[Comparison of corneal refractive power and astigmatism measured by the new anterior segment optical coherence tomographic device and Scheimpflug imaging device in age-related cataract patients].
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Objective: To compare the difference and agreement of corneal refractive power and astigmatism measured by the new swept-source anterior segment optical coherence tomography (SS-AS-OCT) device (CASIA2) and Scheimpflug imaging device (Pentacam) in age-related cataract patients. Methods: In this cross-sectional study, 112 eyes of 112 patients with age-related cataract were examined before phacoemulsification in the Tianjin Medical University Eye Hospital from April to May 2020. The steep keratometry (Ks), flat keratometry (Kf), mean keratometry (Km), degree and axis of astigmatism of the corneal anterior and posterior surfaces and the total cornea were recorded. The difference in astigmatism was analyzed by the arithmetic method and the vector method. The difference of data was evaluated using Paired t test or Wilcoxon test. The agreement of data was evaluated using Bland-Altman plots. Results: The patients were 44 males and 68 females with an average age of (67±10) years. There were no statistically differences in the Ks and Km values of the corneal anterior surface between the Pentacam and the CASIA2 (both P>0.05). There was significant difference in the Kf values of the corneal anterior surface between the Pentacam and the CASIA2 [(44.24±1.73) D vs. (44.14±1.64) D; t=2.278; P 0.05). Vector operation results showed that the astigmatism difference vector (DV) of the Pentacam and the CASIA2 on the anterior surface of the cornea was 0.06 D@57°±0.64 D,>0.50 D in 47 eyes (41.96%). The astigmatism DV on the posterior surface of the cornea was 0.07 D@174°±0.21 D, >0.50 D in 2 eyes (1.79%). The astigmatism DV on the total cornea was 0.13 D@3°±0.69 D,>0.50 D in 59 eyes (52.68%). The results of the two devices were positively correlated (r values of the Ks, Kf, Km, and astigmatism degree on the anterior surface of the cornea were 0.970, 0.968, 0.976, and 0.697, respectively, on the posterior surface of the cornea were 0.918, 0.875, 0.925, and 0.517, respectively, and on the total cornea were 0.951, 0.955, 0.959, and 0.622, respectively; all P<0.01). Bland-Altman analysis showed that the Ks, Kf, Km, and astigmatism degree of the corneal anterior and posterior surfaces measured by the two devices were consistent, with 2.68% to 8.04% of the measured values outside 95% limits of agreement (95%LoA). The 95%LoA of the total corneal Ks, Kf, and Km between the two devices was 0.01 to 2.28 D, 0.06 to 2.27 D, and 0.10 to 2.20 D, respectively, with a wide 95%LoA range and poor consistency. Conclusions: The corneal refractive power and astigmatism measured by the CASIA2 and the Pentacam shows little difference on the anterior surface of the cornea, with good agreement. However, the refractive power results of the posterior surface of the cornea and the total cornea show great difference, suggesting that these two instruments cannot be used interchangeably in clinical practice. (Chin J Ophthalmol, 2021, 57: 48-55).Keywords:
Scheimpflug principle
Astigmatism
Anterior Eye Segment
Astigmatism
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Objective To observe the result of measuring corneal astigmatism with a quantitative microkeratoscope.Methods Refractive error and the axis of corneal astigmatism of 101 eyes from 68 subjects were measured with a quantitative microkeratoscope to obtain the mean values from three measurements,and then the eyes were checked with both a keratometer and keratopographer.The measurements obtained with the three instruments were statistically analyzed for agreement.Results The corneal astigmatism readings obtained with the microkeratoscope,keratometer and keratopographer were(2.62±1.20)D,(2.66±1.26)D,and(2.66±1.26)D,respectively.And the axis values were 92.29°±10.90°,92.81°±11.15°,and 93.33° ±10.94°,respectively.There were no statistically significant differences among the measurement data from the 3 different devices for degree of corneal astigmatism and the axis of corneal astigmatism.Conclusion When corneal astigmatism is measured with a quantitative microkeratoscope,the measurements are comparable to those obtained by both keratometry and keratopography.
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To determine the agreement of measurements between color light-emitting diode corneal topography (Cassini) and Scheimpflug camera keratometry (Pentacam HR).The current retrospective study investigated 117 right eyes of 117 healthy patients before cataract surgery from June 2017 to July 2017. Steep K, flat K, mean K, astigmatism, and axis for both anterior and posterior corneal surface were measured using the two devices. The measured values were converted into J vectors such as J0 and J45. The mean difference for those measurement values were compared between the two instruments, and the agreement was evaluated using the Bland-Altman plot I.There were statistically significant differences in mean K (44.21D [43.34 to 45.34] and 44.30D [43.30 to 45.10] by Cassini and Pentacam [P = 0.004]) and astigmatism (0.90D [0.58 to 1.30] and 0.70D [0.40 to 1.30] by Cassini and Pentacam [P = 0.002]) on the anterior corneal surface and flat K (- 6.21D [- 6.39 to - 6.07] and - 6.30D [- 6.5 to - 6.10] by Cassini and Pentacam [P < 0.001]), mean K (- 6.39D [- 6.54 to - 6.25] and - 6.40D [- 6.60 to - 6.30] by Cassini and Pentacam [P = 0.019]), and astigmatism (0.33D [0.22 to 0.47] and 0.30D [0.15 to 0.40] by Cassini and Pentacam [P = 0.002]) on the posterior corneal surface. The mean difference (= Cassini - Pentacam) with 95% limit of agreement for mean K and astigmatism of the anterior corneal surface were 0.082D (- 0.60 to 0.76) and 0.11D (- 0.73 to 0.95) for measurements obtained by the two instruments, respectively. Regarding keratometric values from the posterior corneal surface, the mean differences for flat K, mean K, and astigmatism were - 0.081D (- 0.42 to 0.26), - 0.030D (- 0.32 to 0.26), and 0.067D (- 0.33 to 0.46), respectively. Intraclass correlation coefficients for steep K, flat K, mean K, and vector J0 were higher than 0.9 in the anterior cornea. Positive correlation in steep K, flat K, mean K, astigmatism, and J0 was found between two devices in both anterior and posterior cornea (P < 0.001).Corneal refractive power and astigmatism tend to be higher when measured using Cassini than Pentacam HR in both anterior and posterior cornea. The two different devices might not be used interchangeably.Retrospectively registered. Registration number: KC17RESI0439 .
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Purpose.: Description of total corneal refractive power (TCRP) astigmatism by ray tracing using a Scheimpflug tomographer.
Scheimpflug principle
Meridian (astronomy)
Astigmatism
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Objective
This study was to investigate the characteristics of posterior corneal astigmatism (PCA) and aberration in cataract patients with high myopia.
Methods
A retrospective study was designed.Two hundred and eighty-two eligible eyes of 190 cataract patients were enrolled in Eye and ENT Hospital of Fudan University from September to December, 2014.The eyes were classified into two groups according to axial length (AL): high myopia group with 139 eyes (AL≥26 mm) and control group with 143 eyes (AL was 20 to 25 mm). The mean keratometric mid-radius of curvature (Km), corneal central thickness (CCT), astigmatism and aberrations were measured by the rotating Scheimpflug System (Pentacam), and the AL were measured by the partial coherence interferometry (IOL Master). This study followed the Helsinki declaration, and was approved by the Ethic Committee of Eye and ENT Hospital, Fudan University.Informed consent was signed from each patient.
Results
In high myopia group, the mean PCA was 0.3 D (range 0~0.9 D) and 92.8% eyes had PCA values <0.5 D. The steep corneal meridian was aligned vertically (60°~120°) in 87.1% eyes for the posterior corneal surface.There was no significant difference in PCA between the high myopia group and the control group (P=0.797). Significant positive linear correlations was found between PCA and anterior corneal astigmatism (ACA), PCA and anterior corneal root mean square (RMS), PCA and anterior lower-order RMS, PCA and posterior corneal RMS, PCA and posterior high-order RMS, PCA and posterior lower-order RMS (r=0.235, P=0.005; r=0.217, P=0.010; r=0.229, P=0.007; r=0.395, P=0.000; r=0.243, P=0.004; r=0.384, P=0.000). Compared with total corneal astigmatism (TCA), anterior corneal measurements overestimated with-the-rule astigmatism (WTR) by a mean of (0.27±0.18)D in 65.67% eyes, underestimated against-the-rule astigmatism (ATR) by (0.27±0.18)D in 88.10% eyes and underestimated oblique astigmatism (Obl) by (0.22±0.10)D in 63.33% eyes.Compared with total corneal aberrations, anterior corneal aberrations measurements overestimated by (0.275±0.176)μm in 87.05% eyes, and the anterior corneal astigmatism types had no effect on the result.
Conclusions
In high myopia group, 92.8% eyes had PCA values <0.5 D and the main astigmatism type in posterior corneal surface was ATR.The posterior corneal astigmatism and aberration were needed to consider in choosing intraocular lens (IOL) before cataract surgery.
Key words:
High myopia; Secondary cataract; Posterior corneal surface; Astigmatism; Aberration
Scheimpflug principle
Meridian (astronomy)
Astigmatism
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SettingsThe Faculty of Medicine, Alexandria University, Egypt.PurposeThe aim of this work was to study the contribution of posterior corneal astigmatism to total corneal astigmatism.Patients and methodsA descriptive prospective observational study that included 100 eyes of 100 patients aged 18 years and above. Scheimpflug camera imaging was performed using a Pentacam. The following data were recorded: anterior corneal radii of curvature, posterior corneal radii of curvature and astigmatism, simulated keratometry (sim K) and astigmatism, the true net power and astigmatism, and central corneal pachymetry. All included participants signed a written informed consent.ResultsThe mean age was 38.11 ± 12.69 years. The orientation of the steep axis of the anterior corneal surface was vertical in 70% of the cases, resulting in with-the-rule astigmatism. For the posterior corneal surface, the steep axis orientation was vertical in 94% of the cases, resulting in against-the-rule (ATR) astigmatism. The mean sim K astigmatism was higher than that of the true net K astigmatism by 0.12 ± 0.18 D (range -0.3-0.4 D) at 4 ± 5° (range 0-21°).ConclusionAnterior corneal with-the-rule astigmatism tends to change to ATR astigmatism with age. The posterior corneal surface showed ATR astigmatism regardless of the age. Using data from the anterior corneal surface only resulted in a higher astigmatism of 0.12 D compared with using data from both the anterior and the posterior surfaces. Also, data from the anterior corneal surface alone resulted in a difference in the axis of more than 10° in 11% of the cases.
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Astigmatism
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Purpose: To assess the repeatability and accuracy of corneal astigmatism measurement with a spectral-domain optical coherence tomography (OCT) system (Avanti, Optovue) and compare them with Scheimpflug imaging (Pentacam HR, Oculus) and swept-source optical biometry (IOLMaster 700, Carl Zeiss Meditec AG). Setting: Casey Eye Institute, Oregon Health & Science University, Portland, Oregon. Design: Prospective cross-sectional observational study. Methods: 60 pseudophakic eyes with monofocal nontoric intraocular lens that previously had refractive surgery were analyzed. To assess accuracy, simulated keratometry (SimK) and net corneal astigmatism, obtained from each device, were compared with subjective manifest refraction astigmatism. Repeatability for corneal astigmatism was assessed for OCT and Pentacam HR by the coefficient of repeatability from 3 repeated measures. Results: Compared with manifest refraction, SimK readings produced with-the-rule astigmatic bias that was reduced for net astigmatism for the 3 devices. Except for OCT net astigmatism, all instruments significantly overestimated the magnitude of the astigmatism (linear mixed-effects model [LMM], P < .05). OCT net astigmatism showed the highest accuracy for manifest astigmatism prediction with the smaller 95% confidence ellipse for the mean difference vector. OCT net mean absolute difference was 0.57 diopters (D), significantly smaller than that of the other modalities (LMM, P < .05). Net corneal astigmatism measured with OCT showed the best repeatability (coefficient of repeatability = 0.29 D). Conclusions: OCT has the capability to measure net corneal astigmatism with higher precision and accuracy than Pentacam HR Scheimpflug imaging and IOLMaster 700 swept-source optical biometry in postrefractive subjects.
Scheimpflug principle
Repeatability
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Keratoconus is a chronic, progressive, noninflammatory, ectatic corneal disorder that deteriorates vision because of myopia and irregular astigmatism [1].The condition usually arrests in the third to fourth decades of life, although it can commence later and progress at any age [1].Currently, a rigid gas-permeable contact lens, intrastromal corneal ring segment implantation, corneal collagen cross-linking, photorefractive keratectomy, and a phakic intraocular lens (IOL) are the treatment options for keratoconus.Collagen cross-linking affects the progression of and can
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Meridian (astronomy)
Astigmatism
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Objective
To evaluate the distribution characteristics of the asphericity (Q-value) of the corneal surfaces in a Chinese population who were candidates for excimer laser surgery; to provide some theoretical bases for clinical diagnosis and treatment.
Methods
This was a perspective study. Using the Pentacam HR measuring and analyzing system based on Scheimpflug photography, the right eyes of 75 Chinese myopes were evaluated for excimer laser surgery. Patients were divided into a low corneal astigmatism (<+1.00 D) group and a medium-high corneal astigmatism (≥+1.00 D) group according to the anterior corneal surface astigmatism. The analysis was based on the distribution characteristics of the mean Q-values of both the anterior and posterior corneal surfaces and the distribution characteristics of the Q-value at different angles (20°, 25° and 30°) and along different semi-meridians (superior, inferior, nasal and temporal). Single factor analysis of variance was used to determine if there was a difference among Q-values within a particular group. The differences between the two groups were analyzed by an independent samplest-test.
Results
The mean Q-values of the 30° angle in Chinese myopes evaluated for excimer laser surgery were-0.17±0.09 and-0.02±0.16 on the anterior and posterior corneal surfaces, respectively. The mean Q-values of the anterior corneal surface at different angles were negative and there was no statistically significant difference between the low corneal astigmatism group and medium-high corneal astigmatism group. There was a significant difference between the Q-values of the 2 groups at different angles (F=6.340, 9.963,P 0.05). In the medium-high corneal astigmatism group, QT30 was significantly bigger than QN30(P QN30 and QI30>QS30, but there was no statistically significant difference between QT30 and QS30.
Conclusion
The curvature along the anterior corneal surface becomes flatter from the center to the periphery, while it becomes steeper from the center to the periphery at the posterior corneal surface. The rate of the flattening of the anterior corneal surface increased as the range of the angle increased, while the rate decreased as the posterior corneal surface decreased. All the shapes on the anterior surface along different semi-meridians were long ovals. Corneal astigmatism does not affect corneal shape. The shapes of the posterior surface along the superior and inferior semi-meridians were short ovals, but were long ovals along the nasal and temporal semi-meridians.
Key words:
Cornea; Asphericity; Scheimpflug Photography
Scheimpflug principle
Astigmatism
Chinese population
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Quadrant (abdomen)
Astigmatism
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