Journal of Refractive Surgery

Original Article Supplemental Data

Comparison of Multicolored Spot Reflection Topographer and Scheimpflug-Placido System in Corneal Power and Astigmatism Measurements With Normal and Post-refractive Patients

Weicong Lu, MD; Yaxin Miao, MD; Yue Li, MD; Xiuli Hu, MD; Qingjie Hu, MD; Jinhai Huang, MD, MS, PhD

Abstract

PURPOSE:

To evaluate the repeatability of corneal power and astigmatism derived by a novel multicolored spot reflection topographer system (Cassini; i-Optics, Hague, Netherlands) and compare its agreement with a Placido-Scheimpflug system (Sirius; Costruzione Strumenti Oftalmici, Florence, Italy) in normal and post-refractive patients.

METHODS:

This prospective study comprised patients who underwent myopic excimer laser refractive surgery (96 eyes) and normal patients (102 eyes). Each patient was measured three times with the Cassini and Sirius. The simulated keratometry (SimK), total corneal power (TCP), and astigmatism were recorded. The repeatability was assessed by one-way analysis of variance. The paired t test was used to compare the differences, whereas the agreement was evaluated by Bland–Altman analysis.

RESULTS:

All parameters obtained by the Cassini demonstrated high repeatability, except for total corneal astigmatism (TCA) in the post-refractive group. The intraclass correlation coefficients of all parameters were greater than 0.85, the correlation of variation values was less than 0.55%, and the test–retest repeatability was less than 0.85 diopters (D). The paired t test showed significant differences in steep keratometry, astigmatism, TCP, and TCA in the normal group and in J0, TCP, and TCA in the post-refractive group. The 95% limits of agreement (LoA) in the normal group demonstrated good agreement, except for TCP. Only J0 and J45 of astigmatism and TCA remained narrow for 95% LoA in the post-refractive group.

CONCLUSIONS:

These results suggested that the Cassini provided high repeatable measurements in corneal power and astigmatism, except the TCA of post-refractive patients. The parameters could be used interchangeably in normal patients, except for TCP, whereas only J0 of astigmatism and J0, J45 of TCA showed good agreement in post-refractive patients.

[J Refract Surg. 2019;35(6):370–376.]

Abstract

PURPOSE:

To evaluate the repeatability of corneal power and astigmatism derived by a novel multicolored spot reflection topographer system (Cassini; i-Optics, Hague, Netherlands) and compare its agreement with a Placido-Scheimpflug system (Sirius; Costruzione Strumenti Oftalmici, Florence, Italy) in normal and post-refractive patients.

METHODS:

This prospective study comprised patients who underwent myopic excimer laser refractive surgery (96 eyes) and normal patients (102 eyes). Each patient was measured three times with the Cassini and Sirius. The simulated keratometry (SimK), total corneal power (TCP), and astigmatism were recorded. The repeatability was assessed by one-way analysis of variance. The paired t test was used to compare the differences, whereas the agreement was evaluated by Bland–Altman analysis.

RESULTS:

All parameters obtained by the Cassini demonstrated high repeatability, except for total corneal astigmatism (TCA) in the post-refractive group. The intraclass correlation coefficients of all parameters were greater than 0.85, the correlation of variation values was less than 0.55%, and the test–retest repeatability was less than 0.85 diopters (D). The paired t test showed significant differences in steep keratometry, astigmatism, TCP, and TCA in the normal group and in J0, TCP, and TCA in the post-refractive group. The 95% limits of agreement (LoA) in the normal group demonstrated good agreement, except for TCP. Only J0 and J45 of astigmatism and TCA remained narrow for 95% LoA in the post-refractive group.

CONCLUSIONS:

These results suggested that the Cassini provided high repeatable measurements in corneal power and astigmatism, except the TCA of post-refractive patients. The parameters could be used interchangeably in normal patients, except for TCP, whereas only J0 of astigmatism and J0, J45 of TCA showed good agreement in post-refractive patients.

[J Refract Surg. 2019;35(6):370–376.]

The precise measurement of corneal power is crucial for clinical applications in ophthalmology, such as in the designing of corneal refractive surgery,1 calculation of intraocular lens (IOL) power,2,3 and early screening of keratoconus.4 Currently, the goal of cataract surgery has been transformed from rehabilitation surgery to refractive surgery. In addition, toric IOL implantation has become a popular way to correct corneal astigmatism in cataract, and its importance in precise measurement of corneal astigmatism has been recognized by most researchers. Generally, the simulated corneal astigmatism that is calculated with a fictious reflective index is applied to represent the total corneal astigmatism (TCA), but ignorance of posterior corneal astigmatism can induce postoperative residual astigmatism.5 Koch et al.6 reported that the anterior corneal measurements were underestimated by a TCA of 0.22. Recently, with the introduction of new techniques in clinics, physicians were able to derive more precise data from both anterior and posterior corneal surfaces. Previous studies have proved that the magnitude of posterior astigmatism is −0.30 diopters (D).6,7 Tonn et al.8 also confirmed that the TCA is overestimated by astigmatism of simulated keratometry (SimK) in with-the-rule eyes. Therefore, precise measurement of total corneal power (TCP) is necessary in clinical applications.

Since the introduction of the manual keratometer, the technique has experienced great advances. With the use of the Placido disk system, physicians were able to derive color-coded topography. But these devices can only measure the anterior corneal curvature and calculate the SimK with a fictitious index that assumes a fixed ratio of radius between anterior and posterior surfaces.9 Owing to this drawback, several new devices have been designed. For instance, the Scheimpflug imaging system can provide both anterior and posterior corneal data that are helpful to reconstruct the three-dimensional structure of the cornea. Previous studies have demonstrated that the Scheimpflug system is highly precise in corneal power measurement10–12 and can be used to calculate the IOL power.13 In addition, the Scheimpflug system adopted a ray-tracing technique to acquire TCP according to Snell's law, overcoming the defect of SimK in overestimating the corneal power after myopia refractive surgery.14

Recently, novel multicolored spot reflection topography (Cassini; i-Optics, Hague, Netherlands) has been used in clinics. It projects color LEDs on the anterior cornea and the image processing software locates the feature reflecting point like a “GPS” to present the skew-ray in ring topography without affecting the precision of results. Moreover, the posterior corneal surface can be measured with 7 additional infrared LEDs. Several studies have investigated the validation of the Cassini in cataract, keratoconus, and after laser in situ keratomileusis.15–17 Most of these studies focused only on SimK. Hence, in this study, we aimed to assess the repeatability of SimK, TCP, and astigmatism. Meanwhile, as a novel device it is essential to know the agreement with other biometers, and so we first analyzed the relationship between the Cassini and Sirius (Costruzione Strumenti Oftalmici, Florence, Italy) in normal and post-refractive groups.

Patients and Methods

Patients

A total of 198 patients who visited for regular examination between July and December 2017 at the Eye Hospital of Wenzhou Medical University were recruited in this prospective study. All patients were divided into two groups: normal and post-refractive with one random eye selected. Patients with any corneal abnormality, inability to fixate on the fixation target, contact lens wear within 2 weeks, and previous surgical history other than myopic corneal refractive surgery were excluded. This study was approved by the Ethics Committee of the Eye Hospital of Wenzhou Medical University and adhered to the tenets of the Declaration of Helsinki. All patients were informed of the purpose of this study and provided informed consent.

Instrument and Methods

The Cassini measured the anterior shape of the cornea by using a multicolor-coded LED pattern. It comprised 672 color LEDs (red, yellow, and green) and 7 blue “anchor” LEDs. The location of each reflected spot was calculated according to the unique relationship of its four neighbors that gives each spot a “GPS”–like coordinate. This is because it does not adopt edge detection in its algorithms and the smeared reflected LEDs cannot skew the results in any direction. Meanwhile, the toric shape of the corneal posterior surface was measured with 7 additional infrared LEDs based on the second Purkinje image. TCA was calculated by using a ray-tracing model by integrating the anterior and posterior measurements.

The Sirius is a topographer that adopts the Placido disk and Scheimpflug camera system. The Placido disk consisted of 22 concentric rings with a camera in the central hole for recording the anterior corneal data. The Scheimpflug camera provided 25 medians of corneal and anterior segment images with 30,000 effective data points. After that, internal software was used to integrate the Placido and Scheimpflug data for reconstructing the three-dimensional corneal shape.

The research was conducted by an experienced operator between 10:00 AM and 5:00 PM to reduce the influence of diurnal variation on cornea.18 Each patient was examined three times with the Cassini and Sirius in a random sequence. To guarantee the quality of measurements, only results that met the criteria of each device were analyzed. For instance, the Cassini required all quality factors of greater than 85% in association with focus, centration, coverage, and stability. Similarly, the Sirius only accepted the results with a green acquisition quality.

The recorded parameters included the steepest and flattest SimK values (Ks and Kf), TCP, and astigmatism. The Ks and Kf calculated by the Sirius were the sagittal curvatures from the fourth to eighth Placido rings, whereas the parameters of the Cassini were based on a 3-mm zone. They both adopted a fictitious index of 1.3375. TCP derived from the Cassini is known as equivalent keratometry and the mean corneal power of entrance pupil calculated by ray tracing is the TCP of the Sirius. In this study, we selected a mean corneal power of entrance pupil with a 5-mm diameter.19 Because the astigmatism was a vector parameter that comprised magnitude and axis, we adopted vector analysis to transform astigmatism into J0 and J45.

Statistical Analysis

The data analysis was performed using SPSS software (version 24.0; IBM Corporation, Armonk, NY) and Medcalc software (version 18.2.1; Medcalc, Ostend, Belgium). The results were expressed as mean ± standard deviation. The normally distributed data were analyzed by the Kolmogorov–Smirnov test (P > .05). To evaluate the repeatability, the within-subject standard deviation (Sw), test–retest repeatability (TRT), correlation of variation (CoV), and intraclass correlation coefficient (ICC) were calculated using one-way analysis of variance. The Sw was calculated through three consecutive measurements as an intraobserver deviation. To define the 95% measurement error interval expected to lie, the TRT that is equal to 2.77 Sw was also calculated.20 The CoV is the ratio of Sw to the mean, and a low CoV represents a high repeatability. Because the CoV is not optimal for evaluating parameters with both positive and negative values, the small denominator induces significant errors and the CoV analysis of J0, J45 and astigmatism were not calculated. The ICC with a consistency type and a two-way random model were applied to assess the consistency of quantitative measurements. An ICC value of greater than 0.75 indicated moderate repeatability and greater than 0.90 indicated high repeatability.21 The agreement between the Cassini and Sirius in corneal power measurement was also assessed by Bland–Altman plots and 95% limits of agreement (95% LoA), which was defined as the mean difference of ±1.96 standard deviation between the two devices.

Results

A total of 96 post-refractive patients (42 men and 54 women) and 102 normal patients (41 men and 61 women) with an average age of 27.43 ± 5.54 years (range: 20 to 42 years) and 26.70 ± 3.64 years (range: 18 to 41 years) were included in this study. The mean spherical equivalent in each group of patients was −0.37 ± 0.38 and −6.01 ± 2.42 D, respectively.

Intraobserver Repeatability

Table A (available in the online version of this article) presents the repeatability of corneal power measurements with the Cassini and Sirius in the normal group. All ICC values were greater than 0.97, CoV values were less than 0.5%, and TRT values were less than 0.55 D, indicating good repeatability for all parameters. Similar results were observed with the Sirius: the ICC values were greater than 0.98, CoV values were less than 0.4%, and TRT values were less than 0.45 D, indicating that the repeatability was slightly better than the Cassini. Table B (available in the online version of this article) shows the intraobserver repeatability of the Sirius and Cassini in the post-refractive group. The repeatability of Ks, Kf, TCP, J0, and J45 still showed good repeatability with both devices, except for TCA by the Cassini, because the TRT and ICC values were 0.85 and 0.87 D, respectively. This suggested that the repeatability of the Cassini in TCA was not good enough.

Intraobserver Repeatability Outcomes for Corneal Power Measurements Obtained Using the Cassini and Sirius in the Normal Group

Table A:

Intraobserver Repeatability Outcomes for Corneal Power Measurements Obtained Using the Cassini and Sirius in the Normal Group

Intraobserver Repeatability Outcomes for Corneal Power Measurements Obtained Using the Cassini and Sirius in the Post-refractive Group

Table B:

Intraobserver Repeatability Outcomes for Corneal Power Measurements Obtained Using the Cassini and Sirius in the Post-refractive Group

Agreement

Table 1 shows statistical differences in TCP and TCA in the normal and post-refractive groups. The agreement between the Sirius and Cassini was presented by Bland–Altman plots. Figures AB (available in the online version of this article) showed the agreement of Ks and Kf in the normal group, and the 95% LoA was −0.42 to 0.61 and −0.42 to 0.45 D, respectively. The agreement of the post-refractive group was larger (95% LoA: −1.02 to 0.87 and −1.01 to 0.88 D), indicating that the results of the post-refractive group could not be interchangeable. Similarly, the agreement of TCP showed an obvious discrepancy because the Cassini was nearly 1.13 D greater than the Sirius, whereas the difference was increased to 2.27 D in the post-refractive group.

Mean Difference, Paired t Test, and 95% LoA for Differences Between the Cassini and Sirius

Table 1:

Mean Difference, Paired t Test, and 95% LoA for Differences Between the Cassini and Sirius

Bland–Altman plots in normal eyes with steep keratometry (Ks) (top left), flat keratometry (Kf) (middle left), total corneal power (TCP) (bottom left), astigmatism magnitude (center top), J0 (center middle), J45 (center bottom), total corneal astigmatism (TCA) (top right), J0 of TCA (center right), and J45 of TCA (bottom right). The solid line shows the mean difference (bias), and the upper and lower lines represent 95% limits of agreement.

Figure A.

Bland–Altman plots in normal eyes with steep keratometry (Ks) (top left), flat keratometry (Kf) (middle left), total corneal power (TCP) (bottom left), astigmatism magnitude (center top), J0 (center middle), J45 (center bottom), total corneal astigmatism (TCA) (top right), J0 of TCA (center right), and J45 of TCA (bottom right). The solid line shows the mean difference (bias), and the upper and lower lines represent 95% limits of agreement.

Bland–Altman plots in post-refractive eyes with steep keratometry (Ks) (top left), flat keratometry (Kf) (middle left), total corneal power (TCP) (bottom left), astigmatism magnitude (center top), J0 (center middle), J45 (center bottom), total corneal astigmatism (TCA) (top right), J0 of TCA (center right), and J45 of TCA (bottom right). The solid line shows the mean difference (bias), and the upper and lower lines represent 95% limits of agreement.

Figure B.

Bland–Altman plots in post-refractive eyes with steep keratometry (Ks) (top left), flat keratometry (Kf) (middle left), total corneal power (TCP) (bottom left), astigmatism magnitude (center top), J0 (center middle), J45 (center bottom), total corneal astigmatism (TCA) (top right), J0 of TCA (center right), and J45 of TCA (bottom right). The solid line shows the mean difference (bias), and the upper and lower lines represent 95% limits of agreement.

Discussion

The current study demonstrated that the Cassini and Sirius showed good repeatability for Ks and Kf measurements. Previous studies have reported that the ICC value of the Scheimpflug-Placido topographer was more than 0.93 when evaluating the anterior and posterior corneal power.22,23 Similarly, other results have reported good repeatability with Scheimpflug systems and optical low coherence reflectometers.24,25 As a novel biometer, the repeatability of the Cassini showed similar results when compared to the Sirius, although the TRT value was slightly larger. Ventura et al.26 assessed the repeatability of the Cassini in measuring the corneal power and verified the Sw was 0.32 D, the ICC was 0.960, and the CoV was 0.64%, making the repeatability worse than a reflectometer (Lenstar LS-900). Similar results have been reported by Klijn et al.,27 with Sw of 0.14 and 0.08 D with the Cassini and Pentacam, respectively. Our study showed better results with the repeatability of the Cassini.

The repeatability of the Cassini and Sirius in the post-refractive group did not show significant changes when compared to the normal group in Ks and Kf measurements, because the TRT was less than 0.56 D and the ICC was greater than 0.996. Savini et al.23 showed that the TRT of the Sirius was 0.29 and 0.34 D before and after refractive surgery. Kim et al.28 assessed a dual Scheimpflug-Placido topographer (Galilei) and found that the Sw of the normal and post-refractive groups was 0.08 and 0.09 D, respectively, showing high intraobserver repeatability for SimK. Kanellopoulos and Asimellis16 found that the repeatability of Kf and Ks were 0.74 and 0.64 D, indicating that the Cassini demonstrated precise measurements in terms of Ks and Kf in post-refractive patients, supporting our conclusion that the repeatability of the Cassini was great. Although the TRT of the Cassini was slightly larger than the Sirius, this discrepancy might be induced by different principles of these two devices. The Sirius has adopted a Scheimpflug camera and Placido disk to reconstruct the anterior corneal surface, the SimK was calculated from the fourth to eighth Placido ring, and the valid data were greater than 30,000 points, whereas the Cassini only calculates the corneal information through 672 reflected data points; the more points that are sampled, the more precise results can be obtained. In addition, the high luminance of the color LEDs of the Cassini may induce worse cooperation and extend the examination procedure, finally resulting in poor tear film stability and affecting the results.

There are currently different algorithms for measuring the curvature of the whole cornea with different devices. One is the TCP based on the ray-tracing technique and the other is the true net power (TNP) based on a Gaussian optic formula that considers the cornea as a thin lens. Compared to TNP, TCP takes the real light refraction through the whole cornea into account, deriving the most realistic whole corneal curvature.29 In this study, we analyzed the TCP from the Cassini and Sirius, which showed good repeatability in the normal and post-refractive groups. A similar conclusion has been drawn by Savini et al.,23 wherein the repeatability of the Sirius in measuring TCP showed that the TRT was 0.34 and 0.45 D and the ICC was 0.992 and 0.991 in normal and post-refractive patients, respectively. Aramberri et al.30 reported that the rotating Scheimpflug camera Pentacam showed better repeatability with an excellent TRT value of 0.14 D in normal patients, whereas the dual Scheimpflug analyzer Galilei provided a larger TRT with 0.34 D. Other authors also indicated that the repeatability of TCP was good enough to calculate the precise IOL in normal and post-refractive patients.28,31 Our research verified that the repeatability of the Cassini was close to that of the Sirius, providing high repeatable results.

The investigation of astigmatism and TCA demonstrated good repeatability, except the TCA of the post-refractive group. Visser et al.25 compared six different devices to determine the repeatability of astigmatism, and indicated that most of the devices had a magnitude repeatability with a range of 0.14 to 0.18 D, whereas a wavefront analyzer had an Sw of 0.05 D. Other studies reported the magnitude of astigmatism of TRT to be 0.52 and 0.43 D in normal and post-refractive patients.23 Ventura et al.26 revealed that the Sw of astigmatism magnitude of the Cassini, Placido, and reflectometer was 0.31, 0.18, and 0.13 D, respectively, in 32 normal patients. Our results were better than the Ventura because the Sw of the Cassini was below 0.20 in normal patients; however, the repeatability of TCA was decreased with refractive surgery. This could be due to the fact that TCA consisted of anterior and posterior corneal curvature, whereas astigmatism only involved the anterior surface. Hence, the TCA would introduce two errors from the anterior and posterior surfaces.

Considering that the corneal astigmatism is a vector parameter including axis and magnitude, the vector decomposition of J0 and J45 can assess both magnitude and axis. The J0 and J45 denote a Jackson cross-cylinder with an axis at 0° and 45°.32,33 Cervino et al.34 reported a moderate reliability of J0 and J45 of TCP in normal patients with the Galilei because the ICC was 0.891 and 0.724. The prospective study conducted by Ferreira and Ribeiro35 reported the ICC of J0 to be 0.918, whereas the ICC of J45 was 0.621, indicating that the Cassini had good agreement in J0. However, our study showed better repeatability for ICC, which was 0.9 all over. These conclusions were similar to those of previous studies with other devices,10,36 supporting our conclusion that the repeatability of J0 and J45 was good.

We investigated the agreement between the Cassini and Sirius and found that the 95% LoA of Ks and Kf was −0.42 to 0.61 and −0.41 to 0.45 D in the normal group, indicating that the two devices maintained good agreement for Ks and Kf measurements and could be used interchangeably, although the K value measured by the Cassini was slightly greater than the Sirius. Ventura et al.37 discovered that the 95% LoA of the Cassini and Atlas 900 (Placido-based corneal topographer), the Cassini, and the Galilei ranged from −2.16 to 1.96 and −1.79 to 2.08 D in normal patients, whereas the range was −2.07 to 1.83 and −1.44 to 1.80 D in post-refractive patients. The corneal power measured by the Cassini was smaller than the Galilei and greater than the Atlas 900. Our study also found that the Ks and Kf measurements by the Cassini were slightly larger than the Sirius in normal patients. Other researchers suggested that the Cassini and Lenstar should not be used interchangeably because the range of 95% LoA was nearly 2.10 D.35 However, the agreement obtained by our study showed a narrower 95% LoA range, suggesting that the measurements of Ks and Kf could be interchangeable in normal patients, whereas the difference was statistically significant and could not be used interchangeably in post-refractive patients. Previous studies19,38 verified that the TCP of Scheimpflug systems could be the best option for corneal power measurement after myopic excimer laser surgery. Our research showed that the TCP of the Cassini was significantly larger than the Sirius, particularly in post-refractive patients, proving that the TCP based on ray tracing should not be interchangeable.

The agreement of astigmatism and vector parameters was also investigated. As an extensively used technique, several studies have demonstrated the agreement of the Scheimpflug rotating camera. Savini et al.39 showed that the three commercial Scheimpflug systems were in great agreement when compared to each other. Ortiz-Toquero et al.40 investigated the agreement between the Topolyzer and Galilei, realizing that the two devices could be used interchangeably in healthy eyes because the 95% LoA were −1.13 to 1.15 and −1.20 to 1.10 D. Delrivo et al.41 reported that the 95% LoA of astigmatism magnitude, J0, and J45 were −0.49 to 0.27, −0.22 to 0.14, and −0.36 to 0.29 D in normal patients. As to the Cassini, several studies reported its agreement with other devices. Ferreira and Ribeiro35 assessed the Lenstar, Orbscan, and Cassini, which showed a wide data spread for astigmatism magnitude. Likewise, we found a large 95% LoA range in astig matism magnitude and TCA in post-refractive patients, whereas J0, and J45 showed good agreement, except J45 of astigmatism of the post-refractive group. This was probably because the refractive surgery commonly corrected the subjective refraction including astigmatism, inducing the decrease of corneal astigmatism that affected the agreement.

This study had some limitations. We only enrolled patients who had myopic refractive surgery and excluded hyperopic patients. Most of the patients recruited in this study had low and medium astigmatism with a lack of high astigmatism. However, the repeatability of astigmatism was highly correlated with magnitude.

The repeatability of the Cassini was similar to that of the Sirius in all parameters with high repeatability, except for TCA of post-refractive patients. The agreements are reasonable between the Cassini and Sirius for Ks, Kf, astigmatism, TCA, J0, and J45, and could be used interchangeably in clinics in normal patients. However, in post-refractive patients, the agreement was decreased and could not be interchangeable, except for J0 of astigmatism and J0 and J45 of TCA.

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Mean Difference, Paired t Test, and 95% LoA for Differences Between the Cassini and Sirius

ParameterMean ± SDP95% LoA
Normal
  Ks (D)0.10 ± 0.26< .001−0.42 to 0.61
  Kf (D)0.01 ± 0.22.553−0.42 to 0.45
  Ast (D)0.08 ± 0.21< .001−0.34 to 0.51
  J0 (D)−0.02 ± 0.12.178−0.26 to 0.23
  J45 (D)0.00± 0.11.843−0.21 to 0.21
  TCP (D)0.67 ± 0.23< .0010.21 to 1.13
  TCA (D)0.05 ± 0.24< .001−0.42 to 0.52
  J0-TCA (D)−0.01 ± 0.13.446−0.27 to 0.25
  J45-TCA (D)0.01 ± 0.13.561−0.24 to 0.26
Post-refractive
  Ks (D)−0.07 ± 0.48.142−1.02 to 0.87
  Kf (D)−0.07 ± 0.48.172−1.01 to 0.88
  Ast (D)−0.01 ± 0.40.893−0.79 to 0.78
  J0 (D)0.12 ± 0.121< .001−0.30 to 0.54
  J45 (D)0.03 ± 0.40.425−0.76 to 0.82
  TCP (D)1.29 ± 0.50< .0010.30 to 2.27
  TCA (D)0.25 ± 0.38< .001−0.50 to 1.00
  J0-TCA (D)−0.07 ± 0.23.05−0.52 to 0.39
  J45-TCA (D)0.00 ± 0.19.922−0.38 to 0.39

Intraobserver Repeatability Outcomes for Corneal Power Measurements Obtained Using the Cassini and Sirius in the Normal Group

ParameterDeviceMean ± SDSwTRTICCCoV
Ks (D)Cassini43.87 ± 1.640.180.520.9960.42
Sirius43.77 ± 1.590.160.450.9970.37
Kf (D)Cassini42.67 ± 1.330.190.520.9930.44
Sirius42.66 ± 1.300.120.350.9970.30
Ast (D)Cassini1.19 ± 0.780.180.500.981
Sirius1.11 ± 0.750.130.360.989
J0(D)Cassini−0.49 ± 0.420.090.260.983
Sirius−0.48 ± 0.390.060.180.991
J45(D)Cassini0.04 ± 0.270.060.170.981
Sirius0.04 ± 0.250.040.130.989
TCP (D)Cassini43.39 ± 1.430.180.510.9920.42
Sirius42.72 ± 1.420.160.440.9960.37
TCA (D)Cassini1.10 ± 0.750.200.550.974
Sirius1.04 ± 0.730.160.460.982
J0-TCA (D)Cassini−0.42 ± 0.420.100.290.978
Sirius−0.41 ± 0.390.090.250.982
J45-TCA (D)Cassini0.03 ± 0.280.080.220.972
Sirius0.03 ± 0.280.0470.200.978

Intraobserver Repeatability Outcomes for Corneal Power Measurements Obtained Using the Cassini and Sirius in the Post-refractive Group

ParameterDeviceMean ± SDSwTRTICCCoV
Ks (D)Cassini38.92 ± 1.990.20.560.9960.52
Sirius38.99 ± 1.740.120.330.9980.30
Kf (D)Cassini38.14 ± 1.880.190.540.9960.51
Sirius38.20 ± .660.120.340.9980.32
Ast (D)Cassini0.78 ± 0.490.190.550.939
Sirius0.78 ± 0.420.110.320.973
J0(D)Cassini−0.21 ± 0.320.110.320.950
Sirius−0.33 ± 0.230.050.150.980
J45(D)Cassini−0.01 ± 0.250.080.220.962
Sirius−0.01 ± 0.170.050.140.969
TCP (D)Cassini38.68 ± 2.110.20.570.9960.53
Sirius37.14 ± 1.880.120.350.9980.34
TCA (D)Cassini0.89 ± 0.540.300.850.871
Sirius0.64 ± 0.470.150.440.965-
J0-TCA (D)Cassini−0.20 ± 0.360.180.490.905
Sirius−0.14 ± 0.280.080.230.968
J45-TCA (D)Cassini−0.01 ± 0.30.150.420.900
Sirius−0.02 ± 0.240.060.190.973
Authors

From the School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, Zhejiang, People's Republic of China (WL, YM, YL, QH, JH); Eye Hospital of Wenzhou Medical University, Wenzhou, Zhejiang, People's Republic of China (WL, QH, JH); Wenzhou Medical University, Wenzhou, Zhejiang, People's Republic of China (XH); and Key Laboratory of Vision Science, Ministry of Health People's Republic of China, Wenzhou, Zhejiang, People's Republic of China (JH).

Supported in part by the Medical and Health Science and Technology Program of Zhejiang Province (2017KY493, 2019KY111) and Foundation of Wenzhou City Science & Technology Bureau (Y20180174).

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (WL, JH); data collection (YM, YL, XH); analysis and interpretation of data (WL, YM, QH); writing the manuscript (WL); critical revision of the manuscript (WL, YM, YL, XH, QH, JH); statistical expertise (WL); administrative, technical, or material support (JH); supervision (XH)

Correspondence: Weicong Lu, MD ( lwc717@126.com), and Jinhai Huang, MD, MS, PhD ( vip999vip@163.com), Eye Hospital of Wenzhou Medical University, 270 West Xueyuan Road, Wenzhou, Zhejiang 325027, People's Republic of China. E-mail: lwc717@126.com

Received: October 11, 2018
Accepted: May 09, 2019

10.3928/1081597X-20190510-01

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