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مقاله
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Abstract
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Title:
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Agreement among simulated keratometric astigmatism and total corneal astigmatism measured by vector summation and ray tracing methods
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Author(s):
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Sepehr Feizi, MD, MSc; Siamak Delfazayebaher, MD; Vahid Ownagh, MD; Fatemeh Sadeghpour, MD; Mohammad Ali Javadi, MD
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Presentation Type:
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Oral
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Subject:
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Cornea and Refractive
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Others:
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Presenting Author:
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Name:
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Vahid Ownagh
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Affiliation :(optional)
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Ophthalmic Research Center,Labbafinejad Medical Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
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E mail:
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vownagh@yahoo.com
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Phone:
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22135156
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Mobile:
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09126991021
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Purpose:
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To evaluate agreement among simulated keratometric astigmatism (KASim), total corneal astigmatism calculated by vector summation of anterior and posterior corneal astigmatism (TCAVec), and total corneal astigmatism using ray tracing (TCARay).
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Methods:
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A total of 204 right eyes of 204 normal subjects were enrolled. The eyes were measured using a Galilei double Scheimpflug analyzer. The measured parameters included KASim using keratometric index (1.3375), anterior corneal astigmatism using corneal refractive index (1.376), posterior corneal astigmatism, and TCARay. TCAVec was derived by vector summation of the astigmatism on anterior and posterior corneal surfaces. Magnitudes and axis orientations of KASim, TCAVec, and TCARay were compared using repeated measure ANOVA and Friedman. The Pearson correlation coefficient was calculated to assess the relationship between KASim and TCARay and between TCAVec and TCARay and Bland-Altman plots were used to assess agreement between KASim and TCARay and between TCAVec and TCARay in terms of magnitudes and axis orientations.
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Results:
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The mean KASim, TCAVec, and TCARay magnitudes were 1.09±0.82 D, 0.76±0.57 D, and 1.00±0.78 D, respectively (P<0.001). The mean axis orientations were 85.55±30.51 degrees, 85.12±30.26 degrees, and 89.67±36.76 degrees, respectively (P=0.002). Strong correlations were found between the KASim and TCARay magnitudes (r=0.98, P<0.001) and between the TCAVec and TCARay magnitudes (r=0.96, P<0.001). Moderate associations were observed between the KASim and TCARay axes (r=0.77, P<0.001) and between the TCAVec and TCARay axes (r=0.75, P<0.001). The width of the 95% limits of agreement was narrower between the KASim and TCARay magnitudes (-0.40 to +0.21 D) than between the TCAVec and TCARay magnitudes (-0.33 to +0.82 D). The 95% limits of agreement between the KASim and TCARay axes was (-42.2 to 50.4 degrees) was similar to that between the TCAVec and TCARay axes (-43.0 to 52.1 degrees).
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Conclusion:
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The magnitudes and axes of astigmatisms measured by the three methods cannot be used interchangeably. There are systematic errors between the KASim and TCARay magnitudes and between the TCAVec and TCARay magnitudes.
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Attachment:
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