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H. Mori, Y. Sakurai, S. Koshika, H. Goto, Y. Yasuno, Computational Optics and Ophthalmology group; Diagnosis of Keratoconus by Anterior Segment Three-Dimensional Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5087.
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© ARVO (1962-2015); The Authors (2016-present)
The advent of high-speed anterior segment three-dimensional optical coherence tomography (anterior segment 3D-OCT) has allowed accurate measurement of radius of corneal curvature and creation of accurate corneal curvature mapping. The objectives of this study were to compare the corneal curvature maps obtained from anterior segment 3D-OCT and conventional corneal topography, and to evaluate novel keratoconus screening based on approximation by Bézier curve of third order.
Ten normal eyes and 10 keratoconic eyes were studied. For anterior segment 3D-OCT, the CASIATM instrument (TOMEY Co.) was used. The selected scan pattern was radial scan with a measurement range of 10 mm. Within the scan time of approximately 0.3 second, a set of B-slice images with 512 A-lines in 128 radial directions was obtained. For conventional corneal topography, the TMS-4TM and PentacamTM instruments were used. The B-slice image with the steepest meridian was selected as the target image for keratoconus screening. The anterior corneal curve on the target image was approximated to Bézier curve constructed from one joint and six control points. The curve of the central cornea was approximated to the 3rd and 4th control points. The kurtosis and skewness of the corneal shape were defined by the distance and slope of these two control points were compared between normal and keratoconic eyes.
In mild and moderate keratoconus, the corneal curvature maps obtained from CASIA were similar to the results taken both by TMS-4 and Pentacam. The kurtosis of corneal shape in normal eyes and keratoconic eyes was 5.44 ± 0.1 and 4.62 ± 0.77 mm, respectively (p = 0.003), and the skewness of corneal shape was 0.73 ± 0.32 and 3.36 ± 2.33° (p = 0.002), and significant differences (t-test) were observed.
The corneal curvature maps of keratoconic eyes obtained from CASIA were similar to the results of conventional topography, indicating that CASIA adequately depicts the corneal shape of keratoconus. The kurtosis and skewness of corneal shape defined by the Bézier curve may be used for keratoconus screening.
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