However, the measurements of corneal power and WTW distance is seldom reported. showed that the iTrace device exhibits a high level of repeatability for measuring corneal aberrations. TX, USA) integrates corneal topography with a ray-tracing aberrometer, yielding information about refractive, wavefront and corneal topographic data of the human optical system. The commercially available iTrace system (Tracey Technologies Corp. Clinical wavefront aberrometers allow an objective measurement of optical aberrations other than sphere and cylinder, such as spherical aberration, coma, trefoil, and other higher-order optical aberrations (HOAs), which present diagnostic and therapeutic applications. Currently, corneal wavefront analysis has gained increased importance in-line with the development of wavefront sensing technology. Until recently, the Orbscan II topography system (Bausch & Lomb, Orbtek Inc., UT, USA) has been widely applied for measuring the corneal power and WTW distance and is considered accurate and reproducible. With the wider use of phakic IOLs, accurate determination of the WTW distance has gained increased attention in sizing posterior chamber phakic IOLs and estimating the postoperative vault height in eyes with implantable collamer lenses (ICL STAAR Surgical AG, Nidau, Switzerland). Precise keratometry measurements are particularly crucial in determining the correct IOL power for patients who had previously undergone corneal refractive surgery. The IOL power is usually calculated using standard IOL calculation formulas, which are based on the value of corneal power. Accurate intraocular lens (IOL) power calculations, contact lens fitting, and monitoring postoperative cornea are major clinical applications of these parameters. Measurements of corneal power and WTW distance are important prior to either cataract or refractive surgery. Trial registrationĬlinical trials number: ChiCTR-OCS-14005077 (August 2nd, 2014). Conclusionsįor some clinical applications, the keratometry and WTW distance measurements obtained by the Orbscan II topographer and the iTrace aberrometer differed greatly and therefore were not interchangeable. For the measurement of WTW distance, the range of the 95 % LoA between the two devices was 0.47 mm. For the measurement of corneal power, the 95 % limits of agreement (LoA) between the Orbscan II and iTrace were − 0.21 to 1.21 D for the flat meridian and − 0.15 to 1.25 D for the steep meridian. The mean WTW distance measurements with the Orbscan II and iTrace were 11.57 ± 0.34 and 11.33 ± 0.36 mm, respectively ( P < 0.0001). The mean keratometry values with the Orbscan II and iTrace were 43.16 ± 1.44 and 42.64 ± 1.43 diopter (D), respectively ( P < 0.0001). Statistical evaluation was performed using the paired t test, Pearson correlation, and Bland-Altman analysis for comparison of measurement techniques. Keratometry readings in the flat (Kf) and steep (Ks) meridians and WTW distance were measured with the Orbscan II and iTrace systems in 100 myopic patients. The purpose of this study was to compare corneal power and horizontal corneal diameter (white-to-white distance) readings obtained by the Orbscan II topographer and the iTrace aberrometer.
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