Those with a history of ocular pathology, corneal or intraocular trauma ocular surgery who have worn soft contact lenses within 2 weeks or rigid contact lenses within 4 weeks or who reported subjective dry eye symptoms or who had a tear film break-up time shorter than 5 s were excluded from this study. Ninety-two right eyes of 92 normal and healthy subjects who were well communicated and cooperated with satisfying fixation ability with a best corrected distance visual acuity equal to or better than 20/20 were included in this study. The Declaration of Helsinki was strictly followed in all procedures. Written informed consent, which was approved by the Office of Research Ethical Committee of the hospital, was obtained from all subjects. The present study was conducted at the Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital. Since the more important function of the two devices is the measurement of HOAs, in this study, we estimated the precision (repeatability and reproducibility) and agreement of ocular, corneal and internal HOAs under 4 mm pupil diameter obtained by Topcon KR-1 W and iTrace in normal eyes. In a previous study, we evaluated the repeatability and reproducibility of corneal power measurements obtained by Topcon KR-1 W and iTrace. However, to the best of our knowledge, few studies have reported the assessment of precision (repeatability and reproducibility) and agreement of HOAs obtained by the two devices, simultaneously. Several studies have assessed the repeatability or reproducibility of HOA measurements obtained by Topcon KR-1 W and iTrace, respectively. Both the Topcon KR-1 W system (Hartmann-Shack method) and the iTrace system (ray tracing method) are devices composed of an aberrometer and a corneal topographer. The principles of these aberrometers can be divided into the Hartmann-Shack method, the ray tracing method, the Tscherning principle, etc. Thus intraocular aberrations could be obtained by subtracting the ocular aberrations from corneal aberrations. Recently, ocular aberrations have been obtained using data from the aberrometers. Traditionally, corneal topographers can provide corneal aberrometry according to special algorithms based on elevation data. During the past decade, aberrometers have been used in many fields of ophthalmology and optometry, including the observation of refractive errors, the diagnosis of dry eye diseases and keratoconus, and refractive surgery. Several wavefront analysers (known as aberrometers) have been developed to detect wavefront aberrations (especially HOAs). Higher order aberrations (HOAs) are small irregularities or imperfections of the eye that cannot be corrected by conventional spectacles. Wavefront aberrations include defocus, astigmatism, and higher order aberrations. The two aberrometers should not be interchangeable in clinical application because of the significant differences in HOA measurements between them. The ray tracing and Hartmann-Shack method aberrometers provided excellent repeatability but less reliable reproducibility in the measurement of HOAs (except for SA). No significant differences were observed in the ocular SA and internal coma. For the ocular, corneal and internal HOA measurements, statistically significant differences existed between the Topcon KR-1 W and iTrace (all P < 0.05). The ICCs of the internal HOAs of interobserver reproducibility were less than 0.75 except for spherical aberration (SA) (0.862), and interobserver reproducibility of the counterpart showed similar but lower results. Resultsįor intraobserver repeatability of the ocular, corneal and internal HOAs, Topcon KR-1 W showed a 2.77Sw of 0.079 μm or less and ICCs of 0.761 or more and iTrace showed a 2.77Sw of 0.105 μm or less and ICCs of 0.805 or more. The within-subject standard deviation (Sw), test-retest repeatability (TRT) and intraclass correlation coefficient (ICC) were used to assess the precision, while Bland-Altman plots were performed to assess the agreement. About one week later, one observer performed an additional 3 consecutive scans to obtain the intersession reproducibility. Two observers performed 3 consecutive scans to determine the intraobserver repeatability and interobserver reproducibility. Data from the right eyes of 92 normal subjects obtained using the two devices were included in this study. Prospective evaluation of the diagnostic test. To assess the precision and agreement of measurements of higher order aberrations (HOAs) obtained with a ray tracing aberrometer (iTrace) and a Hartmann-Shack aberrometer (Topcon KR-1 W).
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