![]() Although it is necessary to stop wearing the RGP lens to avoid its effects before measurements are obtained, it is very difficult for patients with keratoconus to stop wearing the RGP lenses for long periods before measurements. Another limitation is that our study may have included some effects of contact lens–induced corneal warpage that were undetectable on topographic maps. ![]() It is necessary to analyze the serial changes of each Zernike vector term with a contact lens in keratoconic eyes when considering the effects of centration or movement of the contact lenses on HOAs. In addition, the HOAs might change because of movement of the contact lenses. The HOAs were measured only for a 4-mm-diameter pupil, to determine the optical quality for day vision and because of the difficulty digitizing the Hartmann images accurately up to the 6-mm diameter in some subjects. We excluded patients with advanced keratoconus because of the difficulty of digitizing the Hartmann images. The magnitudes of all Zernike vector terms in the CONT group were not significantly different with and without the RGP lens. The magnitudes of the spherical aberration in the KC and KCS groups changed from negative to positive as a result of the RGP lens wear, but the difference between the values with and without the RGP lens was not significant. Although the magnitude of the tetrafoil aberration in the KC group was significantly ( P = 0.003) reduced from 0.10 ± 0.06 to 0.05 ± 0.04 by the RGP lens, the difference in the tetrafoil in the KCS group with and without the RGP lens was not significant. The magnitude of trefoil, coma, and secondary astigmatism aberrations in the KC and KCS groups also were significantly reduced by the RGP lens. The total HOAs in the KC and KCS groups were significantly reduced from 0.72 ± 0.35 and 0.46 ± 0.29 to 0.31 ± 0.14 and 0.19 ± 0.06, respectively, by the RGP lens ( P < 0.001, P = 0.012). The magnitude of the total HOAs, trefoil, coma, tetrafoil, secondary astigmatism, and spherical aberrations measured with and without the RGP lens are shown in Table 2. The Hartmann-Shack system has been described in detail. All data from the wavefront analyzer (KR-9000PW Topcon) database were extracted by using a prototype program for Zernike vector analysis. 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.
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