Comparison and repeatability of keratometric and corneal power measurements obtained by Orbscan II, Pentacam, and Galilei corneal tomography systems

Repeatability of Scheimpflug-Placido camera in mild dry eye versus normal eyes according to the topographical position of the cornea

We aimed to investigate the repeatability of various corneal measurements according to topographical location in the entire cornea measured by dual rotating Scheimpflug-Placido camera and to explore the differences in repeatability between patients with mild dry eye and those with normal eyes. In both the normal and dry eye groups, divided based on BUT or the height of the tear film, there were no statistically significant differences in the ratio of unacceptable variation (RUV) and ICC. The consistency of the examination of the anterior and posterior refractive values and corneal thickness according to the corneal location, measured three times repeatedly using the Galilei anterior segment camera, was high. There was no difference based on the height of the tear film or the tear film break-up time. However, caution is needed when interpreting the values of the anterior corneal refractive values, as there can be changes of more than 0.5D within 3 mm of the central area.

Reliability and Agreement of Keratometry Measurements Obtained With Eye Surface Profilometry and Partial Coherence Interferometry

PURPOSE

The aim of this study was to assess the repeatability of keratometry parameters obtained using the Eye Surface Profiler (ESP) system and their agreement with the IOL Master 500 device.

METHODS

Seventy-one eyes of 71 healthy participants were evaluated. Three repeated measurements were performed using the ESP system. Simulated keratometry in the flat (SimKf) and steep (SimKs) meridians, astigmatism, and axis were obtained. The same parameters were measured using the IOL Master 500 device. The J0 and J45 vector components of the astigmatism were calculated. The intrasession repeatability was analyzed using within-subject SD (Sw) and intraclass correlation coefficient (ICC). Agreement was assessed using paired statistical tests and the Bland-Altman method.

RESULTS

The Sw was 0.07 mm, 0.04 mm, 0.51 D, 0.33 D, and 0.22 D, and the ICC was 0.96, 0.98, 0.74, 0.61, and 0.55 for SimKf, SimKs, astigmatism, J0, and J45, respectively. The mean difference and limits of agreement when comparing the ESP system with the IOL Master 500 device were 0.37 mm (0.08/0.66) for SimKf ( P < 0.001), 0.18 mm (0.00/0.35) for SimKs ( P < 0.001), -0.93 D (-2.42/0.56) for astigmatism ( P < 0.001), 0.51 D (-0.22/1.24) for J0 ( P < 0.001), and 0.06 D (-0.48/0.60) for J45 ( P = 0.09).

CONCLUSIONS

The ESP system provides consistent values for simulated keratometry, showing moderate consistency for astigmatism parameters. Contact lens practitioners should be aware that the ESP system and IOL Master 500 device provide different simulated keratometry from a clinically viewpoint.

Corneal Tomography in a Commercially Available Optical Coherence Tomography Device and Comparison With a Rotating Scheimpflug Camera

OBJECTIVE

To compare the outcomes of corneal tomography obtained with an anterior-to-posterior segment optical coherence tomography device (Revo, Optopol Technologies Sp. z o.o.) and a rotating Scheimpflug camera (Pentacam AXL, Oculus Optikgeräte, Wetzlar, Germany).

METHODS

In healthy subjects, agreement in stereometric parameters commonly used in cataract and refractive surgery was assessed. Comparison between the devices was performed using correlation coefficients, the Bland-Altman method, and a paired t test.

RESULTS

Results of right eyes of 78 patients (47 women) aged 25.24±5.56 years were analyzed. The flat and steep anterior keratometry values were significantly higher for Revo than Pentacam (43.65±1.58 D vs. 42.99±1.47 D; P = 0.000, and 44.53±1.57 D vs. 43.82±1.49 D; P =0.000, respectively) and showed excellent correlation ( r =0.978 and 0.974, respectively). The results for maximal keratometry manifested a higher difference (45.89±1.69 D vs. 44.27±1.51 D for Revo and Pentacam, P =0.000) but were also strongly correlated ( r =0.871). Revo showed significantly lower corneal thickness values than Pentacam, both for apex pachymetry (535.54±32.45 vs. 550.74±31.55 μm; P =0.000) and for thinnest pachymetry (522.58±32.16 vs. 547.25±31.95 μm; P =0.000). The correlation coefficients for anterior and posterior corneal elevation at the thinnest point showed weak positive correlation ( r =0.179 and 0.185), while the correlation for corneal asphericity was moderate ( r =0.317).

CONCLUSIONS

There was a significant difference between keratometric values obtained with Revo and the Pentacam AXL, although the measurements showed excellent correlation. Similar results were found for corneal thickness measurements, but not for corneal surface elevation and corneal asphericity.

Comparison of a New Scheimpflug Camera and Swept-Source Optical Coherence Tomographer for Measurements of Anterior Segment Parameters

INTRODUCTION

This study evaluated the differences and agreement between a new Scheimpflug camera (Scansys) and a swept-source anterior segment optical coherence tomographer (CASIA 2) for measurements of the anterior segment of the eye in normal subjects.

METHODS

This prospective study included 84 eyes from 84 normal adult subjects who underwent three consecutive measurements with the Scansys and the CASIA 2 in random order. The mean keratometry (Km), astigmatism magnitude (AST), J0, and J45 vectors for both anterior and posterior corneal surfaces, central corneal thickness (CCT), thinnest corneal thickness (TCT), and anterior chamber depth (ACD) were obtained by both devices. The difference between these two devices was assessed using paired t test and violin plots. Bland-Altman plots and 95% limits of agreement (LoAs) were used to evaluate agreement.

RESULTS

No statistically significant differences between the two devices were found for the anterior AST, anterior J45, and posterior J45 (P > 0.05). The remaining parameters were statistically significant (P ≤ 0.05), but the differences not clinically significant. The violin plots showed that the distribution and probability density of the measured parameters were similar for both devices. Bland-Altman plots revealed high agreement for the measured parameters between the Scansys and CASIA 2, with narrow 95% LoAs.

CONCLUSIONS

In terms of assessing parameters for the anterior segment, our study indicated that Scansys and CASIA 2 generally showed significant agreement. The two devices used in this study's assessment of all the parameters can be used interchangeably in refractive analysis.

Variability of CLMI-X parameters, zonal Kmax, and single-point Kmax in keratoconus progression

OBJECTIVES

To compare the repeatability of Cone Location and Magnitude Index expanded (CLMI.X) parameters of 2 mm diameter zone of greatest corneal curvature (Cspot-Axi) and 1 mm diameter zone of thinnest pachmymetry (Spot-Pach) with the maximum single point keratometry (Kmax), 3 mm Zonal Kmax (Z-Kmax3), and thinnest single point pachymetry (TP) in keratoconus (KC).

METHODS

In this Comparative repeatability study, data from 36 eyes of 36 normal individuals and 72 eyes of 72 KC patients (28 eyes with ≤50.0D and 44 eyes with >50.0D Z-Kmax3) were analyzed. For each enrolled eye, imaging was done 6 times (3 consecutive acquisitions with a half hour break). For each parameter, the within-subject standard deviation (Sw) was calculated from the data of the six exams.

RESULTS

In the normal group, Cspot-Axi-Sw was different from Kmax-Sw (p = 0.0004). Also, Z-Kmax3-Sw was different from Kmax-Sw (p = 0.0297). The difference between Cspot-Axi-Sw and Z-Kmax3-Sw was statistically significant (p = 0.0482). In the KC group, Sw were significantly different between Cspot-Axi and Kmax (p < 0.0001), and between Z-Kmax3 and Kmax (p < 0.0001). In the Z-Kmax3 ≤ 50.0D subgroup, Sw were different between Cspot-Axi and Kmax (p = 0.0002). In the Z-Kmax3 > 50.0D subgroup, Sw were different between Cspot-Axi and Kmax (p < 0.0001), and between Z-Kmax3 and Kmax (p < 0.0001). Sw differences between Spot-Pach and TP were not significant in any of the study groups (all P > 0.05).

CONCLUSIONS

In the diagnosis and follow up of KC, the zonal averages of Cspot-Axi and Z-Kmax3 are more reliable than the single point Kmax. The repeatability of Spot-Pach is similar to TP and both variables should suit the purpose equally.

Normative Topographic Anterior and Posterior Corneal Astigmatism: Axis Distribution and Its Relations with Ocular and Biometric Parameters

Corneal astigmatism correction is a key factor when planning refractive treatment for ametropies with intraocular lenses. We aim to obtain normative anterior and posterior corneal astigmatism (ACA and PCA, respectively) data in a local population and to describe their axis distribution and their association with other parameters. A total of 795 patients with no ocular diseases were evaluated with corneal tomography and optical biometry. Only data of the right eye were included. Mean ACA and PCA were 1.01 ± 0.79 and 0.34 ± 0.17 D, respectively. Vertical steep axis distribution was 73.5% for ACA and 93.3% for PCA. Axis orientation between ACA and PCA matched best for vertical orientation (especially 90° to 120°). Vertical ACA orientation frequency decreased with age, with a more positive sphere and less ACA. Vertical PCA orientation frequency increased with higher PCA. Eyes with vertical ACA orientation were younger and showed a greater white-to-white (WTW) measurement, anterior corneal elevations, ACA and PCA. Eyes with vertical PCA orientation were younger and showed greater anterior corneal elevations and PCA. Normative ACA and PCA data in a Spanish population were presented. Steep axis orientations presented differences with age, WTW, anterior corneal elevations and astigmatism.

Optical Biometry and IOL Calculation in a Commercially Available Optical Coherence Tomography Device and Comparison With Pentacam AXL

PURPOSE

Optical devices are the gold standard for ocular biometry; however, they are unable to obtain high-quality optical coherence tomography (OCT) images. The current study aimed to evaluate ocular measurements and intraocular lens (IOL) calculation used in an anterior/posterior segment OCT device and to compare the results with those of a validated biometer.

DESIGN

Prospective evaluation of a diagnostic tool.

METHODS

This study enrolled healthy subjects at the Hygeia Clinic, Gdańsk, Poland, between October 2021 and November 2021. All individuals had ocular biometry measured with a validated biometer (Pentacam AXL) and with a new module of an anterior/posterior segment OCT device (Revo 80, Optopol Technologies). All IOL calculations were performed for the right eye with keratometric values from the Pentacam for one IOL: the Alcon AcrySof IQ SN60WF, with plano target setting.

RESULTS

The mean age of the 144 participants was 25.23 ± 7.15 years. The axial length measured with Revo was longer than with Pentacam AXL (24.08 ± 1.13 vs 23.98 ± 1.13; P < .0001), a 0.10 ± 0.04 mm difference. This translated into a significantly lower IOL power to achieve emmetropia for all formulas (-0.34 ± 0.15, -0.32 ± 0.13, -0.34 ± 0.19, and -0.30 ± 0.15 for the Hoffer Q, Holladay I, Haigis, and SRK/T formulas, respectively). The study showed high agreement between the devices: nearly 90% of eyes were within ±0.50 diopters for all of the analyzed formulas (r > 0.99).

CONCLUSIONS

The present study demonstrates that the results of IOL calculation with the OCT biometer have a very strong correlation with those obtained with the Pentacam AXL; however, axial length measurements and calculated IOL power cannot be considered interchangeable.

Comparative Analysis of Corneal Parameters Performed with GalileiG6 and OCT Casia 2

BACKGROUNDS

To compare keratometry (Ks and Kf), astigmatism (Ast.), and the astigmatism axes (Ax.) of the posterior surface of the cornea; the total, central cornea thickness (CCT); and the thinnest corneal thickness (TCT) measured using two different measurement methods.

METHODS

Patients qualified for cataract surgery at the Chair and Clinical Department of Ophthalmology, Division of Medical Science in Zabrze, Medical University of Silesia, Katowice, Poland, were included in the study and monitored with the following two devices: OCT-CASIA2 and Dual Scheimpflug Analyzer GalileiG6. Our work was a randomized, prospective study in which compliance with the agreement of measurements between the devices was evaluated using the Bland-Altman method.

RESULTS

A total of 110 patients (62 females and 48 males) were examined. Overall, 100 eyes of patients that qualified for cataract surgery were enrolled in the study. No statistically significant difference was observed for Total-Ks and Total-Kf. A significant difference was observable for the following parameters: total Ks-ax, total Kf-ax, the total power of astigmatism, and in all parameters of the part of the cornea and corneal thickness (CCT and TCT).

CONCLUSIONS

The measurements obtained using Casia2 and the Dual Scheimpflug Analyzer GalileiG6 were significantly different and not interchangeable except for total Ks and Kf.

Agreement between a new swept-source ocular coherence tomography and a Placido disc-dual Scheimpflug ocular biometric devices

PURPOSE

To evaluate the agreement between two biometry devices, the Heidelberg Anterion and the Galilei G6 Lens Professional.

METHODS

Eyes were scanned with both biometry devices. Analysis of inter-device agreement was conducted for the following metrics: flat (K1), steep (K2) and mean K (Km) for anterior, posterior and total cornea, lens thickness (LT), central corneal thickness (CCT), anterior chamber depth (ACD), white to white (WTW) and axial length (AL). Generalised Estimating Equations were used to account for inter-eye correlation. Bland-Altman analysis was conducted to derive the mean difference (MD) and limits of agreement (LoA) between devices. Differences were deemed clinically significant if they would result in a change in post-operative refraction of 0.25D or more.

RESULTS

159 eyes of 91 patients were included. For the anterior cornea, no significant MD was found for K1 (-0.11D) and K2 (-0.10D), although a significant MD was found for Km (-0.10D). For posterior cornea, while there were no significant MDs between devices, the LoAs were wide for both posterior K1(-0.70, 0.68) and posterior K2 (-1.01, 1.29). For total corneal power, significant MDs were found in K1 (0.36D), and Km (0.26D) but not for K2 (0.17D). Significant MDs were found for LT (0.179mm), CCT (-0.005mm), ACD (-0.111mm) and WTW (-0.158mm), but not for AL (-0.021mm, p > 0.05).Conclusion: There are statistically but not clinically significant differences between Anterion and Galilei G6 Lens Professional in anterior Km, LT, CCT, ACD and WTW. Measurements of the posterior and total cornea are not interchangeable between devices.

Simulated keratometry and central corneal thickness measured in cats by autokeratometer, ultrasonic pachymeter, and Galilei G6™

OBJECTIVE

The aims of this study were to compare the central corneal thickness (CCT) measured by an ultrasonic pachymeter (SP-100, Tomey, Japão) versus the Galilei G6™ (Ziemer Ophthalmics System AG, Port, Switzerland) and to compare the simulated keratometry (SimK) measured by an autokeratometer (KM 500 Nidek) versus the Galilei G6™.

ANIMAL STUDIED

Eighteen mixed-breed cats, 10 males, and eight females, aged between 18 and 48 months, were evaluated (n = 36 eyes).

PROCEDURE(S)

The cats were manually restrained using a blanket. The operator held the autokeratometer close to the eye and measured the SimK. Next, one anesthetic eye drop was applied; the operator lightly touched the corneal using the ultrasound pachymeter and measured the CCT. At another moment, the cats were sedated using meperidine and xylazine and then evaluated using the Galilei. Student's t-test was employed to perform the statistical analyzes.

RESULTS

Considering the CCT, the ultrasound pachymeter provided mean ± SD of 623.03 ± 48.17 μm and the Galilei 617.34 ± 53.38 μm. The autokeratometer produced a SimK of 38.20 ± 0.84D (8.84 ± 0.20 mm) and the Galilei 38.37 ± 0.83D (8.80 ± 0.19 mm). The CCT and SimK did not differ statistically regardless of the device used.

CONCLUSION

To the best of the authors' knowledge, this is the first work to compare the CCT measured by the Galilei versus the ultrasonic pachymeter and to compare the SimK measured by the Galilei versus the keratometer in cats. No statistical difference was found considering the CCT and the SimK measured by the different devices.

Dual-Scheimpflug-Placido-disc corneal analysis in cats

OBJECTIVE

To evaluate the corneal topography and tomography of cats using a dual Scheimpflug and Placido disc device.

ANIMAL STUDIED

Sixteen mixed-breed cats (32 eyes).

PROCEDURE(S)

Cats were sedated using meperidine (4.3 mg/kg/IM) and xylazine (0.5 mg/kg/IM), and evaluated using the software Galilei™. Values assessed included anterior and posterior corneal curvature, total corneal power, and corneal thickness.

RESULTS

Ten males and six females aged between 18 and 48 months were evaluated. The simulated keratometry (SimK) was 38.37 ± 0.83D, mean posterior keratometry -4.89 ± 0.34D, and mean total corneal power 38.04 ± 0.94D. The mean central corneal thickness (CCT) was 617.34 ± 53.38 μm with a mean thinnest point of 583.74 ± 60.60 μm.

CONCLUSION

The Galilei™ examination was feasible in cats, enabling a detailed study of the cornea. To the best of our knowledge, this is the first study evaluating the corneal topography and tomography of cats using a device that integrates data from a dual Scheimpflug and Placido disc system.

Agreement between two swept-source ocular coherence tomography biometry devices

PURPOSE

To assess the agreement between two swept-source ocular coherence tomography (SS-OCT) biometry devices, Anterion and IOLMaster 700.

SETTING

Tertiary referral centre, Brisbane, Australia.

DESIGN

Prospective comparative study.

METHODS

Bland Altman analysis was used to assess agreement between devices for flat (K1), steep (K2) and mean (Km) keratometry for anterior, posterior and total cornea, lens thickness (LT), anterior chamber depth (ACD), central corneal thickness (CCT), white to white (WTW) and axial length (AL). Generalised Estimating Equations were used to control for within-patient between-eye correlations. Inter-device differences were considered clinically significant if they were likely to alter the spherical refractive outcome by 0.25D or more.

RESULTS

159 eyes of 91 patients (41 male, 50 female) were included. Statistically significant differences were found for K1, K2 and Km for anterior, posterior and total cornea. When Anterion was compared to IOLMaster 700, the mean differences were as follows: anterior K1: -0.17D, anterior K2: -0.18D, anterior Km: -0.17D, posterior K1: -0.38D, posterior K2: -0.36D, posterior Km: -0.37D, total K1: -0.65D, total K2: -0.82D, total Km: -0.74D. The difference in posterior and total K metrics were clinically significant. Statistically significant differences were noted for LT: 0.159mm, CCT: -0.004mm, ACD: 0.054mm and WTW: -0.152mm, although these were not found to be clinically significant. There was no significant difference between devices for AL.

CONCLUSION

This study found statistically and clinically significant differences for both posterior and total keratometry between Anterion and IOLMaster 700. Posterior and total corneal parameters cannot be considered interchangeable between devices.

Prediction of residual astigmatism in cataract surgery at different diameter zones using optical biometry measurement

The studies for astigmatism prediction error at different diameters using optical biometry are scant. We investigated patients who underwent cataract surgery with monofocal, nontoric intraocular lens (IOL) from 2017 through 2019 in a medical center. Patients with prior refractive surgeries, corneal opacity, or surgical complications were excluded. Corneal astigmatism (CA) was measured using AL-Scan at 2.4- and 3.3-mm diameter zones and calculated using the Barrett toric calculator preoperatively and postoperatively. The mean absolute error and centroid prediction error for the two zones were computed using double-angle plots. In total, 101 eyes of 76 patients were analyzed. Mean patient age was 68.7 ± 9.3 years and mean preoperative CA power was 0.7 ± 0.5 D. The overall centroid prediction error a 3.3 mm (0.09 ± 0.58 D@25) was significantly lower than that at 2.4 mm (0.09 ± 0.68 D@87) on the X-axis (P = 0.003). The 3.3-mm measurement also had a lower centroid prediction error than the 2.4-mm did for eyes with against-the-rule (ATR) and oblique astigmatism (P = 0.024; 0.002 on X-axis, respectively). The 3.3-mm measurement provided a more accurate CA estimation than the 2.4-mm did, particularly for ATR astigmatism. Diameter zone and astigmatism type should be considered crucial to precise astigmatism calculation.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Agreement between swept-source optical biometry and Scheimpflug-based topography measurements of posterior corneal curvature

PURPOSE

To evaluate agreement of posterior corneal curvature parameters between a swept-source optical coherence tomography-based biometer (IOLMaster 700) and Scheimpflug topography (Pentacam HR) in healthy, myopic eyes.

SETTING

Department of Ophthalmology, Osmangazi Aritmi Hospital, Bursa, Turkey.

DESIGN

Retrospective study.

METHODS

In this study, 59 eyes of 59 patients who applied as candidates for refractive surgery were included. Measurements of the posterior corneal curvature were performed using IOLMaster 700 and Pentacam HR. J0 and J45 vector components were calculated using astigmatic values. Posterior corneal keratometry (K) measurements at flat (K flat) and steep (K steep) axes and J0 and J45 values were compared between the 2 devices. The agreement between the devices was analyzed using the Bland-Altman method. Intraclass correlation coefficients and within-subject SD were calculated to assess the repeatability.

RESULTS

59 eyes of 59 patients were included in this study. The IOLMaster 700 provided significantly flatter K flat and K steep values (P < .001, for both). Significant differences were found in J0 and J45 values (P = 0.13 and P < .001, respectively). The mean differences between K flat, K steep, and J0 and J45 values were 0.49 diopter (D), 0.53 D, 0.04 D, and -0.05 D, respectively.

CONCLUSIONS

The IOLMaster 700 and the Pentacam HR could not be used interchangeably to measure K flat, K steep, and J0 and J45 values of the posterior corneal curvature in healthy, myopic eyes. Both devices showed high repeatability for posterior corneal curvature measurement.

Comparative analysis of measurements of the anterior segment and the axial length parameters of the eyeball obtained with optical and ultrasound technique

PURPOSE

To compare anterior chamber depth (ACD), keratometry (K1, K2), central corneal thickness (CCT), and axial length (AL) measured by four different devices.

MATERIAL AND METHODS

150 eyes qualified for cataract surgery were included in the study. Four devices: IOL Master 500, OCT CASIA2, Dual Scheimpflug Analyzer Galilei G6, and Quantel Compact Touch ultrasound biometer, were compared. The agreement of measurements between the devices was evaluated by the Bland-Altman method.

RESULTS

ACD was significantly different for Ultrasound and IOL Master 3 ± 0.33 3.12 ± 0.42 respectively Interclass correlation ecoefficiency (ICC):0.69 (95% confidence interval (CI): 0.62; 0.76) p < 0.001. A significant difference was observed between Casia and IOL while measuring K1, 43.5 ± 1.7 vs. 43.61 ± 1.56 ICC:0.84 (95%CI: 0.79; 0.87) and ACD parameters 2.65 ± 0.45 vs. 3.12 ± 0.42 ICC 0.68 (95%: 0.6; 0.75) and K2 42.51 ± 1.62 vs. 44.57 ± 1.59 ICC; 0.83 (95%CI:0.78; 0.87) p < 0.001. Similarly, measurements obtained by Casia, and Galilei were also different K1 43.5 ± 1.7 ICC:0.7 (95%CI:0.62; 0.76), CCT 546.35 ± 34.75 vs. 566.73 ± 37.92 ICC:0.88 (95%CI:0.84; 0.9) p < 0.001. Differences between Galilei and IOL master were not significant p values from 0.175 to 0.999 ICC 0.8 (95%CI:0.75; 0.85) to ICC 0.94 (95%CI:0.92; 0.95).

CONCLUSIONS

The measurements obtained from Casia, and Ultrasound were significantly different and not interchangeable except for IOL master and Galilei.

Agreement and Repeatability of Corneal Thickness and Radius among Three Different Corneal Measurement Devices

SIGNIFICANCE

Corneal refractive surgery screening, orthokeratology, and contact lens fitting require accurate estimation of the corneal thickness and curvature. We found that any of the imaging devices used in this study can be used to image a healthy myopic cornea, which is essential to screen for corneal ectasia.

PURPOSE

This study aimed to compare agreement and repeatability of corneal thickness and radius measurements obtained using Scheimpflug imaging (Pentacam HR), swept-source optical coherence tomography (Casia SS-1000), and Placido-Scheimpflug tomography (Topographic Modeling System, version 5 [TMS-5]).

METHODS

Sixty eyes of 60 subjects with myopia were measured with Casia, TMS-5, and Pentacam for their central corneal thickness (CCT), thinnest corneal thickness, central corneal radius of the steep meridian (Ks), central corneal radius of the flat meridian (Kf), mean central corneal radius (Km), and anterior and posterior best-fit spheres. Two readings were obtained from each instrument. Central corneal thickness was also measured with ultrasound pachymetry. Intraclass correlation coefficient, repeatability coefficient, and coefficient of variation were calculated.

RESULTS

Repeatability coefficient, coefficient of variation, and intraclass correlation coefficient of CCT among the instruments ranged between 2.48 and 12.79, 0.17 and 0.86, and 0.98 and 1.00, respectively. Mean CCT measurements were similar between Casia, TMS-5, Pentacam, and ultrasound pachymetry (P = .13). Intraclass range of correlation for agreement was 0.95 to 0.99 for CCT among instruments. The range of 95% limits of agreement (LoAs) for ultrasound CCT was narrowest with Casia (31.94 μm). Casia-TMS-5 displayed a narrow range of 95% LoA for CCT (12.14 to -12.44), thinnest corneal thickness (12.31 to -11.31), and Ks (0.56 to -0.53), whereas Casia-Pentacam showed a narrow range of 95% LoA for Kf (0.56 to -0.42), Km (0.41 to -0.27), and anterior best-fit sphere (0.03 to -0.07). A significant difference in posterior best-fit sphere measurements was noted among all instruments (P = .01).

CONCLUSIONS

Casia, TMS-5, and Pentacam can be used interchangeably to measure corneal thickness and radius measurement in healthy eyes. Casia had the best agreement with ultrasound pachymeter CCT and exhibited the highest repeatability.

Agreement and repeatability of corneal tomography in healthy eyes using a novel Swept-Source optical coherence tomographer, a rotating Scheimpflug camera and a dual Scheimpflug-Placido system

PURPOSE

To investigate the accordance and repeatability of tomographic parameters measured by a novel Swept-Source optical coherence tomographer (SS-OCT, ANTERION), a rotating Scheimpflug camera (RSC, Pentacam) and a dual Scheimpflug-Placido system (DSP, Galilei G6).

SETTING

Department of Ophthalmology of Univ. Hospital Carl Gustav Carus, Dresden, Germany.

DESIGN

Prospective reliability analysis.

METHODS

Thirty randomly selected eyes of 30 healthy participants were enrolled in this study. Normal tomography were ensured by bilaterally evaluating appropriated parameters using RSC. All subjects received three consecutive measurements on each device by the same operator and in the uniform order RSC, SS-OCT and DSP. Anterior (ACP) and posterior (PCP) corneal parameters such as flat and steep keratometry and corneal thickness were analyzed. Repeatability was assessed by using a coefficient of repeatability (CR) and a coefficient of variation (CV). Agreement between RSC and SS-OCT as well as RSC and DSP were shown by Bland-Altman plots (BA).

RESULTS

CR of ACP did not exceed 0.5 D. There were no statistical differences in repeatability of ACP obtained from the three devices (P>0.05). For PCP and corneal thickness there was statistically significant higher repeatability mostly found for SS-OCT as opposed to RSC and DSP (P<0.05). For a wide range of analyzed parameters there were large limits of agreement (95%-LoA) found between the devices.

CONCLUSION

The SS-OCT showed highly repeatable measurements in healthy subjects regarding anterior, posterior and corneal thickness parameters. Repeatability of ACP did not differ between the devices. A mostly wide range of 95%-LoA prevents interchangeability between the devices.

Orbscan 3 Versus Pentacam HR: Evaluating the Possible Interchangeable Use of Various Parameters

PURPOSE

Many topography/tomography devices are available, and their interchangeable use is frequently questioned. This study aimed to compare the analogous indices of Orbscan 3 and Pentacam HR to detect whether the interchangeable use of the 2 devices is feasible.

METHODS

This retrospective study was conducted at Eye World Hospital, Giza, Egypt. Displays of Orbscan 3 (Bausch & Lomb; Technolas Perfect Vision GmbH) and Pentacam HR (Oculus Optikegrate) for 660 healthy right eyes were explored for various analogous indices. Bland-Altman plots with 95% limits of agreement (LoA) were used for comparisons.

RESULTS

The highest systematic error and lowest agreement existed in the front and back elevations from the best fit sphere (mean differences of 4.7 and 9.2 μm, respectively, and 95% LoA of -2.5 to 12.0 and -10.0 to 28.6, respectively). There was a relatively wide 95% LoA for each pachymetry at the corneal apex (-18 to 22 μm) and at the thinnest location (-22 to 22 μm), anterior chamber depth (-0.88 to 0.95 mm), flattest keratometry (-0.44 to 0.62 D), and steepest keratometry (-0.71 to 0.89 D). By contrast, the lowest systematic error and highest agreement existed for front and back best fit sphere radii of curvature (mean difference of 0.08 mm and 95% LoA of -0.08 to 0.24 and mean difference of 0.03 mm and 95% LoA of -0.17 to 0.23, respectively).

CONCLUSIONS

This study negates the accuracy of the use of devices interchangeably regarding most parameters. Therefore, examinations with the 2 devices should not be regarded comparable.

Repeatability of Zone Averages Compared to Single-Point Measurements of Maximal Curvature in Keratoconus

PURPOSE

To evaluate the repeatability of curvature zone averages centered on the point of maximum curvature (Kmax) compared to that of the single-point Kmax.

DESIGN

Comparative reliability analysis.

METHODS

Setting: American University of Beirut Medical Center, Beirut, Lebanon.

STUDY POPULATION

Sixty-five eyes of 65 adult keratoconus patients. Patients with other ocular disease, history of ocular surgery or trauma, and contact lens wear within 2 weeks of image acquisition were excluded.

OBSERVATION PROCEDURES

Eyes were evaluated with 3 consecutive scans using the Galilei dual Scheimpflug-Placido system.

MAIN OUTCOME MEASURES

Repeatability of axial and instantaneous Kmax single points, and zone averages with radii of 0.1-2.0 mm, centered on them. Repeatability was assessed by within-subject standard deviations, repeatability limits (r), and intraclass correlation coefficients.

RESULTS

Axial curvature zone averaging yielded clinically acceptable repeatability only in eyes with Kmax ≤50 diopters (D), for radii of 1.5 mm and 2.0 mm (r = 0.87 D and r = 0.76, respectively, vs r = 0.91 for the single-point axial Kmax). Compared to instantaneous Kmax, clinically acceptable repeatability was achieved with instantaneous zone averages of at least 1.5 mm radius in eyes with Kmax ≤50 D (r = 0.99 D and r = 0.70 D, respectively) and 2.0 mm radius in eyes with Kmax >50 D (r = 2.28 D and r = 0.87 D, respectively). For all eyes, the repeatability limit of the location of Kmax was 0.82 mm and 0.80 mm for axial and instantaneous curvature, respectively.

CONCLUSIONS

Instantaneous curvature zone averages centered on Kmax yielded a greater improvement in repeatability than axial zone averages and reached clinical adequacy with radii of at least 1.5 mm, for eyes with Kmax ≤50 D, and with a 2.0 mm radius for eyes with Kmax >50 D.

Corneal Topography for Intraocular Lens Selection in Refractive Cataract Surgery

The purpose of this review is to evaluate the usefulness of corneal topography to select premium intraocular lenses (IOLs), including aspherical IOLs, toric IOLs, and multifocal IOLs, in refractive cataract surgery. Corneal topography can detect corneal regular astigmatism, corneal irregular astigmatism (higher-order aberrations [HOAs]) including spherical aberration, and corneal shape abnormalities after corneal refractive surgery. Surgeons can explain to the patients with significant corneal HOAs about its effect on postoperative visual function before surgery. Multifocal IOLs should not be selected for such eyes. For eyes with abnormal corneal shape, appropriate IOL power calculation formulae can be applied. In the case of toric IOLs, regular astigmatism and corneal HOAs should be checked. Before implanting an aspheric IOL, it is ideal to confirm spherical aberration of the cornea is not below the normal range. Because corneal HOAs, abnormal corneal shape after corneal refractive surgery, corneal regular astigmatism, and corneal spherical aberration increase postoperative refractive errors and poor vision quality with premium IOLs, corneal topography before cataract surgery is helpful in screening patients who are not appropriate candidates for premium IOLs.

Repeatability and Interchangeability of Topometric, Anterior Chamber and Corneal Wavefront Data Between Two Scheimpflug Camera Devices

Purpose

This study aims to assess the intra-operator repeatability and correlation of the Pentacam HR (device 1) and Sirius (device 2) in measuring anterior segment parameters and to evaluate the agreement of their readings and therefore their interchangeability in a clinical setting.

Methods

This is a prospective non-randomized study was conducted on the right eyes of 102 subjects coming to Eye World Hospital, Giza, Egypt. With each machine, four scans were taken by a single examiner. Each device was used to measure keratometric indices, corneal thickness, anterior chamber depth, anterior chamber angle, corneal diameter and corneal optical aberrations.

Results

Both devices show high repeatability for corneal thickness, corneal diameter, anterior chamber depth and keratometric indices (except for maximum keratometry, where device 1 shows high repeatability and device 2 shows low repeatability). On the other hand, both devices show poor repeatability for anterior chamber angle, Q-values, root mean square, spherical, coma and trefoil aberrations. The readings of the two devices are strongly correlated as regards only keratometric indices, corneal thickness and anterior chamber depth. In addition, the readings of the devices are in good agreement as regards only keratometric indices (except maximum keratometry), corneal thickness, anterior chamber depth, anterior chamber angle, root mean square, spherical and trefoil aberrations.

Conclusion

Both devices showed variable intra-observer repeatability, with the device 1 showing slightly higher repeatability. Despite the similarity between some of the readings of the two devices, caution is advised before considering them interchangeable. We therefore do not recommend using them in alternation in refractive surgery.

Comparison of Anterior Segment Parameters and Axial Length Using Two Scheimpflug Devices with Integrated Optical Biometers

Purpose

To assess the repeatability of anterior segment parameters and axial length (AL) using Pentacam AXL and Galilei G6 and the agreement between both devices.

Materials and Methods

Eighty-four eyes of 84 participants were measured prospectively with two devices. Outcome measurements included corneal curvatures, anterior chamber depth (ACD), AL, pupil size, and white-to-white distance (WTW). Intra-device repeatability was assessed using intraclass correlation coefficient (ICC), within-subject standard deviation (Sw), test-re-test repeatability (TRT=2.77 Sw), and coefficient of variation (CoV). Agreement between two devices was analyzed using Bland-Altman plots.

Results

For each device, the Sw of corneal curvatures, ACD, and AL were lower than 0.25 D, 0.04 mm, and 0.04 mm, respectively. The ICC was higher than 0.90 in all parameters measured by Pentacam AXL, whereas three parameters measured by Galilei G6 (steep meridian at anterior and posterior cornea, and pupil size) were lower than 0.90. Comparing to Galilei G6, Pentacam AXL led to significantly lower mean anterior cornea curvatures (Km) with the mean difference (95% level of agreement; LoA) of -0.12 D (-0.36, 0.12, P<0.001). For ACD, there was no significant difference between the two devices. Pentacam AXL led to significantly lower AL, pupil size, and WTW, with the mean differences (95% LoA) of -0.04 mm (-0.35, 0.27), -0.18 mm (-0.71, 0.35), and -0.35 mm (-0.61, -0.10), respectively.

Conclusion

We found good repeatability of corneal curvature, ACD, and AL in both devices. Most parameters obtained from Pentacam AXL were statistically significantly different from those obtained from Galilei G6, except for steep meridians and ACD.

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.

Corneal Indices Determined with Pentacam in Possible Candidates for Corneal Refractive Surgery

Objective:

To describe the level of correlation of clinical refractive variables with corneal indices in Pentacam Scheimpflug tomography, demonstrate the usefulness of the study of corneal indices in the diagnosis of keratoconus (KC), and identify the corneal indexes with the greatest influence on the diagnosis of KC.

Methods:

A descriptive, retrospective, and cross-sectional study was conducted in 69 patients (138 eyes) with refractive disorders, possible candidates for corneal refractive surgery, at the Exilaser Ophthalmological Center, Cuenca, Ecuador, from March to August 2019. Corneal indices were studied using Pentacam. Statistical correlation methods, Levene’s test, Fisher’s exact test, Cramérs’ V coefficient, and multiple correspondence analyses were used.

Results:

The variables refractive cylinder and central keratometry had a direct correlation with the corneal indices (p<0.001). An inverse correlation was obtained between central pachymetry and corneal indices (p<0.001). A high level of dependence on central KC index (CKI) (Cramér V = 0.785) and KC index (KI) (Cramér V = 0.775) was obtained with the diagnosis of KC.

Conclusion:

Pentacam is a valuable tool in the analysis of corneal indices for the diagnosis of KC, given its high level of correlation with clinical refractive variables. The selection of candidates for refractive surgery, even when there is no diagnosis of KC, is strengthened with the analysis of the corneal indices. The indices with the most intense level of dependence with the diagnosis of KC are, in order, the following indices: CKI, KI, vertical asymmetry, minimum radius, and variation of the surface.

Biometric Measurement of Anterior Segment: A Review

Biometric measurement of the anterior segment is of great importance for the ophthalmology, human eye modeling, contact lens fitting, intraocular lens design, etc. This paper serves as a comprehensive review on the historical development and basic principles of the technologies for measuring the geometric profiles of the anterior segment. Both the advantages and drawbacks of the current technologies are illustrated. For in vivo measurement of the anterior segment, there are two main challenges that need to be addressed to achieve high speed, fine resolution, and large range imaging. One is the motion artefacts caused by the inevitable and random human eye movement. The other is the serious multiple scattering effects in intraocular turbid media. The future research perspectives are also outlined in this paper.

Analysis of Age, Gender, and Refractive Error-Related Changes of the Anterior Corneal Surface Parameters Using Oculus Keratograph Topography

Purpose

To assess refractive error, gender, and age-related differences in corneal topography of a normal population with Oculus Keratograph 4.

Methods

This cross-sectional study included a total of 500 normal eyes of 500 individuals with ages ranging from 10 to 70 years. All participants underwent detailed ocular examinations, including visual acuity measurement, slit-lamp examination, and refractive error evaluation. Slit-lamp examination was performed for all individuals to rule out apparent corneal diseases. Corneal topography parameters were assessed using Oculus Keratograph. The data were analyzed based on gender, refractive error, and age groups using independent sample t-test and one-way analysis of variance.

Results

Of a total of 500 participants (age: 29.51 ± 11.53 years) recruited for the present study, 66.4% were female, and 33.6% were male. The mean spherical equivalent of refraction was - 0.98 ± 1.65 diopters. Significant differences were noted in steep keratometry (P = 0.035) and corneal astigmatism (P = 0.014) between genders. Assessment of the data based on refractive error revealed significant differences in an index of vertical asymmetry (P < 0.001), index of height asymmetry (P = 0.003), and index of height decentration (P = 0.011). Considering age groups, significant differences were observed in flat keratometry readings (P < 0.001), mean corneal astigmatism (P = 0.02), minimum radius of curvature (P = 0.037), and apex power (P < 0.001).

Conclusions

There was a prominent variation in some topographic parameters based on gender, age, and refractive error. The information on corneal parameters obtained with Oculus Keratograph from normal eyes provides a reference for comparison with diseased corneas.

Agreement between IOLMaster® 500 and Pentacam® HR for keratometry assessment in type 2 diabetic and non-diabetic patients

AIM

To evaluate inter-device agreement of anterior keratometry obtained by the IOLMaster^® 500 and Pentacam^® HR in type 2 diabetic and non-diabetic patients.

METHODS

Corneal measurements were sequentially performed in 60 diabetes mellitus (DM) and 48 age and sex-matched controls undergoing cataract surgery. Variables recorded included flat and steep keratometry, mean keratometry (K_m), astigmatism magnitude, axis location, J0 and J45 components. Bland-Altman plots and intraclass correlation coefficients were used for examination of agreement. Subgroup analyses were performed for astigmatism magnitude, diabetes duration, hemoglobin A1c (HbA1c) levels and diabetic retinopathy (DR) stage.

RESULTS

Agreement for K_m and astigmatism magnitude were considered good and moderate, with 95% limits of agreement (LoA) of -1.09 to 1.23 diopters (D) and -0.83 to 0.86 D in DM group, respectively; and -0.59 to 0.72 D and -0.98 to 0.75 D in non-DM group, respectively. In contrast, the 95% LoA for corneal axis exceeded the clinically relevant margins in both groups. In the total sample, only 41 eyes (38%) had a smaller than 5-degree difference. Diabetes duration, HbA1c levels and DR stage were not found to significantly affect agreement. Logistic regression showed that higher corneal power (P=0.021) and astigmatism magnitude (P=0.011) were associated with a decreased risk of having a difference in axis location greater than 10-degrees.

CONCLUSION

In both groups, IOLMaster and Pentacam agree well for corneal power and moderately for astigmatism. However, axis location disagreement is frequent in eyes with flatter corneas and small amounts of astigmatism.

Cylinder Axis Agreement: Unexpected Scenarios

Background

The purpose of this retrospective study was to evaluate cylinder axis agreement between manifest refraction (MR), cycloplegic refraction (CR), Allegro Oculyzer ІІ and Allegro Topolyzer-Vario.

Methods

We included 82 patients (32 males and 50 females, 28.1 ± 8.7 years old), with 156 eyes scheduled for wavefront optimized laser refractive surgery, photorefractive keratectomy (PRK) in 50 eyes and laser-assisted in situ keratomileusis (LASIK) in 106 eyes, for correction of simple, myopic, hyperopic or mixed astigmatism. Cylinder axis was determined under manifest and cycloplegic refractions and using Allegro Occulyzer ІІ and Allegro Topolyzer-Vario platforms. Cylinder axis agreement was assessed by intraclass correlation coefficient, Pearson correlation coefficient and by the method described by Bland and Altman.

Results

Intraclass correlation coefficient and Pearson correlation coefficient showed statistically significant cylinder axis agreement between manifest refraction, cycloplegic refraction, Allegro Oculyzer ІІ and Allegro Topolyzer-Vario (p <0.001). Despite statistically significant cylinder axis agreement between the four measuring tools, 4 of 156 eyes (2.5%) showed unexpected discrepancy between Allegro Oculyzer ІІ and Allegro Topolyzer-Vario cylinder axis.

Conclusion

Although cylinder axis shows statistically significant agreement between manifest refraction, cycloplegic refraction, Allegro Oculyzer ІІ and Allegro Topolyzer-Vario, unexpected discrepancies occur.

Reproducibility, and repeatability of corneal topography measured by Revo NX, Galilei G6 and Casia 2 in normal eyes

PURPOSE

To test the repeatability and reproducibility of the topography module in posterior segment spectral domain optical coherence tomography with Revo NX (new device) and to compare keratometry values obtained by a Scheimpflug tomography (Galilei G6) and a swept source OCT (Casia 2).

METHODS

In this prospective study, healthy subjects with nonoperated eyes had their central corneal thickness (CCT), anterior and posterior K1/K2 corneal power measured with the new device. Two operators made 6 measurements on the new device to check intraobserver repeatability and reproducibility, and measurement on Casia 2 and Galilei G6. Bland-Altman plots were used to assess the agreement between the devices for each analyzed variable.

RESULTS

94 eyes (94 patients) were studied. All devices produced significantly different mean CCT, the highest for Galilei 569.13±37.58 μm followed by Casia 545.00 ±36.15 μm and Revo 537.39±35.92 μm. The mean anterior K1 was 43.21 ± 1.37 for Casia 2 43.21 ± 1.55 for Revo NX and 43.19 ± 1.39 for Galilei G6, and the differences were insignificant p = 0.617. The posterior K1 for Revo NX was -5.77 ± 0.25 whereas for Casia 2 it was -5.98±0.22 and for Galilei G6-6.09±0.28 D p< 0.0001. The Revo NX showed intraclass correlation coefficient ranging from 0.975 for the posterior K2 surface, and 0.994 for anterior K1 and 0.998 for CCT.

CONCLUSIONS

Revo NX is independent of the user and offers a high level of repeatability for the anterior and posterior cornea. The wide range of differences between the devices suggests they should not be used interchangeably.

Repeatability of OCT Anterior Surface and Bowman's Layer Curvature and Aberrations in Normal and Keratoconic Eyes

PURPOSE

To study the repeatability of anterior surface and Bowman's layer curvature in normal and keratoconic eyes using optical coherence tomography (OCT).

METHODS

In this study, 96 normal and 96 keratoconic eyes underwent corneal imaging using Pentacam (Oculus Optikgeräte, Wetzlar, Germany) and OCT (Triton, Topcon Corporation, Tokyo, Japan). The elevation data from segmented air-epithelium (A-E) and epithelium-Bowman's layer (E-B) interfaces in OCT scans were used to quantify curvature and aberrations. The wavefront aberrations were evaluated with the ray tracing method and 6th order Zernike polynomials. The intraclass correlation coefficient (ICC), within-subject standard deviation (Sw), and coefficient of variation (CoV) were used to assess repeatability.

RESULTS

For curvatures, the Sw was less than 0.25 diopters (D) for the normal and keratoconic eyes. The Sw was highest for root mean square of lower order aberrations (0.14 µm) in keratoconic eyes. The CoV for curvatures was well below 0.5% for both groups. For some aberrations irrespective of groups, the CoV was greater because some individual aberrations (mean of three successive measurements) tended to be smaller in magnitude and even a small Sw resulted in a high CoV. For all variables, the ICC ranged between 0.80 and 0.99 for both the OCT and Pentacam measurements. Most variables were similar between the A-E and E-B interfaces (P > .05) for both groups. However, both differed significantly from all Pentacam variables (P < .05) in normal and keratoconic eyes.

CONCLUSIONS

The repeatability of OCT curvatures and aberrations compared well with the Pentacam indices for normal and keratoconic eyes. [J Refract Surg. 2020;36(4):247-252.].

Clinical Evaluation and Validation of the Dutch Crosslinking for Keratoconus Score

Importance

Defining keratoconus progression is fundamental in clinical decision making because crosslinking treatments are indicated when the disease is considered progressive. Currently, there is no consensus which parameters should be used to define progression.

Objective

To assess and validate a novel clinical scoring system as an easy-to-use assessment tool for crosslinking treatment in patients with keratoconus.

Design, Setting, and Participants

Prospective cohort study at 2 academic treatment centers. Patients with keratoconus referred between January 1, 2012, and June 30, 2014, with 2-year follow-up were included. Analysis began March 2017.

Interventions

The Dutch Crosslinking for Keratoconus (DUCK) score is based on changes in 5 clinical parameters that are routinely assessed: age, visual acuity, refraction error, keratometry, and subjective patient experience. The DUCK score is derived by scoring 0 to 2 points per item, and cutoffs were determined by clinical experience. We compared the DUCK scores to the conventional 1.0-diopter increase in maximum keratometry criterion, within the last 12 months, in a longitudinal discovery and a validation cohort. Sensitivity analyses and intraitem correlations were performed.

Main Outcomes and Measures

Overall treatment rate reduction and the duly withheld treatment rate.

Results

A total of 504 eyes of 388 patients were available for analysis on disease progression in the course of 12 and 24 months. Baseline patient characteristics of the discovery cohort and the validation cohort were comparable in terms of age (mean [SD], 26.8 [8.3] years vs 26.3 [9.1]), sex (216 of 332 [65%] vs 123 of 172 [72%] men), and maximum keratometry (mean [SD], 53.5 [7.1] vs 52.7 [6.3]). Adhering to the DUCK score, rather than maximum keratometry, was associated with a reduction in overall treatment rate by 23% (95% CI, 18%-30%), without increasing the risk of disease progression (ie, the rate of progression for both groups was equal; ±0%). The DUCK score appears to better identify eyes that were duly withheld treatment by 35% (95% CI, 22%-49%).

Conclusions and Relevance

These results provide validation of the DUCK score as a tool to determine whether a crosslinking treatment might be warranted. Compared with the conventional maximum keratometry criterion of more than 1.0 diopter, the DUCK score may better select patients who might benefit from crosslinking treatment. Potentially, it may prevent unnecessary treatments, reduce exposure to treatment risks, and improve the cost effectiveness of crosslinking.

Accommodation response and spherical aberration during orthokeratology

PURPOSE

To evaluate the changes in the accommodative response and in the corneal and internal spherical aberration during 3 months of wear of orthokeratology lenses from the baseline.

METHODS

Fifty children aged 8 to 17 were recruited for a prospective study and were fitted with orthokeratology lenses. Refraction without cycloplegia, high and low uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), accommodation lag, horizontal near phoria without correction, corneal topography, corneal, and total wavefront aberration were performed at baseline, 1 day, 1 week, 1 month, and 3 months. Data were analyzed by Student's t test for related samples, repeated measures ANOVA test, and Pearson correlation test.

RESULTS

The spherical equivalent (SE) before and after 3 months was - 3.33 ± 1.60 D and - 0.30 ± 0.46 D, respectively. Accommodation lag was 0.53 ± 0.38 D and 0.20 ± 0.33 D at baseline and at 3 months, respectively. A moderate correlation between lag at the baseline and its change between baseline and the 3-month visit was found (P < 0.05; R = 0.748). The spherical aberration (SA) increased for anterior corneal and total measurement, being statistically significant for all visits (P < 0.05). The internal SA decreased: - 0.105 ± 0.006 at baseline and - 0.196 ± 0.203 at 1 week (P < 0.05). No difference between baseline and the follow-up visits in posterior corneal SA was found (P > 0.05) CONCLUSION: The negative SA of the lens increases during OK treatment compensated for the increase of the anterior corneal surface positive SA, in addition to increasing the accommodative response.

Posterior corneal astigmatism: a review article

Most human eyes show at least a small degree of corneal astigmatism and it can arise from both surfaces of the cornea. The shape of the anterior corneal surface provides no definitive basis for knowing the toricity of the posterior surface. In the previous studies, average astigmatism of the posterior corneal surface was -0.26 to -0.78 diopter. The radius of the posterior corneal surface is less than the radius of the anterior corneal surface. Most studies have found a clear correlation between the anterior and posterior corneal asphericities and the asphericity of the posterior surface is independent of the vertex radius of curvature, refractive error and gender. In contrast to the anterior corneal surface, the asphericity of the posterior corneal surface varies significantly between meridians. The anterior and posterior corneal surface would have approximately parallel principal meridians and both of these surfaces are often flatter in the horizontal meridian than the vertical one. This is especially true in the higher degrees of corneal astigmatism, and then about 10% of any anterior corneal astigmatism is neutralized by an astigmatism arising from the posterior corneal surface. Although the second corneal surface only contributes to about 10% of the total refractive power of the eye, a precise knowledge of its morphology is needed for the correct diagnosis and monitoring the corneal diseases or the surgical interventions and in many eyes neglecting the posterior corneal surface measurement may lead to significant deviations from the corneal astigmatism estimation. In this article, we have reviewed the shape and the toricity of the posterior corneal surface and also the effect of age on it. We investigated the contribution of posterior corneal astigmatism to the total corneal astigmatism and evaluated the accuracy of corneal astigmatism estimation by neglecting the posterior corneal surface measurement.

Comparison of Corneal Power and Corneal Astigmatism of Different Diameter Zones Centered on the Pupil and Corneal Apex Using Scheimpflug Tomography

PURPOSE

Using Scheimpflug tomography to investigate the difference in corneal power and corneal astigmatism between 3- and 4-mm diameter zones centered on the pupil and corneal apex.

METHODS

A total of 90 eyes were included in this study. Axial keratometry, total refractive power, and true net power centered on the pupil and corneal apex in 3- and 4-mm diameter zones were assessed. The paired sample t test and independent sample t test were used for data comparison.

RESULTS

For corneal power and corneal astigmatism for the 3- and 4-mm diameter zones, the flat K values of axial keratometry, total refractive power, and true net power centered on the pupil (3-mm: 43.99 ± 1.69 D, 43.12 ± 1.71 D, 42.53 ± 1.67 D; 4-mm: 44.04 ± 1.67 D, 43.38 ± 1.71 D, 42.61 ± 1.65 D) were significantly higher than those centered on the apex (3-mm: 43.93 ± 1.69 D, 43.05 ± 1.71 D, 42.46 ± 1.67 D; 4-mm: 44.01 ± 1.67 D, 43.34 ± 1.69 D, 42.58 ± 1.65 D; all P < 0.02). However, the steep K and astigmatism magnitude values centered on the pupil (3-mm: 45.71 ± 1.73 D, 45.01 ± 1.73 D, 44.38 ± 1.69 D; 1.72 ± 0.83 D, 1.89 ± 0.86 D, 1.85 ± 0.84 D; 4-mm: 45.78 ± 1.73 D, 45.28 ± 1.74 D, 44.45 ± 1.68 D; 1.73 ± 0.84 D, 1.90 ± 0.85 D, 1.84 ± 0.85 D) were lower than those centered on the apex (3-mm: 45.81 ± 1.74 D, 45.10 ± 1.72 D, 44.50 ± 1.70 D; 1.88 ± 0.90 D, 2.05 ± 0.90 D, 2.04 ± 0.90 D; 4-mm: 45.85 ± 1.73 D, 45.34 ± 1.73 D, 44.51 ± 1.69 D; 1.83 ± 0.88 D, 2.00 ± 0.90 D, 1.93 ± 0.86 D; all P < 0.01). Compared with the 3-mm diameter zone, the corresponding 4-mm diameter zone showed higher corneal power centered on both pupil and corneal apex.

CONCLUSIONS

The difference in corneal power and corneal astigmatism, measured at 3 and 4 mm, centered on the pupil and the corneal apex should be noted in corneal refractive surgery and toric intraocular lens calculation.

Assessment of total corneal power after myopic corneal refractive surgery in Chinese eyes

PURPOSE

To develop a new regression formula based on the Gaussian thick lens formula and to verify the accuracy of the regression formula.

METHODS

In this prospective study, 207 eyes of 207 myopic subjects and 133 eyes of 67 postoperative subjects were included. For the 133 postoperative eyes, 127 eyes underwent laser-assisted in situ keratomileusis, and 6 eyes underwent photorefractive keratectomy. Subjective refraction and Pentacam HR were performed preoperatively and postoperatively, and IOLMaster was performed in the postoperative group. SimK, keratometry based on the Gaussian optic formula (K_GOF), K_CHM obtained using the clinical history method, and the regression formulas K_RF1 and K_RF2 were calculated.

RESULTS

(1) A statistically significant difference (t = 155.164, P = 0.000) between SimK and K_GOF of 1.24 ± 0.12 D was observed, and there was a good correlation between SimK and K_GOF (r = 0.996, P = 0.000). The first regression formula (K_RF1 = 0.351 + 1.021 × K_GOF) was obtained using linear regression. (2) Statistically significant differences (t = 19.114, - 25.184, 4.702, and all P = 0.000) between SimK and K_CHM, K_GOF and K_CHM and K_RF1 and K_CHM of 0.75 ± 0.45 D, 0.96 ± 0.44 D and 0.18 ± 0.43 D, respectively, were obtained. Good correlations between SimK and K_CHM, K_GOF and K_CHM and K_RF1 and K_CHM (all r ≧ 0.977, all Ps = 0.000) were also observed. The regression formula (K_RF2 = - 1.204 + 1.027 × K_RF1) was obtained using linear regression. (3) Six methods were used for the prediction of IOL power in the postoperative group. The highest results were obtained from the Shammas formula (without preoperative data) combining K_m (obtained by IOLMaster) followed by the K_CHM and K_RF2 combining Haigis formula. The third was obtained from the K_CHM and K_RF2 combining Hoffer Q formula; and the smallest was the K_m combining Haigis formula.

CONCLUSION

The IOL power predicted by K_RF2 in eyes after myopic CRS may be accurate.

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.

Intrasubject Repeatability and Interdevice Agreement of Anterior Chamber Depth Measurements by Orbscan and Pentacam in Different Grades of Keratoconus

OBJECTIVES

To evaluate the repeatability of anterior chamber depth (ACD) measurements by Orbscan and Pentacam imaging devices in different grades of keratoconus.

METHODS

One examiner performed 3 consecutive ACD measurements with both devices on 74 eyes of 42 keratoconus patient. Repeatability was assessed using intrasession test-retest variability. Within-subject SD was determined for repeatability, and the coefficient of variation was calculated for each measurement. The intraclass correlation coefficient (ICC) was also determined to assess the variance of repeated data.

RESULTS

Overall, the three ACD measurements were not significantly different either with Pentacam or Orbscan. The ICC index values were greater than 90% with both devices, and it significantly reduced at higher grades of keratoconus with Pentacam. Interdevice differences were statistically significant. The interdevice agreement with ACD measurements was 0.981, and the agreement was lower at higher grades of keratoconus. The 95% limits of agreement between the 2 devices for ACD was from -0.19 to 0.04.

CONCLUSIONS

Our results indicate acceptable repeatability for ACD measurements with both Orbscan and Pentacam in keratoconus patients. The progression of keratoconus has no significant effect on repeatability results of these devices. The good agreement between them allows their interchangeable use.

Agreement of post-LASIK corneal power and corneal thickness measurements by pentacam and GALILEI corneal tomography systems

BACKGROUND

Post-LASIK corneal conditions cannot be accurately measured by traditional optometric approaches. Therefore, we aimed to analyze the agreement of two rotating Scheimpflug cameras in corneal assessment.

METHODS

Fifty otherwise healthy volunteers who had undergone LASIK were recruited in this study. The values of mean and central total corneal power (TCP), including TCP1, TCP2, and TCP-IOL, were measured by GALILEI Scheimpflug camera. The values of total corneal refractive power (TCRP) readings at both 2 mm ring and 3 and 4 mm zones were detected by Pentacam Scheimpflug camera. Central corneal thickness (CCT) and thinnest corneal thickness (TCT) were quantified by GALILEI and Pentacam respectively. Paired t-tests and Bland-Altman analyses were used to evaluate statistical differences between measurement results obtained by GALILEI and by Pentacam.

RESULTS

Among these 50 subjects, the mean and central TCP1 values (37.31 ± 2.61 and 37.27 ± 2.64) derived from GALILEI measurements were consistent with the TCRP values (37.08 ± 2.76, 37.11 ± 2.74, and 37.19 ± 2.68; p > 0.05) determined by Pentacam at the 2 mm ring apex, 3 mm zone apex, and 4 mm zone apex. There were no statistically significant differences in central corneal thickness (CCT) values measured by the two cameras (463.64 ± 55.67 μm for GALILEI and 470.69 ± 44.04 μm for Pentacam, respectively; p > 0.05). However, the limits of agreement were wide when comparing mean TCP1 (-1.4 to 1.8 D, -1.4 to 1.8 D, and -1.3 to 1.6 D), central TCP1 (-1.2 to 1.6 D, -1.2 to 1.6 D, and -1.2 to 1.4 D) and CCT (-77.2-63.0 μm).

CONCLUSION

Corneal power and corneal thickness are disparate post-LASIK evaluation parameters when comparing the utility of GALILEI with that of Pentacam.

Contribution of Fourier-domain optical coherence tomography to the diagnosis of keratoconus progression

PURPOSE

To determine the anatomic criteria for diagnosing keratoconus progression by corneal optical coherence tomography (OCT).

SETTING

Quinze-Vingts National Ophthalmology Hospital, Paris, France.

DESIGN

Prospective case series.

METHODS

Scanning-slit corneal topography (Orbscan II) and Fourier-domain corneal OCT (RTVue) were performed in eyes with mild to moderate keratoconus (progressive or nonprogressive [stable] ectasia) at each examination to assess the keratoconus. Disease progression was defined as an increase of at least 1.0 diopter (D) in the steepest keratometry (K) measurement over 6 months.

RESULTS

Of the 134 eyes of 134 patients with mild to moderate keratoconus, 98 had had progressive ectasia and 36 nonprogressive ectasia. The mean maximum K increased significantly in the progressive group (2.1 D ± 1.2 [SD], P < .0001) and remained constant in the stable group (-0.03 ± 0.39 D, P = .31). The mean thinnest corneal thickness increased significantly in the progressive group (-7.98 ± 9.3 μm, P < .0001) and remained constant in the stable group (-0.52 ± 4.21 μm, P = .22). The change in maximum K was significantly correlated with changes in the thinnest corneal thickness (r = -0.61, P < .0001). A cutoff value of -5 μm for the change in thinnest corneal thickness was identified on receiver operating characteristic curves as a threshold separating cases of progressive and stable keratoconus (area under the curve, 0.79; sensitivity, 68%; specificity, 89%).

CONCLUSIONS

Topographic data partly reflected the structural changes occurring during the progression of corneal ectasia. Based on the pachymetric parameters provided by OCT, corneal and epithelial thinning was correlated with corneal deformation. The use of corneal OCT might therefore improve the diagnostic sensitivity for keratoconus progression.

Improving precision for detecting change in the shape of the cornea in patients with keratoconus

To investigate a method for precision analysis to discriminate true corneal change from measurement imprecision in keratoconus (KC). Thirty patients with KC and 30 healthy controls were included. Coefficients of repeatability and limits of agreement (LOA) were compared using multiple measurements for inter-observer and inter-device agreement with the Pentacam HR, Orbscan IIz, and Tomey Casia SS-1000. Correlation of repeated measurements was evaluated using a linear mixed effect model (also called random effect model). A formula was derived for the theoretical expected change in precision and compared with measured change. Correlation between measurements from the same eye was small (R = 0.13). The 99.73% LOA (3 SD) of the mean of three measurements, provided better precision than 95% LOA (2 SD) of single cut-off values as expected from statistical theory for uncorrelated measurements for evidence of a significant change in corneal shape in patients with keratoconus. This enabled the determination of cut-off values for the detection of true change in corneal shape. The mean of three repeated measurements will provide better precision when there is minimal correlation. Three (rather than two) standard deviations provides a precise estimate of the LOA within or between observers and can be used as a reliable measure for identifying stage-independent corneal shape changes (progression) in keratoconus.

Comparing Change in Anterior Curvature After Corneal Cross-linking Using Scanning-slit and Scheimpflug Technology

PURPOSE

To evaluate the correlation between anterior axial curvature difference maps following corneal cross-linking (CXL) for progressive keratoconus obtained from Scheimpflug-based tomography and Placido-based topography.

DESIGN

Between-devices reliability analysis of randomized clinical trial data.

METHODS

Corneal imaging was collected at a single-center institution preoperatively and at 3, 6, and 12 months postoperatively using Scheimpflug-based tomography (Pentacam; Oculus Inc, Lynnwood, Washington, USA) and scanning-slit, Placido-based topography (Orbscan II; Bausch & Lomb, Rochester, New York, USA) in patients with progressive keratoconus receiving standard protocol CXL (3 mW/cm² for 30 minutes). Regularization index (RI), absolute maximum keratometry (K Max), and change in K Max (ΔK Max) were compared between the 2 devices at each time point.

RESULTS

Fifty-one eyes from 36 patients were evaluated at all time points. Values were significantly different at all time points (56.01 ± 5.3 diopters [D] Scheimpflug vs 55.04 ± 5.1 D scanning-slit preoperatively [P = .003]; 54.58 ± 5.3 D Scheimpflug vs 53.12 ± 4.9 D scanning-slit at 12 months [P < .0001]) but strongly correlated between devices (r = 0.90-0.93) at all time points. The devices were not significantly different at any time point for either ΔK Max or RI but were poorly correlated at all time points (r = 0.41-0.53 for ΔK Max, r = 0.29-0.48 for RI). At 12 months, 95% limits of agreement were 7.51 D for absolute K Max, 8.61 D for ΔK Max, and 19.86 D for RI.

CONCLUSIONS

Measurements using Scheimpflug and scanning-slit Placido-based technology are correlated but not interchangeable. Both devices appear reasonable for separately monitoring the cornea's response to CXL; however, caution should be used when comparing results obtained with one measuring technology to the other.

Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Effect of Cycloplegia on Corneal Biometrics and Refractive State

Purpose

To determine changes in refractive state and corneal parameters after cycloplegia with cyclopentolate hydrochloride 1% using a dual Scheimpflug imaging system.

Methods

In this prospective cross-sectional study patients aged 10 to 40 years who were referred for optometric evaluation enrolled and underwent autorefraction and corneal imaging with the Galilei dual Scheimpflug system before and 30 minutes after twice instillation of medication. Changes in refraction and astigmatism were investigated. Corneal biometrics including anterior and posterior corneal curvatures, total corneal power and corneal pachymetry were compared before and after cycloplegia.

Results

Two hundred and twelve eyes of 106 subjects with mean age of 28 ± 5 years including 201 myopic and 11 hyperopic eyes were evaluated. Mean spherical equivalent refractive error before cycloplegia was -3.4 ± 2.6 D. A mean hyperopic shift of 0.4 ± 0.5 D occurred after cycloplegia (P < 0.001). The astigmatism power did not significantly change (P = 0.8), however, 26.8% of eyes with significant astigmatism experienced a change of more than 5 degrees in the axis of astigmatism. Changes in posterior corneal curvature were scant but statistically significant (P = 0.001). Moreover, corneal thickness was slightly increased in the central and paracentral regions (P < 0.001 and P < 0.001, respectively).

Conclusion

Cycloplegia causes a hyperopic shift and astigmatism axis changes, along with an increase in central and paracentral corneal thickness and change in posterior corneal curvature. The effects of cycloplegia on refraction and corneal biometrics should be considered before cataract and refractive surgeries.

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.