ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Visual aberrations such as glare and halo have been well documented after laserin-situkeratomileusis (LASIK). These are more likely in patients with higher refractive errors and large pupil diameters. We present a patient with good Snellen acuity but functional impairment by visual aberrations after LASIK. These symptoms resolved after an InterWave-guided LASIK multipass, multistage enhancement treatment to correct spherical aberrations.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Background.The coefficients of normalized Zernike expansion are orthogonal and reflect the relative contribution of each mode to the total root mean square (RMS) wavefront error. The relationship between the level of RMS wavefront error within a mode and its effect on visual performance is unknown.Purpose.To determine for various levels of RMS wavefront error how each mode of the normalized Zernike expansion for the second, third, and fourth orders affect high- and low-contrast acuity.Methods.Three healthy optimally corrected cyclopleged subjects read aberrated and unaberrated high- and low-contrast logarithm of the minimum angle of resolution acuity charts monocularly through a 3-mm artificial pupil. Acuity was defined by the total number of letters read correctly up to the fifth miss. Aberrated and unaberrated charts were generated using a program called CTView. Six levels of RMS wavefront error were used (0.00, 0.05, 0.10, 0.15, 0.20, and 0.25 &mgr;m). Each level of RMS error was loaded into each mode of the second, third, and fourth radial orders individually for a total of 72 charts. Data were normalized by subject, and the normalized data were averaged across subjects.Results.Across modes and within each mode as the level of RMS wavefront error increased above 0.05 &mgr;m of RMS wavefront error, visual acuity decreased in a linear fashion. Slopes of the linear fits varied depending on the mode. Modes near the center of the Zernike pyramid had steeper slopes than those near the edge.Conclusions.Increasing the RMS error within any single mode of the normalized Zernike expansion decreases visual acuity in a linear fashion. The slope of the best fitting linear equation varies with Zernike mode. Slopes near the center of the Zernike pyramid are steeper than those near the edge. Although the normalized Zernike expansion parcels RMS error orthogonally, the resulting effects on visual performance as measured by visual acuity are not orthogonal. New metrics of the combined effects of the optical and the neural transfer functions that are predictive of visual performance need to be developed.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.To measure the wavefront aberration at different locations in progressive-power lenses (PPL’s) isolated andin situ(PPL’s plus eye).Methods.A Hartmann-Shack wavefront sensor was used to measure progressive-power lenses and human eyes either independently or in combination. In each selected zone, the lens was placed and tilted accordingly to simulate natural viewing conditions. We measured 21 relevant locations across an isolated PPL (plano lens of power addition of 2 D). In six of the locations, the wavefront aberration of the eye plus PPL were obtained in two ways: (1) by direct measurement of the system and (2) by adding the individual wavefront aberrations of the eye and the lens for each appropriate zone. In every case, we obtained the wavefront aberration as Zernike polynomials expansions, the root mean square error, the point-spread function, and the Strehl ratio.Results.Along the corridor of the PPL, third-order coma and trefoil, and astigmatism were the dominant aberrations. In areas of the PPL outside the corridor, astigmatism increased, whereas other aberrations remained similar to the lens center. Small differences were found between the direct and calculated methods used to obtain the wavefront aberration of the eye with the lens, and the possible sources of errors were discussed. In some lenses zones, the aberrations of the lens may be compensated by the particular aberrations of the eye, yielding improved optical performance over that present in the lens alone.Conclusions.We designed and built a wavefront sensor to perform spatially resolved aberration measurements in ophthalmic lenses, in particular in PPL’s, either isolated or in combination with the eye. The aberrations appearing in the PPL were compared with those in normal aged eyes.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.Our aim was to obtain a complete description of the interactions of rigid gas permeable (RGP) contact lenses with the optics of normal eyes.Methods.We measured total and anterior-surface aberrations in four subjects, who were all long-term RGP contact lens wearers. The anterior-surface wave aberration was obtained from videokeratographic elevation maps, and ocular wave aberration was measured with a laser ray-tracing technique. Measurements were performed with and without their own spherical contact lenses.Results.With this methodology, we evaluated the optical performance with RGP lenses compared with the natural optics. We estimated the contribution of the anterior surface of the contact lens, the internal ocular optics, flexure, and the tear lens aberrations to the optical performance of eyes wearing RGP contact lenses. We found that in three of four subjects, the contact lens significantly improved the natural optics of the eye. For the subject with higher dominance of corneal aberrations, root mean square (second-order and higher) decreased from 1.36 &mgr;m to 0.46 &mgr;m. Third- and higher-order aberrations decreased from 0.77 &mgr;m to 0.39 &mgr;m. The internal optics and lens flexure imposed limits on aberration compensation. Spherical RGP contact lenses did not produce spherical aberration potentially due to a compensatory role of the tear lens.Conclusions.Aberration measurements are useful to understand the fitting of contact lenses and the interaction with tear, cornea, and internal optics of the eye. Aberrometry can help to choose the best standard RGP lens parameters to improve the optics of individual eyes.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Background.Soft contact lenses produce a significant level of spherical aberration affecting their power on-eye. A simple model assuming that a thin soft contact lens aligns to the cornea predicts that these effects are similar on-eye and off-eye.Methods.The wavefront aberration for 17 eyes and 33 soft contact lenses on-eye was measured with a Shack-Hartmann wavefront sensor. The Zernike coefficients describing the on-eye spherical aberration of the soft contact lens were compared with off-eye ray-tracing results. Paraxial and effective lens power changes were determined.Results.The model predicts the on-eye spherical aberration of soft contact lenses closely. The resulting power change for a ±7.00 D spherical soft contact lens is ±0.5 D for a 6-mm pupil diameter and ±0.1 D for a 3-mm pupil diameter. Power change is negligible for soft contact lenses corrected for off-eye spherical aberration.Conclusions.For thin soft contact lenses, the level of spherical aberration and the consequent power change is similar on-eye and off-eye. Soft contact lenses corrected for spherical aberration in air will be expected to be aberration-free on-eye and produce only negligibly small power changes. For soft contact lenses without aberration correction, for higher levels of ametropia and large pupils, the soft contact lens power should be determined with trial lenses with their power and p value similar to the prescribed lens. The benefit of soft contact lenses corrected for spherical aberration depends on the level of ocular spherical aberration.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.The aim of this study was to investigate the effect of contact lenses on the optical performance of the eye by measuring wavefront aberrations for the eyes with or without contact lenses.Method.A sensitive aberrometer was used to measure wavefront aberrations for 54 eyes in 27 subjects for three conditions: with no contact lens (non-CL), with soft-contact lenses (soft-CL) and with rigid gas permeable contact lenses (RGP-CL). The root mean square (RMS) value of the wavefront aberrations and Zernike aberrations were calculated.Results.A change in the RMS values of wavefront aberrations with CL wear was observed for every eye. The change in wavefront aberrations with CL wearing was found to vary substantially from individual to individual. Relative to the mean RMS value of the group for the non-CL condition, the mean RMS value was increased for the soft-CL condition and was significantly reduced for the RGP-CL condition. A significant increase in mean RMS for the soft-CL condition was found when astigmatisms were removed. Although soft-CL wearing resulted in significant increases in higher orders of Zernike aberrations (fourth, fifth, and higher), the RGP-CL condition led to a significant decrease in second-order Zernike aberrations. For the eyes with low wavefront aberrations in the non-CL condition, either soft-CL wearing or RGP-CL wearing results in increases in the RMS values.Conclusion.Contact lens wearing, either with soft lenses or the RGP lenses, causes changes in the wavefront aberrations of the eye. The changes in wavefront aberrations vary substantially from eye to eye. Although soft-CL wearing tends to induce more higher-order aberrations, RGP-CL effectively reduces the astigmatisms. Both soft-CL and RGP-CL induce more aberrations for the eyes that have low wavefront aberrations. The change in wavefront aberrations due to contact lens wearing may explain the changes in visual performance for contact lens wearers reported previously.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.To assess the repeatability of measurements of ocular aberrations using wavefront sensing in a small group of observers and to assess the potential effect of measurement error on custom corneal correction due to this variability.Method.A Shack-Hartmann wavefront sensor was used to measure the ocular wavefront in nine eyes. Head position was stabilized using a dental bite bar, and the pupil was centred using a cathode ray tube monitor and circular grating. Twenty Shack-Hartmann images were collected for each measurement. Each observer had three sets of measurements taken; the first and the second after careful alignment and the final after regrasping the bite bar in the same position as for the second measurement, but without pupil realignment. The modulation transfer functions for each set were calculated, and the effect of best-aligned custom treatments on the modulation transfer function was estimated.Results.There were highly statistically significant differences in a large number of Zernike modes between the three sets of measurements. The modulation transfer functions calculated for the residual wavefronts after aligned custom treatment were below the diffraction limit. The root mean square wavefront errors were consistently better for the residual wavefronts obtained using the realigned data than using data taken without pupil realignment.Conclusions.Sequential measurement of ocular aberrations shows statistically significant differences in a large number of Zernike modes. If aberrations determined by a single measurement are to be used in a custom correction, the resulting modulation transfer function is likely to remain below the diffraction limit. Pupil realignment is critical in reduction of the residual root mean square wavefront values to a minimum.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID