After not wearing the RGP lens for at least 30 minutes, the eyes of patients with keratoconus or those of keratoconus suspect were measured without the lens. Of the normal control subjects, none wore contact lenses before the wavefront aberrations were measured without an RGP lens. The measurements from eyes evaluated for the effects of the RGP lens were taken when the RGP lens was in the resting position. The measurements were repeated in each eye at least three times to obtain well-focused, properly aligned Hartmann images in a dark room without mydriasis. All subjects were diagnosed by one physician, whereas the wavefront measurements were performed by other physicians independently. The HOAs of the central 4-mm corneal diameter were obtained with the Hartmann-Shack wavefront analyzer (KR-9000PW Topcon Corp., Tokyo, Japan). Although RGP lenses correct the irregular astigmatism, smaller comet-like retinal images in the opposite direction remain due to residual vertical coma. In addition to the larger amount of trefoil, coma, tetrafoil, and secondary astigmatism, keratoconic eyes tend to have a reverse coma pattern and reverse trefoil aberrations compared with normal eyes. Although the total HOAs were significantly (keratoconus and keratoconus suspect, P < 0.001 and P = 0.012, respectively) reduced with an RGP lens, the patterns of the axes of coma and trefoil were reversed with the lens.Ĭonclusions. The mean axes of trefoil in patients with keratoconus (93.8°) and keratoconus suspect (100.6°) differed from that in normal subjects (35.4°), indicating that keratoconus has a reverse trefoil pattern from that of normal eyes. Zernike vector analysis showed prominent vertical coma with an inferior slow pattern, with mean axes of 82.5° or 91.0° in the patients with keratoconus or keratoconus suspect, respectively. Ocular higher-order aberrations (HOAs) were measured with a wavefront sensor for a 4-mm-diameter pupil, and the magnitudes, axes of trefoil, and coma were calculated by vector analysis. To determine the effect of RGP lenses, 19 eyes with keratoconus, 9 eyes with keratoconus suspect, and 17 normal eyes, with and without an RGP lenses, were compared. A total of 76 eyes with keratoconus, 58 eyes with keratoconus suspect, and 105 normal eyes were studied. To measure the magnitude and orientation of the Zernike terms in keratoconic eyes, with and without rigid gas-permeable (RGP) contact lenses. The non-orthogonality of the Zernike modes with respect to the merit function should be taken into account when designing the algorithm for image-based wavefront correction, because it may slow down the process or lead to premature convergence.Purpose. We show that for combinations of Zernike modes with the same azimuthal order, a flatter wavefront in the central region of the aperture is more important than the RMS wavefront error across the full aperture for achieving a better merit function. Using wavefront maps, the PSF, and the MTF, we discuss the physical causes for the non-orthogonality of the Zernike modes with respect to the merit function. In severely aberrated systems, the Zernike modes are not orthogonal to each other with respect to this merit function. We use an image-sharpness metric as merit function to evaluate the image quality, and the Zernike modes as control variables. With a view to future large space telescopes, we investigate image-based wavefront correction with active optics. The evaluation of the quality of aberrated images is conducted with the help of the two widely used metrics: Mean Square Error (MSE) and Peak-Signal to Noise Ratio (PSNR). The presented algorithm (imaging system simulation) is applied on two high resolution remote sensing images, acquired by GeoEye-1 and IKONOS-1 satellites in order to study the effect of aberrations on the satellite images quality in terms of point spread function (PSF) and the modulation transfer function (MTF) variations. The optical aberrations are simulated by Zernike polynomial to determine their effects on the image quality. focal length, pixel size of the CCD, F-number, entrance aperture diameter, etc.) is simulated using MATLAB program. Also a comparative study among different types of aberrations is carried out. This paper investigates the effect of different optical aberrations on satellite image quality. However the light diffraction and optical aberrations are main sources of image quality degradation. A convenient measure of the image quality is the ability of the optical system to transfer various levels of details from object space to image plane. However, there are many distortions associated with images taken by satellites optical sensors which degraded the image quality. Satellite imaging is used for gathering detailed information about earth.
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