetrating keratoplasty (gPK) and corneas of long-term soft contact lens wearers (cCL). The study design was a consecutive cross-sectional trial. CCT was measured using rotating Scheimpflug camera (Pentacam, software version 1.16r04) in 80 cNHE, 79 cIOL, 46 gPK and 78 cCL. Analysis of variance (one-way ANOVA) was performed to compare differences of mean values between these four groups. Pearson's or Spearman's correlation coefficient (r) was determined between CCT value and age, follow up time after penetrating keratoplasty (timePK) or contact lens wearing time (timeCL). Means of CCT measurements were comparable between cNHE (mean CCT±standard deviation, 554±36μm), cIOL (551±40μm) and gPK (534±52μm) as determined by one-way ANOVA. Mean CCT values in cCL (537±37μm) were statistically significantly lower in comparison to cNHE (p=0.026, 95% CI=1.43-31.44). There was no linear correlation between age and CCT values of cNHE and cIOL (p=0.841, r=-0.031 and p=0.931, r=0.011, respectively). No linear relationship was determined between CCT values of cCL and timeCL (p=0.315, r=-0.125). CCT values of gPK did not correlate with timePK (p=0.738, r=0.054). The data reported here indicate that in the same statistical model among CCT values of cNHE, cIOL and gPK only long-term soft contact lenses (CL) wearer have significantly lower CCT measurements.

Comparison between Tonopachy and Other Tonometric and Pachymetric Devices

This study aimed to compare central corneal thickness (CCT) measurement by Tonopachy to that by Pentacam and ultrasound pachymetry, and intraocular pressure (IOP) measurement to that by Goldmann applanation tonometry (GAT). The reproducibility of CCT and IOP measurements by Tonopachy was also evaluated. In 104 eyes of 104 patients, CCT was measured by Tonopachy, Pentacam, and ultrasound pachymetry, and IOP was measured by Tonopachy and GAT. Each CCT and IOP measurement was compared using Pearson correlation, repeated measures analysis of variance, and Bland-Altman plots. In 30 subjects, CCT and IOP measurements by Tonopachy were repeated to evaluate intrasession and intraobserver variability. Both CCT and IOP measurements were highly correlated among all instruments used in this study. CCT measurements by three pachymeters were statistically different (p<0.0001). CCT measured by ultrasound pachymetry was lowest (541.7 ± 30.6 μm) whereas those by Tonopachy and Pentacam showed no difference (557.3 ± 34.3 and 558.0 ± 33.7 μm, respectively). Tonopachy overestimated CCT by 13.9 μm when compared with ultrasound pachymetry. There was a statistically significant difference between IOP measurements by two tonometers (p<0.0001); IOP measurement was higher by Tonopachy than by GAT (13.9 ± 4.2 and 12.5 ± 3.2 mm Hg, respectively). Tonopachy overestimated IOP measurements by 1.2 mm Hg compared with GAT. Intersession agreements for IOP and CCT measurements by Tonopachy were excellent (intraclass correlation, 0.902 and 0.962, respectively) with 95% limits of agreement ranging from -1.4 to 2.2 mm Hg and from -12.9 to 12.1 μm, respectively. Although CCT and IOP measurements obtained by Tonopachy were reproducible and showed close agreement with ultrasound pachymetry and Pentacam, and GAT, careful attention should be paid when comparing Tonopachy CCT measurement to ultrasound pachymetry or its IOP measurement to GAT as the values may not be interchangeable. Tonopachy is a reliable instrument for evaluating CCT and IOP.

Comparison Between Laser Scanning In Vivo Confocal Microscopy and Noncontact Specular Microscopy in Assessing Corneal Endothelial Cell Density and Central Corneal Thickness

To compare central corneal thickness (CCT) and endothelial cell density (ECD) with laser scanning confocal microscope Heidelberg Retina Tomograph (HRT) II Rostock Corneal Module and noncontact specular microscope Tomey EM-3000 and to assess intra- and interobserver agreement in normal corneas. This prospective study included 48 normals (69.6 ± 7.2 years, range: 55-80 years) who underwent CCT and ECD with both Tomey and HRT 3 times by 2 independent observers. Measurement differences between instruments, agreement between devices, and test-retest variability (TRV) were determined. Mean CCTs with Tomey and HRT were 529.4 ± 35.4 and 536 ± 37.6 μm (P = 0.06), respectively; average ECDs with Tomey and HRT were 2473.5 ± 242.2 and 2539.7 ± 338.6 cells per square millimeter (P = 0.04), respectively. The mean of the differences (HRT minus Tomey) was 6.5 ± 17 μm for CCT and 65 ± 135.1 cells per square millimeter for ECD. Differences between instruments were not related to CCT (P = 0.35), whereas significantly increased with increasing ECD (P = 0.0001). Intraexaminer TRV for Tomey and HRT were 3.9 ± 3.7 and 22.2 ± 18.4 μm for CCT and 73 ± 63.4 and 152.2 ± 148.4 cells per square millimeter for ECD, respectively; interexaminer TRV was 4.6 ± 4.2 and 23.8 ± 17.3 μm for CCT and 84.9 ± 72.3 and 159.8 ± 149.8 cells per square millimeter for ECD. HRT II Rostock Corneal Module and the Tomey EM-3000 showed an overall good intermethod agreement. HRT showed a tendency to slightly overestimate CCT measurements, significantly underestimate ECD measurements in eyes with a reduced cell density (< 2290 cells per square millimeter), and overestimate ECD in eyes with a high cell density. Both instruments showed low intra- and interobserver TRV for both CCT and ECD measurements, which tended to be less for Tomey.

Comparison of anterior segment measurements with rotating Scheimpflug photography and partial coherence reflectometry

To compare central corneal thickness (CCT), anterior chamber depth (ACD), and keratometry (K) readings measured using optical low-coherence reflectometry (OLCR) biometry and high-resolution rotating Scheimpflug photography. Eye Hospital of Wenzhou Medical College, Wenzhou, China. Comparative case series. The CCT, ACD endothelium to lens, ACD epithelium to lens, and K (mean; in flattest meridian; in steepest meridian) were measured 5 times using the LenStar/Biograph OLCR biometer and 3 times with the Pentacam Scheimpflug system in eyes of healthy volunteers. Concordance was evaluated using paired t tests, the Pearson correlation, and Bland-Altman analyses. The CCT, ACD endothelium to lens, and ACD epithelium to lens measured with the Scheimpflug system were slightly, albeit significantly, higher than with the OLCR biometer (P<.05); the respective 95% limits of agreement (LoA) were -8.2 μm to 15.7 μm, -0.11 to 0.15 mm, and -0.13 to 0.17 mm. However, the Scheimpflug system gave significantly flatter readings for K in the flattest meridian (95% LoA, -0.54 to 0.32 diopters [D]), K in the steepest meridian (95% LoA, -0.63 to 0.45 D), and mean K (95% LoA, -0.53 to 0.33 D) (P<.001). The CCT, ACD, and K readings were all highly correlated between the 2 devices (r >0.95, P<.001). The CCT and ACD measurements with the OLCR biometer and Scheimpflug system can be used interchangeably in healthy young subjects. However, for K measurements, these devices have wide LoA so may not be interchangeable under certain clinical circumstances.

Central corneal thickness measurements after myopic photorefractive keratectomy using Scheimpflug imaging, scanning-slit topography, and ultrasonic pachymetry

To compare central corneal thickness (CCT) measurements obtained with a dual Scheimpflug camera system (Galilei), a scanning-slit topographer (Orbscan II), and an ultrasound (US) pachymeter (SP-2000) after photorefractive keratectomy (PRK) for myopia. Ophthalmic Research Center, Labbafinejad Medical Center, Tehran, Iran. This prospective study enrolled patients who had PRK to correct myopia or myopic astigmatism and a postoperative follow-up of at least 5 months. The CCT was measured in a single session using Scheimpflug imaging, scanning-slit topography, and US pachymetry. Data were analyzed with paired t tests, linear regression, and Bland-Altman plots. The mean CCT in the 100 eyes (50 patients) was 524.06 microm +/- 38.56 (SD) with Scheimpflug imaging, 505.92 +/- 47.35 microm with scanning-slit topography, and 496.97 +/- 42.74 microm with US pachymetry. The lower to upper 95% limits of agreement (LoA) with US pachymetry were 2.4 to 51.8 microm for Scheimpflug imaging and -22.2 to 40.1 microm for scanning-slit topography. After application of a correction factor (0.95), the mean corrected Scheimpflug CCT measurement was 497.33 +/- 36.59 microm and the lower to upper 95% LoA with US pachymetry were -25.9 to 25.5 microm. The acoustic factor for scanning-slit topography was 0.94. The CCT measurements in eyes that had PRK were thicker with Scheimpflug imaging than with US pachymetry or scanning-slit topography in the late postoperative period. With application of a correction factor, the Scheimpflug measurements were closer to US pachymetry values and had better agreement than scanning-slit topography.

Pachymetric mapping with Fourier-domain optical coherence tomography

To evaluate the repeatability of Fourier-domain optical coherence tomography (OCT) pachymetric mapping and compare central corneal thickness (CCT) measurements by OCT, ultrasound pachymetry, and scanning-slit tomography. Doheny Eye Institute, University of Southern California, Los Angeles, California, USA. A Fourier-domain OCT system was used to map the corneal thickness in normal eyes with scans centered on the corneal vertex or the pupil. Repeatability of central and pericentral map sectors was assessed by pooled standard deviation. The CCT measurements were compared between the OCT, ultrasound, and scanning-slit devices. Pupil centration (SD: 1.3 microm central, 1.8 to 3.8 microm pericentral) provided better repeatability than vertex centration (SD: 1.7 microm central, 2.4 to 5.7 microm pericentral) in all sectors (P<.035). The mean CCT was 536.9 microm +/- 27.0 (SD) by OCT, 556.6 +/- 30.5 microm by ultrasound, and 537.2 +/- 32.6 microm by scanning-slit tomography (acoustic factor 0.92). The CCT measured by OCT was significantly thinner than by ultrasound pachymetry (P = .007; mean difference -19.7 microm; 95% limits of agreement [LoA], -40.4 to 0.9 microm) but not than by scanning-slit tomography (P = .2637; mean difference -0.3 microm; 95% LoA, -24.0 to 23.5 microm). The CCT by OCT correlated well with ultrasound and scanning-slit CCTs (r = 0.940 and r = 0.934, respectively). Pachymetric mapping with Fourier-domain OCT was highly repeatable. Repeatability was better with pupil-centered scans than with corneal vertex-centered scans. Ultrasound pachymetry, Fourier-domain OCT, and scanning-slit tomography should not be used interchangeably for CCT assessment.

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

To compare central corneal thickness (CCT) measurements by the Orbscan II device, contact ultrasound (US) pachymetry, and the noncontact Artemis 2 scanning US system. Department of Ophthalmology, Weill Cornell Medical College, New York, New York, USA. 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. 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. 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.

Comparison and reproducibility of corneal thickness and curvature readings obtained by the Galilei and the Orbscan II analysis systems

To compare central corneal thickness (CCT) and keratometry readings using the Galilei dual Scheimpflug analyzer, the Orbscan II anterior segment analysis system, and the Sonogage ultrasound (US) pachymeter. Lucerne Eye Clinic, Cantonal Hospital, Lucerne, Switzerland. In a prospective single-center study, 85 eyes of 45 healthy volunteers were examined with the Orbscan II and Galilei systems in random order followed by Sonogage US pachymetry. The CCT and keratometry measurements were compared using a paired t test. To assess the intraobserver and interobserver reproducibility of the 2 keratometers, 9 volunteers were examined 3 times by 4 independent observers and the intraclass correlation coefficient (ICC) was calculated. The mean CCT was 551.7 microm+/-36.6 (SD) with the Galilei, 554.8+/-45.1 microm with the Orbscan II, and 558.5+/-38.4 microm with the Sonogage. The CCT readings of the Galilei and Orbscan II did not differ significantly (P= .12). The mean keratometry readings with the Galilei and Orbscan II were similar, although both the steep (Ks) and flat (Kf) axes tended to be flatter with the Galilei system. The ICCs for CCT, Kf, and Ks were high with both keratometers (0.98, 0.97, 0.84 for Galilei and 0.97, 0.96, 0.95 for Orbscan II, respectively), indicating that variation in measurements was mainly due to true subject-to-subject variation rather than observer error. Keratometry and pachymetry readings with the Galilei and Orbscan II systems showed good concordance and high reproducibility, which would allow the examinations to be delegated to nonmedical personnel.