A repeated-measures analysis of variance (ANOVA) with Bonferroni correction was used to compare total ocular aberrations and corneal aberrations between devices and to determine whether these are significantly different. 14 This method computes 95% limits of agreement (LoA), defined as the mean difference ☑.96 The agreement between two devices was studied by using the method described by Bland and Altman. To determine a relationship between measurements of two devices, we performed bivariate correlations to determine the Pearson's correlation coefficient. Data were normally distributed and allowed us to use parametric tests. 8Īll data were collected in a database (Excel Microsoft Office 2003 Redmond, WA) and transferred for data analysis (SPSS for Windows, ver. The time difference of the reflected light is used to determine the aberrations. The retina is scanned with a slit-shaped light beam and the reflected light is captured by an array of rotating photodetectors over a 360° area. 5, 7 The third type, automated retinoscopy, is based on dynamic skiascopy. Aberrations in the optical system cause a shift in the location of the light spot on the retina. Once the position of the first light spot on the retina is determined, the laser beam is moved to a new position, and the location of the second light spot on the retina is determined. It projects a thin laser beam into the eye, parallel to the visual axis and determines the location of the beam on the retina by using a photodetector. 5, 6 A Tscherning, or ray-tracing, aberrometer is an ingoing instrument. The displacement of each spot from the corresponding nonaberrated reference position is used to determine the shape of the wavefront. An array of microlenslets is used to subdivide the outgoing wavefront into multiple beams which produce spot images on a video sensor. It measures the shape of the wavefront that is reflected out of the eye from a point source on the fovea. A Hartmann-Shack aberrometer is an outgoing wavefront aberrometer. Three different wavefront measuring principles are available to measure aberrations: (1) Hartmann-Shack, (2) Tscherning or ray tracing, and (3) automated retinoscopy. 5 However, the success of clinical applications of wavefront analysis depends on the accuracy and reliability of the aberrometers. In addition, it may be used to evaluate eyes with abnormal optics due to ageing or corneal disorders, such as keratoconus and pellucid marginal degeneration. 1 – 4 Wavefront analysis may be performed to design an ideal refractive correction, which corrects not only lower-order aberrations (sphere and cylinder), but also higher-order aberrations. Measurement of higher-order aberrations has changed from a laboratory or research application to a clinical application and may be used for example in wavefront-guided excimer laser surgery, lens implantation surgery, and contact lens fitting. It provides an estimation of the optical quality of the eye that extends beyond the description of spherical and cylindrical refractive errors. Wavefront analysis allows for a detailed evaluation of imperfections in the optical system of the eye, caused by the refractive surfaces of the anterior and posterior cornea and the lens. It would be worthwhile in the future to evaluate aberrometers in patients with more aberrant eyes. Hartmann-Shack aberrometers showed the best repeatability for total ocular aberrations and iTrace for corneal aberrations. ![]() Total ocular and corneal aberrations are not comparable when measured with different aberrometers. The OPD-Scan showed a lower interobserver variability, compared with the Irx3, Keratron, and iTrace. ![]() The repeatability of the corneal aberration measurements was highest for the iTrace, followed by the Keratron and OPD-Scan. The Irx3 showed the highest repeatability in measuring total ocular aberrations, followed by the Keratron, OPD-Scan, and iTrace. Significant differences in measurements were found for several total ocular aberrations (defocus, astigmatism, trefoil, trefoil, and spherical aberration ) and corneal aberrations (defocus and astigmatism ). Second-, third- and fourth-order spherical aberrations were exported for 5.0-mm pupils. In this prospective comparative study, 23 healthy subjects underwent bilateral examination with four aberrometers: the Irx3 (Hartmann-Shack Imagine Eyes, Orsay, France), Keratron (Hartmann-Shack Optikon, Rome Italy), iTrace (ray-tracing Tracey Technologies, Houston, TX), and OPD-Scan (Automated Retinoscopy Nidek, Gamagori, Japan). ![]() To compare total ocular aberrations and corneal aberrations identified with four different aberrometers and to determine the repeatability and interobserver variability.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |