Angle Kappa agreement between Scheimpflug tomography, combined placido Scheimpflug and combined slit scanning placido systems.

PURPOSE: To compare the measured or calculated angle Kappa using Oculus pentacam HR, Sirius and Orbscan III devices. PATIENTS AND METHODS: A prospective randomized cohort study, conducted on 47 eyes of 47 healthy orthotropic individuals, with an age range of 18-50 years and a corrected Snellen's distance visual acuity (CDVA) of 0.8 decimal or better. Angle Kappa is assessed directly using Orbscan® III software version 1.8.165.1. (Bausch and Lomb Rochester, New York, United States), while Pentacam® HR 1.21r.65 (Oculus Optikgeräte GmbH, Wetzlar, Germany) and Sirius device (CSO, version 3.2.1.60, Costruzione Strumenti Oftalmici, Florence, Italy) were used to calculate angle kappa indirectly. RESULTS: Least mean difference of estimated angle Kappa was between Orbscan and Pentacam devices (- 0.18° ± 1.8), and it was statistically insignificant (p value = 0.1294). Differences between both Orbscan and Sirius, and Pentacam and Sirius were statistically significant (p value = 0.0004 and < 0.0001 consecutively). Bland Altman analysis showed a 95% confidence interval between Orbscan III and Pentacam of - 3.76 to 3.4 and between Orbscan III and Sirius of - 3.79 to 2.26. CONCLUSION: Pentacam parameters can be used as a reliable method to calculate angle kappa indirectly, without usage of any additional measurements from other machine. Sirius device parameters could also be used, but with less accurate results. A simple modification to those devices' software to calculate it, and incorporate it in the printout is possible, and highly recommended.

Comparison of white-to-white measurements using four devices and their determination of ICL sizing.

BACKGROUND: To compare the measurements obtained from the Orbscan II, IOLMaster 700, Pentacam AXL, and Castroviejo caliper and their effects on calculating the recommended implantable collamer lens (ICL) size and postoperative vault measurements. METHODS: This is a retrospective cross-sectional study of patients who underwent ICL surgery by a single surgeon from March 1, 2018 to July 31, 2021. Records were reviewed for the anterior chamber depth (ACD) and white-to-white (WTW) measurements obtained from the Orbscan II, IOLMaster 700, Pentacam AXL, and Castroviejo caliper (WTW only). These were used to calculate the recommended ICL size. The actual ICL size implanted, and vault measurements obtained one month postoperatively were also collected. RESULTS: One hundred seven eyes with a mean age of 27.9 ± 7.7 years were included in the study. Mean WTW measurements were significantly different between devices (P < 0.0001), with the IOLMaster 700 having the highest value (12.14 ± 0.04 mm) and the caliper having the lowest value (11.45 ± 0.04 mm). Mean ACD measurements were the lowest in Orbscan II (3.12 ± 0.25 mm) and the highest in Pentacam AXL (3.16 ± 0.24 mm). The Pentacam AXL produced an ICL size similar to the Orbscan in 69.2% of eyes. The IOLMaster yielded an ICL measurement one size larger than Orbscan-based calculations in 64.5% of eyes. Using the Orbscan WTW and ACD, the desired vault of 0.25 to 0.75 mm and 0.25 to 1.00 mm was achieved in 70% and 91% of eyes, respectively. Substituting caliper WTW to IOLMaster 700 or Pentacam AXL WTW increases the percentage of achieving the desired vault to 80%, similar to the Orbscan. CONCLUSIONS: The Orbscan II, IOLMaster 700, and Pentacam AXL cannot be used interchangeably for calculating ICL sizing. Combining the WTW from caliper measurement with the ACD of the IOLMaster 700 or Pentacam AXL could improve ICL sizing and achieve a higher percentage of eyes with the desired vault.

Effect of congenital ptosis correction on corneal topography- A prospective study.

Purpose: The aim of this study was to evaluate the changes in corneal topography, cycloplegic refraction, and best-corrected visual acuity (BCVA) after ptosis correction surgery in patients with congenital ptosis. Methods: Our study represents a prospective observational study conducted on 27 eyes of 21 patients with congenital ptosis. All patients underwent complete ophthalmological evaluation, cycloplegic refraction, and baseline Orbscan prior to ptosis surgery. At 6 months postoperative review, the cycloplegic refraction and Orbscan were repeated to evaluate the changes in these parameters. The main outcome measures in our study were Steepest K, Inferior-Superior Asymmetry (I-S Asymmetry), cycloplegic refraction and BCVA. Results: A significant decrease in Steepest K postoperatively (P < 0.001) was noted. Superior K and Inferior K also decreased, but the decrease in Inferior K was statistically significant (P = 0.044). However, change in I-S Asymmetry was not significant. Variation in BCVA, and cycloplegic sphere and cylinder was minimal. Sim K astigmatism, Surface Regularity Index, I-S Asymmetry and Central Corneal Thickness did not show significant variation. Conclusion: Ptotic eyelid constantly presses on the cornea causing significant changes in corneal contour and surface remodeling. This pressure when relieved, results in significant flattening and regression of anterior corneal surface to its near normal anatomy. This further resulted in improvement of corneal surface irregularity and symmetry.

Repeatability of Orbscan III for anterior segment parameters in normal eyes.

PURPOSE: Assessment of repeatability of Orbscan III in measuring steep keratometry (sKm), flat keratometry (fKm), thinnest corneal thickness (TCT), anterior chamber depth (ACD), white-to-white diameter (WTW) and 3 mm and 5 mm zonal irregularity in healthy eyes. METHODS: In this prospective observatioanl study 100 eyes of 50 participants underwent three consecutive scans on Orbscan III by a single examiner with a gap of 5 minutes between scans. Statistical analysis was performed to assess the repeatability of sKm, fKm, TCT, WTW, ACD and parameters of 3- and 5 mm irregularity. Within subject standard deviation (Sw), coefficient of variation (CoV) and test retest variability (TRT) was calculated for the commonly used parameters. WERE THE MAIN OUTCOME MEASURES.: The repeatability of sKm, fKm, TCT, WTW, ACD, 3 mm and 5 mm zonal irregularity on Orbscan III. RESULTS: Total of 50 patients (25 male and 25 female) who fulfilled inclusion and exclusion criteria were assessed. sKm, fKm, TCT and WTW were found to have a TRT of 0.31, 0.29. 21.5 and 0.27, respectively, and the ICC values were found to be over 0.9, denoting high repeatability. Repeat measurements of parameters of irregularity and ACD were found to be statistically similar, again denoting similarity between repeat measurements. CONCLUSION: Orbscan III provides repeatable measurements of Sim-k, anterior chamber depth, thinnest corneal thickness, 3 mm and 5 mm zonal irregularity and white-to-white diameter in healthy eyes.

Scheimpflug vs Scanning-Slit Corneal Tomography: Comparison of Corneal and Anterior Chamber Tomography Indices for Repeatability and Agreement in Healthy Eyes.

PURPOSE: To evaluate and compare the repeatability and agreement of Scheimpflug vs scanning-slit tomography of the cornea and the anterior chamber in terms of keratometric and tomographic indices in healthy eyes. METHODS: The 20 eyes of 10 healthy participants underwent 3 consecutive measurements using both Scheimpflug-tomography and scanning-slit tomography, diagnostic devices. Multiple corneal and anterior chamber tomographic parameters were recorded and evaluated to include corneal keratometry and its axis; corneal best-fit sphere (BFS), pachymetry mapping, angle kappa, anterior chamber depth (ACD), pupil diameter, and location. Repeatability for each device was assessed using the within each subject standard deviation of sequential exams, the coefficient variation (CV) and the intraclass correlation coefficient (ICC). Agreement between the two devices was assessed using Bland-Altman plots with 95% limits of agreement (LoA) and correlation coefficient (r). RESULTS: Both devices were found to have high repeatability (ICC>0.9) both in keratometric and other tomographic measurements. Scheimpflug tomography's repeatability though appeared superior in the average keratometry values, anterior and posterior BFS, thinnest corneal pachymetry value and location (p<0.05). Agreement: Statistically significant inter-device differences were noted in the mean values of K1, K2, BFS, ACD and thinnest corneal pachymetry (p<0.05). Despite the agreement differences noted, the two devices were well correlated (r>0.8) in respective measurements with Scheimpflug delivering consistently lower values than the scanning-slit tomography device. CONCLUSION: Scheimpflug-tomography repeatability was found to be superior to that of scanning-slit tomography in this specific study, in most parameters evaluated. Inter-device agreement evaluation suggests that reading from the two devices may not be used interchangeably in absolute values, yet they are well correlated with Scheimpflug delivering consistently lower values in most.

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 (CCTUSP), CCT determined by SST (after correction with acoustic factor) (CCTSSTC) was thicker by 7 µm in normal eyes (P < 0.001). There was no significant difference between CCTSSTC and CCTUSP (P = 0.128), but a thickness-dependent deviation in post-LASIK eyes (P = 0.003). The CCT determined by IRP (CCTIRP) was thicker than CCTUSP 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, CCTIRP significantly underestimated CCT compared to CCTSST 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.

Comparison of the efficacy of accelerated corneal cross-linking therapy in different pediatric age groups having progressive keratoconus.

PURPOSE: To report a comparison analysis of accelerated corneal cross-linking (A-CXL) treatment for progressive keratoconus patients in different pediatric age groups. STUDY DESIGN: Retrospective, cross-sectional. METHODS: Patients with progressive keratoconus aged ≤ 18 were retrospectively reviewed. Forty-one eyes of 41 patients were included in the study. Patients were divided into two groups according to their age (≤ 14 years and 15-18 years). All patients underwent epithelium-off A-CXL protocol. Acquired data were compared between the two groups. RESULTS: The mean age was 14.3 ± 1.8 (10-18) years. Twenty-five (61%) of the participants were male, and 16 (39%) were female. Twenty (49%) patients were separated into group 1 (≤ 14 years of age), and 21 (51%) were in group 2 (15-18 years). Age at presentation was found to be the only factor in anticipating the progression of keratoconus at the second postoperative year visit (p < 0.001). Progression in keratometric values was detected in seven (35%) of the 20 eyes in group 1, and one (4%) of the 21 patients in group 2 (Z = - 2.44, p = 0.014). CONCLUSION: Even if proper treatment is applied, the progression of keratoconus is likely in patients younger than 14 years of age. Instead of evaluating pediatric patients as a whole, closer follow-up and early treatment may be useful in younger age groups (≤ 14 years).

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.

Repeatability of curvature measurements in central and paracentral corneal areas of keratoconus patients using Orbscan and Pentacam.

PURPOSE: To determine the repeatability of curvature measurements in 5 corneal rings (1-5 mm from the corneal center) in keratoconus (KCN) patients using the Orbscan and Pentacam and to compare the values of these devices. METHODS: Forty-eight patients with a definite diagnosis of KCN were included in the study. Patients with any corneal scar or active disease or a history of ocular surgery were excluded from the study. The right eye of the patients was studied three times with the Orbscan and Pentacam. The repeatability of the curvatures of 5 corneal rings (1-5 mm from the corneal center) was evaluated using the Orbscan and Pentacam, and the agreement of their values was analyzed. RESULTS: The intraclass correlation coefficient (ICC) of three measurements was at least 0.94 (P < 0.0001) for the Orbscan and at least 0.88 (P < 0.0001) for the Pentacam in all corneal rings. According to the grade of KCN, the Orbscan had a low ICC in the 2 mm ring in grades 2 and 3 (ICC = 0.750 and 0.298, respectively). Repeated measures ANOVA showed no significant difference between the repeated measurements of the Orbscan and Pentacam in all corneal rings. The paired t-test showed a significant difference in curvature measurements in all rings except for the 5-mm ring between the two devices (P < 0.0001). The Bland-Altman plot showed a week agreement between these two devices in 1-4 mm corneal rings in curvatures more than 45 D. CONCLUSIONS: According to the results of this study, keratometry readings are highly repeatable in Pentacam and Orbscan devices in all corneal rings. Despite the high correlation between curvature measurements of the Orbscan and Pentacam, there was a significant statistical and clinical difference between the results of two devices in all corneal rings (except the 5-mm ring), and the curvature measurements of the Pentacam were steeper than Orbscan measurements.

Comparison between Pentacam HR and Orbscan II after Hyperopic Photorefractive Keratectomy.

PURPOSE: The aim of this study was to determine the agreement between Pentacam HR (Scheimpflug imaging, Oculus) and Orbscan II (scanning slit topography, Bausch and Lomb) in measuring corneal parameters after photorefractive keratectomy (PRK) for hyperopia. METHODS: In this prospective cross-sectional study, 38 hyperopic eyes undergoing PRK were examined before refractive surgery and 8 to 10 months postoperatively using Pentacam HR and Orbscan II. Ultrasound (US) pachymetry was also used to measure central corneal thickness (CCT). The radius of anterior (A-) and posterior (P-) best-fit sphere size (BFS), central elevation (CE), and anterior maximum tangential power in 3 mm (TG3) and 3-5 mm (TG5) zones, anterior chamber depth (ACD), and central corneal thickness (CCT) were collected and used in the analyses. To study the agreement between the measurements made by the two devices, the method described by Bland and Altman was used and the 95% limits of agreement were calculated. RESULTS: The 95% limits of agreement show reasonable agreement between the measurements by Pentacam HR and Orbscan II for A-BFS, P-BFS, A-TG3, and CCT, but not for A-CE, P-CE, A-TG5, or ACD. CCT values obtained by both Pentacam HR and Orbscan II correlated well with the values determined by US pachymetry. CONCLUSION: Pentacam HR and Orbscan II after PRK for hyperopia show reasonable agreement for determining A-BFS, P-BFS, A-TG3, and CCT, but not for A-CE, P-CE, A-TG5, or ACD. CCT measurements with Pentacam HR have reasonable agreement with US pachymetry.

Scanning-slit topography in patients with keratoconus.

AIM: To evaluate the anterior and posterior corneal surfaces using scanning-slit topography and to determine the diagnostic ability of the measured corneal parameters in keratoconus. METHODS: Orbscan II measurements were taken in 39 keratoconic corneas previously diagnosed by corneal topography and in 39 healthy eyes. The central minimum, maximum, and astigmatic simulated keratometry (K) and anterior axial power values were determined. Spherical and cylindrical mean power diopters were obtained at the central and at the steepest point of the cornea both on anterior and on posterior mean power maps. Pachymetry evaluations were taken at the center and paracentrally in the 3 mm zone from the center at a location of every 45 degrees. Receiver operating characteristic (ROC) analysis was used to determine the best cut-off values and to evaluate the utility of the measured parameters in identifying patients with keratoconus. RESULTS: The minimum, maximum and astigmatic simulated K readings were 44.80±3.06 D, 47.17±3.67 D and 2.42±1.84 D respectively in keratoconus patients and these values differed significantly (P<0.0001 for all comparisons) from healthy subjects. For all pachymetry measurements and for anterior and posterior mean power values significant differences were found between the two groups. Moreover, anterior central cylindrical power had the best discrimination ability (area under the ROC curve=0.948). CONCLUSION: The results suggest that scanning-slit topography and pachymetry are accurate methods both for keratoconus screening and for confirmation of the diagnosis.

Corneal thickness measurements with Scheimpflug and slit scanning imaging techniques in keratoconus.

PURPOSE: To determine the repeatability of corneal thickness measurements with Scheimpflug (Pentacam) and slit scanning (Orbscan) imaging techniques in different grades of keratoconus. METHODS: This study was conducted as a cross-sectional research. Imaging with Orbscan and Pentacam was performed on patients with different grades of keratoconus. With each device, 3 measurements were taken at 10 min intervals. Repeatability indices in different grades of keratoconus were calculated for each device. RESULTS: Seventy-four eyes of 42 keratoconus patients were enrolled. Repeatability index (RI) of central corneal thickness (CCT) measurements in keratoconus grade 1, 2, and 3, were 12.8, 9.9, and 24.2 with Pentacam, and 23.6, 26.3, and 59.3 with Orbscan, respectively. For the thinnest point, these figures were 9.6, 8.0, and 35.7 with Pentacam and 19.5, 16.6, and 26.8 with Orbscan, respectively. The 95% limit of agreement (LOA) between Pentacam and Orbscan in measuring CCT and thinnest point in grade 1 were -25.5-47.7 mic and -33.3-32.8 mic, respectively. These results for grade 2 were -9.8-50.6 mic and -26.2-43.7 mic, respectively. In grade 3, 95% LoA were -20-64.6 mic and -31.4-60.5 mic, respectively. CONCLUSIONS: The results of this study showed that although repeated measurements of the CCT with Orbscan and Pentacam are strongly correlated, repeatability values of CCT measurements significantly decrease at more advanced grades of keratoconus. In all keratoconus grades, repeatability of CCT measurements was better with Pentacam than Orbscan. These findings indicate that corneal thickness readings have less validity in patients with advanced keratoconus.

The distribution of orbscan indices in young population.

PURPOSE: To determine the distribution of anterior eye biometry indices, such as keratometry pachymetry, anterior chamber depth (ACD), pupil diameter, and corneal diameter, as measured by Orbscan instrument in a young Iranian population. METHODS: A cross-sectional study was conducted, and subjects were selected through multistage cluster sampling from the students of Mashhad University of Medical Sciences. Objective and subjective refraction were performed followed by Orbscan imaging. RESULTS: A total of 1330 subjects were selected, 1121 of which participated in the study. After applying the exclusion criteria, the final analysis was performed on the data of 1051 subjects. The mean age of the participants was 26.1 ± 3.2 years (19-34 years old). The mean ± SD and 95% confidence interval (CI) of maximum keratometry, minimum keratometry, pupil diameter, corneal diameter, ACD, and central corneal thickness was 44.5 ± 1.7 (44.4-44.6), 43.1 ± 1.6 (43.0-43.2), 4.3 ± 0.9 (4.3-4.4), 11.7 ± 0.4 (11.7-11.7), 3.7 ± 0.3 (3.6-3.7), and 550.5 ± 35 (548.4-552.6), respectively. After adjusting for age and the mean spherical equivalent (MSE), maximum keratometry, minimum keratometry, central corneal thickness, and the thinnest pachymetry were statistically significantly higher in female subjects (P < 0.001) whilst the corneal diameter and ACD were higher in male subjects (P < 0.001). The pupil diameter and ACD showed statistically significant changes with age (P < 0.001). The MSE was only correlated with maximum keratometry and ACD (P < 0.001). CONCLUSION: In this study, the distribution of Orbscan measurements for the anterior segment parameters was reported in a large sample of the young Iranian population. Age, gender, and refractive error may affect the orbscan measurements.

Comparison of the Orbscan II topographer and the iTrace aberrometer for the measurements of keratometry and corneal diameter in myopic patients.

BACKGROUND: The purpose of this study was to compare corneal power and horizontal corneal diameter (white-to-white [WTW] distance) readings obtained by the Orbscan II topographer and the iTrace aberrometer. METHODS: Keratometry readings in the flat (Kf) and steep (Ks) meridians and WTW distance were measured with the Orbscan II and iTrace systems in 100 myopic patients. Statistical evaluation was performed using the paired t test, Pearson correlation, and Bland-Altman analysis for comparison of measurement techniques. RESULTS: The mean keratometry values with the Orbscan II and iTrace were 43.16 ± 1.44 and 42.64 ± 1.43 diopter (D), respectively (P < 0.0001). The mean WTW distance measurements with the Orbscan II and iTrace were 11.57 ± 0.34 and 11.33 ± 0.36 mm, respectively (P < 0.0001). For the measurement of corneal power, the 95 % limits of agreement (LoA) between the Orbscan II and iTrace were - 0.21 to 1.21 D for the flat meridian and - 0.15 to 1.25 D for the steep meridian. For the measurement of WTW distance, the range of the 95 % LoA between the two devices was 0.47 mm. CONCLUSIONS: For some clinical applications, the keratometry and WTW distance measurements obtained by the Orbscan II topographer and the iTrace aberrometer differed greatly and therefore were not interchangeable. TRIAL REGISTRATION: Clinical trials number: ChiCTR-OCS-14005077 (August 2nd, 2014).

Topographic Findings of the Porcine Cornea.

The porcine eye is often used as an ex vivo animal model in ophthalmological research. It is well suited for investigations concerning refractive surgery; however, corneal topography data are scarce. This study investigated the corneal topography and pachymetry of the porcine eye to provide further reproducible data. We evaluated freshly enucleated porcine eyes (n = 16) by performing computerized corneal topographies (Orbscan® IIz, Bausch and Lomb, Rochester, NY, USA). We assessed the steepest and flattest keratometric powers (K1 and K2, units in diopters (D)), astigmatism (D), white-to-white (WTW) diameter (mm), thinnest point pachymetry (µm), anterior and posterior best-fit sphere (BFS) (D), refractive power of the anterior and posterior curvatures, and total refractive power of the cornea (D). The mean keratometric powers were 39.6 ± 0.89 D (K1) and 38.5 ± 0.92 D (K2), and the mean astigmatism was 1.1 ± 0.78 D. The mean WTW diameter was 13.81 ± 0.83 mm, and the mean corneal thickness was 832.6 ± 40.18 µm. The BFSs were 38.14 ± 0.73 D (anterior) and 42.56 ± 1.15 D (posterior), and the mean refractive powers were 43.27 ± 1.08 D (anterior) and -5.15 ± 0.20 D (posterior); therefore, the mean of the total refractive power was 38.16 ± 1.00 D. The topography and pachymetry of the porcine cornea showed a specific configuration differing from the human cornea. When using animal ex vivo models such as porcine corneas for experimental corneal surgery, findings such as these should be considered.

Utility of the Swept Source Optical Coherence Tomography for Measurements of Central Corneal Thickness

PURPOSE: To evaluate the efficacy of swept source optical coherence tomography (SS-OCT) by comparing the measurement of central corneal thickness (CCT) to the measurement obtained using Orbscan II, anterior segment optical coherence tomography (AS-OCT) and ultrasound pachymetry. METHODS: One examiner measured the CCT in 65 eyes of 65 healthy subjects using Orbscan II, AS-OCT, SS-OCT and ultrasound pachymetry. The mean values and correlations were analyzed. RESULTS: The average CCT measurements obtained using Orbscan II, AS-OCT, SS-OCT and ultrasound pachymetry were 534.83 ± 38.46, 517.80 ± 32.48, 528.22 ± 33.71 and 528.02 ± 34.90 µm, respectively. A significant linear correlation was observed among Orbscan II, AS-OCT, SS-OCT and ultrasound pachymetry (r > 0.894, p < 0.001). There was no significant difference between the SS-OCT and ultrasound pachymetry (p = 0.782). CONCLUSIONS: The results of the 4 methods were significantly correlated and the SS-OCT reached a high level of agreement when CCT was determined using ultrasound pachymetry. The CCT measurements using SS-OCT is a better alternative for ultrasound pachymetry than Orbscan II and AS-OCT.

Analysis of corneal topography in patients with pure microphthalmia in Eastern China.

OBJECTIVES: To determine the typical corneal changes in pure microphthalmia using a corneal topography system and identify characteristics that may assist in early diagnosis. METHODS: Patients with pure microphthalmia and healthy control subjects underwent corneal topography analysis (Orbscan IIZ® Corneal Topography System; Bausch and Lomb, Bridgewater, NJ, USA) to determine degree of corneal astigmatism (mean A), simulation of corneal astigmatism (sim A), mean keratometry (mean K), simulated keratometry (sim K), irregularities in the 3 - and 5-mm zone, and mean thickness of nine distinct corneal regions. RESULTS: Patients with pure microphthalmia (n = 12) had significantly higher mean K, sim K, mean A, sim A, 3.0 mm irregularity and 5.0 mm irregularity, and exhibited significantly more false keratoconus than controls (n = 12). There was a significant between-group difference in the morphology of the anterior corneal surface and the central curvature of the cornea. CONCLUSIONS: Changes in corneal morphology observed in this study could be useful in borderline situations to confirm the diagnosis of pure microphthalmia.

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 (r (2)) of CCT, as measured by US pachymetry compared with other modalities, were: SL-OCT (r (2)=0.98, P<0.0001), specular microscopy (r (2)=0.98, P<0.0001), and Orbscan (r (2)=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 evaluation in healthy eyes with three different optical devices.

PURPOSE: To compare corneal pachymetry values measured by three different optical devices: Orbscan II, Pentacam HR and Sirius in healthy eyes. METHODS: The central corneal thickness (CCT) of 102 eyes of 102 healthy subjects (mean age of 33.09 ± 8.72 years and mean refractive defect -4.11 ± 4.74 D) was measured by three different physicians using Orbscan II, Pentacam HR and Sirius. The normality of the distribution was evaluated by with Kolmogorov-Smirnov test. The correlations between CCT obtained from each device and refractive defect and age were evaluated using the Pearson test. The differences were evaluated by the Student paired t-test using SPSS 18.0 (IBM Corp. Armonk, New York). RESULTS: Orbscan II provided significant (p < 0.0001) lower CCT measurements then both Pentacam HR (-13.66 ± 16.53 µm) and Sirius (-15.18 ± 17.16 µm); Sirius showed values slightly higher than Oculus Pentacam HR (+1.52 ± 6.21 µm) that appeared to be statistically significant (p < 0.015). CONCLUSIONS: The measurement of CCT by Sirius and Pentacam HR provides similar results. By contrast, the results obtained by Orbscan II are different from those obtained from both Sirius and Pentacam HR.

Comparison of corneal measurements in keratoconic eyes using rotating Scheimpflug camera and scanning-slit topography.

AIM: To compare the anterior segment measurements obtained by rotating Scheimpflug camera (Pentacam) and Scanning-slit topography (Orbscan IIz) in keratoconic eyes. METHODS: A total of 121 patients, 71 males (58.7%) and 50 females (41.3%) (214 eyes) with the diagnosis of keratoconus (KC) were enrolled in this study. Following diagnosis of KC by slit-lamp biomicroscopic examination, central corneal thickness (CCT), thinnest corneal thickness (TCT), anterior chamber depth (ACD), and pupil diameter (PD) were measured by a single examiner using successive instrumentation by Pentacam and Orbscan. RESULTS: There was no significant difference between the two instruments for the measurement of CCT and TCT. In contrast, scanning-slit topography measured ACD (3.46±0.40 mm vs. 3.38±0.33 mm, P=0.019) and PD (4.97±1.26 mm vs 4.08±1.19 mm, P<0.001) significantly larger than rotating Scheimpflug camera. The two devices made similar measurements for CCT (95% CI: -2.94 to 5.06, P=0.602). However, the mean difference for TCT was -6.28 (95% CI: -10.51 to -2.06, P=0.004) showing a thinner measurement by Orbscan than by Pentacam. In terms of the ACD, the mean difference was 0.08 mm (95% CI: 0.04 to 0.12, P<0.001) with Orbscan giving a slightly larger value than Pentacam. Similarly, Orbscan measurement for PD was longer than Pentacam (95% CI: 0.68 to 1.08, P<0.001). CONCLUSION: A good agreement was found between Pentacam and Orbscan concerning CCT measurement while comparing scanning-slit topography and rotating Scheimpflug camera there was an underestimation for TCT and overestimation for ACD and PD.