Repeatability of automatic measurements performed by a dual Scheimpflug analyzer in unoperated and post-refractive surgery eyes

Accuracy comparison of tomography devices for ray tracing-based intraocular lens calculation

PURPOSE

To evaluate the interchangeability of different tomography devices used for ray tracing-based intraocular lens (IOL) calculation.

SETTING

Eye clinic, Castrop-Rauxel, Germany.

DESIGN

Retrospective analysis.

METHOD

Measurements from 3 Placido-Scheimpflug devices and 3 optical coherence tomography (OCT) devices were compared in 83 and 161 other eyes after cataract surgery, respectively. 2-dimensional matrices of anterior local corneal curvature and local corneal thickness are transferred to the ray-tracing software OKULIX. Calculations are performed with the same IOL in the same position of an eye with the same axial length. Differences in spherical equivalent (SE), astigmatism, and spherical aberration are evaluated. Furthermore, the influence of the size of the matrices (optical zone) on the accuracy is quantified.

RESULTS

For the Placido-Scheimpflug devices, the deviations from the average of three measurements taken for each eye in SE (mean ± SD) were 0.17 ± 0.24 diopters (D), -0.26 ± 0.29 D, and 0.08 ± 0.39 D ( P < .001, analysis of variance [ANOVA]), for the centroids of the astigmatic differences 0.04 D/173 degrees, 0.14 D/93 degrees, and 0.10 D/7 degrees, and for the median of the absolute values of the vector differences 0.31 D, 0.33 D, and 0.29 D. For OCT devices, the corresponding results were 0.01 ± 0.21 D, -0.03 ± 0.21 D, and 0.02 ± 0.20 D ( P = .005, ANOVA); 0.18 D/120 degrees, 0.07 D/70 degrees, and 0.22 D/4 degrees; and 0.26 D, 0.30 D, and 0.33 D. The accuracy of the calculated spherical aberrations allows for an individual selection of the best fitting IOL model in most cases.

CONCLUSIONS

The differences are small enough to make the devices interchangeable regarding astigmatism and spherical aberration. Although there are significant differences in SE between Scheimpflug and OCT devices, the differences between OCT devices are also small enough to make them interchangeable, but the differences between Placido-Scheimpflug devices are too large to make these devices interchangeable.

Clinical evaluation of ocular biometry of dual Scheimpflug analyzer, GALILEI G6 and swept source optical coherence tomography, ANTERION

To evaluate the performance of a new swept source optical coherence tomography optical biometer, ANTERION, in ocular biometry and intraocular lens (IOL) calculation compared with the reference standard of Dual Scheimpflug Analyzer (GALILEI, G6). A prospective comparative study was conducted in a tertiary eye center. Cataract patients were scanned with both devices in a random fashion, and parameters from the devices were analyzed in terms of mean difference and intraclass correlation coefficient (ICC). Bland–Altman plots were performed to compare agreement between the devices. Ninety-six eyes from 96 patients were enrolled for evaluation. With the exception of ACD, all parameters were significantly different, but excellent agreement was revealed for all of them. The mean difference in axial length was 0.03 mm, and ICC was 0.999. Calculated IOL power with Barrett formula revealed that 93.75% were within 1 diopter and the prediction error was 0.03 diopter. Biometry of the devices were arithmetically different. However, the mean difference of the key factors in IOL calculation were small and appeared to be negligible for the purposes of clinical application. The performance of ANTERION was comparable to that of G6 in biometric measurement and IOL calculation; however, the devices cannot be used interchangeably.

Comparison of Anterior Segment Measurements between Scheimpflug-Placido Camera and New Swept-source Optical Coherence Tomography

Purpose: We compared anterior segment measurements obtained using a Scheimpflug-Placido topographer (SIRIUS®, Costruzione Strumenti Oftalmici, Florence, Italy) and a new anterior module for a swept-source optical coherence tomography system (ANTERION®, Heidelberg Engineering Inc., Heidelberg, Germany).Methods: Anterior segment measurements were evaluated in 74 eyes of 101 patients with the two devices. Central corneal thickness (CCT), anterior chamber depth (ACD), corneal refractive power (K), J0 (Jackson cross-cylinder with axes at 180° and 90°), J45 vector (Jackson cross-cylinder with axes at 45° and 135°), and white-to-white corneal diameter (WTW) measurements obtained using the SIRIUS® system and the new anterior segment module of ANTERION® were compared.Results: The mean CCTs measured by SIRIUS® and ANTERION® were 558.69 ± 44.65 and 540.26 ± 36.57 μm, respectively. The difference was statistically significant (p < 0.005), and there were high correlations between the two methods (r = 0.915, p < 0.001). The mean ACD measurements were 3.34 ± 0.53 and 3.34 ± 0.51 mm (p = 0.856), respectively, for SIRIUS® and ANTERION®. The measurements were strongly correlated (r = 0.966, p < 0.001). The measurements of WTW, total mean K, and J0 obtained with the two systems differed significantly (p < 0.005, p = 0.017, and p < 0.005, respectively), with high correlations between the two systems (r = 0.875, r = 0.967, and r = 0.933, respectively; all p < 0.001).Conclusions: There were significant differences in measurements of K, CCT, WTW, and J0 between the two devices. Agreement analysis suggests that SIRIUS® and ANTERION® should not be used interchangeably.

A Multicenter Study of the Distribution Pattern of Posterior-To-Anterior Corneal Curvature Radii Ratio in Chinese Myopic Patients

Estimation of corneal refractive power (CRP) is of crucial importance to refractive and cataract surgery. The ratio of posterior to anterior curvature radii of the cornea (P/A ratio) is one of the key factors to determine the actual CRP (True-K). While the traditional method to calculate the CRP (Sim-K) is based on a constant P/A ratio (0.82), it is suggested that the P/A ratio varies in different people and exhibits a distribution pattern, which may have an impact on the accuracy of CRP estimation and postoperative refractive outcome. In this multicenter study, we aimed to investigate the distribution pattern of the P/A ratio in a large number of myopic patients, and further explore the relationship between P/A ratio and ΔK (the difference between True-K and Sim-K). We found that distribution of the P/A ratio ranged from 0.72 to 0.86 with an average value of 0.82 ± 0.01. The compensation effect of the refractive power of the posterior on the anterior surface of the cornea decreased with the increase of P/A ratio. There was a significant correlation between P/A ratio and ΔK in all eyes (r = 0.9764, P &lt; 0.0001). A change of 0.1 in P/A ratio could cause a change of 0.75 D in ΔK. Our study suggests that the actual P/A ratio should be taken into consideration in refractive and cataract surgery when calculating the CRP and power of the intraocular lens in eyes with significantly deviated P/A ratios.

The effect of topical bimatoprost on corneal clarity in primary open-angle glaucoma: a longitudinal prospective assessment

PURPOSE

To study the effect of topical bimatoprost on the corneal optical density values using a dual Scheimpflug Placido analysis system.

METHODS

This longitudinal case-control study included 18 patients with newly diagnosed primary open-angle glaucoma who received topical bimatoprost as a first-line treatment and 20 healthy individuals (age and sex-matched controls). Corneal densitometry data were obtained using the dual Scheimpflug analyzer at pre-treatment and 1st, 6th, 12th, 18th months of post-treatment. Repeated measures of ANOVA and Pearson correlation tests were used for statistical analysis.

RESULTS

There were statistically significant differences between pre-treatment and post-treatment 1st and 6th months corneal densitometry values (p < 0.001, p = 0.007, respectively). However, there was no statistically significant difference between the post-treatment 12th and 18th months (p > 0.05). Corneal densitometry values decreased during the 1st month. Intraocular pressure (IOP) differences were statistically significant between baseline and 1 month after treatment (P < 0.001), however not statistically significant between the 1st and 6th, 6th and 12th, 12th and 18th months after treatment (p > 0.05, for all). Corneal densitometry was not correlated with IOP (r = - 0.037, p = 0.44). In the control group, there was no statistically significant difference between baseline and post-baseline 18th-month corneal densitometry measurements (p > 0.05).

CONCLUSIONS

Topical bimatoprost administration might result in a decrease in corneal densitometry measurement. It is of clinical importance that topical bimatoprost administration can affect corneal transparency and cause a possible alteration in corneal properties.

The Precision of a New Anterior Segment Optical Coherence Tomographer and Its Comparison With a Swept-Source OCT-Based Optical Biometer in Patients With Cataract

PURPOSE

To assess the precision of a new spectral-domain optical coherence tomographer (SD-OCT)/Placido topographer (MS-39; CSO) and its comparison with a swept-source OCT (SS-OCT) biometer (Argos; Movu, Inc) in patients with cataract.

METHODS

Fifty-three right eyes from 53 patients were examined by two experienced operators three times using both devices randomly. Employing the within-subject standard deviation (S_w), test-retest variability, coefficient of variation, and intraclass correlation coefficient to evaluate intraoperator repeatability and interoperator reproducibility; the double-angle plots to analyze astigmatism; and Bland-Altman plots and 95% limits of agreement to verify the agreement between devices.

RESULTS

The SD-OCT/Placido tomographer showed high precision, with coefficient of variation of 0.44% or less, intraclass correlation coefficient of 0.945 or greater for all parameters, test-retest variability of 4.21 µm or less for central corneal thickness (CCT), 0.03 mm or less for anterior chamber depth (ACD) and aqueous depth (AQD), and 0.25 diopters (D) or less for mean keratometry (Km), J₀, and J₄₅. The inter-device differences in Km, J₀, and J₄₅ were statistically insignificant, whereas the remaining were statistically but not clinically significant. The 95% limits of agreement of CCT, ACD, AQD, Km, J₀, and J₄₅ were -3.70 to 15.25 µm, -0.06 to 0.04 mm, -0.06 to 0.04 mm, -0.28 to 0.35 D, -0.27 to 0.26 D, and -0.27 to 0.21 D, respectively. The double-angle plot confirmed the high agreement in astigmatism.

CONCLUSIONS

For CCT, ACD, AQD, Km, and astigmatism measurements in patients with cataract, the new SD-OCT/Placido tomographer has excellent precision and high agreement with the Argos SS-OCT biometer, and can be used interchangeably. [J Refract Surg. 2021;37(9):616-622.].

Repeatability and comparability of the Galilei-G4 and Cassini in measuring corneal power and astigmatism in normal and post-refractive surgery eyes

To assess the repeatability and comparability of the Galilei G4 versus the Cassini topographer in post-refractive eyes and in normal eyes, including older patients representative of an initial cataract evaluation. Simulated keratometric (simK), total corneal and posterior corneal power and astigmatism were evaluated in both post-refractive and normal eyes. Repeatability was measured by calculating within-subject standard deviation (Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Vector analyses and Bland-Altman plots were employed to assess agreement between devices. We studied 32 subjects with a history of refractive surgery and 32 subjects without a history of refractive surgery undergoing cataract surgery. The mean age was 55 ± 18.5 years and the age range was 21.5-91.5 years. In non-refractive and post-refractive eyes, the ICC was > 0.9 (P < 0.001) for all corneal powers and for simK and total corneal astigmatism for both analyzers. The ICC for posterior corneal astigmatism magnitude using the Galilei was 0.62 and 0.67 and for the Cassini 0.55 and 0.38 in normal and post-refractive eyes, respectively. In both post-refractive and normal eyes, the Galilei G4 and Cassini analyzers have high repeatability in simK, total, and posterior corneal power and low repeatability for posterior corneal astigmatism.

Applying a dual-Scheimpflug camera to measure tear film thickness

PURPOSE

To assess the tear film thickness in healthy individuals by using a dual-Scheimpflug camera and topical 0.1% fluorescein.

METHODS

A prospective study on healthy individuals who underwent a bilateral tomography examination using the GALILEI dual-Scheimpflug with assessments of the thinnest and central corneal thickness (TCT and CCT, respectively), at baseline and 1 min after applying 2 and 4 µl of 0.1% fluorescein (30 min apart) under topical anesthesia with Oxybuprocaine 0.4%. Inclusion criteria were lack of dry eye disease symptoms and exclusion criteria were contact lens usage, eye drops usage, previous refractive surgery or any ocular surgery. All individuals scored zero on the ocular surface disease index (OSDI) questionnaire.

RESULTS

A total of 62 eyes of 31 participants were included in this study. The mean age was 35.3 ± 10.88 (range 18-62). The mean TCT in was 549.16 µm in the right eye (RE) and 547.84 µm in the left eye (LE). After instillation of 2 µl of 0.1% fluorescein mean TCT increase by 27.84 µm in the RE and by 26.35 µm in the LE. CCT change was 27.58 µm increase in RE and 27.23 µm increase in LE. After instillation of 4 µl of 0.1% fluorescein the mean increase in TCT and CCT were 30.09 and 30.26 µm for OD and 28.33 and 30.15 µm for OS respectively. Comparison between the post instillation of 2 and 4 µl measurements showed no significant differences.

CONCLUSION

Combining a dual-Scheimpflug camera and 0.1% fluorescein may serve as a method to assess the pre-corneal tear film.

Comparison of Subjective and Objective Methods of Corneoscleral Limbus Identification from Anterior Segment Optical Coherence Tomography Images

SIGNIFICANCE

This study evaluates the reliability and validity of an automatic method of the external and internal limbal points identification from anterior segment optical coherence tomography (OCT) images in comparison with manual delineation.

PURPOSE

The purpose of this work was to evaluate the repeatability and precision of a previously proposed automatic method of external and internal limbal points identification and to compare them with the manual delineation by experienced clinicians in terms of limbus diameter.

METHODS

Optical coherence tomography tomograms obtained for 12 healthy volunteers without a history of eye diseases were analyzed. Fifteen OCT tomograms were captured for each patient. For all the images, the external and internal limbal points were determined using both the automatic and manual methods. The external and internal limbus diameters were used as the comparative parameter between the methods under consideration. The statistical analysis included mean, standard deviation, the Passing-Bablok regression, and the Pearson correlation coefficient.

RESULTS

A strong linear dependence between the automatic and manual methods was identified. While compared with the subjective estimates from clinicians, the automatic technique overestimated the external limbus diameter (bias equals 0.21 mm for optometrist and 0.23 mm for ophthalmologist) and slightly underestimated the internal limbus diameter (bias equals 0.13 mm for optometrist and 0.04 mm for ophthalmologist). The automatic method showed significantly better repeatability than the manual method in the case of external limbal points identification and comparably high repeatability for internal limbal points recognition.

CONCLUSIONS

Because of high precision and excellent repeatability, the automatic method of limbal points identification may be successfully used for estimation of the dynamic changes in the geometry of the anterior segment of the eye, where the large number of captured OCT images needs to be processed automatically with high precision.

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.

Corneal topography, anterior segment and high-order aberration assessments in children with ≥ 2 diopter astigmatism

PURPOSE

To assess topographic findings, anterior segment parameters and high-order aberrations (HOAs) by using corneal tomography in children with 2 diopters (dp) or more astigmatism.

METHODS

Children with 2 dp or more astigmatism (study group) and children with astigmatism less than 1 dp (control group) were recruited. Corneal astigmatism, mean, steep, flat keratometry (K) findings, anterior and posterior K results and anterior segment parameters including anterior chamber depth, kappa distance, horizontal corneal diameter, mean, central, middle, peripheral corneal thicknesses (CT), white-to-white (WTW) distance and pupil diameter were measured by Galilei G4 Dual Scheimpflug corneal tomography. HOAs were also assessed and compared between groups.

RESULTS

Fifty-eight eyes of 37 children in the study group and 37 eyes of 37 children in the control group were enrolled. The mean ages of groups were 9.7 ± 2.4 years and 9.3 ± 1.6 years in study and control groups, respectively. The mean astigmatism was 3.3 ± 1.1 dp and 0.5 ± 0.3 dp in study and control groups, respectively (p < 0.05). Total corneal astigmatism was 3.3 ± 0.84 dp and 1.14 ± 0.47 dp in study and control groups, respectively (p < 0.05). There was a significant difference between groups in terms of posterior steep K and posterior astigmatism values. Among anterior segment parameters, mean CT and WTW values were statistically different between groups. HOAs were found to be statistically different between groups.

CONCLUSION

Higher posterior corneal astigmatism, thinner mean CT and lower WTW distance were found in children with 2 dp or more astigmatism. Besides, HOAs were much more in these astigmatic children.

Comparison of corneal curvature parameters obtained from two different instruments-Pentacam and VX120

AIM

To explore whether the same corneal curvature parameters and anterior chamber depth measured by Pentacam and VX120 have a good consistency and can replace each other.

METHODS

This study enrolled 140 eyes of 70 patients ranging in age from 19 to 53y. All eyes underwent a comprehensive ophthalmologic examination including an anterior segment analysis with the VX120 system (Visionix-Luneau Technologies, Chartres, France) and Pentacam (Oculus Optikgerate GmbH) respectively. The comparison on corneal curvature parameters was done between Pentacam and VX120 using clustered signed rank test; the interclass correlation coefficients (ICC) with 95% confidence intervals (CI) was calculated for each parameter between Pentacam and VX120; the Bland-Altman plot of each parameter was supplemented.

RESULTS

The anterior corneal curvature measured by VX120 was Ks: 44.00±1.78 D, KsAt: 89.45±22.18, Kf: 42.84±1.58 D, KfAt: 93.91±79.34; which measured by Pentacam was Ks: 43.80±1.82 D, KsAt: 91.17±21.40, Kf: 42.61±1.64 D, KfAt: 91.16±78.69. There was statistical difference between Pentacam and VX120 for anterior corneal curvature parameter (P<0.001). The posterior corneal curvature measured by VX120 was Ks: -6.42±1.23 D, KsAt: 91.00±23.45, Kf: -5.85±1.24 D, KfAt: 95.93±79.11; which measured by Pentacam was Ks: -6.44±0.32 D, KsAt: 92.24±11.75, Kf: -6.01±1.05 D, KfAt: 74.43±80.64. There was statistical difference between Pentacam and VX120 for posterior corneal curvature parameters (P<0.001). Anterior chamber depth (ACD) measured by Pentacam and VX120 was statistically different. Pentacam and VX120 achieved high consistency only on corneal anterior surface, including Ks and Kf. The ICCs were 0.96 (95%CI: 0.95, 0.97) and 0.95 (95%CI: 0.94, 0.97) respectively. For other corneal surface curvature parameters, all ICCs of between Pentacam and VX120 were below 0.87. Bland-Altman plots indicated of low consistency of corneal surface curvature parameters measured by Pentacam and VX120.

CONCLUSION

The corneal curvature parameters and anterior chamber depth measured by Pentacam and VX120 were statistically different. Data measured by Pentacam and VX120 is not suggested to replace each other, mixing data measured by Pentacam and VX120 together is not suggested either.

Intraobserver Repeatability of Corneal and Anterior Segment Parameters Obtained Using a Scheimpflug Camera-Placido Corneal Topography System

Objectives:

The aim of this study was to assess the intraobserver repeatability of central corneal thickness, peripheral corneal thickness (PCT), keratometry values (steep K, flat K), white-to-white diameter, and anterior chamber depth using the Sirius topography device (Costruzione Strumenti Oftalmici, Florence, Italy) in healthy eyes.

Methods:

A Sirius device was used by a single examiner to assess 100 eyes in 50 healthy patients. Two consecutive scans were acquired for each eye. Repeatability was assessed using test–retest variability, the coefficient of variation (COV), and the intraclass correlation coefficient (ICC).

Results:

Fifty patients (100 eyes) met the inclusion criteria. There were 18 women (36%) and 32 men (64%), with an age range of 23 to 56 years. The mean age was 30.38±8.03 years. A COV of 0.4% or less and an ICC of more than 0.99 (showing excellent repeatability) were achieved for most parameters, with the exception of PCT (at 2.5-mm temporal, superior, inferior, and nasal thickness).

Conclusion:

The anterior segment parameters obtained using the Sirius Scheimpflug camera- Placido corneal topography system were highly repeatable.

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.

Validation of refraction and anterior segment parameters by a new multi-diagnostic platform (VX120)

BACKGROUND

The VX120 (Visionix Luneau, France) is a novel multi-diagnostic platform that combines Hartmann-Shack based autorefraction, Placido-disk based corneal-topography and anterior segment measurements made with a stationary-Scheimpflug camera. We investigate the agreement between different parameters measured by the VX120 with accepted or gold-standard techniques to test if they are interchangeable, as well as to evaluate the repeatability and reproducibility.

METHODS

The right-eyes of healthy subjects were included in the study. Autorefraction of the VX120 was compared to subjective refraction. Agreement of anterior segment parameters was compared to the Sirius (CSO, Italy) including autokeratometry, central corneal thickness (CCT), iridiocorneal angle (IA). Inter and intra-test repeatability of the above parameters was assessed. Results were analyzed using Bland and Altman analyses.

RESULTS

A total of 164 eyes were evaluated. The mean difference between VX120 autorefraction and subjective refraction for sphere, spherical equivalent (SE), and cylinder was 0.01±0.43D, 0.14±0.47D, and -0.26±0.30D, respectively and high correlation was found to all parameter (r>0.75) except for J₄₅ (r=0.61). The mean difference between VX120 and the Sirius system for CCT, IA, and keratometry (k1 and k2) was -3.51±8.64μm, 7.6±4.2°, 0.003±0.06mm and 0.004±0.04mm, respectively and high correlation was found to all parameter (r>0.97) except for IA (r=0.67). Intrasession repeatability of VX120 refraction, CCT, IA and keratometry yielded low within-subject standard deviations. Inter-session repeatability showed no statistically significant difference for most of the parameters measured.

CONCLUSIONS

The VX120 provides consistent refraction and most anterior segment measurements in normal healthy eyes, with high levels of intra and inter-session repeatability.

Mean Posterior Corneal Power and Astigmatism in Normal Versus Keratoconic Eyes

Purpose:

To compare mean posterior corneal power and astigmatism in normal versus keratoconus affected eyes and determine the optimal cut-off points to maximize sensitivity and specificity in discriminating keratoconus from normal corneas.

Methods:

A total of 204 normal eyes and 142 keratoconus affected eyes were enrolled in this prospective comparative study. Mean posterior corneal power and astigmatism were measured using a dual Scheimpflug camera. Correlation coefficients were calculated to assess the relationship between the magnitudes of keratometric and posterior corneal astigmatism in the study groups. Receiver operating characteristic curves were used to compare the sensitivity and specificity of the measured parameters and to identify the optimal cut-off points for discriminating keratoconus from normal corneas.

Results:

The mean posterior corneal power was −6.29 ± 0.20 D in the normal group and −7.77 ± 0.87 D in the keratoconus group (P < 0.001). The mean magnitudes of the posterior corneal astigmatisms were −0.32 ± 0.15 D and −0.94 ± 0.39 D in the normal and keratoconus groups, respectively (P < 0.001). Significant correlations were found between the magnitudes of keratometric and posterior corneal astigmatism in the normal (r=−0.76, P < 0.001) and keratoconus (r=−0.72, P < 0.001) groups. The mean posterior corneal power and astigmatism were highly reliable characteristics that distinguished keratoconus from normal corneas (area under the curve, 0.99 and 0.95, respectively). The optimal cut-off points of mean posterior corneal power and astigmatism were −6.70 D and −0.54 D, respectively.

Conclusion:

Mean posterior corneal power and astigmatism measured using a Galilei analyzer camera might have potential in diagnosing keratoconus. The cut-off points provided can be used for keratoconus screening.

Agreement between total corneal astigmatism calculated by vector summation and total corneal astigmatism measured by ray tracing using Galilei double Scheimpflug analyzer

PURPOSE

To evaluate the agreement between total corneal astigmatism calculated by vector summation of anterior and posterior corneal astigmatism (TCA_Vec) and total corneal astigmatism measured by ray tracing (TCA_Ray).

METHODS

This study enrolled a total of 204 right eyes of 204 normal subjects. The eyes were measured using a Galilei double Scheimpflug analyzer. The measured parameters included simulated keratometric astigmatism using the keratometric index, anterior corneal astigmatism using the corneal refractive index, posterior corneal astigmatism, and TCA_Ray. TCA_Vec was derived by vector summation of the astigmatism on the anterior and posterior corneal surfaces. The magnitudes and axes of TCA_Vec and TCA_Ray were compared. The Pearson correlation coefficient and Bland-Altman plots were used to assess the relationship and agreement between TCA_Vec and TCA_Ray, respectively.

RESULTS

The mean TCA_Vec and TCA_Ray magnitudes were 0.76±0.57D and 1.00±0.78D, respectively (P<0.001). The mean axis orientations were 85.12±30.26° and 89.67±36.76°, respectively (P=0.02). Strong correlations were found between the TCA_Vec and TCA_Ray magnitudes (r=0.96, P<0.001). Moderate associations were observed between the TCA_Vec and TCA_Ray axes (r=0.75, P<0.001). Bland-Altman plots produced the 95% limits of agreement for the TCA_Vec and TCA_Ray magnitudes from -0.33 to 0.82D. The 95% limits of agreement between the TCA_Vec and TCA_Ray axes was -43.0 to 52.1°.

CONCLUSION

The magnitudes and axes of astigmatisms measured by the vector summation and ray tracing methods cannot be used interchangeably. There was a systematic error between the TCA_Vec and TCA_Ray magnitudes.

Precision of a new ocular biometer in children and comparison with IOLMaster

To assess the repeatability and reproducibility of AL-Scan in agreement with those by the IOLMaster in healthy children, two skilled operators measured ocular parameters in 58 children. The parameters included keratometry (K) values, anterior chamber depth (ACD), axial length (AL), central corneal thickness (CCT), pupil diameter (PD), and corneal diameter (CD). The cohort comprised of 32 boys and 26 girls. The AL-Scan measurements showed high repeatability, as the test-retest repeatability (TRT) values of AL, CCT, ACD, Kf, Ks, Km, CD, and PD were 0.09 mm, 5.1 μm, 0.04 mm, 0.28 D, 0.24 D, 0.21 D, 0.39 mm, and 0.22 mm, respectively. The within-subject coefficient of variation (CoV) was low (<0.35%) and the intraclass correlation coefficients (ICC) of all parameters were >0.85. The interobserver reproducibility was excellent with low values of TRT and ICC > 0.95. The CoV of AL, CCT, ACD, and K was <0.22%. The 95% limits of agreement between the AL-Scan and the IOLMaster were narrow for all parameters except for CD. The repeatability and reproducibility of the new biometer, Al-Scan, was excellent for all parameters and can be routinely used in children to measure the biometric values.

Intrasession repeatability of ocular anatomical measurements obtained with a multidiagnostic device in healthy eyes

Background

To evaluate the intrasession repeatability of anterior chamber depth (ACD), central (CCT) and peripheral corneal thickness (PCT), white-to-white diameter (WTW), and irido-corneal angle (IA) measurements obtained with a multidiagnostic device in healthy eyes.

Methods

A total of 107 eyes of 107 patients ranging in age from 23 to 65 years were examined with the VX120 system (Visionix-Luneau Technologies). Three consecutive measurements were obtained with this device to assess the intrasession repeatability of ACD, CCT, PCT at different nasal and temporal locations, WTW, and nasal and temporal IA. Data analysis included the calculation of within-subject standard deviation (S_w), intrasubject precision (1.96xS_w), coefficient of variation (CV) and intraclass correlation coefficient (ICC).

Results

The S_w and CV for ACD was 0.03 mm and 1.16%, respectively, with an ICC of 0.992. The S_w values for central and peripheral pachymetric measurements were below 9 μm, with CV of less than 1.6% and ICC of 0.976 or higher. For IA measurements, S_w values of 0.84 or lower were found, with a CV between 1 and 2%, and an ICC of more than 0.970. The S_w for WTW was 0.24 mm and the CV was 1.95%. No statistically significant correlations were found between any anatomical parameter evaluated and their S_w and CV values associated (−0.220 ≤ r ≤ 0.204, p ≥ 0.125).

Conclusions

The VX120 system is able to provide repeatable measurements of anatomical parameters in healthy eyes. Inter-observer repeatability should be evaluated in future studies.

Placido disk-based topography versus high-resolution rotating Scheimpflug camera for corneal power measurements in keratoconic and post-LASIK eyes: reliability and agreement

AIM

To compare the repeatability/reproducibility of measurement by high-resolution Placido disk-based topography with that of a high-resolution rotating Scheimpflug camera and assess the agreement between the two instruments in measuring corneal power in eyes with keratoconus and post-laser in situ keratomileusis (LASIK).

METHODS

One eye each of 36 keratoconic patients and 20 subjects who had undergone LASIK was included in this prospective observational study. Two independent examiners worked in a random order to take three measurements of each eye with both instruments. Four parameters were measured on the anterior cornea: steep keratometry (Ks), flat keratometry (Kf), mean keratometry (Km), and astigmatism (Ks-Kf). Intra-examiner repeatability and inter-examiner reproducibility were evaluated by calculating the within-subject standard deviation (Sw) the coefficient of repeatability (R), the coefficient of variation (CoV), and the intraclass correlation coefficient (ICC). Agreement between instruments was tested with the Bland-Altman method by calculating the 95% limits of agreement (95% LoA).

RESULTS

In keratoconic eyes, the intra-examiner and inter-examiner ICC were >0.95. As compared with measurement by high-resolution Placido disk-based topography, the intra-examiner R of the high-resolution rotating Scheimpflug camera was lower for Kf (0.32 vs 0.88), Ks (0.61 vs 0.88), and Km (0.32 vs 0.84) but higher for Ks-Kf (0.70 vs 0.57). Inter-examiner R values were lower for all parameters measured using the high-resolution rotating Scheimpflug camera. The 95% LoA were -1.28 to +0.55 for Kf, -1.36 to +0.99 for Ks, -1.08 to +0.50 for Km, and -1.11 to +1.48 for Ks-Kf. In the post-LASIK eyes, the intra-examiner and inter-examiner ICC were >0.87 for all parameters. The intra-examiner and inter-examiner R were lower for all parameters measured using the high-resolution rotating Scheimpflug camera. The intra-examiner R was 0.17 vs 0.88 for Kf, 0.21 vs 0.88 for Ks, 0.17 vs 0.86 for Km, and 0.28 vs 0.33 for Ks-Kf. The inter-examiner R was 0.09 vs 0.64 for Kf, 0.15 vs 0.56 for Ks, 0.09 vs 0.59 for Km, and 0.18 vs 0.23 for Ks-Kf. The 95% LoA were -0.54 to +0.58 for Kf, -0.51 to +0.53 for Ks and Km, and -0.28 to +0.27 for Ks-Kf.

CONCLUSION

As compared with Placido disk-based topography, the high-resolution rotating Scheimpflug camera provides more repeatable and reproducible measurements of Ks, Kf and Ks in keratoconic and post-LASIK eyes. Agreement between instruments is fair in keratoconus and very good in post-LASIK eyes.

Repeatability of posterior and total corneal curvature measurements with a dual Scheimpflug-Placido tomographer

PURPOSE

To evaluate the repeatability of the Galilei G4 dual Scheimpflug analyzer in measuring simulated keratometric, total, and posterior corneal curvature in normal and post-refractive surgery eyes.

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA.

DESIGN

Prospective evaluation of diagnostic technology.

METHODS

A single observer performed 3 consecutive measurements in 1 eye of each subject. The following were evaluated in both eyes and in eyes that had previous myopic excimer-laser surgery: (1) simulated keratometric corneal power and astigmatism, (2) total corneal power and astigmatism, and (3) posterior corneal power and astigmatism. Repeatability was assessed by calculating the within-subject standard deviation (Sw), coefficient of variation (CoV), and intra-class correlation coefficient (ICC).

RESULTS

The study evaluated 41 normal eyes and 36 post-refractive surgery eyes. In normal eyes, the Sw was 0.08 diopters (D), 0.10 D, and 0.03 D for simulated keratometric, total, and posterior corneal power, respectively. The CoV ranged from 0.16% to 0.40%, and the ICC was 0.992 or more (P < .001) for all corneal powers. In post-refractive surgery eyes, the Sw was 0.09 D, 0.09 D, and 0.02 D for simulated keratometric, total, and posterior corneal power, respectively. The CoV ranged from 0.19% to 0.32%, and the ICC was 0.990 or more (P < .001) for all corneal powers. For posterior corneal astigmatism, the ICC was 0.814 and 0.886 for normal and post-refractive surgery eyes, respectively.

CONCLUSIONS

In normal corneas and corneas that had undergone myopic excimer laser ablation, the dual Scheimpflug analyzer showed high intra-observer repeatability for simulated keratometric, total, and posterior corneal power measurements and moderate repeatability for posterior corneal astigmatism.

FINANCIAL DISCLOSURE

Drs. Koch, Weikert, and Wang received research support from Ziemer USA, Inc. No other author has a financial or proprietary interest in any material or method mentioned.

Repeatability and Reproducibility of Anterior Segment Measurements in Normal Eyes Using Dual Scheimpflug Analyzer

OBJECTIVES

To assess the repeatability and reproducibility of anterior segment measurements including aberrometric measurements provided by a dual Scheimpflug analyzer (Galilei) system in normal eyes.

MATERIALS AND METHODS

Three repeated consecutive measurements were taken by two independent examiners. The following were evaluated: total corneal power and posterior corneal power, corneal higher-order wavefront aberrations (6.0 mm pupil), pachymetry at the central, paracentral, and peripheral zones, and anterior chamber depth (ACD). Repeatability was assessed by calculating the within-subject standard deviation, precision, repeatability, and intraclass correlation coefficient (ICC). Bland-Altman analysis was used for assessing reproducibility.

RESULTS

Thirty eyes of 30 patients were included. The best ICC values were for corneal pachymetry and ACD. For both observers, acceptable ICC was also achieved for the other parameters, the only exceptions being posterior corneal astigmatism and total high order aberration. The 95% LoA (Limits of Agreement) values for all measurements showed small variability between the two examiners.

CONCLUSION

The Galilei system provided reliable measurements of anterior segment parameters. Therefore, the instrument can be confidently used for routine clinical use and research purposes.

Influence of Posterior Corneal Astigmatism on Total Corneal Astigmatism in Eyes With Keratoconus

PURPOSE

To measure posterior corneal astigmatism (PCA) and investigate its influence on total corneal astigmatism (TCA) in eyes with keratoconus.

METHODS

Keratometric astigmatism (KA), PCA, and TCA were investigated by means of a dual Scheimpflug analyzer in patients with keratoconus. Vector analysis was carried out with the Næser polar value method.

RESULTS

We enrolled 119 eyes. PCA magnitude averaged 0.77 ± 0.43 diopters (D) and exceeded 0.50, 1.00, and 2.00 D in 73.9%, 21.8%, and 16.8% of eyes, respectively. PCA averaged 0.95 ± 0.48, 0.55 ± 0.28, and 0.70 ± 0.35 D in eyes with with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism. The steepest posterior meridian was oriented vertically (between 61 and 119 degrees) in 55.5% of eyes, thus generating ATR astigmatism. The difference between the location of the steepest meridian of KA and that of TCA was >10 degrees in 8.4% of eyes. On average, KA overestimated TCA in eyes with WTR astigmatism by 0.16 D and underestimated TCA in eyes with ATR astigmatism by 0.22 D. The PCA power oriented along the steeper anterior corneal meridian averaged -0.83 ± 0.40, -0.40 ± 0.37, and -0.53 ± 0.43 D for WTR, ATR, and obliquely astigmatic eyes, respectively. Linear regression disclosed a statistically significant correlation (P < 0.0001, r = 0.16) between the meridional powers of TCA and PCA.

CONCLUSIONS

In eyes with keratoconus, PCA displays large, variable values and is correlated to TCA. The influence of PCA on TCA cannot be disregarded when planning astigmatism correction by toric intraocular lenses.

Reproducibility and repeatability of central corneal thickness measurement in healthy eyes using four different optical devices

Aim

The aim of the study is to compare the measurements of central corneal thickness (CCT) performed by two examiners with four different methods at different times inter- and intra-individually.

Methods

Thirty healthy people were included in the study. In these measurements, an optical low-coherence reflectometry (OLCR), an optic coherence tomography (OCT), a specular microscopy (SM), and a corneal topography (CT) were used. Two examiners performed the measurements in a consecutive manner. After 1–7 days of the first measurements, the second measurements were performed again consecutively. The mean of three measurements was taken in each session for all devices.

Results

In OCT measurements, there was a significant difference between two examiners in both sessions (p < 0.001), while no significant differences were found between two examiners in first and second sessions in SM, CT, and OLCR measurements. When each examiner’s measurements were compared to two sessions, there were no significant differences (p > 0.05, for all) except the SM measurements of the first examiner (p = 0.041). When the first measurements of two examiners were compared, the smallest values were of OCT. At the first session of two examiners, there was a significant difference between OCT and CT measurements, and between OCT and OLCR (p < 0.001, p = 0.002 for the first examiner and p < 0.001 for the second examiner, respectively).

Conclusion

Our study showed that CCT measurements made by CT and OLCR methods were almost same and highly correlated for both the examiners’ measurements. CCTs measured by OCT were on average 30 μm thinner than CT and OLCR.

Repeatability and comparability of corneal power and corneal astigmatism obtained from a point-source color light-emitting diode topographer, a Placido-based corneal topographer, and a low-coherence reflectometer

PURPOSE

To assess the repeatability and agreement of corneal power and astigmatism obtained from the Cassini point-source color light-emitting diode (LED) topographer, Humphrey Atlas 9000 Placido-based corneal topographer, and Lenstar LS-900 low-coherence reflectometer in normal eyes.

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA.

DESIGN

Evaluation of diagnostic test or technology.

METHODS

Consecutively enrolled patients with normal corneas were enrolled. Three sets of measurements were obtained using the color-LED topographer, the Placido topographer, and the reflectometer. Vector analysis was used in the astigmatism analysis. The repeatability was evaluated using the within-subject standard deviation, coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Agreement was verified using Bland-Altman plots. The paired Student t test was used to assess statistical significance.

RESULTS

Thirty-two eyes (32 patients) were evaluated. All devices provided highly repeatable corneal power and astigmatism measurements (ICC > 0.9) except for the Placido topographer with regard to J45 (ICC = 0.721). The color-LED topographer and the reflectometer obtained similar mean values of corneal power, astigmatism magnitude, J0, and J45 (P > .05), which was also true when comparing the color-LED topographer and the Placido topographer, except for the mean corneal power (P = .0007). The Bland-Altman plots showed a wide data spread for all analyzed variables.

CONCLUSIONS

The color-LED topographer provided highly repeatable corneal power and astigmatism measurements. Even though it obtained values similar to those of the reflectometer and the Placido topographer, the wide data spread discourages their interchangeable use to assess corneal power and astigmatism.

FINANCIAL DISCLOSURE

Drs. Wang, Koch, and Weikert are consultants to Ziemer USA, Inc. Dr. Koch is a consultant to Abbott Medical Optics, Inc., Alcon Surgical, Inc., and i-Optics, Corp. Drs. Ventura and Al-Mohtaseb have no financial or proprietary interest in any material or method mentioned.

No change in anterior chamber dimensions after femtosecond LASIK for hyperopia

Objective:

To compare the changes in anterior chamber volume (ACV), anterior chamber depth (ACD) and anterior chamber angle (ACA) before and 6 months after femtosecond laser in situ keratomileusis (LASIK) for hyperopia using the Pentacam HR device.

Methods:

A total of 24 eyes of 24 consecutive hyperopic patients undergoing femtosecond LASIK were examined preoperatively and 6 months postoperatively. Anterior chamber volume; ACDs in the central, superior, inferior, nasal, and temporal quadrants; and ACA were measured using the Pentacam HR device. Comparisons of preoperative versus postoperative values were performed using paired Student t test. Linear regression analysis was performed to evaluate correlations between ACV change, central ACD change, age, and attempted maximum ablation depth.

Results:

Preoperative and postoperative mean ACVs were 153.6 and 158.2 μL, respectively. Preoperative and postoperative mean ACDs were 2.81, 2.28, 2.53, 2.16, and 2.61 mm, and 2.84, 2.31, 2.54, 2.16, and 2.65 mm, respectively. Preoperative and postoperative mean ACAs were 33.3° and 32.0°, respectively. There were not statistically significant differences in ACV, ACDs, and ACA from preoperatively to 6 months after femtosecond LASIK (all P>0.05). The change of central ACD was correlated significantly with age at 6 months postoperatively (R²=0.18, P=0.039).

Conclusions:

Anterior chamber profiles, including ACV, ACA, and central and peripheral ACDs did not significantly change after femtosecond LASIK for hyperopia.

Correcting Interdevice Bias of Horizontal White-to-White and Sulcus-to-Sulcus Measures Used for Implantable Collamer Lens Sizing

PURPOSE

To assess the agreement and repeatability of horizontal white-to-white (WTW) and horizontal sulcus-to-sulcus (STS) diameter measurements and use these data in combination with available literature to correct for interdevice bias in preoperative implantable collamer lens (ICL) size selection.

DESIGN

Interinstrument reliability and bias assessment study.

METHODS

A total of 107 eyes from 56 patients assessed for ICL implantation at our institution were included in the study. This was a consecutive series of all patients with suitable available data. The agreement and bias between WTW (measured with the Pentacam and BioGraph devices) and STS (measured with the HiScan device) were estimated.

RESULTS

The mean spherical equivalent was -8.93 ± 5.69 diopters. The BioGraph measures of WTW were wider than those taken with the Pentacam (bias = 0.26 mm, P < .01), and both horizontal WTW measures were wider than the horizontal STS measures (bias >0.91 mm, P < .01). The repeatability (Sr) of STS measured with the HiScan was 0.39 mm, which was significantly reduced (Sr = 0.15 mm) when the average of 2 measures was used. Agreement between the horizontal WTW measures and horizontal STS estimates when bias was accounted for was г = 0.54 with the Pentacam and г = 0.64 with the BioGraph.

CONCLUSIONS

Large interdevice bias was observed for WTW and STS measures. STS measures demonstrated poor repeatability, but the average of repeated measures significantly improved repeatability. In order to conform to the US Food and Drug Administration's accepted guidelines for ICL sizing, clinicians should be aware of and account for the inconsistencies between devices.

Repeatability and intrasession reproducibility obtained by the Sirius anterior segment analysis system

OBJECTIVE

To analyze repeatability and intrasession reproducibility of anterior segment measurements using the newly developed Sirius Scheimpflug system.

METHODS

Three consecutive measurements on 100 eyes of 50 healthy subjects were performed on the same session by the same technician using the Sirius device at the Assuta Optic Laser Center, Tel-Aviv, Israel. For each eye, the following parameters were measured: anterior chamber angle (ACA), anterior chamber volume (ACV), and anterior chamber depth (ACD), thinnest corneal location, keratometry (anterior and posterior), cylinder, and axis. Repeatability was assessed using the coefficient of variation (CV). Intrasession reproducibility was assessed using intraclass correlation coefficient (ICC).

RESULTS

Coefficient of variation of 2% and less was observed for ACA, ACD, thinnest corneal location, and anterior keratometry. Intraclass correlation coefficients were high for ACA, ACD, anterior keratometry measurements and moderate for anterior cylinder and axis. Higher CV with relatively low ICC values was noticed with ACV, posterior keratometry measurements, and posterior cylinder, and axis. The last 2 have the highest CV and lowest ICC: 48.79% (range: 37.64%-59.95%) and 0.38%, respectively.

CONCLUSIONS

The Sirius Scheimpflug system has a very high repeatability and intrasessional reproducibility when measuring the ACD, ACA, anterior curvature parameters, and the thinnest corneal location. Thus, it can be used with confidence in clinical practice.

Agreement between clinical history method, Orbscan IIz, and Pentacam in estimating corneal power after myopic excimer laser surgery

The purpose of this study was to investigate the agreement between the clinical history method (CHM), Orbscan IIz, and Pentacam in estimating corneal power after myopic excimer laser surgery. Fifty five patients who had myopic LASIK/PRK were recruited into this study. One eye of each patient was randomly selected by a computer-generated process. At 6 months after surgery, postoperative corneal power was calculated from the CHM, Orbscan IIz total optical power at the 3.0 and 4.0 mm zones, and Pentacam equivalent keratometric readings (EKRs) at 3.0, 4.0, and 4.5 mm. Statistical analyses included multilevel models, Pearson’s correlation test, and Bland-Altman plots. The Orbscan IIz 3.0-mm and 4.0 mm total optical power, and Pentacam 3.0-mm, 4.0-mm, and 4.5-mm EKR values had strong linear positive correlations with the CHM values (r = 0.90–0.94, P = <0.001, for all comparisons, Pearson’s correlation). However, only Pentacam 3.0-mm EKR was not statistically different from CHM (P = 0.17, multilevel models). The mean 3.0- and 4.0-mm total optical powers of the Orbscan IIz were significantly flatter than the values derived from CHM, while the average EKRs of the Pentacam at 4.0 and 4.5 mm were significantly steeper. The mean Orbscan IIz 3.0-mm total optical power was the lowest keratometric reading compared to the other 5 values. Large 95% LoA was observed between each of these values, particularly EKRs, and those obtained with the CHM. The width of the 95% LoA was narrowest for Orbscan IIz 3.0-mm total optical power. In conclusion, the keratometric values extracted from these 3 methods were disparate, either because of a statistically significant difference in the mean values or moderate agreement between them. Therefore, they are not considered equivalent and cannot be used interchangeably.

Precision of corneal thickness measurements obtained using the scheimpflug-placido imaging and agreement with ultrasound pachymetry

Purpose. To assess the reliability and comparability of measuring central corneal thickness (CCT) and thinnest corneal thickness (TCT) using a new Scheimpflug-Placido analyzer (TMS-5, Japan) and ultrasound (US) pachymetry. Methods. Seventy-six healthy subjects were prospectively measured 3 times by 1 operator using the TMS-5, 3 additional consecutive scans were performed by a second operator, and ultrasound (US) pachymetry measurements were taken. The test-retest repeatability (TRT), coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were calculated to evaluate intraoperator repeatability and interoperator reproducibility. Agreement among the devices was assessed using Bland-Altman plots and 95% limits of agreement (LoA). Results. The intraoperators TRT and CoV were <19 μm and 2.0%, respectively. The interoperators TRT and CoV were <12 μm and 1.0%, respectively, and ICC was >0.90. The mean CCT and TCT measurements using the TMS-5 were 15.97 μm (95% LoA from −26.42 to −5.52 μm) and 20.32 μm (95% LoA from −30.67 to −9.97 μm) smaller, respectively, than those using US pachymetry. Conclusions. The TMS-5 shows good repeatability and reproducibility for measuring CCT and TCT in normal subjects but only moderate agreement with US pachymetry results. Caution is warranted before using these techniques interchangeably.

Central and peripheral corneal thickness measurement in normal and keratoconic eyes using three corneal pachymeters

Purpose:

To assess the agreement among ultrasonic pachymetry, the Galilei dual Scheimpflug analyzer, and Orbscan II for central and peripheral (Galilei vs. Orbscan) corneal thickness (CCT and PCT) measurement in normal and keratoconic eyes.

Methods:

In this prospective study, CCT and PCT were measured in 88 eyes of 88 refractive surgery candidates and 128 eyes of 69 keratoconic patients with ultrasonic pachymetry, the Galilei, and Orbscan II. The readings by the three instruments were compared using one-way analysis of normal variance. Agreement among the three devices was assessed using Pearson and intraclass correlation coefficients, and Bland–Altman plots. The same analyses were employed to evaluate agreement between Galilei and Orbscan II for PCT measurement.

Results:

In the normal group, mean CCT was 551.0±39.4, 566.9±33.5, and 565.5±40.9 μm measured by ultrasonic pachymetry, the Galilei, and Orbscan II, respectively (P<0.001). The corresponding figures in the keratoconus group were 492.0±61.7, 502.0±42.1, and 470.6±56.9 μm, respectively (P<0.001). Mean PCT was 612.5±35.3 and 640.9±38.0 μm in the normal group (P<0.001) and 567.6±35.2 and 595.1±41.4 μm in the keratoconus group (P<0.001) by the Galilei and Orbscan II, respectively. CCT and PCT measurements obtained by different devices were significantly correlated in both groups.

Conclusion:

To measure CCT, the Galilei and Orbscan II can be used interchangeably in normal eyes, but not in keratoconic eyes. For PCT, there is a systematic error between measurements obtained by the Galilei and Orbscan II. However, it is possible to change optical pachymeter readings into those obtained by ultrasonic pachymetry using a constant.

New Scheimpflug camera device in measuring corneal power changes after myopic laser refractive surgery

PURPOSE

To assess the accuracy of a combined Scheimpflug camera-Placido disk device (Sirius, CSO, Italy) in evaluating corneal power changes after myopic photorefractive keratectomy (PRK).

METHODS

Two hundred and thirty-seven eyes of 237 patients that underwent myopic PRK with a refractive error, measured as spherical equivalent, ranging from -10.75 D to -0.5D (mean -4.63 ± 2.21D), were enrolled in this study. Corneal power evaluation using Sirius were performed before, 1, 3 and 6 months after myopic PRK. Mean simulated keratometry (SimK) and mean pupil power (MPP) were measured. Correlations between changes in corneal power, measured with SimK and MPP, and variations in subjective refraction, calculated at corneal plane, were evaluated using Pearson test at every follow up; differences between preoperative and postoperative data were evaluated with the Student paired t-test.

RESULTS

A good correlation has been detected between the variations in subjective refraction measured at corneal plane 1, 3 and 6 months after myopic PRK and both SimK (R(2) = 0.8463; R(2) = 0.8643; R(2) = 0.7102, respectively) and MPP (R(2) = 0.6622; R(2) = 0.5561; R(2) = 0.5522, respectively) but corneal power changes are statistically undervalued for both parameters (p < 0.001).

CONCLUSIONS

Even if our data should be confirmed in further studies, SimK and MPP provided by this new device do not seem to accurately reflect the changes in corneal power after myopic PRK.

Comparison of anterior chamber depth measurements of Nidek AL-Scan and Galilei Dual Scheimpflug Analyzer

PURPOSE

We aimed to compare anterior chamber depth (ACD) measurements between the Nidek AL-Scan and the Galilei Dual Scheimpflug Analyzer.

SETTING

Turgut Ozal University Medical Faculty, Ankara, Turkey.

DESIGN

Prospective masked bilateral randomized study.

METHODS

Sixty-three individual patient eyes with normal ocular examination findings and no prior ocular surgery were analyzed. Paired two-tailed t-test was used to evaluate agreement between devices. Interobserver repeatability was evaluated in 22 patients using intraclass correlation coefficient (ICC) and Bland-Altman analysis.

RESULTS

The mean ± standard deviation (SD) ACD for Nidek and Galilei was 3.57 ± 0.29 (range from 2.92 to 4.32) and 3.65 ± 0.29 (range from 3.01 to 4.40), respectively. Comparing the two instruments using paired samples t-test, a statistically significant difference was found between the measurements obtained for ACD (P = 0). Two observers' intraclass correlation coefficients (ICC) were 0.996 for Nidek and 0.968 for Galilei. For Nidek, ACD mean difference was 0mm (P < 0.001); 95% limits of agreement was from -0.05 to 0.05. For Galilei ACD mean difference was -0.01 mm (P < 0.001); 95% limits of agreement was from -0.14 to 0.12. The Galilei Dual Scheimpflug Analyzer measured longer ACD values than the Nidek AL-Scan.

CONCLUSION

This comparative study showed that the difference in ACD between the measurements of the Nidek AL-Scan and the Galilei Dual Scheimpflug Analyzer was statistically significant but clinically it was negligible. Further studies are needed, especially on IOL calculation formulas that include ACD and its effect on postoperative spherical equivalent values.

Anterior chamber depth measurements using Scheimpflug imaging and optical coherence tomography: repeatability, reproducibility, and agreement

PURPOSE

To determine the repeatability, reproducibility, and agreement of anterior chamber depth (ACD) measurements obtained with 3 Scheimpflug cameras and an anterior segment optical coherence tomography (AS-OCT) device.

SETTING

Eye Hospital of Wenzhou Medical University, Zhejiang, China.

DESIGN

Observational cross-sectional study.

METHODS

Two observers took 3 consecutive measurements in healthy right eyes using each device to assess intraoperator repeatability. The mean values obtained at different sessions by the first operator were used to determine the intersession reproducibility. Three consecutive measurements obtained by the first operator at the first session were averaged and used to assess agreement.

RESULTS

The ACD measurements obtained by 2 observers in 71 eyes were highly repeatable using the 4 devices, with a test-retest repeatability of 0.04 to 0.07 mm for intraoperator repeatability. The interoperator and intersession reproducibility of ACD measurements were high, and the test-retest repeatability ranges of interoperator and intersession reproducibility were 0.06 to 0.07 mm and 0.05 to 0.08 mm, respectively. The ACD measurements of the 4 systems were sorted from the thickest to the thinnest (Galilei G2 > Visante > Sirius > Pentacam). The differences in the measurements were statistically significant except between the ACD measurements obtained by the Sirius device and the Visante device. However, good agreement with narrow 95% limits of agreement was found between these devices.

CONCLUSIONS

The 4 devices provided high intraoperator repeatability and interoperator and intersession reproducibility for ACD measurements. Good agreement in ACD measurements was found between the devices in healthy eyes.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Comparison of central corneal thickness, thinnest corneal thickness, anterior chamber depth, and simulated keratometry using galilei, Pentacam, and Sirius devices

PURPOSE

The aim was to evaluate the agreement in the central corneal thickness (CCT), thinnest corneal thickness (TCT), anterior chamber depth (ACD), and mean simulated keratometry (simK) measurements using Pentacam, Galilei, and Sirius Scheimpflug systems in normal eyes.

METHODS

Anterior segment measurements were performed with Pentacam, Galilei, and Sirius devices in 32 healthy subjects. The right eye of each participant was selected. Measurements obtained with the 3 systems were compared using repeated-measures analysis of variance and Bonferroni multiple comparisons test.

RESULTS

Analysis of variance determined a significant difference in the anterior segment measurements of CCT, TCT, ACD, and simK between the 3 devices (P < 0.001). Pairwise comparisons of CCT and TCT measurements were significantly different except for the comparison between Pentacam and Sirius. All pairwise comparisons for ACD were statistically significant. The pairwise comparison results for simK values showed that the Galilei and Sirius systems demonstrated better agreement with each other than with Pentacam.

CONCLUSIONS

The results of this study suggest that the Pentacam, Galilei, and Sirius Scheimpflug systems should not be accepted as interchangeable for CCT, TCT, ACD, and simK in healthy subjects.

Geometrical custom modeling of human cornea in vivo and its use for the diagnosis of corneal ectasia

AIM

To establish a new procedure for 3D geometric reconstruction of the human cornea to obtain a solid model that represents a personalized and in vivo morphology of both the anterior and posterior corneal surfaces. This model is later analyzed to obtain geometric variables enabling the characterization of the corneal geometry and establishing a new clinical diagnostic criterion in order to distinguish between healthy corneas and corneas with keratoconus.

METHOD

The method for the geometric reconstruction of the cornea consists of the following steps: capture and preprocessing of the spatial point clouds provided by the Sirius topographer that represent both anterior and posterior corneal surfaces, reconstruction of the corneal geometric surfaces and generation of the solid model. Later, geometric variables are extracted from the model obtained and statistically analyzed to detect deformations of the cornea.

RESULTS

The variables that achieved the best results in the diagnosis of keratoconus were anterior corneal surface area (ROC area: 0.847, p<0.000, std. error: 0.038, 95% CI: 0.777 to 0.925), posterior corneal surface area (ROC area: 0.807, p<0.000, std. error: 0.042, 95% CI: 0,726 to 0,889), anterior apex deviation (ROC area: 0.735, p<0.000, std. error: 0.053, 95% CI: 0.630 to 0.840) and posterior apex deviation (ROC area: 0.891, p<0.000, std. error: 0.039, 95% CI: 0.8146 to 0.9672).

CONCLUSION

Geometric modeling enables accurate characterization of the human cornea. Also, from a clinical point of view, the procedure described has established a new approach for the study of eye-related diseases.

Comparative evaluation of dual Scheimpflug imaging parameters in keratoconus, early keratoconus, and normal eyes

PURPOSE

To determine the efficacy of various parameters measured by dual Scheimpflug imaging technology in differentiating eyes with keratoconus or early keratoconus from normal eyes.

SETTING

Cornea Service, Wills Eye Institute, Philadelphia, Pennsylvania, USA.

DESIGN

Comparative case series.

METHODS

A retrospective evaluation was performed of the parameters provided by the Galilei dual Scheimpflug analyzer in keratoconus, early keratoconus, and normal eyes. Logistic regression and receiver operating characteristic curve analysis were used to compare the mean values and to calculate the sensitivity and specificity of these parameters.

RESULTS

Many parameters were statistically significantly different between keratoconus and normal eyes compared with early keratoconus eyes (P<.05). Total cornea power-steep and posterior curvature-steep keratometry had the highest area under the curve (AUC) score (0.99) for differentiating keratoconus eyes from normal eyes. All anterior curvature parameters were statistically significant in differentiating keratoconus eyes from normal eyes, whereas only the anterior curvature-steep was statistically significant in differentiating early keratoconus eyes from normal eyes. The central pachymetry and thinnest pachymetry were statistically significant in differentiating keratoconus and early keratoconus eyes from normal eyes. Third-order root mean square (RMS) and total RMS had the highest AUC scores (0.83 and 0.82, respectively) for differentiating early keratoconus eyes from normal eyes.

CONCLUSION

Total corneal power, anterior curvature, posterior curvature, pachymetry, and corneal aberration data generated from the dual Scheimpflug analyzer showed promising results in differentiating keratoconus and early keratoconus eyes from normal eyes.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.