Comparison of keratometric and topographic cylinder and axis measurements on normal corneas with low astigmatism (original) (raw)
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Journal of Cataract & Refractive Surgery, 2012
To compare the corneal astigmatism (magnitude and axis location) derived by total corneal power (TCP), automated keratometry, and simulated keratometry. Siriraj Hospital, Mahidol University, Bangkok, Thailand. Prospective comparative study. Eyes with previous ocular surgery or abnormalities were excluded. All patients were examined with the ARK 730A autokeratometer and the Galilei analyzer. The steepest and flattest corneal power along with the steepest axis of the TCP, automated keratometry, and simulated keratometry were recorded. Vector analysis (J0 and J45) was calculated. Analysis of variance with Bonferroni correction was performed for multiple comparisons. Outcome measures were the magnitude and axis location of astigmatism. One hundred eyes of 100 cataract patients were randomly selected. There was no statistically significant difference in the mean steepest axis between TCP (93.31 ± 68.75 [SD]), automated keratometry (94.24 ± 64.78), and simulated keratometry (92.42 ± 64.30). However, the mean magnitude of astigmatism measured by TCP (1.23 ± 0.75) was significantly higher than that measured by automated keratometry (0.93 ± 0.68) (P=.01) but not than that measured by simulated keratometry (1.08 ± 0.68) (P=.43); there was no statistically significant difference in J0 or J45. Twenty two (40%) of 54 eyes with more than 1.00 diopter of TCP astigmatism had more than 10 degrees of axis difference from automated keratometry. The magnitude of TCP astigmatism was higher than that of automated keratometry. The axis location was similar. However, there was more than 10 degrees of axis difference between automated keratometry and TCP in patients with high astigmatism. No author has a financial or proprietary interest in any material or method mentioned.
Correlation Between Anterior Corneal Elevation Differences in Main Meridians and Corneal Astigmatism
Eye & Contact Lens: Science & Clinical Practice, 2019
To assess the correlation between anterior corneal elevation (ACE) and anterior corneal astigmatism (ACA) obtained with two different topographers in healthy subjects at different corneal diameters. Methods: A retrospective, comparative, and observational study was conducted. Topography data from 305 patients obtained with the Oculus Pentacam (Oculus, Wetzlar, Germany) and Sirius (CSO, Florence, Italy) systems were collected. Subjects were divided into four groups depending on the magnitude of ACA. The ACE was evaluated in the principal meridians at 2, 3, and 4 mm from the corneal apex. The difference in ACE between meridians (ACE-M) and in superior-inferior and nasal-temporal semimeridians (ACE-SM) was calculated. Results: A strong positive correlation between ACE-M and ACA with both topographers was found for all corneal diameters (P,0.001). A linear equation to calculate the ACE-M differences as a function of the astigmatism at 8 mm of diameter was obtained: y¼23.417x+1.40, where y is ACE-M in microns and x is ACA in diopters. Significant differences in ACE along SM were found for all groups studied according to the magnitude of ACA for the horizontal SM (P.0.001). The temporal meridian was more elevated at 4-and 6-mm diameters, and the nasal semimeridian was the most elevated for 8 mm. Conclusion: Anterior corneal astigmatism and elevation differences are strongly correlated, providing more corneal topography knowledge that could be applied in the contact lens fitting. A toric orthokeratology lens may be indicated in ACA greater than 0.75 D.
Comparability and repeatability of different methods of corneal astigmatism assessment
Clinical ophthalmology (Auckland, N.Z.), 2018
To assess the comparability and repeatability of keratometric and astigmatism values measured by four techniques: Orbscan IIz(Bausch and Lomb), Lenstar LS 900(Haag-Streit), Cassini(i-Optics), and Total Cassini (anterior + posterior surface), in healthy volunteers. Fifteen healthy volunteers (30 eyes) were assessed by the four techniques. In each eye, three consecutive measures were performed by the same operator. Keratometric and astigmatism values were recorded. The intraclass correlation coefficient (ICC) was used to assess comparability and repeatability. Agreement between measurement techniques was evaluated with Bland-Altman plots. Comparability was high between all measurement techniques for minimum keratometry (K1), maximum keratometry (K2), astigmatism magnitude, and astigmatism axis, with ICC >0.900, except for astigmatism magnitude measured by Cassini compared to Lenstar (ICC =0.798) and Orbscan compared to Lenstar (ICC =0.810). However, there were some differences in t...
Astigmatic Vector Analysis of Posterior Corneal Surface; Healthy versus Keratoconic Corneas
Egyptian Journal of Ophthalmology, (Mansoura Ophthalmic Center), 2022
To define an unconventional diagnostic factor for keratoconus. Design: Observational descriptive comparative cross sectional study Method: This study included two hundred and forty-four eyes of 244 patients divided into groups; normal corneas, or controls (C, n [100]), fruste (FFKc, n [28]) and manifest keratoconus (Kc, n [116]). Full Ophthalmic examination was performed. All candidates were examined using a rotating Scheimpflug corneal tomographer (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) to obtain corneal measurements. Astigmatic vector analyses were carried out according to the method proposed by Thibos. Results: The area under receiver operating characteristic curve (AUC) for posterior corneal APV between normal and manifest keratoconus was 0.73 (95% confidence interval): 0.66-0.80. By using ROC curve Sensitivity, Specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy at cutoff 0.30 were (65.0%, 80.0%, 78.9%, 66.1% and 73.1% respectively). As regard posterior corneal Blur; the AUC between normal and manifest keratoconus was 0.92 (95% confidence interval): 0.88-0.96. By using ROC curve Sensitivity, Specificity, PPV, NPV and accuracy at cutoff 6.65 were (85.3%, 89.0%, 90.0%, 84.0% and 86.1%) respectively. Conclusion: Vector analysis of posterior corneal astigmatism; APV and Blur, is a simple, unbiased and complementary way in the differentiation of normal from manifest keratoconus.
Journal of Cataract and Refractive Surgery, 2014
Prospective case series. METHODS: Corneal astigmatism was measured using a Scheimpflug camera combined with a corneal topographer (Sirius). Keratometric astigmatism, anterior corneal astigmatism, posterior corneal astigmatism, and total corneal astigmatism were evaluated. Vector analysis was performed according to the Naeser method. RESULTS: One hundred fifty-seven eyes were enrolled. Keratometric astigmatism was with the rule (WTR), against the rule (ATR), and oblique in 84.0%, 11.5%, and 4.5% of eyes, respectively. Posterior corneal astigmatism exceeded 0.50 D and 1.00 D in 55.4% of eyes and 5.7% of eyes, respectively. The mean posterior corneal astigmatism was 0.54 D, inclined 91 degrees in relation to the steeper anterior corneal meridian. The steepest meridian was vertically aligned in 93.0% of cases. Compared with total corneal astigmatism, keratometric astigmatism overestimated WTR astigmatism by a mean of 0.22 D G 0.32 (SD), underestimated ATR astigmatism by 0.21
Ophthalmic and Physiological Optics, 2009
A knowledge of the shape of the cornea is of major importance for the planning and monitoring of surgery, and for the correct diagnosis of corneal diseases. Many authors have studied the geometry of the second corneal surface in the central region and it has been stated that there is a high correlation between the central radii of curvature and asphericities of the two corneal surfaces. In this work we extend this study to a larger, central, 6-mm diameter of the cornea. Surface height data, obtained with an Oculus Pentacam from 42 eyes from 21 subjects, were analysed to yield surface power vectors. Corneal heights of both surfaces were also decomposed into low-order Zernike polynomials and the correlations between each of the power vectors and low-order Zernike coefficients for the two surfaces were studied. There was not only a strong correlation between spherical powers and Zernike defocus coefficients, but also between the astigmatic components. The correspondence between the astigmatisms in both surfaces found here can be of the utmost importance in planning optical surgery, since perfect spherical ablation of the first surface does not assure total correction of corneal astigmatism.
Distribution of the anterior, posterior, and total corneal astigmatism in healthy eyes
International ophthalmology, 2017
To evaluate the magnitude and axis orientation of the anterior, posterior, and total corneal astigmatism in normal healthy eyes of an Iranian population. In a prospective cross-sectional study, ophthalmic and anterior segment parameters of 153 healthy eyes of 153 subjects were evaluated by Galilei dual Scheimpflug analyzer. The magnitude and axis orientation [with-the-rule (WTR), against-the-rule (ATR), and oblique] of the anterior, posterior, and total corneal astigmatism measurements (ACA, PCA, and TCA) were compared according to the age, sex, and other ophthalmic parameters. The mean ± SD age of the study population was 30 ± 5.9 years. The mean magnitude was 1.09 ± 0.76 diopters (D) for ACA, 0.30 ± 0.13 D for PCA, and 1.08 ± 0.77 D for TCA. Males had a significantly higher magnitude of PCA than females (p = 0.041). Most eyes had a WTR anterior astigmatism and an ATR posterior astigmatism. The WTR astigmatism had a higher mean magnitude compared to the ATR and oblique astigmatism ...
Ophthalmology Research: An International Journal, 2020
Purpose: This Clinical research was targeted to experimentally investigate the reliability between Placido topography and Scheimpflug topography in normal corneas with astigmatism ≤ ±0.50 Dc by comparing the refractive powers at the 4 main meridians (180⁰ - 90⁰) in order to study any differences between the two topographers and their reliability. Comparing the reliability measurements of Placido disk topography (CSO- Modi 02 Corneal Topographer with Phoenix Full & Pupil Module Software) with those of a high-resolution rotating Scheimpflug camera (Pentacam-Oculus,) and assess the agreement between these two topographers in measuring corneal power in normal eyes without astigmatism (≤ 0.50 Dc). Methods and Materials: Measurements were taken from 56 eyes corresponding to a proportion of patients, of which 26 were men with a mean age of ± 30 years and 30 were women with a mean age of ± 27 years. Refractive power maps were taken from the anterior cornea, having results for the steep meri...
Journal of ophthalmic & vision research, 2013
To determine the prevalence of keratoconus (KCN) and subclinical KCN among subjects with two or more diopters (D) of astigmatism, and to compare Pentacam parameters among these subjects. One hundred and twenty eight eyes of 64 subjects with astigmatism ≥2D were included in the study. All subjects underwent a complete ophthalmic examination which included refraction, visual acuity measurement, slit lamp biomicroscopy, retinoscopy, fundus examination, conventional corneal topography and elevation-based topography with Pentacam. The diagnosis of KCN and subclinical KCN was made by observing clinical findings and topographic features; and confirmed by corneal thickness and elevation maps of Pentacam. Several parameters acquired from Pentacam were analyzed employing the Mann-Whitney U Test. Mean age of the study population was 29.9±9.8 (range 15-45) years which included 39 (60.9%) female and 25 (39.1%) male subjects. Maximum corneal power, index of vertical asymmetry, keratoconus index a...