Measuring ocular aberrations and image quality in peripheral vision with a clinical wavefront aberrometer (original) (raw)
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BMC ophthalmology, 2004
Recently, instruments for the measurement of wavefront aberration in the living human eye have been widely available for clinical applications. Despite the extensive background experience on wavefront sensing for research purposes, the information derived from such instrumentation in a clinical setting should not be considered a priori precise. We report on the variability of such an instrument at two different pupil sizes. A clinical aberrometer (COAS Wavefront Scienses, Ltd) based on the Shack-Hartmann principle was employed in this study. Fifty consecutive measurements were performed on each right eye of four subjects. We compared the variance of individual Zernike expansion coefficients as determined by the aberrometer with the variance of coefficients calculated using a mathematical method for scaling the expansion coefficients to reconstruct wavefront aberration for a reduced-size pupil. Wavefront aberration exhibits a marked variance of the order of 0.45 microns near the edge...
Validating Theoretical Pupil Size Scaling Formula For The Estimation Of Ocular Wavefront Aberrations
Purpose: To validate the mathematical pupil size scaling formula by comparing the estimates of the Zernike coefficients with corresponding clinical measurements obtained at different pupil sizes. Methods: The iProfiler aberometer (Carl Zeiss, Germany) was used to measure the wavefront aberrations and it provides Zernike coefficients for two pupil sizes (3mm and the maximum natural pupil size). 81 eyes (40 OD, 41 OS) of 49 visually normal subjects (mean age 57±7 yrs) whose maximum pupil size was ≥4.8mm were enrolled. For those subjects with pupil size >4.8mm, Zernike coefficients were recalculated from the measured data for a pupil size of 4.8mm.1 To validate a scaling procedure, Zernike coefficients were estimated for a 4.8mm pupil size using the measured data for the 3mm pupil size. The conversion matrix [C] derived by Lundstrom and Unsbo2 was used to generate the estimated Zernike coefficients. MATLAB software version (R2010b) was used to code the procedure. The estimated coeff...
Wave aberration of human eyes and new descriptors of image optical quality and visual performance
Journal of Cataract and Refractive Surgery, 2010
The expansion of wavefront-sensing techniques redefined the meaning of refractive error in clinical ophthalmology. Clinical aberrometers provide detailed measurements of the eye's wavefront aberration. The distribution and contribution of each higher-order aberration to the overall wavefront aberration in the individual eye can now be accurately determined and predicted. Using corneal or ocular wavefront sensors, studies have measured the interindividual and age-related changes in the wavefront aberration in the normal population with the goal of optimizing refractive surgery outcomes for the individual. New objective optical-quality metrics would lead to better use and interpretation of newly available information on aberrations in the eye. However, the first metrics introduced, based on sets of Zernike polynomials, is not completely suitable to depict visual quality because they do not directly relate to the quality of the retinal image. Thus, several approaches to describe the real, complex optical performance of human eyes have been implemented. These include objective metrics that quantify the quality of the optical wavefront in the plane of the pupil (ie, pupil-plane metrics) and others that quantify the quality of the retinal image (ie, image-plane metrics). These metrics are derived by wavefront aberration information from the individual eye. This paper reviews the more recent knowledge of the wavefront aberration in human eyes and discusses the image-quality and optical-quality metrics and predictors that are now routinely calculated by wavefront-sensor software to describe the optical and image quality in the individual eye.
Repeatability of wavefront measurements in pseudophakic eyes
Spektrum der Augenheilkunde, 2019
Background Higher-as well as lower-order aberrations influence uncorrected visual quality after successful cataract surgery. Different techniques are used for measuring ocular wavefront aberrations, such as Hartmann-Shack aberrometers, laser ray tracing aberrometers, and automatic retinoscopy. The aim of our study was to assess the repeatability of a Hartmann-Shack aberrometer measurement in a pseudophakic study population. Methods This prospective study included patients who underwent cataract surgery 1 month prior to recruitment. Three consecutive Hartmann-Shack measurements (WASCA, Carl Zeiss Meditec AG, Germany) were performed after pharmacological dilation of the pupil. Results In total, 156 eyes of 156 patients were included. Repeatability of measurements was good in pseudophakic eyes for all Zernike polynomials up to the fourth order. The median values of the SD of all three measurements ranged between 0.042 and 0.125 for the Tecnis intraocular lens (IOL) and 0.028 and 0.148 for the CT Asphina 409MP IOL. Intraclass correlation coefficients ranged between 0.793592 and 0.97955 for the Tecnis IOL and between 0.673894 and 0.989172 for the CT Asphina 409MP IOL. Conclusion Postoperative unsatisfactory image quality, sometimes reported by patients, despite good defocus and astigmatism values calls for examination of higher-order aberrations. Hartmann-Shack measurements with the WASCA offers good repeatability
Optics express, 2010
Peripheral vision and off-axis aberrations not only play an important role in daily visual tasks but may also influence eye growth and refractive development. Thus it is important to measure off-axis wavefront aberrations of human eyes objectively. To achieve efficient measurement, we incorporated a double-pass scanning system with a Shack Hartmann wavefront sensor (SHWS) to develop a scanning Shack Hartmann aberrometer (SSHA). The prototype SSHA successfully measured the off-axis wavefront aberrations over +/- 15 degree visual field within 7 seconds. In two validation experiments with a wide angle model eye, it measured change in defocus aberration accurately (<0.02microm, 4mm pupil) and precisely (<0.03microm, 4mm pupil). A preliminary experiment with a human subject suggests its feasibility in clinical applications.
Biomedical Optics Express, 2012
Conventional optical systems usually provide best image quality on axis, while showing unavoidable gradual decrease in image quality towards the periphery of the field. The optical system of the human eye is not an exception. Within a limiting boundary the image quality can be considered invariant with field angle, and this region is known as the isoplanatic patch. We investigate the isoplanatic patch of eight healthy eyes and measure the wavefront aberration along the pupillary axis compared to the line of sight. The results are used to discuss methods of ocular aberration correction in wide-field retinal imaging with particular application to multi-conjugate adaptive optics systems.
Aberrations and retinal image quality of the normal human eye
Journal of the Optical Society of America A, 1997
We have constructed a wave-front sensor to measure the irregular as well as the classical aberrations of the eye, providing a more complete description of the eye's aberrations than has previously been possible. We show that the wave-front sensor provides repeatable and accurate measurements of the eye's wave aberration. The modulation transfer function of the eye computed from the wave-front sensor is in fair, though not complete, agreement with that obtained under similar conditions on the same observers by use of the double-pass and the interferometric techniques. Irregular aberrations, i.e., those beyond defocus, astigmatism, coma, and spherical aberration, do not have a large effect on retinal image quality in normal eyes when the pupil is small (3 mm). However, they play a substantial role when the pupil is large (7.3-mm), reducing visual performance and the resolution of images of the living retina. Although the pattern of aberrations varies from subject to subject, aberrations, including irregular ones, are correlated in left and right eyes of the same subject, indicating that they are not random defects.
Journal of The Optical Society of America A-optics Image Science and Vision, 2002
Ocular aberrations were measured in 71 eyes by using two reflectometric aberrometers, employing laser ray tracing (LRT) (60 eyes) and a Shack-Hartmann wave-front sensor (S-H) (11 eyes). In both techniques a point source is imaged on the retina (through different pupil positions in the LRT or a single position in the S-H). The aberrations are estimated by measuring the deviations of the retinal spot from the reference as the pupil is sampled (in LRT) or the deviations of a wave front as it emerges from the eye by means of a lenslet array (in the S-H). In this paper we studied the effect of different polarization configurations in the aberration measurements, including linearly polarized light and circularly polarized light in the illuminating channel and sampling light in the crossed or parallel orientations. In addition, completely depolarized light in the imaging channel was obtained from retinal lipofuscin autofluorescence. The intensity distribution of the retinal spots as a function of entry (for LRT) or exit pupil (for S-H) depends on the polarization configuration. These intensity patterns show bright corners and a dark area at the pupil center for crossed polarization, an approximately Gaussian distribution for parallel polarization and a homogeneous distribution for the autofluorescence case. However, the measured aberrations are independent of the polarization states. These results indicate that the differences in retardation across the pupil imposed by corneal birefringence do not produce significant phase delays compared with those produced by aberrations, at least within the accuracy of these techniques. In addition, differences in the recorded aerial images due to changes in polarization do not affect the aberration measurements in these reflectometric aberrometers.
Optometry and Vision Science, 2003
Repeated measures of wavefront aberrations were taken along the line-of-sight of seven eyes using two instruments: an objective, cross-cylinder aberroscope (OA) and a Shack-Hartmann (SH) aberrometer. Both instruments were implemented on the same optical table to facilitate interleaved measurements on the same eyes under similar experimental conditions. Variability of repeated measures of individual coefficients tended to be much greater for OA data than for SH data. Although Zernike coefficients obtained from a single measurement were generally larger when measured with the OA than with the SH, the averages across five trials were often smaller for the OA. The Zernike coefficients obtained from the two instruments were not significantly correlated. Radial modulation-transfer functions and point-spread functions derived from the two sets of measurements were similar for some subjects, but not all. When average Zernike coefficients were used to determine optical quality, the OA indicated superior optics in some eyes, but the reverse trend was true if Zernike coefficients from individual trials were used. Possible reasons for discrepancies between the OA and SH measurements include difference in sampling density, quality of data images, alignment errors, and temporal fluctuations. Multivariate statistical analysis indicated that the SH aberrometer discriminated between subjects much better than did the objective aberroscope. (Optom Vis Sci 2003;80:15-25)